Дисертації з теми "E-Fuel"

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Desde os primórdios da indústria automobilística no mundo, o uso da gasolina como principal combustível, trouxe consequências políticas e econômicas, com o crescimento da frota circulante. A gasolina como principal derivado do petróleo, gerou a necessidade de expansão de sua extração e da descoberta de novos campos petrolíferos, para atender ao crescente mercado consumidor, trazendo problemas financeiros em diversos países a partir das crises de energia, devido às flutuações ou ao aumento de preços. Para evitar maiores problemas decorrentes da dependência do petróleo oriundo de regiões com turbulências políticas e religiosas, vários países se organizaram na busca por alternativas ao uso da gasolina no transporte veicular. Neste trabalho são analisadas as políticas energéticas automotivas dos Estados Unidos, Japão e Europa, o desenvolvimento tecnológico automotivo e a questão do uso do etanol como combustível nos veículos flex fuel no Brasil. São analisadas também as implicações do uso da gasolina nos veículos flex fuel, pois com o lançamento do novo regime automotivo no Brasil, deve-se estar atento à eficiência energética.

The main problem of PEMFCs and DMFCs, is linked with the high price of Pt-based electrocatalysts, on one side, and durability issues, on the other side. In this work electrocatalysts for oxygen reduction reaction (ORR) were developed, synthesized and tested for the fuel cell systems based on hydrogen or methanol. Moreover, tests under sub-freezing conditions at temperatures below 0°C, were conducted to assess the performance of FCs systems in harsh environmental conditions. Specifically, the electrochemical performance of three types of electrocatalysts for the oxygen reduction reaction, based respectively on a hollow core mesoporous shell carbon (HCMSC), an ultrasonic spray pyrolysis mesoporous carbon (USPMC) and a graphene reduced oxide (GRO) were compared. These catalysts were then evaluated electrochemically in a three-electrode one-compartment cell, using a 0.5 M H2SO4 solution as electrolyte, an auxiliary electrode and a reversible hydrogen electrode (RHE), as counter and reference electrodes, respectively. X-ray photoelectron spectroscopy (XPS), X-ray scattering (XRD), Brunauer-Emmett-Teller (BET) and Transmission electron microscopy (TEM) were carried out in order to understand chemical-physical phenomenon, and electrochemical tests were conducted via linear sweet voltammetry (LSV) and cyclic voltammetry (CV). On the other hand, the effects of methanol concentration, temperature, freezing/thawing (F/T) tests and cell purging time, evaluating the performance of a single direct methanol fuel cell (DMFC), were investigated. Specific purging conditions were optimized to increase the durability of MEAs. SEM analysis of MEAs after F/T cycles showed that a significant MEA degradation occurred when the produced water is not removed. Such a degradation affected the subsequent cell performance and durability, which depend of the purging procedure, purging time, and purge flow. By opportunely modifications of the purging procedure, the performance of single DMFCs remained almost constant after 25 F/Ts.

Mestrado em Contabilidade, Fiscalidade e Finanças Empresariais
A indústria aérea tem se deparado com a crescente volatilidade que tem existido no mercado do petróleo, uma vez que afeta os seus custos, tendo o combustível um peso de cerca de 30% dos custos operacionais da indústria. Esta situação leva ao uso de várias estratégias de gestão do risco do combustível por parte das companhias aéreas, com o objetivo de redução dos custos do combustível e eliminação da volatilidade dos preços de mercado. Face a situação atual nos mercados, este trabalho visa analisar os custos operacionais de duas companhias aéreas, a IAG e a Finnair. Tem o objetivo de estudar a evolução das receitas e dos custos que as organizações incorreram com as atuais estratégias de hedging do combustível e da taxa de câmbio para assim poder comparar os resultados obtidos pelas diferentes estratégias utilizadas e identificar qual das duas foi a mais eficiente. Iniciamos o estudo através de uma análise da estatística descritiva dos custos e receitas operacionais de cada empresa, recorrendo a medidas standard da aviação. Posteriormente, recorremos a regressões lineares para estudar o impacto do preço do petróleo e como o câmbio interfere no custo unitário do combustível, utilizando variáveis de controlo nas regressões.
The Aviation industry as struggled against the increased volatility that exists in the oil market, affecting its costs, with the fuel weighing 30% in the industries operational costs. This situation leads to the adoption of several risk management strategies for fuel by aviation companies with the goal of fuel cost reduction and thus mitigating the volatility in market prices. In light of current market situation, this work aims to study the operational costs of two airlines, IAG and Finnair, the goal is to check the evolution of their costs an revenues against their hedging strategies for both fuel and currency exchange and thus comparing results achieved by both airlines and find the most efficient one. The study began with a statistical analysis of operational costs and revenue for both entities using standard aviation metrics and later integrating linear regressions to study the impact of oil (price) and currency exchange rate in the cost of fuel, control variables were also used.
info:eu-repo/semantics/publishedVersion

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Compostos oxigenados são usados como aditivos para elevar a octanagem da gasolina automotiva. Esses compostos substituem outros que são ambientalmente mais nocivos, como é o caso do chumbo tetraetila. No Brasil, o oxigenado empregado é o etanol anidro, usado em teores que variam de 20% e 25%. Nos últimos anos foi iniciada a comercialização de veículos equipados com motores projetados para funcionar com misturas de gasolina C e álcool hidratado em qualquer proporção, o flex fuel. Com o objetivo de contribuir para melhor compreender as propriedades do flex fuel, neste trabalho foram medidos dados de pressão de vapor reid na temperatura de 37,8°C, curvas de destilação e massa específica das misturas de gasolina A e etanol anidro, gasolina C (20% e 25%) e etanol hidratado em vários teores (0 a 100%). O método utilizado para a medição da pressão de vapor da gasolina baseia-se nos métodos ASTM D 5191 e ASTM D 6378. Os resultados mostram que a presença do etanol e da água presente no álcool hidratado afetam fortemente a volatilidade do flex fuel em relação à gasolina A. Com uma abordagem do equilíbrio líquido-vapor, considerando o flex fuel como uma mistura pseudoternária gasolina A/etanol/água, os dados foram correlacionados pelo modelo NRTL. O desvio médio obtido foi inferior 0,30 ao desvio padrão de 1,5 kPa esperado nas medidas

Orientador: Maria Beatriz Machado Bonacelli
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociências
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Resumo: Os veículos flex fuel representam cerca de 90% da atual produção de veículos de passeio no Brasil. Historicamente a utilização de etanol como combustível automotivo remete ao início do século XX, em grande escala à década de 1970 com a conformação do Proálcool e, após um período de descrença, o etanol ressurgiu nos anos 2000 com a difusão da tecnologia flex. Este trabalho tem por objetivo central analisar a constituição da tecnologia flex fuel no país e para isso se apoia nos conceitos de paradigmas e trajetórias tecnológicas, os quais permitem compreender o processo evolutivo dos automóveis, seus sistemas de alimentação de combustível e das diversas alternativas à gasolina e ao motor de combustão interna. Ao lado disso, explora-se a história brasileira na utilização de etanol, sobretudo no período recente a partir de entrevistas e, também, em análises de dados sobre as atividades de Pesquisa, Desenvolvimento e Inovação relacionadas à tecnologia flex brasileira e seus desdobramentos, que estão representados em veículos de maior eficiência energética e com menores índices de emissão de poluentes. Por fim, realiza-se uma análise crítica do marco regulatório atual, o qual dá suporte às atividades do setor automobilístico brasileiro, e indica-se possíveis ações de indução à melhoria da tecnologia flex fuel e do uso do etanol como combustível no país. Uma das hipóteses que baseiam o trabalho de pesquisa aponta que a instabilidade relativa do mercado de etanol e a falta de competição entre as montadoras (no que toca o desenvolvimento de motores) limita a demanda tecnológica e provoca desestímulo à busca por maior eficiência ou mesmo por mudanças mais substanciais da tecnologia flex fuel desenvolvida no país. Conclui-se, dentre outros, que a atual legislação brasileira e o marco regulatório não se apresentam como indutores para alterações substantivas à iniciativa do veículo flex fuel, estimulando apenas melhorias incrementais sem tocar mais fortemente na concorrência da indústria, não explorando as oportunidades abertas pela tecnologia flex fuel
Abstract: Flex fuel vehicles represents nearly 90% of the current production of passenger cars in Brazil. Historically the use of ethanol as an automotive fuel refers to the early twentieth century, in large-scale at the 1970s with the beginning of Proálcool (Brazilian Ethanol Program), and after a disrepute period, ethanol reemerged in the 2000s with the flex fuel technology. This work¿s main objective is to analyze the constitution of flex fuel technology in Brazil, for that is based on the concepts of paradigms and technological trajectories, which allows one to understand the evolutionary movement of developing vehicles, their fuel supply systems and the pursuit of gasoline alternatives and of the internal combustion engine. Alongside this, it explores the brazilian history in ethanol use, especially in the recent period, with interviews and also based on data analysis of Research, Development and Innovation activities related to the flex fuel technology in Brazil, which makes possible the development of more energy efficient vehicles and lower pollutants emissions. Finally, it holds a critical analysis of the current brazilian legal framework, which supports the activities of the brazilian automotive industry, and specifies different ways to induce broader improvements to the use of ethanol as a fuel and the flex fuel technology in the country. One of the hypotheses that based this research points out that the relative uncertainty of the ethanol market and the lack of competition among automakers (concerning to the development of engines) constrains the technological demand and discourages the pursuit of greater efficiency or even more substantial changes on the brazilian flex fuel technology. In conclusion, among others, the current brazilian legal framework is not presented as an inducer for substantive changes on the flex fuel vehicle, encouraging only incremental improvements without leading to stronger competition in the industry, not taking advantage from the opportunities offered by flex fuel technology
Mestrado
Politica Cientifica e Tecnologica
Mestre em Política Científica e Tecnológica

O presente estudo descreve as alterações metalúrgicas e topográficas do cilindro de blocos de motor de combustão interna fabricados em ferro fundido cinzento, após a realização de testes de durabilidade em dinamômetro. O motor testado tem tecnologia Flex-Fuel, e pode ser operado com qualquer proporção de mistura gasolina comum/etanol. Um motor foi testado com combustível etanol e o outro com gasolina comum, buscando-se assim representar duas condições extremas de trabalho em termos de combustível. A pesquisa constituiu-se da revisão bibliográfica e da parte prática que envolveu: a realização de testes de durabilidade de motor em dinamômetro; a caracterização metalúrgica e topográfica do cilindro após teste com ambos os combustíveis, utilizando técnicas de microscopia eletrônica de varredura, metalografia por microscopia óptica, perfilometria e quantificação de parâmetros de rugosidade, entre outros; a análise crítica, discussão dos resultados e apresentação da conclusão.
The present study approaches the metallurgical and topographical alterations on the cylinder of an internal combustion engine block made of gray cast iron, after durability dynamometer tests. The tested engine has flexible fuel technology (Flex-Fuel), and is capable to work with both gasoline/ethanol fuels, in any mixture proportion. One engine has been tested with ethanol and another one tested with gasoline, and so representing two extreme conditions on which the engine may work in terms of fuel. The research has been developed basically through the conceptual approach by the bibliographic review and the experimental steps that involved: general engine durability test at dynamometer bench; metallurgical and topographic characterization analysis at laboratory, after the test with both fuels, applying Scanning Electronic Microscopy SEM, optical microscopy metallography, profilometer and roughness parameters quantification, and so forth; critical analysis on the results, discussion and final conclusion.

Na maioria dos equipamentos mecânicos há movimento relativo entre componentes, e como resultado desse deslizamento relativo, as forças de atrito na superfície geram deformação plástica e/ou remoção de massa (ou volume) do material. Nos motores de combustão interna a geração da potência é realizada pela transformação da energia química em calor por meio da combustão do combustível com o ar, gerando o movimento alternativo de mecanismos (pistões, biela, virabrequim). Já no caso dos motores flex-fuel, o etanol como combustível aumenta a potência, levando a maiores carregamentos termomecânicos e, consequentemente, tribológicos nos seus componentes. Um dos sistemas do motor mais afetado pela mudança no combustível é o par válvula-sede, motivo pelo qual é necessário investigar os mecanismos de desgaste, os efeitos dos parâmetros de operação no comportamento frente ao atrito, e escolher apropriadamente pares deslizantes de materiais que apresentem baixas perdas de massa (taxas de desgaste) e coeficientes de atrito. Ensaios do tipo reciprocating tinham sido empregados para realizar estudos tribológicos de materiais de válvulas e com tratamentos superficiais. As condições de ensaio mais representativas são de operação do motor. Portanto, a seleção de parâmetros como carga, velocidade e temperatura não é fácil: para alguns equipamentos de teste, as variáveis não são independentes. Além disso, devido à complexidade do sistema tribológico, a interação entre as variáveis afeta os resultados. O objetivo deste trabalho de pesquisa foi dividido em duas frentes. A primeira, analisar isoladamente o efeito da temperatura, força normal e velocidade no coeficiente de atrito e no desgaste. O tribômetro SRV-4 do tipo reciprocating foi usado com uma esfera de aço AISI 52100 e distintos materiais de disco (aços e ligas intermetálicas sinterizadas de Nb). A segunda parte consistiu na caracterização dos mecanismos de desgaste de válvulas e sedes de motores distintos, após diferentes tipos de ensaios (dinamômetro e campo em veiculo). O coeficiente de atrito (?) e a perda de massa foram medidos para determinar o desempenho tribológico dos sistemas estudados. Além disso, as superfícies das marcas de desgaste tanto no disco quanto na esfera, assim como das válvulas e sedes foram analisadas por microscopia óptica (MO), microscopia eletrônica de varredura (MEV) com espectroscopia de energia dispersiva de raios-X (EDS) e espectroscopia Raman. Para as distintas ligas intermetálicas de Nb ensaiadas com esfera de aço AISI 52100, encontrou-se que os mecanismos de desgaste nas superfícies após uma análise de MEV-EDS foram particularmente abrasão, adesão e oxidação. Já no caso dos motores que foram avaliados, muitos dos danos observados estavam presentes em ambas as válvulas e sedes de admissão e escape; no entanto, a oxidação ocorreu apenas nas válvulas de escape, provavelmente produzido pela alta temperatura durante a operação do motor.
In most of the mechanical assemblies there is relative motion between components, and as a result of this relative sliding action, frictional forces on the sliding surface result in removal or displacement of mass (or volume) of the material. The power generation of internal combustion engines comes from chemical energy transformation into heat through air fuel combustion with further expansion of gases generating the reciprocating movement of power cell (pistons, rod and crankshaft). For flex fuel engines, the ethanol increases power, leading to higher thermo-mechanical forces and consequently higher friction between its components. The valve/valve seat pair is one of the most affected system due to this change, leading to the need of more accurate analysis of its wear mechanisms, its operating parameters effects and his behavior regarding the friction so making possible to choose properly materials with lower mass loss (wear rate) and coefficient of friction. Reciprocating tests had been used to tribological studies of valve materials with surface treatment purpose. The most important test boundary conditions are the engine operating conditions. Therefore, the load, speed and temperature parameters definition is not easy since for some test equipment those variables are not independent. Besides due to tribological system complexity the variable interaction affects its results. The present research goal was divided in two groups. The first one analyzes the normal force, frequency and temperature effect on friction coefficient and wear, independently of each other. It was used a SRV-4 reciprocating tribometer with a sphere (AISI 52100 steel) against several disc materials (steel and sintered intermetallic alloys of Nb). The second one consisted in the characterization of wear mechanisms of valve/valve seat from different engines that were submitted to different test (engine dynamometer test bench and vehicle). The coefficient of friction (?) and mass loss were measured in order to define the studied systems tribological performance. Besides the both disc and sphere wear scars such as valve/valve seat were analyzed using optical microscopy (OM), scanning electron microscopy (SEM) with energy dispersive spectroscopy of X-ray (EDS) and Raman spectroscopy. For the tested intermetallic alloys of Nb with AISI 52100 sphere it was found the following wear mechanisms after SEM-EDS analyses: abrasion, adhesion and oxidation. In the case of the evaluated engines, several damages were observed in both intake and exhaust valves/valve seats; however, the oxidation occurred only on exhaust valves, probably due to high operating temperature.

PEM Fuel Cells are expected to gradually substitute internal combustion engines as electrical and co-generation power sources thanks to high efficiency, low operating temperature, fast startup time and favourable power-to-weight ratio. However, while PEMFCs have achieved significant progresses in the last decade, their short lifetime and high cost still continue to impede large-scale commercialization. The first subject of the present work had been the study of the PEM fuel cells degradation mechanisms with the aim of: a) find out the most relevant phenomena concerning the fuel cell lifetime, b) testing some methods able to promptly detect the degradation mechanisms and, mostly, c) find out the mitigation strategies able to increase the fuel cells lifetime. At the end of the research three mitigation strategies had been developed and tested: cell voltage monitoring, the current modulation and the stack shunt. According to the tests results all these mitigation strategies, if adopted all together, can effectively led to doubling the fuel cells lifetime. In parallel to the fuel cell lifetime increase, a deep investigation on system components integration had been conducted. Following this principle, the system cost has been considerably reduced mostly thanks to the DC-DC converter integration with the stack and the coolant circuit simplification. The prototypes realized during this work has been taken as example for the production of new fuel cell power systems with increased lifetime at lower cost

The control of a proton exchange membrane fuel cell system (PEM FC) for domestic heat and power supply requires extensive control measures to handle the complicated process. Highly dynamic and non linear behavior, increase drastically the difficulties to find the optimal design and control strategies. The objective is to design, implement and commission a controller for the entire fuel cell system. The fuel cell process and the control system are engineered simultaneously; therefore there is no access to the process hardware during the control system development. Therefore the method of choice was a model based design approach, following the rapid control prototyping (RCP) methodology. The fuel cell system is simulated using a fuel cell library which allowed thermodynamic calculations. In the course of the development the process model is continuously adapted to the real system. The controller application is designed and developed in parallel and thereby tested and verified against the process model. Furthermore, after the commissioning of the real system, the process model can be also better identified and parameterized utilizing measurement data to perform optimization procedures. The process model and the controller application are implemented in Simulink using Mathworks` Real Time Workshop (RTW) and the xPC development suite for MiL (model-in-theloop) and HiL (hardware-in-the-loop) testing. It is possible to completely develop, verify and validate the controller application without depending on the real fuel cell system, which is not available for testing during the development process. The fuel cell system can be immediately taken into operation after connecting the controller to the process.

The control of a proton exchange membrane fuel cell system (PEM FC) for domestic heat and power supply requires extensive control measures to handle the complicated process. Highly dynamic and non linear behavior, increase drastically the difficulties to find the optimal design and control strategies. The objective is to design, implement and commission a controller for the entire fuel cell system. The fuel cell process and the control system are engineered simultaneously; therefore there is no access to the process hardware during the control system development. Therefore the method of choice was a model based design approach, following the rapid control prototyping (RCP) methodology. The fuel cell system is simulated using a fuel cell library which allowed thermodynamic calculations. In the course of the development the process model is continuously adapted to the real system. The controller application is designed and developed in parallel and thereby tested and verified against the process model. Furthermore, after the commissioning of the real system, the process model can be also better identified and parameterized utilizing measurement data to perform optimization procedures. The process model and the controller application are implemented in Simulink using Mathworks` Real Time Workshop (RTW) and the xPC development suite for MiL (model-in-theloop) and HiL (hardware-in-the-loop) testing. It is possible to completely develop, verify and validate the controller application without depending on the real fuel cell system, which is not available for testing during the development process. The fuel cell system can be immediately taken into operation after connecting the controller to the process.

Avvalendosi di una prospettiva di network, il presente lavoro di ricerca pone al centro della propria analisi gli accordi inter-organizzativi sottostanti un'innovazione dall'evidente connotazione radicale: la fuel cell technology. Lo studio proposto consta di tre fasi esplorative interdipendenti. In primo luogo, attraverso interviste a manager di aziende coinvolte, è definito un modello interpretativo che consenta di distinguere i diversi attori del network in classi di organizzazioni similari. In conformità a tale modello, il primo obiettivo della ricerca è rilevare la presenza di pattern relazionali ricorrenti nel contesto di interesse; in modo specifico, si vuole verificare se i vari accordi si configurino in modo conforme alla logica di value chain, costituendo così il prodromo di un futuro comparto industriale. Successivamente, si vuole determinare quali tipologie di organizzazioni assumano una posizione strategica all'interno del network collaborativo, prefigurandosi come i catalizzatori dell'innovazione tecnologica. risultati emersi producono implicazioni a livello teorico e pratico. Da un lato, è approfondito il dibattito circa i fattori antecedenti al posizionamento di un'organizzazione all'interno di un network collaborativo; dall'altro, è offerto un contributo ai principali studi relativi alla fuel cell technology, attraverso un'indagine delle dinamiche inter-organizzative presenti.
The aim of the study is to analyze interorganizational relationships related to a radical innovation through a network perspective. The research model is the result of three interrelated steps: the definition of an interpretive model through exeperts interviews, the recurrent relational patterns analysis through relational contingency tables, and the network actors centrality antecedent through statistic regression. The results suggest some theoretical and practical implications.

Avvalendosi di una prospettiva di network, il presente lavoro di ricerca pone al centro della propria analisi gli accordi inter-organizzativi sottostanti un'innovazione dall'evidente connotazione radicale: la fuel cell technology. Lo studio proposto consta di tre fasi esplorative interdipendenti. In primo luogo, attraverso interviste a manager di aziende coinvolte, è definito un modello interpretativo che consenta di distinguere i diversi attori del network in classi di organizzazioni similari. In conformità a tale modello, il primo obiettivo della ricerca è rilevare la presenza di pattern relazionali ricorrenti nel contesto di interesse; in modo specifico, si vuole verificare se i vari accordi si configurino in modo conforme alla logica di value chain, costituendo così il prodromo di un futuro comparto industriale. Successivamente, si vuole determinare quali tipologie di organizzazioni assumano una posizione strategica all'interno del network collaborativo, prefigurandosi come i catalizzatori dell'innovazione tecnologica. risultati emersi producono implicazioni a livello teorico e pratico. Da un lato, è approfondito il dibattito circa i fattori antecedenti al posizionamento di un'organizzazione all'interno di un network collaborativo; dall'altro, è offerto un contributo ai principali studi relativi alla fuel cell technology, attraverso un'indagine delle dinamiche inter-organizzative presenti.
The aim of the study is to analyze interorganizational relationships related to a radical innovation through a network perspective. The research model is the result of three interrelated steps: the definition of an interpretive model through exeperts interviews, the recurrent relational patterns analysis through relational contingency tables, and the network actors centrality antecedent through statistic regression. The results suggest some theoretical and practical implications.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
O combustível nuclear metálico tipo placa em dispersão é um combustível versátil que pode ser projetado para ser utilizado tanto em reatores de testes quanto em reatores de potência. A elevada densidade das ligas metálicas de urânio com elementos de transição, como, Zr, Nb, Mo, etc, propicia o emprego deste combustível utilizando urânio com baixo teor de enriquecimento, o que o torna mais seguro no sentido de conter a proliferação nuclear. Além disso, as excelentes propriedades mecânicas e a grande resistência à corrosão das ligas metálicas de U-Zr-Nb, tornam a escolha desta liga na forma de combustível tipo placa em um desenvolvimento de grande atratividade devido às possibilidades de se alcançar um combustível de alto desempenho. Neste trabalho foram investigadas as transformações de fases das ligas U-2,5Zr-7,5Nb e U- 3Zr-9Nb em diferentes condições de tratamentos térmicos, bem como foi desenvolvido o processo de cominuição destas ligas pelo processo de hidretação-desidretação. As transformações de fases foram obtidas realizando-se a homogeneização das ligas de U- 2,5Zr-7,5Nb e U-3Zr-9Nb em elevadas temperaturas (1000 oC, durante 1 e 16 h), seguido de têmpera em água, bem como de envelhecimento a 600 oC em diferentes tempos (0,5, 3 e 24h), também, seguido de têmpera em água. As fases obtidas foram caracterizadas por intermédio das técnicas de difração de raios X, microdureza, microscopia ótica, microscopia eletrônica e EDS. Nestas condições experimentais, foram obtidas duas microestruturas distintas. Uma microestrutura monofásica constituída da fase gama () martensítica de cristalinidade cúbica de corpo centrado. A outra com estrutura do tipo lamelar perlítica, constituída da mistura das fases alfa e gama (α e ). A fase α tem cristalinidade ortorrômbica. Diferentemente da fase gama martensítica de alta estabilidade mecânica e elevada resistência à corrosão, a estrutura do tipo perlita não possui boas propriedades mecânicas e é pouco resistente à corrosão. Os resultados da microdureza revelaram uma boa correlação entre dureza e a estrutura cristalina da amostra. Observou-se que as ligas tratadas isotermicamente até 3 horas, as quais são constituídas predominantemente pela fase  cúbica, apresentaram baixos valores de dureza. Por outro lado, essas ligas tratadas isotermicamente por 24 horas transformaram-se majoritariamente em fase α com estrutura ortorrômbica e elevados valores de dureza. Isso mostra que a estrutura do tipo perlita é mais dura do que a fase . Os pós das ligas dúcteis de U-2,5Zr-7,5Nb e U-3Zr-9Nb foram obtidos pela cominuição das mesmas com uso do hidrogênio. A cominuição realizada pelo processo de hidretaçãodesidretação foi feita na temperatura de cerca de 200 oC, em diferentes tempos variando entre 20 minutos a 4 horas. Os pós assim obtidos foram caracterizados por intermédio de microscopia ótica, difração de raios X e determinação da distribuição do tamanho de partículas por meio do equipamento a laser CILAS. O processamento utilizado permitiu a obtenção de pós com duas classes de tamanhos dependendo do tipo de tratamento. Os pós de ambas as ligas envelhecidos a 600 oC durante 0,5 e 3 horas apresentaram pós com granulometria de 180 a 200 m e, por outro lado, os pós de ambas as ligas envelhecidas a 600 oC durante 24 horas apresentaram pós com granulometria superior a 220 m. Os pós de ambas as ligas homogeneizados a 1000 oC e envelhecidos até 3 horas a 600 oC com granulometria na faixa de 180 a 200 μm são adequados para serem utilizados na dispersão do cerne para a obtenção de combustível tipo placa para uso em reatores de teste e de potência de pequeno e médio portes.
Plate-type dispersion metallic nuclear fuel is a versatile fuel that can be designed to be used in both test and power reactors. The high density of uranium alloys with transition elements, such as Zr, Nb, Mo, etc, allows the use of this fuel with low uranium enrichment, which makes it safer in order to prevent nuclear proliferation. Furthermore, the excellent mechanical properties and high corrosion resistance of U-Zr-Nb metallic alloys makes the choice of this alloy as plate type fuel in a development of great attractiveness due to the possibilities of achieving a high performance fuel. In this study, it was investigated the phase transformations of the U-2.5Zr-7.5Nb and U-3Zr- 9Nb in distinct heat treatments, as well as it was developed the process of comminution of these alloys by the hydriding-dehydriging process. The phase transitions were obtained by performing the homogenization of the U-2.5Zr-7.5Nb and U-3Zr-9Nb alloys at high temperatures (1000 oC for 1 and 16 h) followed by water quenching, as well as by aging at 600 oC at different times (0.5, 3 and 24 h). The obtained phase transitions were characterized through the X-ray diffraction, micro hardness, optical microscopy, electron microscopy and EDS techniques. Under these experimental conditions, it was obtained two different microstructures. A single phase microstructure consisting of the martensitic  phase of body centered cubic crystallinity. The other one with the lamellar pearlite type structure, consisting on a mixture of α and  phases. The α phase has orthorhombic structure. Unlike of the high stability and good corrosion resistance martensitic structure, the two phases pearlite type structure has poor mechanical properties and low corrosion resistance. The results of microhardness have revealed a good correlation between hardness and crystal structure of the sample. It was observed that alloys isothermally treated up to three hours, which are predominantly the  cubic phase showed lower hardness values. Moreover, these alloys isothermally treated for 24 hours were processed mostly in α-phase with orthorhombic structure and high hardness values. This shows that the pearlite type structure is harder than the  phase. The powders from ductile U-2.5Zr-7.5Nb and U-3Zr-9Nb alloys were obtained by hydrogen comminution. The comminution process carried out by hydriding-dehydriding was performed at a temperature of about 200 oC, at different times ranging from 20 minutes to 4 hours according to the composition and phase of each alloy. The obtained powders were characterized by optical and electronic microscopy, X-ray diffraction and determination of particle size distribution by means of laser CILAS equipment. The utilized process allowed the production of powders with two particle size classes depending on the type of treatment. The powders of both alloys aged at 600 oC for 0.5 and 3 hours presented powders with particle sizes of about 180-200 μm, on the other hand, powders of both alloys aged at 600 oC for 24 hours presented powders with particle sizes greater than about 220 μm. The powders of both alloys homogenized at 1000 oC and aged up to 3 hours at 600 oC with particle size in the range from 180 to 200 μm are suitable for use in the dispersion of the fuel core to be utilized in test and power of small and medium sizes reactors.

Orientadores: Wagner dos Santos Oliveira, João Carlos Castro Abrantes
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química
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Resumo: As pilhas a combustível de óxido sólido (SOFC) têm um horizonte muito promissor graças ao uso de hidrogênio e outros combustíveis menos poluentes, eficiência alta devido à temperatura de operação ser acima de 800ºC e sua vasta gama de aplicações, desde alguns quilowatts até centenas de megawatts. Um dos seus componentes mais importantes é o eletrólito, que cumpre o papel de fazer a condução dos íons O2- do cátodo para o ânodo e fazer ainda a separação física entre os eletrodos. No estudo das SOFCs há dois materiais de grande interesse para uso como eletrólitos: a zircônia dopada com ítria (YSZ) e a céria dopada com gadolínia (CGO). Neste trabalho se busca otimizar as propriedades condutoras e mecânicas destes materiais. Sinterizaram-se amostras destes dois materiais e para as análises utilizou-se MEV ao se avaliar as microestruturas e mensurá-las, e também espectroscopia de impedâncias para a medição do comportamento condutivo. A YSZ é o material mais estudado para eletrólitos em SOFCs, dada sua alta condutividade iônica a temperaturas acima de 800ºC e sua resistência mecânica. Neste trabalho sinterizou-se uma amostra de YSZ a partir de prensagem a quente, diminuindo a temperatura de 1500ºC para 1200ºC e utilizando uma pressão de 65 MPa. A amostra apresentou satisfatória densificação, condutividade semelhante à amostra de referência, porém sua condutividade nos contornos de grão foi inferior à referência. Quanto à CGO, este é um dos materiais mais cotados para se tornar o eletrólito para as SOFCs de temperatura intermediária, entre 500ºC-700ºC, já que nessa temperatura possui condutividade iônica maior do que a YSZ. O objetivo é sinterizar amostras de CGO com dopagem heterogênea, adicionando pequenas quantidades de céria e gadolínia. Verificou-se que os aditivos, tanto a céria quanto a gadolínia, migraram para os contornos de grão e modificaram sobremaneira os valores de condução iônica e em alguns casos até o mecanismo de condução
Abstract: The solid oxide fuel cell (SOFC) has a very promising horizon due to the use of hydrogen and other cleaner fuels, efficiency due to high operating temperature, above 800°C and its wide range of uses, from a few kilowatts to hundreds of megawatts. One of its most important components is the electrolyte, as its role is the conductor of O2- ions from the cathode to the anode and to separate physically the electrodes. In the study of SOFC there are two materials with large interest for use in electrolytes: yttria doped zirconia (YSZ) and ceria doped with gadolinia (CGO). This paper seeks to optimize mechanical and conductive properties of these materials. Some samples were sintered for each one of the two materials and SEM analysis was used to evaluate the microstructures and measure them, and impedance spectroscopy for the measurement conductive behavior. The YSZ is the most studied material for electrolytes in SOFC, due to its high ionic conductivity at temperatures above 800°C and mechanical strength; this paper will attempt to densify a sample of YSZ using hot pressing, reducing the temperature of 1500°C to 1200ºC and with a pressure of 65 MPa. The sample had a satisfactory densification, and its conductivity was similar to reference sample, but its conductivity at the grain boundaries was lower than the reference. The CGO is one of the most-quoted to become the electrolyte for intermediate temperature SOFC, between 500ºC-700°C, because in this temperature CGO has higher ionic conductivity than YSZ. This paper aims to sinter samples of CGO heterogeneous doping, adding small amounts of ceria and gadolinia. It was found that the additives, both as ceria and gadolinia, migrated to the grain boundary and changed greatly the values of ion conduction and in some cases the conducting mechanism
Mestrado
Ciencia e Tecnologia de Materiais
Mestre em Engenharia Química

Questo progetto di ricerca ha l’obiettivo di illustrare il funzionamento dell’impianto TCR®-500 dimostrativo messo in opera nell’ambito del progetto europeo TO-SYN-FUEL e installato presso il sito industriale di Hohenburg, distretto di Sulzbach-Amberg in Baviera (Germania), attraverso un’esperienza diretta nel luogo di ubicazione dell’impianto. L’impianto combinato TCR-PSA-HDO ha l’obiettivo di dimostrare l’efficacia del processo di pirolisi con reforming termo-catalitico associato al processo di Pressure Swing Adsorption per la separazione di idrogeno presente all’interno del syngas e al processo di idro-deossigenazione per il miglioramento della qualità dell’olio di pirolisi per ottenere un sostituto completamente equivalente a diesel e benzina in accordo con gli standard europei EN590 e EN228, rispettiva-mente. Vengono quindi esposte nel dettaglio le fasi dell’intero processo operativo e le attività che sono state svolte durante il periodo di lavoro nel sito industriale, al fine di esporre le operazioni di gestione e le eventuali problematiche. Per comprendere la qualità dei prodotti, sono stati analizzati campioni di bio-olio e biochar presso i laboratori del Centro Ricerche Energia, Ambiente e Mare situato a Marina di Ravenna (RA). I risultati hanno mostrato coerenza con le aspettative del progetto TO-SYN-FUEL, in partico-lare per quanto riguarda l’efficacia del processo di idro-deossigenazione per la completa rimo-zione di ossigeno nel TCR-oil e la completa rimozione di zolfo durante il corso dell’intero pro-cesso. I risultati ottenuti dalle analisi del biochar rispecchiano efficacemente le reazioni che avvengono all’interno del post-reformer e, attraverso l’analisi dei rapporti H/C e O/C, si prospetta che il biochar abbia una buona capacità potenziale di rimozione degli inquinanti organici nel terreno e di miglioramento della stabilità del suolo.

After the analysis of three tendencies in the energy field: substitution of liquid and solid fuels by gaseous fuels for electricity production; advent of distributed electricity generation; and the possibility of integration in fuel-cell hybrid systems for electricity production, the micro gas turbine comes as the most promising solution. Aiming at sustainable solutions, the micro gas turbine is intended for flexible fuel utilization, thus biogas is considered as well as natural gas. Biogas is produced via anaerobic digestion, the main types of reactors and feedstock are discussed. The resulting biogas composition is presented and besides a composition of 60% methane, 40% carbon dioxide, the purification for utilization in gas turbines is also featured. With the objective of designing a compact reverse flow annular combustor operating with lean pre-mixed flames (for reduced nitrogen oxides emissions), initially for a 100 kW micro gas turbine, a preliminary design phase has been carried out where the combustor main dimensions (diameters, lenghts and passage widths) were determined. Lately it was suggested by the research team the design of a similar combustor for a 1500 kW MGT, the preliminary design has been adapted and the refinement phase proceeded. The design refinement perfomance targets are: low pattern factor (obtained with proper dilution jets positioning and flow rate); contained liner temperatures (obtained with proper positioning of the splash rings that provide cooling air films) and low total pressure losses (obtained with a constant optimization of flow passages, avoiding recirculation and stagnation zones). The combustor should also be able to burn biogas or natural gas with a flame that does not touch the combustor liner or interferes with liner cooling. CH4 and CO emissions should also result low. The design methodology of the refinement phase included four main subjects, the improvement of a feature in one of them usually has brought a beneficial aspect in another, these main subjects are: injector improvement (for proper fuel pre-mixing); primary zone flow adequacy (for proper flame positioning and reduced recirculation zones in the combustion chamber); cooling adequacy (for the liner temperatures lying below the safety value of 1150 K) and dilution adequacy (for the pattern factor shall lie below 0.21). Tangential injectors were adopted since they allow for a compact combustor and a reduced number of injectors. The disposition adopted is three injector in an upstream plane (β1) and three injectors in a downstream plane (β2). CFD simualations models used are: energy equation; Reynolds-Averaged NavierStokes (RANS) with k − realizable model (since it deals with the presence of flows with complex secondary features), turbulent kinetic energy production limiter (avoid buildup in stagnation zones) and use of standard wall function (which limits total number of cells in the domain); Species transport with volumetric reactions with the turbulence-chemistry interaction modeled using Finite-rate/Eddydissipation, the mechanism chosen was methane-air 2-step. Simulations workflow consisted in non-reactive simulations where fuel-premixing in the injector could be studied and optimized followed by reactive simulations and reactive simulation with conjugate heat transfer analysis across the liner walls. A detailed analysis of results (total pressure, velocity, equivalence ratio, rate of reaction and temperature fields) for natural gas and biogas utilization has been produced. The total number of different combustors geometries is sixty-one. The final combustor model satisfies the project requirements in terms of performance and emissions while respecting the given geometric constrains (based on turbine dimensions) and boundary conditions.

Orientador: Roseana da Exaltação Trevisan
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: Apesar de todos os avanços tecnológicos, o desenvolvimento de projeto, na grande maioria das vezes, ainda é executado de forma interativa, empírica e intuitiva, baseado unicamente na experiência, inteligência ou criatividade dos engenheiros. O desenvolvimento de processo e máquinas para solda em plástico de tanques de combustível soprados não é exceção. Assim como na fase de desenvolvimento, a alteração ou correção de um projeto já existente também é realizada de forma empírica. Visando identificar as falhas de projeto de um processo de solda existente e orientar ações de correção e melhoria, o autor deste estudo utilizou uma metodologia de desenvolvimento sistêmico de projeto, no caso o Axiomatic Design, como uma ferramenta de análise. Para tanto, ele coordenou a construção da matriz de design do processo estudado para identificar os acoplamentos existentes. Num segundo momento, baseando-se nos documentos de controle de produção diário do período de 2005 a 2007, buscou-se estimar os valores anuais do conteúdo de informação deste sistema (Isys). A correção ou melhoria dos acoplamentos que obtivessem as menores eficiências no ano de 2005 foi priorizada. O cálculo dos valores de conteúdo de informação dos anos de 2006 e 2007 visou avaliar a eficácia do método proposto. Os resultados destes cálculos comprovaram que o projeto axiomático pode ser utilizado como ferramenta de análise.
Abstract: Despite all technological and scientific breakthroughs, design is being done empirically on a trial-and-error basis, depending on intuitive and innate reasoning rather than a rigorous scientific study. Design of welding machines for fuel plastic tanks is no exception. Refurbishment and corrective maintenance tasks are also made without any scientific basis. This work intended to demonstrate the use of axiomatic design as an analytic tool for an existent machine design in use on the shop floor. Based on the literature review about Axiomatic Design and Plastic Welding, the author determined the design matrix of an existent fuel tank welding machine, identifying the coupled elements. Moreover, based on production data from 2005 to 2007, the information content (Isys) of this machine was evaluated. The correction or improvement of design parameters with low information content values in 2005 was prioritized. In order to validate the efficacy of using axiomatic design as an analytic tool, the information content values of 2006 and 2007 were evaluated. The result proves that axiomatic design can be used as an analytical tool.
Mestrado
Materiais e Processos de Fabricação
Mestre em Engenharia Mecânica

La ricerca nel campo dei motori a combustione interna è sempre più rivolta ad identificare una soluzione alternativa all’utilizzo dei combustibili derivati dal petrolio, per ragioni di carattere ambientale, politico ed economico. Il gas naturale (NG) è un combustibile ideale per motori a combustione interna, essendo caratterizzato da basso impatto ambientale e consumi ridotti rispetto ai combustibili convenzionali (benzina e gasolio). Inoltre esso è particolarmente adatto ad essere utilizzato in motori ad elevato rapporto di compressione volumetrico, ed è caratterizzato da un ampio campo di infiammabilità. Quest’ultimo aspetto promuove la combustione magra di miscele di aria e NG, ottenendo un ulteriore incremento di rendimento ed un’ulteriore diminuzione dei consumi. I motori dual-fuel NG/diesel permettono di estendere il limite magro d’infiammabilità rispetto ai motori ad accensione comandata alimentati a NG, ed allo stesso tempo consentono di ridurre il trade-off NOX-PM di cui soffrono i motori diesel. Tale tecnologia consiste nell’introduzione del NG come combustibile principale in un motore diesel. Una certa quantità di gasolio viene ancora iniettata, ed agisce come sorgente d’accensione per la miscela di aria e NG. La facilità di conversione rende la tecnologia dual-fuel particolarmente allettante come retrofit di motori diesel già esistenti che in futuro si troverebbero a non soddisfare i sempre più stringenti limiti sulle emissioni inquinanti. Nel presente lavoro, la combustione dual-fuel, con la sua inerente complessità, viene analizzata seguendo un approccio misto numerico-sperimentale. L’attività sperimentale ha come obiettivo l’analisi dei vantaggi e dei problemi connessi con la conversione di un motore diesel heavy-duty al funzionamento dual-fuel, sulla base delle prestazioni e delle emissioni inquinanti. L’attività numerica è caratterizza da un approccio misto 1-D/3-D, ed è stata inizialmente condotta per la corretta comprensione del complesso meccanismo di combustione in modalità dual-fuel. L’analisi multi-dimensionale (3-D) dettagliata del sistema cilindro–pistone è stata successivamente effettuata per la corretta rappresentazione dei fenomeni termo-fluidodinamici evolventi in camera di combustione. Una tale strategia permette la completa descrizione del comportamento dell’intero sistema motore e della combustione dual-fuel nel dettaglio.
The research activity on internal combustion engines is increasingly cast to find an alternative solution to reduce the wide utilization of petroleum fuels like diesel oil and gasoline, for environmental, political and economic concerns. Natural gas (NG) is an ideal fuel to be operated in internal combustion engines, since its characteristics allow for much lower environmental impact and reduced fuel consumption with respect the conventional fuels. It also is particularly suitable to be operated under high volumetric compression ratio engines, thus providing higher efficiency, and moreover it is characterized by a wide flammability range. This latter aspect promotes the employment of a lean burn strategy, thus further increasing the engine efficiency and reducing the exhaust emissions. The dual-fuel natural gas/diesel concept allows extending the lean flammability limit of NG with respect to SI-NG operations and simultaneously reducing the NOX-PM trade-off affecting diesel combustion. Such a technology consists in introducing NG as main fuel in a conventional diesel engine. A certain amount of diesel pilot injection is preserved to act as the ignition source for the air/NG mixture. The easiness of dual-fuel conversion makes such technology rather inviting especially as a retrofit for the existing diesel vehicles, which could not meet the more and more stringent emission regulations in the future. In the present study, the dual-fuel combustion process with its inherent complexity is investigated both from an experimental and a numerical point of view. The experimental activity has the main target to analyze the problems connected with the conversion of a heavy-duty diesel engine to dual-fuel operation, and to put into evidence the influence of the main engine parameters on performance and pollutants formation. The numerical activity, characterized by a mixed 1-D/3-D approach, has been carried out with the initial target of a correct understanding of the complex dual-fuel combustion mechanism. A detailed multi-dimensional simulation of the whole working cycle of the engine has been subsequently performed, to provide for the correct representation of the fluid-dynamic effect involved in dual-fuel operations. Such an approach allows for the complete description of the engine overall behavior and the dual-fuel combustion in detail.

Desde a sua invenção, o motor a combustão interna sofreu significantes evoluções, como redução do consumo de combustível, aumento da sua potência e durabilidade a um menor custo. Outros setores também evoluíram, como a busca por alternativas de combustível, tendo como exemplo o etanol hidratado combustível, que trouxe vantagens tais como maior desempenho e menor emissão de poluentes, porém com solicitações mecânicas, térmicas e termomecânicas mais severas. Sua menor lubricidade, quando comparada a da gasolina tipo C também intensificou o desgaste no par tribológico válvula e sede de válvula. Neste trabalho foram analisados diversos pares de válvulas e sedes de válvulas provenientes de quatro motores pós teste, sendo dois deles de mesma especificação técnica e submetidos às mesmas condições de ensaio, variando somente o combustível utilizado (etanol hidratado combustível e gasolina comum tipo C). A topografia da superfície de contato foi avaliada através de exames das superfícies com lupa estereoscópica, microscópio eletrônico de varredura e perfilômetro óptico a fim de identificar os danos encontrados. Ao término das análises foi realizada a comparação dos danos encontrados entre a superfície de contato das válvulas e sedes do motor que operou com etanol hidratado combustível e gasolina comum tipo C, de forma a evidenciar as diferenças proporcionadas pelos combustíveis. Este trabalho faz parte do \"Consórcio de P&D e Desafios Tribológicos em Motores Flex-Fuel\" patrocinado pela FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo) com participação da indústria automotiva, para identificar os modos de desgaste atuantes.
Since its invention the internal combustion engine presented significant improvements like lower fuel consumption, higher power and durability increase at reduced costs. Other industries sectors did also improve as the search for new alternative fuels such as hydrated ethanol fuel which brought advantages like higher performance with lower pollutant emissions, although with it came more severe mechanical, thermal and thermo-mechanic stresses. Ethanol lower lubricity when compared to type C gasolines did also increase the valve/ valve seat insert wear. This study presents the results of contact surface analysis of several pairs valve/ valve seat insert from four engines after test being two of them of same technical specification and submitted to the same test cycle with only difference their fuel (hydrated ethanol and regular type C gasoline). The contact surface topography was evaluated through surface exams using optical microscopy, scanning electron microscope and non-contact profiler, to evaluate damages. At the end of analysis, a comparison between valves and valve seats from the engines that operated with hydrated ethanol and regular type C gasoline in order to put in evidence the damage difference provided by the fuels. This study is part of \"Consórcio de P&D e Desafios Tribológicos em Motores Flex-Fuel\", sponsored by FAPESP (\"Fundação de Amparo à Pesquisa do Estado de São Paulo\") with participation of automotive industries, to characterize the existent wear.

Doutoramento em Nanociências e Nanotecnologia
The main objective of this dissertation is the development and processing of novel ionic conducting ceramic materials for use as electrolytes in proton or oxide-ion conducting solid oxide fuel cells. The research aims to develop new processing routes and/or materials offering superior electrochemical behavior, based on nanometric ceramic oxide powders prepared by mechanochemical processes. Protonic ceramic fuel cells (PCFCs) require electrolyte materials with high proton conductivity at intermediate temperatures, 500-700ºC, such as reported for perovskite zirconate oxides containing alkaline earth metal cations. In the current work, BaZrO3 containing 15 mol% of Y (BZY) was chosen as the base material for further study. Despite offering high bulk proton conductivity the widespread application of this material is limited by its poor sinterability and grain growth. Thus, minor additions of oxides of zinc, phosphorous and boron were studied as possible sintering additives. The introduction of ZnO can produce substantially enhanced densification, compared to the un-doped material, lowering the sintering temperature from 1600ºC to 1300ºC. Thus, the current work discusses the best solid solution mechanism to accommodate this sintering additive. Maximum proton conductivity was shown to be obtained in materials where the Zn additive is intentionally adopted into the base perovskite composition. P2O5 additions were shown to be less effective as a sintering additive. The presence of P2O5 was shown to impair grain growth, despite improving densification of BZY for intermediate concentrations in the range 4 – 8 mol%. Interreaction of BZY with P was also shown to have a highly detrimental effect on its electrical transport properties, decreasing both bulk and grain boundary conductivities. The densification behavior of H3BO3 added BaZrO3 (BZO) shows boron to be a very effective sintering aid. Nonetheless, in the yttrium containing analogue, BaZr0.85Y0.15O3- (BZY) the densification behavior with boron additives was shown to be less successful, yielding impaired levels of densification compared to the plain BZY. This phenomenon was shown to be related to the undesirable formation of barium borate compositions of high melting temperatures. In the last section of the work, the emerging oxide-ion conducting materials, (Ba,Sr)GeO3 doped with K, were studied. Work assessed if these materials could be formed by mechanochemical process and the role of the ionic radius of the alkaline earth metal cation on the crystallographic structure, compositional homogeneity and ionic transport. An abrupt jump in oxide-ion conductivity was shown on increasing operation temperature in both the Sr and Ba analogues.
O principal objetivo deste trabalho é o desenvolvimento e processamento de novos materiais cerâmicos protónicos e iónicos para utilizar como eletrólito das células de combustível de óxidos sólidos (PCFCs e SOFCs, respetivamente). Com este estudo pretende-se, então, desenvolver novas formas de processamento e/ou materiais que apresentem características eletroquímicas atrativas, à base de óxidos cerâmicos nanométricos de pós preparados por processos mecanoquímicos. Existem alguns requisitos que devem ser tidos em conta de forma a garantir a máxima eficiência das PCFCs, destacando-se a elevada condutividade protónica do eletrólito aquando da operação numa gama de temperaturas intermédias, 500-700ºC. Os materiais do tipo “perovskite” foram apresentados como potenciais candidatos a incorporar o eletrólito das PCFCs, sendo o BaZrO3 dopado com 15 mol% de ítrio (BZY) o material base escolhido neste trabalho. Apesar da sua conhecida elevada condutividade protónica, estes materiais apresentam algumas limitações, tais como a fraca sinterabilidade e crescimento de grão. De forma a ultrapassar esta dificuldade, foram adicionadas pequenas quantidades de óxidos de zinco, fósforo e boro que foram estudados como possíveis aditivos de sinterização. A adição de ZnO mostrou melhorias significativas na densificação quando comparado com o material não modificado (BZY), permitindo ainda reduzir a temperatura de sinterização de 1600ºC para 1300ºC. Neste trabalho estudou-se, também, qual o melhor mecanismo de solução sólida para a adição deste aditivo, tendo-se obtido a máxima condutividade protónica nos materiais em que o Zn é intencionalmente introduzido na composição de base de “perovskite”. O P2O5 mostrou ser menos efetivo como aditivo de sinterização. A sua presença foi bastante prejudicial no crescimento de grão, apesar dos elevados níveis de densificação obtidos quando adicionado em quantidades entre 4 e 8 mol%. Porém, a utilização de fósforo mostrou também ser dramática no transporte elétrico, diminuindo a condutividade não só no interior do grão (“bulk”) como nas suas fronteiras. Já a adição de H3BO3 ao BaZrO3 (BZO) mostrou-se muito efetiva para a sinterização deste componente. Contudo, quando adicionado ao sistema dopado com ítria (BaZr0.85Y0.15O3-, BZY), o comportamento é diferente, produzindo níveis deficientes de densificação quando comparado com o BZY puro. Este fenómeno ocorre devido à formação de fases secundárias de borato de bário, cujas temperaturas de fusão são bastante elevadas. Na última parte deste trabalho foi estudado um novo material com condutividade iónica de iões óxido, o (Ba,Sr)GeO3 dopado com K. Neste estudo pretendia-se, não só avaliar a possibilidade de preparar estes pós com recurso a processos mecanoquímicos, como também estudar o papel da variação do raio iónico do catião metálico alcalino-terroso no transporte iónico, homogeneidade composicional e estrutura cristalina. Verificou-se que este material apresenta uma alteração significativa na condutividade iónica com o aumento da temperatura de operação em ambas as composições (Ba e Sr).

Il processo produttivo degli iniettori di combustibile può essere significativamente migliorato con un accurato controllo di posizionamento durante l’assemblaggio per interferenza di componenti sensibili. Il lavoro di tesi presenta un’innovativa stazione di assemblaggio che combina un cilindro idraulico ed un attuatore piezoelettrico, per raggiungere accuratezze micrometriche nel posizionamento assiale. Il cilindro idraulico esegue grandi corse mente l’attuatore piezoelettrico fornisce l’azione dinamica e l’elevata accuratezza necessaria. La caratterizzazione sperimentale del prototipo di pressa viene presentata, insieme con i fenomeni fisici che ne influenzano le prestazioni. I campioni di prova sono progettati e realizzati per ottenere un’interferenza nota. I sistemi di assemblaggio tradizionali non sono in grado di realizzare accuratezze micrometriche, mentre la nuova stazione di assemblaggio presentata può superare questi limiti grazie all’avanzato algoritmo di controllo sviluppato: quando l’attuatore piezoelettrico è alimentato da un segnale sinusoidale modulato in ampiezza, è possibile raggiungere un’accuratezza di posizionamento di ± 2 μm per forze di inserimento fino a 20 kN. Le performance ottenute con provini dedicati sono state testate su due casi applicativi reali: un processo di calibrazione a secco di iniettori GDI, nella regione balistica, usando azoto invece di un liquido di test ed il processo di assemblaggio della valvola di controllo a solenoide di un iniettore diesel common rail, che necessita di un’elevata accuratezza geometrica. Questi studi hanno dimostrato le possibilità del prototipo di stazione di assemblaggio presentato in casi applicativi reali; perciò la pressa può essere inserita in contesti industriali reali, raggiungendo lo scopo della ricerca.
The production processes of fuel injectors can be significantly improved by a more accurate positioning control in the assembly of key components by interference fit. This thesis presents an innovative press-fitting station in the assembly line, that combines a hydraulic cylinder and a piezoelectric actuator to reach micrometric accuracy in axial positioning. The hydraulic cylinder permits a long operational range, while the piezo actuator provides dynamic action and micrometric accuracy. The experimental characterization of the prototype press is presented together with the physical phenomena influencing the overall system performance. The tests are done using cylindrical plugs and sleeves to replicate the insertion of shafts into holes. The test samples are designed and machined to obtain a predefined interference fit. The presented new press-fit station can overcome these limits thanks to the developed advanced control strategy: when the piezo actuator is driven by an amplitude modulated sinusoidal signal, final positioning of ±2 μm is reached insertion forces up to 20 kN. The remarkable performances obtained using dedicated samples have been then tested for real components in two different use cases: dry calibration process for GDI injector and assembly of a solenoid control valve for state of the art common rail diesel injector. The first is a cleaner process for calibration of GDI injector in the ballistic region, that uses Nitrogen instead of a liquid working fluid. With this approach a substantially lower error for the injected quantity in the low quantity region can be accomplished. The second application case is an assembly between the pin and the armature of the solenoid control valve of a common rail diesel injector. These studies have confirmed the possibilities of the press prototype in real application cases; thus, the press can be inserted in real industrial process, achieving the scope of the research.

Le celle a combustibile microbico vegetali, Plant Microbial Fuel Cells (PMFC), sono sistemi in grado di raccogliere energia elettrica dall'attività di microbi e piante viventi. Questa tecnologia combina 2 processi noti: la rizodeposizione e la generazione di elettricità da composti organici in una cella a combustibile microbico (MFC). Anche se non sono in grado di competere con altre fonti di energia verde, come i pannelli fotovoltaici in termini di produzione di energia, le PMFC hanno una minore tensione di risorse sulla terra e difficoltà di smaltimento a fine vita. Le PMFC hanno anche varie potenziali applicazioni complementari, come il trattamento simultaneo delle acque reflue, oppure possono essere utilizzate in combinazione con la produzione alimentare e persino nella bonifica dei terreni contaminati. La ricerca è stata condotta in seguito alla collaborazione tra la start-up olandese Plant-e e il Centro di Ricerca e Innovazione per la Sostenibilità (RISC) della corporate tailandese MQDC. Il test sul campo di PMFC in Tailandia mira a raccogliere dati per indagare se la tecnologia attualmente utilizzata nei Paesi Bassi è applicabile anche in un clima tropicale e quantificare le differenze di prestazione tra gli impianti nei Paesi Bassi e in Tailandia. Dai risultati è emerso chiaramente che le condizioni in Tailandia sono favorevoli al funzionamento della tecnologia di Plant-e e in generale delle P-MFC in termini di potenza massima e di tempo di avviamento. La tecnologia esistente, i tubi per le zone umide, ha avuto prestazioni maggiori in Tailandia piuttosto che nei Paesi Bassi. Con l’obiettivo di offrire un servizio di recupero energetico completamente integrato in natura ed alimentato dai composti organici rilasciati dall'apparato radicale delle piante, il sistema tubolare P-MFC sviluppato da Plant-E può essere indicato come la soluzione migliore del suo campo.

O petróleo é uma mistura complexa consistindo em um número muito grande de hidrocarbonetos. A descrição completa de todos os hidrocarbonetos existentes nessas misturas é inviável experimentalmente ou consome tempo excessivo em simulações computacionais. Por esta razão, uma abordagem molecular completa para cálculos de propriedades dessas misturas é substituído por uma abordagem pseudo-componente ou por correlações entre propriedades macroscópicas. Algumas dessas propriedades são utilizadas de acordo com a regulamentação de venda de combustíveis, e.g., para gasolina. Dependendo do esquema de refino e do óleo cru utilizado para produção desse combustível, uma larga variedade de valores é encontrada para as propriedades de correntes de processo que compõe o combustível final. A fim de planejar com precisão adequada a mistura dessas correntes, modelos devem estar disponíveis para o cálculo preciso das propriedades necessárias. Neste trabalho, oito séries de combustíveis brasileiros e duas séries de combustíveis estrangeiros foram analisadas: frações de gasolina, querosene, gasóleo e diesel. As propriedades analisadas para as frações são: número de octano, teor de aromáticos, teor de enxofre, índice de refração, densidade, ponto de fulgor, ponto de fluidez, ponto de congelamento, ponto de névoa, ponto de anilina, pressão de vapor Reid e número de cetano. Diversas correlações foram avaliadas e os melhores desempenhos foram destacados, permitindo uma estimação precisa das propriedades do combustível avaliado. Um processo de re-estimação de parâmetros foi aplicado e novos modelos foram ajustados em comparação com os dados experimentais. Esta estratégia permitiu uma estimativa mais exata das propriedades analisadas, sendo verificada por um aumento considerável no desempenho estatístico dos modelos. Além disso, foi apresentado o melhor modelo para cada propriedade e cada série
Fuel fractions are complex mixtures consisting of a huge number of compounds. A complete description of all non-trace substances of these mixtures is experimentally unfeasible or computationally time consuming. For this reason, a complete molecular approach for calculation of properties of these mixtures is replaced by a pseudo-component approach or by correlations between bulk properties. Some of these properties are used in the regulation of fuel sells, e.g., for gasoline. Depending on the refining scheme and on the crude oils used to produce these fuels, a large variety of values are found for the properties of process streams that compose the final fuel. In order to accurately plan the blending of these streams, models have to be readily available for accurate calculation of the needed properties. In this work, eight sets of fuel Brazilians and two sets of fuel strange were analyzed: gasoline, kerosene, gas oil and diesel fractions. The properties analyzed for fractions were octane number, aromatics content, sulfur content, refractive index, density, pour point, flash point, freezing point, cloud point, aniline point, Reid vapor pressure and cetane number. Several correlations were evaluated, and the best performances were pointed out, allowing an accurate estimate of properties of the studied fuels. A parameter re-estimation procedure was applied, and new models were tuned against the experimental information. This technique allowed an accurate estimate of properties of the samples, verified by a considerable enhancement in the statistical performance of the models. Furthermore, the best model for each property and each series was presented

Research estimated toxicity of refuse-derived fuel fly ash (RDF-FA) on two earthworms species, Lumbricus terrestris and Eisenia foetida. Specific objectives were to: (1) Compare their 14-day LC50s under light and dark conditions; (2) separate toxicity due to osmotic, pH and physical factors from that of heavy metal contaminants; (3) compare relative differences of artificial soil and commercial soil as exposure media for evaluating toxicity to earthworms. The 14-d LC50s for L. terrestris in dark and light were 57.0 and 48.34 % RDF-FA, and 59.25 and 41.00 % RDF-FA for E. foetida using artificial soil. All of the toxicity resulted from heavy metals within the RDF-FA. Using L. terrestris, the LC50s for artificial soil and commercial soil were 52.30 and 64.34%.

This Ph.D. thesis focuses on testing and modelling PEMFC single cell systems, to better understand internal phenomena and to find out operative solutions able to increase the overall cell performance. Thus, the first step is based on the creation and validation of a wide spectrum of multi-physics models of PEMFC fed with hydrogen or methanol, by using Comsol® Multi-physics platform coupled with Matlab®. All models are able to work under different operating conditions and with materials of different characteristics (membranes and catalysts). Moreover, the efforts were also focused on the creation of models of systems similar to fuel cell, as the gas diffusion electrode (GDE). The GDE is usually employed to analyze the electrochemical properties of the catalytic layer. Each single model was validated against a huge set of experimental data (partly obtained at POLITO, partly provided by the partners of two research projects: DURAMET and NAMEDPEM). After the model validation, these models were used to investigate the internal phenomena, and how materials, geometry and operative conditions affect the cell performance. Furthermore, particular problems affecting the entire FC system such as water flooding, methanol crossover, flow patterns design and current density distribution were deeply investigated to provide reasonable solutions. In general, the 3D multi-physics, multi-component, multi-phase and not-isothermal models developed in this Ph.D. include Maxwell-Stefan, Navier-Stokes-Brinckman, and extended two-phase Darcy-law to solve velocity, pressure, and mass transfer equations, and modified Butler-Volmer and Tafel equations to describe the electrochemical kinetics. All the equations are coupled to each other to simulate the performance of a single cell PEMFC (or GDE), reproducing the electrochemical, fluid-dynamics, and thermal phenomena. Each model was validated by comparing the simulated results, in terms of electric performance (polarization curves and power density curves), with experimental data obtained by changing several parameters: -Type of membranes: Nafion® (N112, N115, N117), Fumapem® (F1850) for the DMFC, Nafion® (N-HP and NR-212) for the hydrogen-fed PEMFC. -Dimensions of active area of the single cell: 5cm2 and 25cm2. -Catalyst: eight different catalysts for the DMFC, four for the hydrogen-fed PEMFC, three for the GDE (commercial Pt/C, PtRu/C and lab-made FeNC-based catalysts). -Operative conditions: pressure, methanol inlet concentration, air or oxygen at the cathode, cell and flow temperatures, anode and cathode flow rates, humidification and stoichiometric ratio (for the hydrogen-fed PEMFC). -Flow field designs: unique serpentine, four parallel serpentines and four inlet serpentine. After the validation, the models were used to reproduce and study the multi-dimensional trends of particular phenomena which produce system losses and/or affect the performance. In first istance, the multi-physics analysis was used to improve the way to deposit the catalyst, thus the catalytic layer distribution was investigated in order to have a better uniformity in the current density distribution at the membrane/anodic catalyst interface. The proposed solutions, the 3-Layers MEA, was modelled in Comsol® and tested in the lab. It should avoid hot-spots on the membrane as a consequence of the better uniformity in the current density distribution, with a consequent increase in the life-time of the MEA (chapter I) The second step was the analysis of the influence of water flooding and catalyst materials. The extended two-phase Darcy-law was used into the model to describe the mass transport inside the micro-porous structure of the noble/non-noble metal cathode catalyst, produced in our labs. The multi-physics analysis displays a direct relationship between the water saturation, the oxygen diffusion flow, and the oxygen consumption. Thus, water condensation inside the micro-pores may produce the flooding of micro and meso-porous, showing a consequent link between condensation and decreasing of cell performance (chapter II). The third step of the multi-physics analysis was the study of the influence of FF design (unique serpentine, four parallel serpentines, four inlet serpentines.) and types of membrane on system performance. A large amount of lab tests and simulation were performed for each FF, by changing the temperatures, the inlet flow rates, the inlet methanol concentrations and the type of cathode flow. Pulse Field Gradient (PFG) NMR spectroscopy was used to get a direct measurement of the diffusion coefficients of water and methanol through the membranes. Thus, the model was used as a tool to investigate anodic overpotentials, water and methanol crossover flow rates, current density distribution along the membrane, understanding the relationship between the shape of the FF and cell performance (i.e. pressure and methanol consumption).(chapter III) To improve the research on the area of catalyst properties, the study focused on the cathode using the gas diffusion electrode (GDE), trying to find out key parameters which influence the performance of catalysts for the oxygen reduction reaction. A commercial Pt-based catalysts and the non-noble metal Fe–N–C catalyst prepared in-house were tested and modelled, to carry out a sensitive analysis by varying the inlet oxygen flow rate, showing the influence of oxygen diffusive flow on the catalyst performance. The multi-physics analysis provides the way to increase the performance of the non-noble metal catalyst by changing some system properties as tortuosity, porosity and hydrophobicity (chapter IV) After the large analysis developed for DMFC, the PhD work continued with the modelling of hydrogen-fed PEMFC, to complete, in such way, the general sensitivity analysis on PEMFC systems. Obviously, some innovations and changings were introduced to adapt the model with the new inlet fuel, as new equations and parameters for the electrochemical behaviours, initial and boundary conditions, H2 crossover and controlled parameters, i.e., relative humidity. The multi-physics analysis and the lab tests show how the relative humidity influence the performance, in relation to the variation of pressure and temperature (chapter V) After the experimental and modelling studies, the PhD work was focused on several aspects, in order to improve the performance of the single cell with Fe-N-C catalyst on the cathode, related to material improvement and the single cell system: the active surface area, the percentage of micro-pores present in the catalytic layer, the membrane type, the procedure of catalyst deposition, the back pressure and the closing force. Thus, the modelling and lab work performed outcome in an excellent result: the system performance increases four times than the initial computed value, from about 10 mW cm–2 to 40.6 mW cm–2.

L'incremento delle sorgenti ad energia rinnovabile porterà  un grande cambiamento sulla rete elettrica nazionale, la quale dovrà operare in modo intelligente per gestire la fornitura di molti produttori di energia distribuita e per compensare l'imprevedibilità delle rinnovabili. Tuttavia, per poter far ciò, le reti elettriche del futuro necessitano di generatori distribuiti capaci di assicurare servizi quali l'inseguimento del carico, l'accumulo di energia, la compensazione dei disturbi e che abbiano un effetto mitigante sui picchi di carico e/o di generazione. I sistemi a celle a combustibile, specialmente quelli alimentati ad idrogeno, hanno raggiunto considerevoli target in termini di prestazioni in condizioni di laboratorio. Combinando alta efficienza ed un comportamento dinamico veloce (disponibilità  di potenza immediata su richiesta), anche a carichi parziali e con piccole taglie, i sistemi a cella a combustibile di tipo PEM sono sempre di più analizzati nell'ottica del loro impiego nelle nascenti reti di potenza. Lo scopo di questo lavoro è mostrare le attuali performance delle fuel cell, il loro comportamento durante il funzionamento con la rete elettrica ed, in particolare, i fenomeni relativi alla degradazione dei materiali che possono verificarsi in questo tipo di applicazioni. Dapprima l'attività di ricerca è stata indirizzata allo sviluppo di un sistema da 5 kW di tipo PEM, considerando le procedure di start up e di warm up, l'analisi del comportamento dinamico in funzione della variazione della temperatura e del carico elettrico. Conseguentemente, alcuni test sono stati condotti sia su sistemi che su monocella in modo da poter confrontare le prestazioni in caso di carichi in corrente continua ed alternata. Infatti, la potenza in reti monofase contiene una fluttuazione sinusoidale a bassa frequenza che procura un ripple sulla corrente di uscita dello stack. I test hanno mostrato la degradazione del materiale del catalizzatore dovuta a questo tipo di dinamica.
An increase in renewable energy sources (RWE) will bring about a great change in the national electric grid, which will operate intelligently (smart grid) in order to manage the supply of several energy producers and to cover the unpredictability of RWE [1]. Nevertheless, in order to become smart, the future electrical networks need active distributed units able to assure services like load following, back-up power, power quality disturbance compensation and peak shaving. Fuel cell systems, especially those fed with hydrogen, have reached considerable performance targets in laboratory conditions. Combining high efficiency and fast regulating behaviour (power on demand), even at partial loads and on small size units, PEM fuel cell systems are more and more investigated as components of the incoming power networks. The aim of this work is to highlight the fuel cells actual performances, their behaviour during grid connected operation and, particularly, the phenomena of materials degradation that can appear in these applications. At first, the research activity was addressed to the investigation on a developed 5 kW PEM fuel cell system, including the start-up and warm up procedure, the analysis of the dynamic behaviour linked to temperature and load variations. Accordingly, tests were conducted both on fuel cell systems and single cells in order to compare the performances evaluated with dc and ac loads. In fact, power drawn by single phase grids contains a low frequency sinusoidal fluctuation that brings a large ripple on the stack output current. The tests on single cells have determined the degradation occurred on catalyst material due to the effect of this kind of dynamic loads.

2012 - 2013
The present dissertation illustrates the complete procedure of developing a model-based diagnosis algorithm and shows its application to a pre-commercial Solid Oxide Fuel Cell (SOFC) system. The main motivations of this work can be found in the increasing demand for diagnostic techniques aimed at both ensuring system optimal performance and required lifetime. The purpose of a diagnostic algorithm is to detect and isolate undesired states (i.e. faults) within the system under study (e.g. both the stack and balance of plant – BOP – components of an SOFC system). The understanding of the main mechanisms inducing malfunctions or, in the worst case, abrupt interruptions (i.e. failures) of the system allows the definition of suitable control strategies to avoid these events and to ensure the required system performance. Among all the diagnostic techniques available in literature, a model-based fault diagnosis methodology is taken into account. According to this technique, a process model is exploited to treat the data measured during the system operation to obtain insightful indicators of the system state. More in details, the measured data are compared to simulated variables to extract features, i.e. mathematical residuals, which are representative of the monitored variables behavior. The residuals computation is performed during the monitoring process. The detection of undesired or unexpected system behaviors is carried out through the comparison of the collected residuals to reference threshold values. These values are suitably tuned to take into account several uncertainties, like model inaccuracy and measurement noise, and the necessity to detect incipient faults. The comparison of the computed residuals to these thresholds allows the generation of analytical symptoms, which indicate whether an undesired event is occurring or not. The arise of a symptom points out that the behavior of the related variable is abnormal, completing the detection process. At this stage, although the occurrence of a fault is observed, its type is still unknown. To accomplish this last task, a reference set of information is exploited for the identification of the malfunction nature and for the isolation of the faulty component(s) (isolation process). These information comprise the main faults the system can be affected by and the variables conditioned by the occurrence of these faults. The symptoms collected during the detection phase, which are representative of the variables showing an irregular (or unexpected) behavior, are compared to the reference information to correctly locate the fault on the system. The first part of this manuscript entails the design procedure of a generic model-based diagnosis algorithm, describing in detail the development of the mathematical model and the definition of the reference information required by the methodology. The presented model derives from an SOFC system model, developed by Sorrentino et al. [1][2]. This model is based on a lumped approach and is able to simulate both steady and dynamic behaviors of the system state variables. The stack is assumed planar and co-flow and its voltage behavior is represented by a non-linear regression, function of fuel utilization, current density, excess of air and the temperatures at the stack inlet and at the stack outlet. On one hand, the temperature regulation of the stack inlet flows is achieved by means of two by-pass valves, one at the anode side and one at the cathode side. On the other hand, the stack inner temperature control is fulfilled through a PI controller, which acts on the air blower power to regulate the inlet air flow. The novelty of the presented model consists in several submodels specifically developed to simulate the considered system both in normal and in faulty conditions. This feature allows the utilization of the model for the offline definition of the reference information exploited for the isolation process. The reference information help in the isolation of the undesired event(s) occurring in the system during its normal operation. This task can be achieved through the correct identification of the relationships among the symptoms, generated during the detection process, and the possible faults the system can cope with. In the present work, a Fault Signature Matrix (FSM) developed by Arsie et al. [3] following a Fault Tree Analysis (FTA), is considered as the basis for the development of the aforementioned reference information. This FSM is improved through the simulation of different kind of faults in order to understand both the direct and the indirect correlations among the faults and the system variables. Moreover, the real effects induced by the considered fault on the affected variables are defined in terms of quantitative drifts of the variables values from the normal condition. To achieve this task, the fault sub-models previously introduced are exploited to simulate the effects of several faults. For the purpose of this work, five different faults related to an SOFC system are simulated, that are i) an increase in the air blower mechanical losses, ii) an air leakage, iii) a temperature controller failure, iv) a pre-reformer heat exchange surface corrosion and v) an increase in cell ohmic resistance. Through the faults simulation, a set of residuals is collected and its comparison with different threshold levels highlights the quantitative relationships among the faults and the conditioned variables. In this way, it is possible to point out the difference between an FSM developed through a heuristic approach (i.e. the FTA), accounting only for the qualitative relationships among the faults and the symptoms, and the one developed considering also the system sensitivity to the faults magnitude. The second part of this thesis entails the characterization and the validation of the developed diagnostic algorithm on a pre-commercial micro-Combined Heat and Power (μ-CHP) SOFC system, the Galileo 1000N, manufactured by the Swiss company HEXIS AG. A dedicated experimental activity has been performed in order to induce controlled faulty states in the system. The further original feature of this work consists in the design of well-defined procedures to mimic faults on a real SOFC system. In some cases, the procedure involves only suitable maneuvers via software control system, whereas in other cases, specific hardware modifications are required. Before applying the developed diagnostic algorithm to the Galileo 1000N, an adaptation process is performed, in order to suit each part of the algorithm to the system under analysis. The need for a fast and handy model, which can be rapidly tuned by the algorithm user, led to the development of a maps-based model to simulate the system in normal conditions and to extract residuals. This model exploits the average values of the monitored variables through numerical maps, which are function of the operating condition set-point values. Additionally, the FSM improved off-line via faults simulation is further modified taking into account the number of variables practically monitorable and the system control strategies. Moreover, a statistical hypothesis test is implemented in order to evaluate the probability of false alarm and missed fault. These analysis is significant for the correct interpretation of the generated symptoms during the detection phase. Concerning the impact of the present research activity, the developed algorithm aims at improving both the performance and the lifetime of an SOFC system by its implementation into a comprehensive control strategy. In this way it is possible to associate to the diagnosis of the system status specific counteractions performed by the system controller. In this way, both the manufacturer and the final users can obtain significant advantages in terms of management costs reduction (i.e. maintenance and materials costs) and overall efficiency increase. To summarize, the main contributions and innovative features of this research activity are listed in the following: · the development of a diagnostic algorithm following a model-based approach; · the improvement of an FSM, based on an FTA, through the exploitation of fault models simulation to evaluate the sensitivity of the monitored variables to the faults magnitudes; · the implementation of a statistical hypothesis test for the evaluation of false alarm and miss detection probability; · the design of specific procedures and hardware modifications to mimic faults in a controlled way on a real SOFC system (i.e. the Galileo 1000N) for the diagnostic algorithm validation; · the offline and the online validation of the proposed algorithm implemented on-board and controlled through a graphic user interface. It is worth noting that the innovative features presented in this manuscript are a pioneering contribution in the available literature. Most of the results presented in this dissertation have been carried out within the framework of the European Project GENIUS (Generic diagnosis instrument for SOFC systems) and received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) for the Fuel Cell and Hydrogen Joint Technology Initiative under grant agreement N° 245128. [edited by author]
XII n.s.

The research program developed during the Ph.D. School is focussed on the study of advanced materials for applications in the intermediate temperature solid oxide fuel cells (IT-SOFCs). Fuel cells (FCs) are often considered as the best solution to produce clean energy starting from various primary resources. FCs are employed for the direct production of electric power by electrochemical conversion of the potential energy of a fuel. Fuel cells work as a common galvanic cell: the fuel is oxidised at the anode and the combustive (usually air) is reduced at the cathode. Among the various kind of fuel cells, solid oxide fuel cells are very interesting thanks to their singular properties, such as the high output powers (reaching megawatts) and the excellent efficiency (until about 70% with the co-generation). Another interesting characteristic is the ability to work with different type of fuels. Beyond hydrogen (whose usage involves the well know difficulties concerning production, transportation and storage), SOFCs can operate with alcohols (such as methanol and ethanol) or hydrocarbons. This can offer significant opportunity in renewable energy field taking into consideration fuels derived from bio-masses and urban or industrial rubbish. A common SOFC usually works at very high temperature (800÷1100°C). Anyway, many studies have been carried out to develop new materials able to guarantee the best performances at lower temperatures (500÷700°C) and build the new generation of SOFCs: the so-called Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFCs). Nevertheless it is, necessary to develop new electrolyte materials characterized by high anionic conduction at lower temperatures and new electrodes with electronic, or better mixed ionic-electronic conductivity (MIEC) and a suitable activity toward fuel oxidation and combustive reduction. In the present study, several perovskite based oxide materials have been considered. These particular compounds show a wide range of interesting chemical and physical properties. Moreover, these characteristics can be tuned employing different constituting elements and different kinds and amounts of dopant elements. Taking into account the literature research outcomes, two kinds of perovskites have been studied: gallates and cuprates. The first ones are lanthanum gallate doped with strontium and iron and with strontium and copper (La0.8Sr0.2Ga0.8Fe0.2O3-?, named LSGF, La0.8Sr0.2Ga0.8Cu0.2O3-?, LSGC), while the second types derive from lanthanum cuprate (LaCu0.8Co0.2O3-?, LCC1, and La2Cu0.8Co0.2O4-?, LCC2). The samples have been prepared by means of two wet-chemistry procedure (Pechini process and the Polyacrylamide Gel method) to avoid using the high temperature ceramic route and to study the influence of the preparation procedure. The obtained catalysts were characterized by means of X-Ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and Diffuse Reflectance Infrared spectroscopy Fourier Transform (DRIFT) Spectroscopy. In general, XRD revealed the presence, beside the desired one, of minor phases whose amount and typology is influenced by the composition and doping. In the case of LCC1, in contrast, a mixture of La2Cu0.8Co0.2O4-? and CuO, was obtained instead of LaCu0.8Co0.2O3-?. XPS investigation testifies the surface segregation of strontium as carbonate and of lanthanum as oxide and hydroxide. Copper is present as copper oxide both in LCC1 and LCC2. As a general consideration, the presence of carbonate species and hydroxyl groups is mainly a surface phenomenon. Interesting information have been obtained from the catalytic tests. The reactivity of the materials has been investigated toward methanol and ethanol under several conditions: tests with pure alcohol vapours, under oxidising atmosphere (enriching the carrier gas with O2) and in steam reforming conditions, have been carried out at several temperatures between RT and 400°C. The experiments were performed employing a home made continuous flow reactor monitoring the exit stream by IR and QMS. Significant differences have been observed between the samples obtained by means of the two different preparation procedures: the results, as a whole, indicate that the samples obtained by Gel procedure show a higher activity. Both in alcohol oxidation (carried out with oxygen) and in alcohol steam reforming the higher activity of cuprate based materials is evident. LSGF and LSGC, in contrast, exhibit lower reactivity. It has also to be considered that a certain poisoning of the catalysts surfaces was observed as a consequence of the interaction with the reaction products (carbon dioxide, as an example). This is particularly true when the reaction is carried out with the only alcohols or under steam reforming conditions. The cathodic activity was investigated by measuring the oxygen permeability throughout the materials pressed as a pellet. The permeation mechanism is specific for O2 and provides useful information concerning both redox and transport properties (for oxide anions) for the investigated material. Permeability measurements were carried out employing a home made reactor. This is expressly conceived, realized and optimized during the PhD term. A detailed study concerning the materials (ceramic macor) and fittings has been done (paying particular attention to the pasting of the samples on the ceramic support). The tests have been monitored by means of QMS and show particularly interesting results for the cuprates.

Quando dois ou mais mercados, anteriormente separados, começam a apresentar certa convergência de preços, diz-se que eles estão integrados. Geralmente, os pesquisadores têm objetivado o estudo da integração entre mercados externos e internos (integração espacial) ou entre os diferentes elos de uma cadeia produtiva (integração vertical), mas de um único produto. Após uma importante mudança na tecnologia, concretizada através do lançamento dos motores flex-fuel no Brasil, a presente pesquisa teve por desafio analisar a existência de integração entre os mercados da gasolina e do etanol, dita como "integração de mercados por substituição". Para tal fim, e depois de filtradas as séries de preços mediante os testes de estacionariedade (Dickey-Fuller Aumentado e Phillips-Perron), foi feito uso de modelos de transmissão de preços, mais especificamente os testes de Cointegração, o do Mecanismo de Correção de Erro (MCE) e o da Causalidade. No período em análise (de março de 2003 até julho de 2008), foi constatada a presença de cointegração entre os dois mercados. Também foi observado que um incremento de 1% no preço da gasolina é responsável por um incremento de 2,74% no preço do etanol. Ainda que tenha sido pequeno o parâmetro do Mecanismo de Correção de Erro obtido, ele indica que é possível relacionar o comportamento de curto com o de longo prazo, nas séries analisadas. Dos resultados obtidos, pode-se concluir que os mercados do etanol e da gasolina estão integrados a longo prazo, onde variações no preço da gasolina causam variações no do etanol (GRANGER, 1969).
When two or more markets, previously separated, start showing a price convergence, it is possible to say that they are integrated. Usually, the researchers have focused the integration study between external and internal market (spatial integration) or between the different links of a productive chain (vertical integration), but just of an unique product. After an important technological change, materialized in the releasing of flex-fuel motors in Brazil, this work had as a challenge analyze the existence of the integration between the gasoline and ethanol markets, referred as "integration of substitution markets". Therefore, after filtering the prices series through stationary tests (Augmented Dickey-Fuller and Phillips-Perron), it was made the use of price transmission models, specifically the cointegration tests, and the Error Correction Mechanism (ECM) and the causality. In the analyzed period (from March 2003 to July 2008), it was verified the existence of cointegration between the two markets. Also it was observed that an increase of 1% in the gasoline price is responsible for the increase in 2.74% of the ethanol price. Although it was small the parameter of the correction mechanism in the obtained error, it points out that is possible to relate the behavior in the short and long term, in the analyzed series. Taking in consideration the obtained results, we arrived to the conclusion that the ethanol and gasoline markets are integrated in the long term, where variations in the gasoline price cause variations in the ethanol market.

2013/2014
Durability and cost are the major limiting factors in current PEM fuel cells development and commercialization. Electrocatalyst materials are the main responsible of both cost of the entire fuel cell stack and its degradation during operation [1,2]. In this research durability and degradation have been investigated in high temperature PEM fuel cells (HT-PEMFCs). Specific diagnostic techniques have been studied and tested for the investigation of electrocatalyst structural properties. An experimental sensibility analysis has been carried out with the purpose to assess advantages and limitations of the use of cyclic voltammetry to determine the electrocatalyst ECSA in H3PO4/PBI high temperature PEM fuel cells. Small angle x-ray scattering (SAXS) has been used to obtain structural information of the electrocatalyst nanoparticles, such as size and distribution. A procedure to characterize HT-PEMFCs MEAs by means of SAXS has been developed and tested. Transmission electron microscopy (TEM) is a complementary technique to SAXS: it has been used to validate the diagnostic method and to compare the results. Electrocatalyst evolution during long-term operation has been studied and related with performance loss. Specific stress test protocols have been developed to accelerate electrocatalyst degradation in commercial HT-PEMFC MEAs operated in single cell configuration. Two MEAs have been subjected to load cycling and one to start/stop cycling. One of the two testing protocols based on load cycling included open circuit (OC) condition in each cycle with the purpose to study the effects of frequent and short OCs during operation on MEA durability and electrocatalyst evolution. Specific start-up and shutdown procedures have been used in the start/stop test in order to limit other degradation mechanisms. Cell voltage and polarization curves have been recorded to monitor cell performance during the durability tests. The electrocatalyst structural evolution induced by load cycling has been characterized with SAXS and TEM. The stress test protocols have been effective to accelerate performance and electrocatalyst degradation of the MEA. The voltage decay rate at 200 mAcm-2 was higher than 25 μVh-1 in the samples subjected to load cycles. The start/stop cycling caused a performance degradation of 18 μV/cycle at 222 mAcm-2 during the first 450 cycles of the test. Regarding the diagnostic techniques used to characterize the electrocatalyst, cyclic voltammetry (CV) seems not to be particularly reliable when performed at high temperatures (>100°C) due to the high dependence of the voltammogram shape to humidity conditions. SAXS, on the other hand, seems to be an effective tool to investigate structural properties of PEMFC electrocatalysts. SAXS analysis showed that after 100,000 load cycles the mean size of the platinum nanoparticles more than doubled. TEM results varied about 30% from the SAXS results: this divergence could be due to a very different population size of the nanoparticles that have been analysed in the two methods. Moreover, the preparation of the sample used in TEM may have strongly influenced the electrocatalyst structure. Finally, a visualization of the electrocatalyst structural evolution on large areas of the MEAs subjected to load cycling showed preferential directions of the particles growth that could be due to the position of the channels on the flow-field plates of the fuel cell.
XXVII Ciclo
1987

E’ noto che per una effettiva immissione nel settore automotive delle celle a combustibile ad elettrolita polimerico (PEFCs) alimentate a idrogeno, una delle principali barriere da superare è legata durata dei materiali adoperati. Il fenomeno di sintering del platino e la corrosione che quest’ultimo assieme al supporto, subiscono operando alle alte temperature richieste dal settore automotive (120 ÷ 130 °C), si traduce in una riduzione del tempo di vita del catalizzatore nel suo complesso. Gli effetti del sintering e della corrosione del catalizzatore si traducono in una perdita di area superficiale attiva del platino e di conseguenza una diminuzione della potenza erogata dal sistema. Un’altra problematica da superare, per una diffusione concorrenziale nel settore automotive delle PEFCs rispetto ai classici motori a combustione interna, è il carico totale di platino. Ad oggi, le potenze erogate da questi apparati (ca. 100 kW) richiedono, soprattutto nel comparto catodico, una quantità notevole di metallo prezioso che, di riflesso, causa un aumento del costo complessivo del prodotto finito. Risulta ovvio che l’abbassamento del tenore di platino nel catalizzatore catodico gioca un ruolo determinante per una effettiva ed efficace immissione delle celle a combustibile all’interno di questo vasto mercato. Scopo di questo dottorato di ricerca è stato lo sviluppo di nuovi elettrocatalizzatori supportati in grado resistere al sintering ed alla corrosione. Per ridurre il carico di platino questi materiali devono anche essere caratterizzati da una maggiore efficienza. Si è deciso, quindi, di sviluppare catalizzatori a base di platino e di leghe platino-cobalto con caratteristiche chimico-fisiche ben definite. La scelta del cobalto deriva dalle numerose indagini effettuate su questi catalizzatori; queste hanno mostrato che alcuni catalizzatori di leghe binarie di Pt-M (dove M = Co, Fe, Ni, Cu, ecc) presentano una maggiore attività elettrocatalitica per la reazione di riduzione dell’ossigeno rispetto ai catalizzatori di solo Pt. Tra queste la lega PtCo sembra risultare quella più promettente. Ancora, vari studi hanno indicato che per i catalizzatori supportati Pt/C si ha un’attività massima a circa 3 nm come compromesso adatto tra il numero di siti e la fase cristallografica con basso indice di Miller caratterizzata da alta attività intrinseca. Obiettivo di questa attività è stato, quindi, quello di sintetizzare catalizzatori supportati a base di Pt e leghe PtCo con dimensione di particelle minore di 3 nm e contraddistinti da un adeguato grado di lega. I catalizzatori sviluppati sono stati infine caratterizzati dal punto di vista chimico-fisico ed elettrochimico (in semicella ed in cella singola) ad elevate temperature (75 °C ÷ 130 °C) con lo scopo di analizzarne il comportamento e approfondire le cause della loro degradazione.
Large scale application of polymer electrolyte fuel cell (PEFC) system technology requires a reduction of its high cost as well as improvement of performance and stability. The catalysts employed for operation in the present PEMFC are nanosized platinum particles supported on carbon. The reduction of the noble metal content and enhancement of catalytic stability are significant challenges for this fuel cell technology on the way to become cost competitive. High temperature PEFC operation (130°C) requires the development of catalyst with proper resistance to sintering and corrosion under working conditions. In order to reach these goals, the aim of this research was the development of practical carbon supported Pt anode and cathode catalysts with high metal surface area capable of operation at high temperature (130°C) with suitable resistance to corrosion, Pt dissolution, thermal and electrochemical sintering. Another aspect was the development of new alloyed electrocatalysts. Several papers in the current literature address to the development of binary and ternary Pt-alloys. In fact, results show more active and less expensive Pt-alloy for oxygen reduction reaction (ORR) catalysts with better stability than pure Pt based catalysts. Accordingly, the work was focused on the development of practical carbon supported Pt-Co alloyed catalysts. The choice of cobalt as a transition metal in alloy with platinum was derived from literature, as many of investigations shown that it is the most promising catalyst for high temperature PEFC operation. The purpose of this work was addressed on the achievement of a proper crystalline structure with face-centered-cubic phase and a high degree of alloying for the catalysts with small mean particle size (< 3 nm). The synthesis method was optimized to obtain a suitable dispersion of the metal particles on the support for high metal concentration catalysts (50 wt.%) with a mean particle size smaller than 3 nm for both Pt and Pt-Co alloyed electrocatalysts. Moreover, further studied were addressed to different pre-leaching methods on the performance and stability of synthesized Pt-Co alloy catalysts supported on carbon. These treatments were adopted to reduce the dissolution of cobalt from the particle surface in PEFCs. To understand catalysts behaviour in terms of resistance to corrosion and electrochemical sintering, different analyses (XRD, cycling voltammetry and polarization) were carried out before and after various accelerated degradation tests (ADTs) performed in a gas-fed sulphuric acid electrolyte half cell at 75°C and in a PEM single cell in a temperature range of 80 – 130°C. In conclusion, an appropriate synthesis method was developed to obtain Pt and PtCo electrocatalysts with a small particle size (< 3 nm) and suitable degree of alloying in the bimetallic electrocatalysts. Pre-leaching treatments were adopted to improve the catalytic activity and the resistance towards sintering and degradation. Accelerated degradation tests in sulphuric acid gas-fed half cell were carried out in order to investigate the influence of different pre-leaching treatments on the electrochemical behaviour. These analyses showed that the particle size of all catalysts increased after the tests. It was observed that after the Pt degradation test, the HClO4 pre-leached catalyst showed the best performance in terms of electrochemical activity and resistance to sintering.

La ricerca sulle celle a combustibile ad ossidi solidi (SOFC) ed a membrana ad elettrolita polimerico è attualmente indirizzata al miglioramento delle performance e della loro vita utile, così come alla riduzione dei costi. Tali aspetti sono importanti per rendere questi dispositivi più interessanti per il mercato, sia nelle applicazioni stazionarie che automotive. Da questo punto di vista, per la tecnologia PEMFC sembra necessario un incremento della temperatura (da 80°C a 110-120°C, high temperature PEMFC o HT-PEMFC). Ciò porterebbe ad una migliore resistenza alle impurezze di CO nel fuel, un migliore thermal and water management ed una migliore efficienza per la co-generazione. Al contrario, la tecnologia SOFC va verso temperature intermedie (IT-SOFC); ciò permetterebbe una riduzione dei costi nello sviluppo di celle planari, grazie a processi di fabbricazione meno onerosi ed ad un incremento della stabilità. Questi modi di estendere l'applicazione sono ben studiati per celle singole, ma il processo di scale-up verso dispositivi di potenza necessita di ulteriori specifici approfondimenti. Inoltre, tecnologie differenti necessitano di procedure di test differenti, adattate a specifici settori applicativi. In questa tesi di Dottorato, sono stati testati dispositivi a celle a combustibile basati su tecnologia ad ossidi solidi od ad elettrolita polimerico per applicazioni specifiche. In particolare, sono stati studiati stack di fuel cells di potenza nominale pari ad 1kW, per verificare la possibilità dell'utilizzo di fuel cell per applicazioni di piccola taglia. Attualmente, i dispositivi basati su HT-PEMFC stanno suscitando interesse per lo sviluppo delle celle a combustibile. Nonostante una profonda conoscenza delle proprietà dei materiali, la valutazione degli stessi a livello di stack è stata oggetto di un piccolo numero di studi. In questa attività di ricerca è stato approfondito proprio questo aspetto. La tecnologia IT-SOFC è considerata adatta per applicazioni stazionarie e per la produzione di energia distribuita, poiché può usare combustibile poco costoso in processi elettrochimici ad elevata efficienza. Inoltre, per applicazioni relative ad utenze residenziali, i dispositivi studiati possono essere considerati come la base per lo sviluppo di un sistema turn-key e non come la versione downscaled per studi da laboratorio. Questa tesi di Dottorato include considerazioni per applicazioni sia stazionarie che automotive, analizzando stack di fuel cells di potenza sufficiente per essere considerati come proof-of-concept. In altre parole, la potenza è sufficiente per studiare i principali fenomeni che appaiono in stack di dimensioni superiori orientate ad applicazioni pratiche. L'intera attività può essere suddivisa in due parti: 1) test di short stack HT-PEMFC per la valutazione delle performance in condizioni tipiche del settore automovtive (corrente, temperatura, umidificazione, pressione) e per individuare il punto di lavoro ottimale; 2) test di stack IT-SOFC in gas naturale per valutare la perdita di prestazioni per fenomeni legati a cicli redox che possono avvenire durante l'uso reale. Tecniche di diagnosi, come il metodo di interruzione di corrente e la spettrocopia d'impedenza hanno completato lo studio fornendo informazioni circa l'ottimizzazione dell'assemblaggio degli stack. La sperimentazione è stata interamente condotta in laboratorio, per controllare in maniera accurata le variabili di processo; nonostante ciò, le prestazioni ottenute sono comunque utili per applicazioni concrete, una volta che siano state definite condizioni di lavoro appropriate come compromesso tra prestazioni e costi.
Research activities on solid oxide (SOFC) or polymer electrolyte membrane (PEMFC) fuel cells are currently focused on performance and lifetime enhancement as well as costs reduction. These aspects are relevant to make such systems more attractive for the market, both for stationary and automotive applications. From this point of view, an increase of temperature (from 80°C to 110-120°C) appears necessary for PEMFC technology (high temperature PEMFC, or HTPEMFC). This would allow more resistance to CO contaminants in the fuel, better thermal and water management and a better efficiency for co-generation. On the contrary, SOFC technology is moving towards intermediate temperature (IT-SOFC); this would allow cost reduction while developing planar cells, due to less critical construction processes and an increase of stability. These ways to enhance the fuel cells applications are well studied for single cell but the scale-up process to significant power production devices needs specific investigations. Moreover, different technologies need different field test procedures, tailored on the specific application sectors. In this Ph.D. thesis, fuel cell devices exploiting either solid oxide or polymer electrolyte technologies, were tested for specific applications. In particular, 1kW fuel cell stacks were tested in order to verify the possibility of fuel cell use in small size applications. Nowadays, HT-PEMFC devices are creating lot of interest for FC technology development. Anyway, despite a deep knowledge of material properties, the assessment of the new materials at stack level have undergone only few studies. In this research activity this aspect was investigated. Moreover, IT-SOFC technology is considered valuable for stationary applications and distributed energy production, using cheap fuels and a highly efficient electrochemical process. Nevertheless, for residential energy consumption, the studied SOFC device can be considered not as a downscaled device for laboratory study, but as the base to develop a complete system. This Ph.D. thesis involves considerations for both stationary and automotive applications, by analysing fuel cells stack with a size large enough to be considered a proof-of-concept. In other words, the size appears sufficient to investigate main phenomena visible in larger stack oriented to real world applications. The whole activity can be divided in two lines: 1) tests of HT-PEMFC short stacks that were carried out to evaluate their performance in typical automotive working conditions (current, temperature, humidification, pressure) and to establish an optimal operating point. 2) tests of IT-SOFC stacks in natural gas, in order to evaluate performance decay and its response to detrimental effects due to thermal and redox cycles that can appear in "out of laboratory" usage. Diagnostic analysis such as current interrupt method and electrochemical impedance spectroscopy completed the study by supplying information about the optimization of stack assembling procedure. The whole experimental activities were carried out in laboratory, to accurately control the process variables; nevertheless, the recorded performances are anyway meaningful with respect to real world applications, once defined tailored working conditions by a good compromise between performances and costs.

Forest fires in the Alps can have severe impacts on mountain forests reducing their protection capacity against rock falls and avalanches and increasing flood runoff, mud and debris flows (Moody and Martin 2001, Robichaud et al. 2007). Due to climate change, several studies have shown that the impact of forest fires in the Alpine environment will increase in the coming decades (Elkin et al. 2013, Lorz et al. 2010, Wastl et al. 2012). A key issue in modern forest fire management is the accurate mapping of forest fuels in order to determine spatial fire hazard, plan mitigation efforts, and active fire management (Krasnow et al. 2009). Several surface fuel description systems are currently used by land management agencies in the USA, Europe, Canada and Australia, and most of these systems have the same categories, components and description variables (Sandberg et al. 2001, Scott and Burgan 2005). A generalized description of fuels based upon average fuel properties is called a “fuel model”. A fuel model is a set of fuelbed inputs (e.g. load, bulk density, fuel particle size, heat content and moisture of extinction) used by a specific software for predicting the fire behaviour (e.g. FARSITE). Standard fuel models were developed in the USA by Anderson (1982) and more recently by Scott and Burgan (2005). Standard fuel models that fit the main local vegetation characteristics can be used as input for fire spread modelling and in combination with custom fuel models when available (Duguy et al. 2007, Arca et al. 2009, Jahdi et al. 2015). However, the Standard or custom fuel models have seldom been applied in the Alps. In this study we tested the possibility of defining some custom fuel models for the Eastern Italian Alps, which might allow a more reliable fire behaviour prediction when fire simulator systems are used. The custom fuel models definition was done by means of three steps: In the first step we studied local fire regime and fire behaviour and we tested the hypothesis that the decrease in burned area is related to an improvement in fire-fighting efficiency since the beginning of the 3rd millennium. In the second step fuel properties were measured in the field and analyzed. In the third step we made three fuel model sets based on three different approaches (Forest type association, Prometheus classification, Cluster classification). Then, using FARSITE (Finney 2004), we simulated ten fires that occurred in the Veneto Region from 2003 to 2013. Every fire was simulated using the three custom model sets and the Standard fuel models (Anderson 1982, Scott and Burgan 2005). Lastly, the fuel model set having the higher accuracy was adjusted in order to improve its performance in simulating real fire behaviour. In the Veneto Region, there was a decreasing number of fires per year from 1981 to 2004 and a much more evident decrease in the annual burned area. Fires in both mountain areas and the lowlands usually behave as surface fires and the burned area is seldom larger than ten hectares. We tested the hypothesis that the decrease in burned area is related to an improvement in fire-fighting efficiency since the beginning of the 3rd millennium. The power-law distribution of burned areas seems to confirm that suppression efficiency has been improved because the exponent of the power-law distribution was much higher in the last decade than in the previous two. In mountain areas fuel load paralleled what is reported in the literature for similar forests, but in the lowlands fuel load appeared much higher, probably because those forests are affected by phytosanitary problems that cause a higher amount of deadwood. We found significant differences in fuel load among vegetation types (chestnut, hop hornbeam forests, conifer plantations and shrubland), The most significant difference was litter load (p<0.001 in the lowlands; p=0.0015 in mountain areas). Significant differences were also found between forest managements (coppiced, high forest, unmanaged). Mainly shrubs load (p<0.0018 in the lowlands) and herbs (p=0.0029 in mountain areas). The fuel distribution in size classes was never normal but, as commonly reported in the literature, it followed a logarithmic or a power-law trend. The tests on fire behaviour fuel models showed that Prometheus and Cluster fuel model sets led to inaccurate fire behaviour predictions. Standard fuel models (Anderson 1982, Scott and Burgan 2005) generally performed well and Forest type fuel models were the best in predicting fire behaviour, despite a frequent underestimation of flame height and rate of spread. By using a calibration process, we modified the Forest type fuel models and improved the performance in FARSITE. The resulting Calibrated fuel models could be suggested for further fire behaviour applications in the Eastern Italian Alps.
Nelle Alpi gli incendi boschivi possono avere un impatto severo sulle foreste montane riducendo la loro capacità di protezione contro frane, valanghe e colate di fango e detriti (Moody and Martin 2001, Robichaud et al. 2007). A causa dei cambiamenti climatici, molti studi hanno evidenziato che l’impatto degli incendi boschivi in ambiente alpino sarà destinato ad aumentare nei prossimi anni (Elkin et al. 2013, Lorz et al. 2010, Wastl et al. 2012). Un argomento chiave nella moderna gestione degli incendi boschivi è l’accurata mappatura dei combustibili forestali in modo da realizzare carte di rischio, piani antincendi boschivi ed interventi di riduzione del rischio incendi (Krasnow et al. 2009). Esistono vari sistemi di classificazione dei combustibili forestali utilizzati dai vari enti che si occupano di incendi in USA, Europa, Canada e Australia. Molti di questi sistemi hanno le stesse categorie, componenti e variabili (Sandberg et al. 2001, Scott and Burgan 2005). Un modello di combustibile è una descrizione generale delle proprietà dei combustibili forestali (es. carico, densità, contenuto calorico, ed umidità di estinzione) utilizzata nei software di predizione del comportamento del fuoco (es. FARSITE). I modelli di combustibile Standard sono stati sviluppati negli stati uniti da Anderson (1982) e più recentemente da Scott e Burgan (2005). I modelli di combustibile Standard che rispecchiano le caratteristiche della vegetazione locale possono essere utilizzati come input per la modellizazione del fuoco, anche in combinazione con modelli di combustibile locali (Duguy et al. 2007, Arca et al. 2009, Jahdi et al. 2015). Ciononostante i modelli di combustibile sia Standard e sia locali sono stati raramente applicati nelle Alpi. In questo studio abbiamo studiato la possibilità di definire dei modelli di combustibile locale per le Alpi Orientali Italiane, al fine di permettere un migliore l’utilizzo dei software di propagazione del fuoco. La definizione dei modelli di combustibile locali è stata attraverso tre fasi di lavoro: Nella prima fase abbiamo studiato il regime degli incendi ed il comportamento del fuoco ed abbiamo testato l’ipotesi che la diminuzione dell’area bruciata sia in relazione con il miglioramento dell’efficienza del sistema antincendi boschivi che è avvenuto a partire dall’inizio del terzo millennio.. Nella seconda parte abbiamo misurato in bosco e analizzato le principali proprietà dei combustibili forestali. Nella terza parte abbiamo realizzato tre gruppi di modelli di combustibile utilizzando tre diversi sistemi di classificazione (associazione alla tipologia forestale, classificazione Prometheus, classificazione per cluster). Quindi, utilizzando FARSITE (Finney 2004), abbiamo simulato dieci incendi avvenuti nella Regione del Veneto dal 2003 al 2013. Ogni incendio è stato simulato utilizzando sia i tre gruppi di modelli locali e sia i modelli Standard (Anderson 1982, Scott and Burgan 2005). Infine il gruppo di modelli con la migliore accuratezza nella simulazione dell’area bruciata è stato migliorato in modo da aumentare le sue capacità di simulare il reale comportamento del fuoco. Nella Regione del Veneto c’è stata una diminuzione del numero di incendi per anno dal 1981 al 2004 ed una ancora più evidente diminuzione nell’area bruciata annuale. Sia in montagna che in pianura gli incendi sono generalmente di superficie e raramente superano i dieci ettari. La distribuzione potenza assunta dalle aree bruciate sembra confermare il miglioramento dell’efficienza del sistema antincendio in quanto l’esponente della distribuzione è stato molto più alto nell’ultima decade rispetto alle due precedenti. Nelle aree montane il carico di combustibili è in linea con quanto riportato in letteratura per tipologie forestali simili, mentre nei Colli Euganei è superiore al normale, probabilmente a causa di problemi fitosanitari che causano una elevata disponibilità di legno morto. Abbiamo trovato differenze significative nel carico di combustibili fra le tipologie forestali (castagneti, orno ostrieti, impianti di conifera, cespuglieti), la differenza principale riguarda il carico di lettiera (p<0,001 in pianura, p=0,0015 in montagna). Sono state notate anche differenze significative fra i tipi di gestione forestale (ceduo, fustaia, abbandono), principalmente carico di cespugli (p=0,0018 in pianura) ed erbe (p=0,0029 in montagna). La distribuzione dei carichi di combustibile distinti per classi diametriche non era mai normale ma sempre logaritmica o potenza, come normalmente riportato in letteratura. I test dei modelli di combustibile hanno mostrato che i gruppi Prometheus e Cluster non hanno simulato accuratamente il comportamento del fuoco. I Modelli Standard (Anderson 1982, Scott and Burgan 2005) hanno funzionato generalmente bene, ed i modelli di combustibile per tipologia forestale hanno dato la migliore predizione dell’area bruciata, nonostante una frequente sottostima dell’altezza di fiamma e della velocità di avanzamento. Infine attraverso il processo di calibrazione abbiamo migliorato i modelli “Tipologia forestale” in modo da ottenere una migliore simulazione del comportamento del fuoco. Ottenendo così un nuovo gruppo di modelli Calibrati. Per le future applicazione di simulazione del comportamento del fuoco suggeriamo di utilizzare i modelli di combustibile Calibrati

A contaminação de ambientes aquáticos decorrente de acidentes com gasolina, álcool combustível e misturas binárias representa um risco crescente, tendo em vista as projeções do setor para os próximos 50 anos. O objetivo do presente estudo foi avaliar a toxicidade aguda da Gasolina C, Gasolina P e álcool combustível isoladamente e em misturas binárias, assim como de suas respectivas Frações Solúveis em Água (FSA) e Frações Dispersas em Água (FDA) sobre Daphnia similis. O estudo ainda incluiu a avaliação da toxicidade aguda remanescente na matriz água de uma contaminação antiga (intemperismo) com a Gasolina C. Paralelamente, foram conduzidos ensaios de toxicidade aguda com amostras ambientais (água subterrânea, superficial e elutriato a partir de sedimentos) de uma área alagada com histórico de contaminação antiga. O cultivo e os ensaios com D. similis foram de acordo com a NBR 12.713 (2009). Tanto a gasolina C quanto a P foram extremamente tóxicas para os organismos, apresentando valores médios de CE50% em 48 h de 0,00113% e 0,058% respectivamente. As diferenças entre os resultados obtidos com a Gasolina C e aqueles obtidos com suas frações FSA e FDA foram significativas (p < 0,05), sendo que não houve diferença significativa entre a toxicidade aguda da FSA e da FDA (p < 0,05). Os resultados obtidos com os ensaios com Gasolina P e FDA não apresentaram diferenças significativas entre si (p < 0,05), mas, foram significativamente diferentes daqueles obtidos com FSA (p < 0,05). Os resultados dos ensaios de toxicidade aguda com misturas binárias sugeriram efeito menos que aditivo (antagonismo). Os resultados da simulação de uma contaminação antiga demonstraram redução acentuada da toxicidade para D. similis ao longo de apenas 28 dias. Entretanto, com relação aos ensaios com as amostras ambientais da área com histórico de contaminação, apesar da ausência ou baixa toxicidade nas amostras de água superficial (sugerindo intemperismo), toxicidade alta foi observada em amostras de água subterrânea e no elutriato de sedimentos, sugerindo condições de adsorção aos sedimentos com alto teor de argila e/ou aprisionamento dos compostos em zona saturada.
The contamination of aquatic environments due to accidents with gasoline, alcohol fuel and their mixtures represents an increasing risk due to the projections made by the petroleum-based fuels industry for the next 50 years. The objective of the present study was to assess the acute toxicity of gasoline C, gasoline P, ethanol fuel separately and in mixtures, as well as their respective water-soluble fractions (WSF) and water-disperse fraction (WDF) on the bioindicator Daphnia similis. The study also included the assessment of the remaining acute toxicity in an aged gasoline C-contaminated water matrix with aging simulation for a 28-day period. Parallel to that, toxicity assays were conducted with environmental samples, including surface water, elutriate of sediments and groundwater from an aged contaminated area. The cultivation and the assays with D. similis were carried out according to NBR 12.713 (2009). Both gasoline C and P were highly toxic to D. similis, with CE50% in 48 h of 0.00113% e 0.058% respectively. The differences in acute toxicity between Gasoline C and its fractions WSF and WDF were significant (p <0.05). However, no significant difference was found between WSF and WDF fractions. Gasoline P and its WDF fraction had no significant differences (p < 0.05), but their toxicity were significant different from that one obtained with the FSA fraction (p < 0.05). Acute toxicity assays carried out with gasoline C and P mixed with ethanol fuel suggested effect less than additive (antagonism). The results obtained with the simulation of an aged contamination with Gasoline C showed sharp reduction in toxicity along 28 days. However, regarding the assays with environmental samples from an aged contamination, although absence or low toxicity was observed in the superficial water, severe toxicity was found in the sediments elutriate and in the groundwater, which was confirmed by the high concentrations of gasoline hydrocarbons in both matrixes. The results suggest that the contaminant was entrapped in the saturated zone and/or adsorbed to the sediments with high clay content.

Defining key parameters for a charge sustaining supervisory (torque split) control strategy as well as an engine and catalyst warm-up strategy for a Split Parallel Architecture Extended-Range Electric Vehicle (SPA E-REV) is accomplished through empirically and experimentally measuring vehicle tailpipe emissions and energy consumption for two distinct control strategies. The results of the experimental testing and analysis define how the vehicle reduces fuel consumption, petroleum energy use and greenhouse gas emissions while maintaining low tailpipe emissions. For a SPA E-REV operating in charge sustaining mode with the engine providing net propulsive energy, simply operating the engine in regions of highest efficiency does not equate to the most efficient operation of the vehicle as a system and can have adverse effects on tailpipe emissions. Engine and catalyst warm-up during the transition from all-electric charge depleting to engine-dominant charge sustaining modes is experimentally analyzed to evaluate tailpipe emissions. The results presented are meant to define key parameters for a high-level torque-split strategy and to provide an understanding of the tradeoffs between low energy consumption and low tailpipe emissions. The literature review gives a background of hybrid and plug-in hybrid vehicle control publications including tailpipe emissions studies, but does not include experimental results and comparisons of supervisory strategies designed for low fuel consumption and low tailpipe emissions the SPA E-REV architecture. This paper details the high-level control strategy chosen for balancing low energy consumption and low tailpipe emissions while the engine is operating. Vehicle testing data from a chassis dynamometer is presented in support of the research.
Master of Science

Orientador: Ana Maria Canesqui
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Ciências Médicas
Made available in DSpace on 2018-08-17T02:59:24Z (GMT). No. of bitstreams: 1 Trevisan_ElisabethAparecida_D.pdf: 2255946 bytes, checksum: 21bfee6974f67d6aaa879770bdef9838 (MD5) Previous issue date: 2010
Resumo: Embora os acidentes envolvendo caminhões carregados de produtos perigosos façam parte do noticiário com certa frequência, pois suas consequências costumam ser catastróficas, seja para o trabalhador, para o meio ambiente ou para as populações residentes nas proximidades do acidente; poucos são os estudos que buscam entender em que condições eles ocorrem. A preocupação maior tem sido criar alternativas para o sistema logístico, buscando atender com maior rapidez e eficiência o escoamento da produção. Embora, essa categoria seja de fundamental importância na economia nacional, ela não tem recebido a devida atenção das autoridades e muitos trabalhadores continuam adoecendo, morrendo em acidentes que, não bastasse pela perda imensurável da sua vida, ainda põem em risco o meio ambiente e as populações lindeiras às rodovias que trafegam. Submetidos à especificidade do processo de trabalho, a qual envolve a condução de um veículo de grande porte, o transporte de combustíveis e as relações sociais, esses trabalhadores também representam, vivenciam e experimentam o trabalho de maneira específica. Assim sendo, estudamos a forma pela qual eles elaboram as suas relações com aquele processo de trabalho e o vivenciam em sua prática cotidiana
Abstract: Although the accidents involving loaded trucks of dangerous products are part of the reporter with certain frequency, therefore its consequences use to be catastrophic, either for the worker, the environment or the resident populations in the neighborhoods of the accident; few are the studies that they search to understand where conditions they occur. The concern biggest has been to create alternative for the logistic system, searching to take care of with bigger rapidity and efficiency the draining of the production. Although, this category is of basic importance in the national economy, it has not received the had attention from the authorities and many workers are still getting sick, dying in accidents that, were not enough for the immeasurable loss of its lifes, still they put at risk the environment and the bordering populations to the highways that pass through. Submitted to the specificity of the work process, which involves the conduction of a vehicle of great transport, the fuel transport and social relations, these workers also represent, live deeply and try the work in specific way. Therefore, it is proposed to study the way they prepare their relations with that process work and experience in their daily practice
Doutorado
Saude Coletiva
Doutor em Saude Coletiva

The aim of the present work has regarded the development of nanostructured membranes produced by electrohydrodynamic techniques and evaluation of their performances in relation to energy and environmental applications. Specifically, in this study the attention has been focused on the production of electrospun/electrosprayed composite membranes in relation to their application as proton exchange membranes (PEM) and photocatalytic filters for the abatement of volatile organic compounds in the context of indoor pollution. The investigation carried in this work is related to the evaluation of different approaches in the production of the final membranes according to the selected applications, highlighting the advantages and the drawbacks of each in comparison to reference materials or traditional methodologies.
Lo scopo del seguente lavoro di tesi ha riguardato lo sviluppo di membrane nanostrutturate ottenute mediante tecniche elettroidrodinamiche e la valutazione delle loro prestazioni in relazione ad applicazioni concernenti l’energia e la protezione dell’ambiente. Nello specifico in questo studio l’attenzione è stata focalizzata sulla produzione di membrane composite mediante electrospinning ed electrospraying in relazione al loro impiego come membrane a scambio protonico e come filtri catalitici per l’abbattimento di composti organici volatili. Lo studio condotto è in particolar modo rivolto alla valutazione di diversi approcci per la produzione delle membrane finali in relazione alle applicazioni individuate, sottolineando i vantaggi e gli svantaggi di ognuno in relazione a materiali di riferimento o metodologie tradizionali.

Nenhuma
Neste trabalho foi realizada a modelagem geométrica computacional das Cetapas de prensagem e sinterização da pastilha e da laminação da placa de combustível nuclear contendo microesferas de (Th,25%U)O2 dispersas em matriz de aço inoxidável com o objetivo de avaliar a distribuição destas microesferas nas diversas etapas do processamento. As regras de modelagem foram desenvolvidas baseadas nos parâmetros de cada etapa da fabricação da placa combustível. Para isto foram obtidas placas através do processamento por laminação de molduras de chapas de aço inoxidável, contendo pastilha fabricadas com microesferas de (Th,25%U)O2 com carregamentos de 10, 20 e 40% em peso de combustível disperso em matriz de aço inoxidável. Os dados das placas com carregamentos de 30 e 50% foram obtidos por interpolação da curva. As microesferas, obtidas pelo processo sol-gel, foram previamente secas, reduzidas e sinterizadas a 1700oC, durante 2 horas, sob atmosferas de hidrogênio. As microesferas sinterizadas alcançaram uma densidade de cerca de 98% da densidade teórica, e possuem um diâmetro médio de cerca de 300 mm e uma elevada resistência à fratura, de aproximadamente 40 N/microesfera. As regras implementadas neste modelo foram aplicadas nas coordenadas dos centros das esferas virtuais, que simulam as microesferas combustíveis de (Th,25%U)O2, obtendo-se novas coordenadas espaciais para cada uma delas nas etapas de prensagem e sinterização da pastilha e da laminação da placa combustível. Este modelo foi projetado com o uso de técnicas de análise de sistema estruturada, implementado utilizando a linguagem de programação Delphi e os resultados visualizados através do programa AutoCAD. Os resultados do modelo foram validados comparando-se as frações volumétricas experimentais em cada um dos carregamentos estudados com as frações simuladas. Este trabalho será de grande valia para o estudo do carregamento de microesferas na placa combustível, permitindo obter um combustível de elevado desempenho mecânico, térmico e neutrônico mesmo em mais alto carregamento.
The computational geometric modeling of the pressing, sintering and lamination stages for nuclear fuel plates composed by (Th,25%U)O2, microspheres dispersed into stainless steel matrix has been done in order to investigate the microspheres distribution in the various processing stages. The modeling standards were based on the parameters related to each fuel plate manufacturing stage. Accordingly, the plates were obtained through lamination processing of stainless steel plate frames comprising (Th,25%U)O2 microspheres pellets dispersed into stainless steel powder with loading of 10, 20 and 40% of microspheres dispersed into stainless steel matrix. The data for plates with loading of 30 and 50% have been obtained by linear interpolation. The microspheres produced by the sol-gel method were previously reduced and sintered at 1700 0C during 2 hours at hydrogen atmosphere. These sintered microspheres have reached about 98% of the theoretical density, with a mean diameter of 300 mm and a high resistance to fracture, near to 40 N/microsphere. The implemented standards in this model were applied at the virtual spheres center coordinates, which simulate the (Th,25%U)O2 fuel microspheres, and generate the new spatial coordinates to each of them in the pressing, sintering and lamination stages. This model was developed using structured system analysis techniques and it has been implemented using the Delphi programming language. The results were displayed through the AutoCAD program and validated comparing the experimental volumetric fractions in each of the studied loading, with the simulated fractions. The results indicate that this work could be a powerful tool in the investigation of microspheres loading in the fuel plate, allowing the attainment of a high mechanical and neutronic performance fuel, even for higher level loading.

2013/2014
Lo sviluppo sostenibile è una sfida prioritaria per la nostra società. La possibilità di costruire un futuro sostenibile, mantenendo al contempo alti standard nella qualità della vita e preservando risorse e ambiente, dipende dalla disponibilità di metodi per la produzione verde di energía e prodotti chimici. La produzione simultanea di prodotti chimici ed energía può essere ottenuta nelle celle a combustibile che impiegano combustibili liquidi (Direct Liquid Fuel Cells – DLFC), dispositivi in cui l’energia chimica contenuta nelle molecole di combustibile è convertita direttamente in energía elettrica. Le DLFC impiegano solitamente combustibili a base di piccole molecole organiche quali ad esempio alcoli ed acido formico. Questi combustibili sono di particolare interesse, dal momento che possono essere ottenuti a partire da biomassa, con un impatto minore sulle emissioni di gas serra rispetto ai combustibili fossili. Allo stato attuale le DLFC impiegano platino in quantità elevate. Questo per due ragioni: i) il platino è un buon catalizzatore sia per l’ossidazione di composti organici che per la riduzione dell’ossigeno e ii) il platino è stabile in ambiente acido. E’ importante sottolineare che le attuali DLFC impiegano membrane a scambio protonico come elettroliti e dunque richiedono ambienti fortemente acidi per avere un’adeguata conducibilità. Le DLFC impiegano carichi di platino maggiori di 1 mg cm-2, un fatto che ne limita molto la possibilità di diffusione commerciale. In questo lavoro, grazie alla disponibilità di membrane a scambio anionico ad elevata conducibilità (Tokuyama A-201), abbiamo sviluppato delle DLFC alcaline (Anion Exchange Membrane Direct Liquid Fuel Cells – AEM-DLFC). Ciò e’ stato fatto con l’obiettivo di eliminare il platino dai dispositivi. E’ infatti noto che il palladio è un catalizzatore molto attivo per l’ossidazione delle piccole molecole organiche in ambiente alcalino e che la reazione di riduzione dell’ossigeno puo’ essere catalizzata da composti di ferro e cobalto (es. ftalocianine). La tecnología qui riportatata si basa sull’impiego di anodi di palladio supportati da carbon black (Vulcan XC-72), membrane a scambio anionico e ftalocianine di ferro e cobalto subbortate da carbon black con maggiore area superficiale rispetto a quello impiegato all’anodo (Ketjen Black 600). Un fatto importante è che le ftalocianine di ferro e cobalto non sono attive per l’ossidazione di molecole organiche. Ciò è particolarmente rilevante per le fuel cells perché il cross-over del combustibile attraverso la membrana non produce significative cadute di potenziale e quindi dell’efficienza energetica. La parte sperimentale della tesi inizia con un capitolo in cui si decrivono le prestazioni di AEM-DLFC esenti da platino ed alimentate ad etanolo. Questa parte del lavoro è particolarmente rilevante dal momento che è la prima e completa caratterizzazione della performance energetica di questi dispositivi. In particolare si sono determinati i seguenti parametri: i) massima densità di potenza, ii) efficienza energetica e iii) l’energia prodotta per singolo batch di combustibile. Tutti questi parametri sono stati determinati in funzione della composizione del combustibile. Abbiamo scoperto che la composizione del combustibile che massimizza uno dei parametri sopra riportati generalmente ha effetti negativi sugli altri. E’ dunque necesario definire la composizione del combustibile in funzione della particolare applicazione cui il dispositivo è destinato. Abbiamo inoltre studiato l’effetto dell’aggiunta di un ossido promotore, la ceria, al catalizatore anódico, mostrando che le prestazioni migliorano significativamente. In alcuni casi l’efficienza energetica può essere migliorata anche di più del 100% grazie alla semplice aggiunta di dell’ossido promotore. Il capitolo successivo e’ dedicato alle celle a combustile che impiegano combustibili a base di formiato (Direct Formate Fuel Cells – DFFC). In questo caso si sono impiegati catalizzatori nanostrutturati di Pd supportato da Vulcan XC-72 e ftalocianine di ferro e cobalto, rispettivamente all’anodo ed al catodo, ottenendo un potenziale di circuito aperto superiore ad 1 V. Le celle alcaline al formiato hanno prodotto una densità massima di potenza superiore alle celle alcaline che impiegano metanolo ed etanolo, ed anche alle celle acide che impiegano acido formico. In particolare l’efficienza energetica delle celle al formiato è stata superiore di un fattore 4 a quella delle migliori celle alcaline ad etanolo. Questo e’ un punto cruciale per l’applicazione pratica della tecnología proposta. Infatti l’efficienza energetica e’ uno dei cardini per il raggiungimento della sostenibilità e, senza dubbio, il vincolo principale per i sistemi che devono produrre grandi quantita’ di energía, come la generazione stazionaria di energía elettrica. Anche nel caso delle celle al formiato, abbiamo osservato che la composizione del combustibile è essenziale nel definire la performance energetica. Abbiamo mostrato che la massima densità di potenza si ottiene con un combustibile che contiene formiato 2 M e KOH 2 M, mentre l’energia per singolo batch di combustibile, la migliore conversione del combustibile e l’efficienza energetica sono migliori per il formiato 4 M e KOH 4 M. Al fine di migliorare la capacità del palladio di catalizzare l’ossidazione elettrochimica di composti organici rinnovabili, abbiamo sviluppato un metodo elettrochimico originale per il trattamento delle superfici degli elettrodi. Il trattamento consiste nell’applicazione di un potenziale ad onda quadra (Square Wave Potential – SWP) che produce un aumento della rugosità superficiale e una modifica della distribuzione delle terminazioni cristalline della superficie, incrementando la densità degli atomi di Pd superficiali a basso numero di coordinazione (< 8). Il trattamento si è rivelato efficace nel migliorare la cinetica di ossidaizione dell’etanolo, dell’etilen glicole e del glicerolo. I trattementi sviluppati hanno prodotto incrementi dell’attività fino ad un fattore 5.6. L’analisi FTIR dei processi di ossidazione ha dimostrato che anche la distribuzione dei prodotti di ossidazione e’ affetta dal trattamento. In particolate abbiamo riscontrato un incremento nella capacità dei catalizzatori ottenuti per SWP di rompere il legame C-C. Il trattamento elettrochimico con potenziale ad onda quadra è stato sviluppato anche per le superfici di platino, con l’obbiettivo di fornire uno strumento per ridurne il contenuto nelle fuel cells quando non sia possibile eliminarlo completamente. Nel caso del platino si è riscontrato che il parámetro piu’ importante per l’efficienza del trattamento è il periodo dell’onda quadra. Le superfici più attive si sono ottenute con un periodo di trattamento di 120 minuti, mentra la stabilità massima si e’ avuta per campioni trattati con onde quadre con periodo di 360 minuti. Tramite esperimenti FTIR si è inoltre concluso che nel caso del platino il trattamento inibisce la rottura del legame C-C. Questo fatto è importante perchè limita la formazione di frammenti CO che sono le principali specie che avvelenano gli elettrocatalizzatori a base di platino. Il capitolo 7 è dedicato allo studio dei meccanismi di deattivazione dei catalizzatori di palladio per l’ossidazione elettrochimica in ambente alcalino di alcoli. L’argomento è rilevante poichè la deattivazione è una delle principali cause che limita la diffusione di questi dispositivi. Abbiamo dimostrato che la formazione di ossidi è la causa che determina maggiormente la degradazione della performance catalítica. Siamo giunti a questa conclusione combinando le informazioni proveniente da indagini elettrochimiche ed esperimenti che impiegano la radiazione di sincrotrone. L’analisi degli spettri XANES (Near Edge X-ray Absorption Spectroscopy) ha mostrato che il palladio è presente nella sua forma metallica nei catalizzatori freschi, mentre è completamente ossidato dopo l’impiego in fuel cells. Nello studio si conclude che per allungare la vita degli anodi a base di palladio è necesario che il catalizzatore anodico non sia esposto a potenziali superiori a 0.7 V. Ciò è possibile in pratica con una semplice elettronica di controllo da abbinare alla cella. Al fine di aumentare la cinetica di ossidazione abbiamo provveduto ad effettuare esperimenti di ossidazione dell’etanolo a temperatura intermedie (> 100 °C) in autoclave. Abbiamo osservato che l’incremento della temperatura aumenta in misura significativa la capacità dei catalizzatori di ossidare l’etanolo in ambiente alcalino. Questo fatto è stato ascritto prevalentemente al miglioramento della capacità di adsorbire specie idrossido alla superficie del palladio. Lo stesso miglioramento non è stato osservato per esperimenti condotti in ambiente acido. Si sono inoltre realizzati esperimenti di ossidazione dell’etanolo su superfici di carburo di tungsteno in matrice di cobalto. Si è provato che questo materiale non mostra un’attività significativa per l’ossidazione di etanolo in ambiente alcalino. In ogni caso si è osservato che il materiale è stabile in ambienti alcalini, in un range di temperatura compreso tra 100 e 200 °C. Questo fatto unitamente all’elevata conducibilità suggerisce che il carburo di tungsteno in matrice di cobalto possa essere impiegato come supporto per la fase attiva dei catalizzatori, quali appunto il palladio. Lo stesso materiale ha mostrato una debole attività nell’ossidazione dell’etanolo ad una temperatura di 50 °C in ambiente acido. La stabilità non era però suficiente per permettere la caratterizzatione delle proprietà catalitiche in soluzioni acide a temperatura superiori.
Amongst current societal challenges sustainability is certainly a priority. The possibility of building a sustainable future, while maintaining high standards in the quality of life and preserving environment and resources, strongly relies on the availability of methods for the green production of energy and chemicals. The production of chemicals together with the on-demand power generation can be achieved in Direct Liquid Fuel Cells (DLFCs), devices in which the chemical energy of a liquid fuel is converted into electrical energy. DLFCs usually employ Small Organic Molecules (SOMs), such as alcohols or formic acid, as fuels. These fuels can be obtained from biomass feedstock. Consequently their use generates a significantly lower atmospheric CO2 with respect to the use of fossil fuels, resulting in a potential mitigation of the “greenhouse effect”. At the present stage, DLFCs rely on the use of the rare and costly platinum. This is for two reasons: i) platinum is a good catalyst for both SOMs oxidation and Oxygen Reduction Reaction (ORR); ii) platinum is stable in acidic environment. It is worth mentioning that most of DLFCs employ proton exchange membranes as electrolytes and need strongly acidic conditions for achieving low resistivity. In these systems also the water management can be a problem, as it is attracted to the cathode side for polarization and water is frequently introduced in the feed stream to the fuel cell. At present acidic DLFCs operate with a platinum content largely exceeding 1 mg cm-2, a fact that severely hampers the diffusion of such devices. In this investigation, thanks to a low resistivity Anion Exchange Membranes (AEM), the Tokuyama A-201, we have developed efficient alkaline direct liquid fuel cells (AEM-DLFCs). This has been done with the purpose of eliminating platinum from the devices. Indeed it is known that palladium effectively catalyzes SOMs oxidation in alkali; besides, oxygen reduction reaction can also be effectively achieved by using iron and cobalt phtalocyanines (Pc). Consequently the membrane electrode assembly (MEA) of a AEM-DLFC can be assembled using: i) a palladium based anode, ii) a Tokuyama A-201 membrane and iii) a cathode containing FePc-CoPc/C as electrocatalyst obtained from the high temperature pyrolysis of FePc-CoPc. An important fact is that FePc-CoPc/C is not active at all for the oxidation of SOMs. This has the major implication that fuel crossover through the membrane does not result in significant potential (and so energy efficiency) drop in fuel cells. The experimental part of this thesis starts with a chapter devoted to the analysis of the energy performance of platinum-free AEM-DLFCs fueled with ethanol (Chapter 3). This work is the first exhaustive analysis of the energy performance of such devices. Particularly we have determined the major parameters that characterize the fuel cell operations: i) maximum power density, ii) energy efficiency and iii) energy delivered per single fuel batch. All these parameters have been determined as a function of the fuel composition. We have discovered that the fuel concentration that maximizes one of the parameters can be detrimental to the others with the fundamental consequence that fuel composition must be selected according to the selected application. The effect of adding a promoting oxide, CeO2, to the anode catalyst has also been investigated. In some cases efficiency can be improved up to the 100% by simply adding cerium oxide to the anode catalyst. We have also proved that DEFCs are suitable candidates for the µ-fuel cells technology as we have shown their ability to operate with no or little performance degradation for 3 months at low power density (< 1 mW cm-2). Chapter 4 is dedicated to the Direct Formate Fuel Cells (DFFCs). Nanostructured Pd/C and FePc-CoPc/C have been employed at the anode and cathode side respectively. A large open circuit voltage (≥1.0 V) was obtained. This has been attributed to the larger (as compared with DEFCs) Nernst potential of the DFFCs and the use of FePc-CoPc/C as cathode electrocatalyst to restrain the reduction of cell voltage by fuel crossover. Our DFFCs have shown maximum power density larger than state of the art AEM-DLFCs and also Direct Formic Acid Fuel Cells (DFAFCs). AEM-DFFCs are also very effective in exploiting the energy content of the fuel. Indeed we have shown that DFFCs energy efficiency is four times the energy efficiency of analogous DEFCs. This point is very important to exploit the technology as the energy efficiency is the key issue for achieving sustainability and the major constraints for systems devoted to massive energy production. Again we have found that fuel composition is essential for the performance. The best power density was obtained by the cell fuelled with 2 M formate plus 2 M KOH, while best delivered energy, fuel utilization and energy efficiency were delivered by cell equipped with 4 M formate plus 4 M KOH. To enhance the ability of palladium to catalyze SOMs oxidation in alkaline environment, we have developed an original electrochemical treatment (Chapter 5). The treatment consisted of the application of a Square-Wave Potential (SWP) to the electrode and resulted in surface roughening and change in the distribution of the crystal surface terminations. Particularly we have found that after SWP an increase of the density of low coordination (Coordination Number < 8) Pd surface atoms occurs. We have found significant activity enhancement (from 4 to 5.6 times as compared to untreated surface) for the oxidation of all the investigated alcohols. Furthermore, FTIR spectra have shown that the reaction products distribution was also affected. Particularly we determined an increased tendency of the SWP treated Pd surface to cleave the C-C bond as compared to the untreated ones. A tailored SWP treatment for enhancing the catalytic activity of platinum was also developed (Chapter 6). The essential reason behind the study is to provide a tool for reducing Pt content in fuel cells when it cannot be completely eliminated. For platinum, it has turned out that the period of the square wave is the most important parameter. The most active platinum surface for Ethanol Oxidation Reaction (EOR) in alkali has been produced with a square wave period of 120 min, while the maximum stability of the catalytic performance has been obtained with the sample produced with a period of 360 min. Via in situ FTIR we have also found that the treated samples limit C-C cleavage as compared to the untreated ones. This suggests that SWP on Pt could provide an effective strategy to minimize the formation of CO, a major poisoning agent for platinum based catalysts. Chapter 7 is devoted to the investigation of the degradation mechanism of palladium electrocatalysts in platinum-free AEM-DLFCs. This is among the main issues still preventing the full exploitation of palladium in DLFCs. We have demonstrated that palladium oxide formation is the major cause for the catalytic performance degradation. We came to this conclusion by combining the information derived from electrochemical measurements and synchrotron light experiments (X-ray Absorption Spectroscopy). X-ray Absorption Near Edge Structure (XANES) spectra of the Pd Kα edge before and after DEFC run have shown that Pd is present in its metallic form in the pristine catalyst, while it is almost completely oxidized after work in an ethanol fed fuel cell. This has enabled us to conclude that to extend the service life of palladium electro-catalysts in alkali, the anode potential has not to exceed 0.7 V. In practice this can be achieved with a simple electronic control of the device. Increasing the operating temperature of fuel cells is an alternative strategy to improve the performance of fuel cells fed with SOMs containing fuels. In chapter 8, palladium has been investigated as a catalyst for ethanol oxidation at intermediate temperatures (> 100 °C) in a pressurized vessel. We have found that the increase of the temperature dramatically enhances the ability of catalyzing EOR in alkali. This fact has been ascribed to the improved adsorption of the hydroxyl species on the palladium surface. The same enhancement has not been observed in acidic environment. A few experiments on the use of tungsten carbide in a cobalt matrix (WC-Co) have also been performed. We have proved that WC-Co does not catalyze significantly the ethanol oxidation reaction in alkaline media, while it does in acidic electrolyte at medium temperature (~50 °C). At larger temperature the stability in acidic environment is not enough to allow a reliable assessment of the catalytic performance. Larger stability has been achieved in alkali where tungsten carbide is a potential candidate for supporting other active phases such as noble metals.
XXVII Ciclo
1987

In the last decades, electrochemistry has been regarded as a powerful tool to address some of the key challenges that in the framework of sustainability and green energy. In particular, the application of smart, hierarchical materials as electrocatalysts is generating new opportunities for interesting developments. Nanostructured carbon has been heavily employed as a fundamental component for the proposed catalytic materials due to its outstanding electronic and textural properties. This thesis focuses on the exploitation of strategically designed materials based on carbon as electrocatalysts to be used in devices such as new generation fuel cells, electrolyzers for the production of hydrogen peroxide and sensors for its electrochemical detection. Each of these devices is envisioned as a way of reducing the environmental impact, by either being a sustainable source of energy, or substituting energy consuming and non-environmentally friendly processes. In particular, a hybrid Pd/CeO2/C material, prepared through a strategic protocol that allows an intimate contact among the three phases, has been employed as anodic electrocatalyst in both Anion Exchange Membrane Fuel Cells (AEM-FC) and Direct Alcohol Fuel Cells (DAFCs) working in alkaline media and fed with biomass derived polyalcohols. Concerning H2O2 electrosynthesis, N-doped carbon embedding Co nanoparticles have been studied for the Oxygen Reduction Reaction (ORR) in acidic environment, and the material’s outstanding selectivity has been correlated to its N-type species distribution, as well as its porosity and the indirect electronic interaction between the doped carbon phase and the internal metal. Finally, a metal-free electrosensor for the detection of hydrogen peroxide has been produced exploiting the electronic properties of a -COOH decorated graphene, obtained through a controlled functionalization protocol. In all cases, the strategic synthetic procedure gives rise to materials with enhanced catalytic performances in terms of activity, selectivity and stability, and the work has been communicated through publication (already published or in the process of being published) in peer-reviewed journals.
In the last decades, electrochemistry has been regarded as a powerful tool to address some of the key challenges that in the framework of sustainability and green energy. In particular, the application of smart, hierarchical materials as electrocatalysts is generating new opportunities for interesting developments. Nanostructured carbon has been heavily employed as a fundamental component for the proposed catalytic materials due to its outstanding electronic and textural properties. This thesis focuses on the exploitation of strategically designed materials based on carbon as electrocatalysts to be used in devices such as new generation fuel cells, electrolyzers for the production of hydrogen peroxide and sensors for its electrochemical detection. Each of these devices is envisioned as a way of reducing the environmental impact, by either being a sustainable source of energy, or substituting energy consuming and non-environmentally friendly processes. In particular, a hybrid Pd/CeO2/C material, prepared through a strategic protocol that allows an intimate contact among the three phases, has been employed as anodic electrocatalyst in both Anion Exchange Membrane Fuel Cells (AEM-FC) and Direct Alcohol Fuel Cells (DAFCs) working in alkaline media and fed with biomass derived polyalcohols. Concerning H2O2 electrosynthesis, N-doped carbon embedding Co nanoparticles have been studied for the Oxygen Reduction Reaction (ORR) in acidic environment, and the material’s outstanding selectivity has been correlated to its N-type species distribution, as well as its porosity and the indirect electronic interaction between the doped carbon phase and the internal metal. Finally, a metal-free electrosensor for the detection of hydrogen peroxide has been produced exploiting the electronic properties of a -COOH decorated graphene, obtained through a controlled functionalization protocol. In all cases, the strategic synthetic procedure gives rise to materials with enhanced catalytic performances in terms of activity, selectivity and stability, and the work has been communicated through publication (already published or in the process of being published) in peer-reviewed journals.

The present thesis focuses on studying structure/morphology/activity relationships in bimetallic Pt-Sn nanostructured electrodes for proton exchange membrane (PEM) fuel cells by adopting a rigorous surface science approach where: i) Model electrocatalysts are prepared in ultra-high-vacuum (UHV) conditions as ultrathin (UT) films (PtSnx/Pt(110) and SnOx/Pt(110)) to ensure a very reproducible control down to the atomic level; ii) Composition, morphology and structure of the UT nanostructured films are studied in situ by adopting state-of-the-art characterization tools; iii) Quantum mechanical calculations are carried out adopting the density functional theory (DFT) in order to determine the atomic structure of the UT films. A systematic search for possible Sn alloy or oxides on Pt(110) surface phases was carried out. Three surface alloys (including one already reported surface alloy) and two surface oxides on Pt(110) surface were identified. The two novel surface alloys: p(3×1)PtSn/Pt(110) and p(6×1) PtSn/Pt(110) can be prepared by means of UHV Sn deposition on Pt(110) at different thickness and by a subsequent annealing at proper temperature. Besides, two SnOx oxides surfaces, namely the c(2×4)SnOx/Pt(110) and the c(4×2) SnOx/Pt(110), were prepared by oxidizing the surface alloys. With optimization of the preparation conditions, a phase diagram for the surface alloys and surface oxides on Pt(110) was outlined. The two novel surface alloys were characterized by low energy electron diffraction (LEED), scanning tunnelling microscopy (STM) and synchrotron radiation photoemission spectroscopy (SRPES). STM images of the two surface alloys are characterized by a highly corrugated row structure whereas photoemission data indicate a complex intermixing between Pt and Sn which leads to the formation of extended near-surface alloys. Some models for the two surfaces were proposed on the basis of the experimental evidences. These models were then compared with DFT calculations and the simulated STM images of the models were used as final assessment of their validity. The reactivity of the surface alloys with CO was investigated both experimentally by thermal programmed desorption (TPD) and theoretically by DFT calculations. The results reveal a scarce reactivity towards CO on the two surfaces due the lower adsorption energy with respect to pure Pt(110) surface, indicating their use as highly CO tolerant catalysts. Based on the DFT results, the surfaces can have also an improved performance in CO oxidation reaction (COOR) on the basis of the calculated d-band centroid value. The two surface oxides (c(2×4)SnOx/Pt(110) and c(2×4)SnOx/Pt(110) ) were investigated by LEED, STM and SRPES. Some models for the two surfaces were proposed based on the experimental results, and investigated by DFT calculations. The good agreement between the simulated STM images with the experimental data suggests a good reliability of the proposed structures. The reactivity towards CO for the two oxidised phases was also investigated. The c(4×2) structure, constituted by a slightly oxidised Sn overlayer, demonstrated to be scarcely reactive, whereas the more oxidized c(2×4) phase proved to be able to efficiently oxidize CO. These results were also confirmed by DFT. The decomposition of methanol on c(2×4) surface was also investigated by TPD and SRPES, indicating that the methanol can be oxidised efficiently into CO2 and H2O. However the body of our experimental data points to a quite complex oxidation mechanism whose selectivity changes dynamically according to the experimental conditions. The fully oxidised c(2×4) can efficiently oxidise methanol to CO2 at low temperature, but this reaction path is progressively suppressed as soon as the phase is reduced. In this regime the methanol is oxidized to CO2 at higher temperature and less efficiently, the microscopic mechanism of the reaction implies the supply of oxygen by c(2×4) islands on reduced Pt or PtSn areas by spillover, where the actual reaction takes place. When the spillover is not anymore possible, because the methanol decomposition has removed most oxygen, methanol is simply oxidatively dehydrogenated to CO and H2, similarly to what happens on the clean Pt(110) surface but at a slightly lower temperature.
La presente tesi si concentra sullo studio della relazione struttura / morfologia / reattività in elettrodi bimetallici nanostrutturati Pt - Sn per celle a combustibile a membrana a scambio protonico (PEM), adottando un rigoroso approccio di scienza delle superfici sviluppato come segue: i) sistemi modello di elettrocatalizzatori sono stati preparati in condizioni di ultra - alto vuoto (UHV) depositando via epitassia da fasci molecolari (MBE) strati ultrasottili (UT) di PtSnx e SnOx su superfici di Pt monocristallino orientate (110), al fine di garantire un controllo fine e riproducibile su scala atomica; ii ) composizione, morfologia e struttura dei film nanostrutturati UT sono stati studiati in situ mediante l'adozione di strumenti di caratterizzazione in linea con le più avanzate tecniche offerte dallo stato dell’arte; iii ) calcoli quanto-meccanici basati sulla teoria del funzionale densità (DFT) sono quindi stati effettuati per determinare la struttura atomica dei film UT, in modo da razionalizzare e supportare i risultati sperimentali ottenuti al punto precedente. Una ricerca sistematica è stata effettuata allo scopo di identificare nuove possibili fasi di superficie di Sn o ossidi di Sn supportate su Pt (110). In questo modo, tre leghe di superficie (di cui una risulta già nota in letteratura) e due ossidi di superficie su Pt (110) sono stati identificati. Le due innovative leghe da film UT, la p(3 × 1) PtSn / Pt (110) e la p(6 × 1) PtSn / Pt (110) possono essere sintetizzate mediante deposizione di Sn su Pt (110), preparando spessori diversi e sottoponendo le superfici così ottenute a trattamenti termici effettuati a diverse temperature. Conseguentemente, l’ossidazione ad alta temperatura delle leghe superficiali ha permesso l’ottenimento di due nuove fasi ossidate di superficie, la (c(2 × 4) SnOx / Pt (110) e la c(4 × 2) SnOx / Pt (110). Infine, data l’elevata flessibilità delle tecniche di preparazione e caratterizzazione offerte dalla scienza delle superfici, è stato possibile delineare con grande accuratezza un diagramma di fase sia per le leghe che per gli ossidi di superficie sopra descritti. Le due nuove leghe superficiali sono state caratterizzate mediante diffrazione di elettroni a bassa energia cinetica (LEED), microscopia a scansione ad effetto tunnel (STM) e spettroscopia di fotoemissione da radiazione di sincrotrone (SRPES). Le immagini STM delle due leghe superficiali sono caratterizzate da una struttura a righe altamente corrugata; i dati di fotoemissione indicano inoltre un complesso intermixing tra Pt e Sn che porta alla formazione di leghe localizzate in prossimità della superficie. Alcuni modelli per le due superfici così ottenute sono state proposte sulla base delle evidenze sperimentali. Tali modelli sono stati poi confrontati con calcoli DFT; in particolare, sono state generate simulazioni di immagini STM che sono state quindi confrontate con i dati sperimentali ed usate come valutazione finale della validità dei modelli proposti. La reattività delle leghe di superficie rispetto al CO è stata studiata sia sperimentalmente, mediante desorbimento termico programmato (TPD), sia ricorrendo a calcoli DFT. I risultati rivelano una scarsa reattività delle due superfici nei confronti del CO a causa dell’energia di adsorbimento inferiore rispetto alla stessa superficie di Pt (110) presa come riferimento; tale fenomenologia indica pertanto il promettente impiego di tali sistemi come catalizzatori caratterizzati da elevata tolleranza al CO. Come già descritto per le leghe di superficie, i due ossidi superficiali (c(2 × 4) SnOx / Pt (110 ) e c(4 × 2) SnOx / Pt (110) ), sono stati studiati mediante LEED, STM e SRPES. Alcuni modelli per le due superfici sono stati proposti sulla base dei risultati sperimentali, la cui validità è stata supportata da calcoli DFT. Il buon accordo tra le immagini STM simulate e i dati sperimentali suggeriscono una buona affidabilità delle strutture proposte. La reattività verso il CO per le due fasi ossidate è stata inoltre indagata mediante TPD supportata da calcoli quantomeccanici. La struttura c(4 × 2), costituita da uno strato UT di SnOx sub-stechiometrico, ha dimostrato di essere poco reattiva, mentre la fase più ossidata c(2 × 4) ha dimostrato di essere in grado di ossidare efficacemente il CO. Lo studio della decomposizione del metanolo sulla fase c(2 × 4), effettuato mediante TPD e SRPES, indica come il metanolo possa essere ossidato in modo efficiente a CO2 e H2O. Tuttavia, i dati sperimentali indicano un meccanismo di ossidazione piuttosto complesso, la cui selettività cambia dinamicamente in base alle condizioni sperimentali. Ad ogni modo, la fase completamente ossidata c(2 × 4) può facilmente ossidare il metanolo a CO2 già a bassa temperatura, tuttavia tale reattività viene progressivamente soppressa non appena inizia la riduzione della fase con la perdita di ossigeno reticolare. In questo regime l’ossidazione del metanolo a CO2 richiede temperature più elevate; in particolare, il meccanismo microscopico della reazione implica la fornitura di ossigeno da parte della fase c(2 × 4) ad isole ridotte di Pt o PtSn, siti nei quali avviene effettivamente la reazione di ossidazione. Con il procedere della decomposizione del metanolo, il progressivo consumo di ossigeno porta ad una drastica soppressione della diffusione di superficie di quest’ultimo. In questo modo, il metanolo viene semplicemente deidrogenato a CO e H2 analogamente a quanto accade sulla superficie pulita di Pt (110), sebbene a temperature inferiori.

In order to produce alternative fuels derived from renewable resources (biomass) and environmentally friendly, it was investigated in this work the catalytic activity of three metal complexes showing Lewis acid character: Butyltin chloride dihydroxide (BCDH-Sn), Butyltintrichloride (BTC-Sn) and dibutyltin dichloride (DBDC-Sn).These complexes were tested for catalytic soybean oil methanolysis and esterification of oleic acid in order to obtain a mixture of Fatty Acid Alkyl-Esters, when it is used as a fuel known as biodiesel. In methanolysis experiments, the reactions were performed in a glass reactor equipped with a reflux condenser or a closed reactor. The reactions were performed at temperatures ranging from 80 ° C, 120 ° C and 150 ° C, and the reaction time ranged from 15 minutes to 10 hours. The reaction products, obtained by transesterification, were analyzed by gas chromatography with flame ionization detector (GC-FID). In case of esterification of the oleic acid, was subjected to the same conditions of methanolysis using only the closed reactor. In this case, monoester analysis content was determined by acid-base titration. For characterization of catalysts, spectroscopic techniques were used in infrared and nuclear magnetic resonance. To determine reaction mechanism (trans) esterification, a set of reactions were made with subsequent NMR study 1H and 119Sn. In transesterification, the sequence in terms of catalytic efficiency was: BTC-Sn>BCDHSn>DBDC-Sn. In the esterification, the sequence was: BTC- Sn> DBDC -Sn>BCDHSn. These reactive differences were attributed to factors such as steric hindrance, catalyst solubility in reaction environment, interactions between the catalyst and substrate reaction and the acid strength of the catalysts. RMN's results of 1H and 119Sn indicated that the reactions of transesterification and esterification using three organometallic complexes of tin occur through Lewis´s acid-base mechanism.
No intuito de produzir combustíveis alternativos oriundos de recursos renováveis (biomassa) e ambientalmente corretos, foi investigada neste trabalho a atividade catalítica de três complexos organometálicos exibindo caráter ácido de Lewis: n-butilclorodihidróxiestanho (BCDH-Sn), nbutiltricloroestanho (BTC-Sn) e di n-butildicloroestanho (DBDC-Sn). Esses complexos foram testados na metanólise do óleo de soja e na esterificação do ácido oléico visando obtenção de uma mistura de ésteres alquílicos de ácidos graxos (biodiesel). Nos experimentos de metanólise, as reações foram realizadas em um reator de vidro acoplado a um condensador de refluxo ou num reator fechado. As reações foram realizadas em temperaturas de 80 °C, 120 ºC e 150 °C, e o tempo reacional variou de 15 min a 10 h. Os produtos reacionais, obtidos por transesterificação, foram analisados por cromatografia gasosa com detector de ionização de chama (CG-FID). No caso da esterificação do ácido oléico, foram empregadas as mesmas condições da metanólise empregando apenas reator fechado. Nesse caso, a análise do teor de monoéster foi determinada por titulação ácido-base. Para caracterização dos complexos, foram usadas técnicas de espectroscopia no infravermelho e ressonância magnética nuclear de hidrogênio. A fim de estabelecer o mecanismo reacional de transesterificação e esterificação, foi realizado um conjunto de reações com acompanhamento por espectroscopia de RMN de 1H e 119Sn. Na transesterificação, a seqüência em termos de eficiência catalítica foi: BTC-Sn>BCDH-Sn>DBDC-Sn. Já na esterificação, a seqüência foi: BTC-Sn>DBDC-Sn>BCDH-Sn. Essas diferenças reacionais foram atribuídas a fatores como impedimento estéreo, solubilidade do catalisador no meio reacional, interações entre o catalisador e o substrato na reação e força ácida dos catalisadores. Resultados de RMN´s de 1H e 119Sn indicaram que as reações de transesterificação e esterificação usando os 3 complexos organometálicos de estanho ocorrem através de mecanismo ácido-base de Lewis.

Nowadays, the energy challenge is one of the largest driving forces behind many research efforts. Future energy strategies include smart ways to store and convert energy on demand. On this exciting perspective, fuel cells and flow batteries play a key role, the former in converting energy into propulsion, the latter in storing renewable energy surplus. Nevertheless, some main technological issues still must be overcome, such as limited peak performances often caused by poor fluid-mechanic efficiency. The fluid-dynamic optimisation of fuel cells and flow batteries systems is the main aim of the present thesis work. To this end, the focus is set on studying liquid-vapour two-phase flows and dispersion dynamics in fibrous porous media, by means of Lattice-Boltzmann numerical models, in order to catch the effects of microscale phenomena on macroscale features of both technologies. Present findings offer new insights into understanding fundamental physical behaviours in fuel cells and flow batteries, and give a guideline for good and innovative design practice.
Al giorno d'oggi, la sfida energetica è una delle più importanti spinte alla ricerca scientifica. Le strategie energetiche future includono vie alternative ed efficienti per stoccare e convertire l'energia su richiesta. In questa prospettiva entusiasmante, le celle a combustibile e le batterie a flusso svolgono un ruolo chiave, le prime nella conversione dell'energia in propulsione, le seconde nello stoccaggio dei surplus derivanti da energia rinnovabile. Tuttavia, rimangono ancora da superare alcuni importanti aspetti tecnologici, come ad esempio le limitate prestazioni di picco spesso causate da una scarsa efficienza fluido-meccanica. L'obiettivo principale della presente tesi è l'ottimizzazione fluidodinamica delle celle a combustibile e delle batterie a flusso. A tal fine, la ricerca si focalizza sullo studio dei flussi bifase liquido-vapore e delle dinamiche di dispersione in mezzi porosi, mediante modelli numerici Lattice-Boltzmann, al fine di studiare gli effetti dei fenomeni microscopici sulle caratteristiche macroscopiche di entrambe le tecnologie. I risultati di questo studio forniscono nuove interpretazioni nella comprensione dei comportamenti fisici fondamentali nelle celle a combustibile e nelle batterie di flusso, ed offrono linee guida per una buona e innovativa pratica di progettazione.