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Greenup, Carrazana Lisbet. "Coeficiente de partição do C'O IND 2' no processo de injeção de água carbonatada." [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/264295.
Testo completoAbstract (sommario):
Orientador: Osvair Vidal Trevisan<br>Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica e Instituto de Geociências<br>Made available in DSpace on 2018-08-21T10:14:32Z (GMT). No. of bitstreams: 1
GreenupCarrazana_Lisbet_M.pdf: 2844806 bytes, checksum: ff0d858899d8b8fdc591e5be21757f81 (MD5)
Previous issue date: 2012<br>Resumo: O processo de recuperação de óleo pelo deslocamento com CO2 é um método líder na recuperação melhorada de óleos leves e médios. No entanto, a rápida irrupção do CO2 no poço produtor e a baixa eficiência de varrido diminuem sua atratividade. Uma alternativa mais eficiente é a injeção de água carbonatada (IAC). Um dos fatores mais importantes para a compreensão deste processo é o coeficiente de partição, que quantifica a quantidade de CO2 transferida da água carbonatada injetada para o óleo do reservatório durante o deslocamento. A sua determinação é de vital importância para o planejamento e a simulação da injeção de água carbonatada. Contudo, há poucos estudos experimentais publicados sobre o levantamento deste parâmetro. O objetivo deste trabalho é estudar o coeficiente de partição do CO2 entre as fases óleo e água, para determinadas condições PVT e obter uma gama de parâmetros que possam ajudar na simulação e avaliação do processo para uma futura aplicação no campo. Considerando que a repartição de CO2 entre ambas as fases é refletida no aumento dos volumes iniciais da salmoura e do óleo (testes de inchamento), é desenvolvida uma metodologia baseada num estudo teórico e experimental, que avalia o aumento do volume conjunto da mistura do óleo recombinado e a salmoura carbonatada ao entrarem em contato, nas condições de injeção (pressão de 9.000 psi, temperatura de 64 ºC. Outras medidas de interesse, na caracterização do processo, são o ponto de bolha, o fator volume-formação do óleo, a razão gás-óleo, viscosidades e densidades. Duas etapas foram desenvolvidas para a avaliação do inchamento da mistura de água carbonatada com óleo: teórica, com um programa de simulação de PVT (WinProp), e experimental, com um sistema de garrafas PVT e com uma célula PVT visual. Dentro dos resultados mais significativos consta uma caracterização do óleo do reservatório com sua representação numérica por meio da equação de estado de Peng-Robinson (1978). Assim como a estimativa do coeficiente de partição do CO2 entre as fases óleo e água para as condições especificadas de pressão, temperatura e razão molar óleo-água. Alem disso, descreve-se uma metodologia para a determinação do coeficiente de partição, que durante sua execução, revelou vários aspetos, que fornecem um grande aprendizado para trabalhos futuros relacionados com o tópico<br>Abstract: Oil recovery process by carbon dioxide displacement is the leader improved recovery method applied to light and medium oil reservoirs. Nevertheless, the effects of early breakthrough and poor reservoir sweep let it a less attractive method. The flooding with carbonated water is a more efficient choice. The partition coefficient is one of the key parameters driving the process; it quantifies the CO2 amount transferred from the injected carbonated water to reservoir oil. The aim of the present investigation is to study the CO2 partition coefficient between oil and water phases for specific PVT conditions and to obtain some experimental data for the reservoir simulation input. Taking into account that CO2 partition between both phases reflects in the increase of the initial volumes of the brine and oil, a methodology based on theoretical and experimental study was created. It made possible to estimate, under injection condition (9000 psi the pressure and 64 ºC the temperature), the swelling of the final volume of carbonate water and oil mixture. Other essential parameters, as reservoir oil bubble point, oil formation volume factor, gas oil ratio, densities and viscosities were measured. Two stages were performed to evaluate the mixture swelling effect of carbonate water with oil: the simulation modeling, by using the PVT simulation program (WinProp) and lab experiments, by using a PVT bottle and a PVT cell. With the obtained results the reservoir oil was characterized with its numerical representation via a Peng-Robinson equation of state (1978). The CO2 partition coefficient value between oil and water was assessed for specific conditions of pressure, temperature and molar water-oil ratio. Also a methodology for estimation of the partition coefficient was described and tested<br>Mestrado<br>Reservatórios e Gestão<br>Mestra em Ciências e Engenharia de Petróleo
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Souza, Amanda Pereira de. "A cana-de-açucar e as mudanças climaticas : efeitos de uma atmosfera enriquecida em 'CO IND. 2' sobre o crescimento, desenvolvimento e metabolismo de carboidratos de Saccharum ssp." [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/317739.
Testo completoAbstract (sommario):
Orientadores: Marcos Silveira Buckeridge, Marilia Gaspar<br>Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia<br>Made available in DSpace on 2018-08-09T03:07:16Z (GMT). No. of bitstreams: 1
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Previous issue date: 2007<br>Resumo: Desde o início da Revolução Industrial as concentrações de CO2 atmosférico aumentaram em cerca de 30% e estimativas apontam que esta concentração poderá atingir aproximadamente 720 ppm até a metade deste século. Estudos sobre o efeito do alto CO2 no desenvolvimento de diversas espécies vegetais já foram realizados, porém poucos com espécies de gramíneas tropicais do tipo C4, como é o caso da cana-de-açúcar. Considerando a importância econômica da cana e seu potencial na obtenção de biocombustíveis é importante saber como esta cultura irá responder ao aumento previsto na concentração de CO2 atmosférico. Sendo assim, o objetivo deste trabalho foi estudar o efeito do aumento do CO2 atmosférico sobre o crescimento, desenvolvimento e metabolismo de carboidratos da cana-de-açúcar visando avaliar o potencial de seqüestro de carbono e o impacto das mudanças climáticas sobre a produtividade. Parâmetros fisiológicos, bioquímicos e moleculares foram analisados em plantas cultivadas em câmaras de topo aberto durante 50 semanas com atmosfera de CO2 ambiente (~370 ppm) e elevada (~720 ppm). Os principais resultados obtidos indicam incremento em altura, na taxa fotossintética e em biomassa de colmo e folhas das plantas cultivadas sob elevado CO2. Ao final das 50 semanas foi detectado no colmo das plantas crescidas em tais condições, um aumento no teor de sacarose, de fibras e no conteúdo de celulose. A análise do perfil de transcritos de folhas após 9 e 22 semanas de cultivo usando microarranjos revelou expressão diferencial de 37 genes, sendo que 14 foram reprimidos e 23 foram induzidos e correspondem principalmente a genes de fotossíntese e desenvolvimento. Nossos resultados indicam que a cultura da cana-de-açúcar tem capacidade para seqüestro de carbono e potencial para aumento na produtividade em condições de alta concentração de CO2<br>Abstract: Since the beginning of the Industrial Revolution, the concentrations of CO2 in the atmosphere increased about 30% and the current forecasts point out that this concentration will reach approximately 720 ppm until the middle of this century. Studies about the effect of CO2 on the development of several plant species have been performed. However, few studies have been performed with tropical grass species having photosynthesis C4, as is the case of sugar cane. Due to the economic importance of sugar cane and its high potential to obtain biofuel, it is important to known how this crop will respond to the forecasted increase in the CO2 concentration in the atmosphere. Therefore, the goal of this work was to study the effects of increased CO2 concentration on growth, development and carbohydrate metabolism of sugar cane aiming the evaluation of the potential of this specie for carbon sequestration and the impact of the global climatic change on its productivity. Physiological, biochemical and molecular features of these plants have been analyzed during 50 weeks of growth in Open-Top-Chambers (OTCs) with ambient (~370 ppm) and elevated (~720 ppm) CO2 concentrations. After 50 weeks of growth under these conditions, we observed an increase of sucrose content, fiber an also in cellulose contents in stems of plants grown under elevated CO2. The microarray analysis of the transcriptome of leaves was obtained after 9 and 22 weeks and revealed differential expression of 37 genes. Fourteen genes were repressed and 23 induced by elevated CO2. The latter correspond mainly to the processes of photosynthesis and development. Our results indicate that the sugar cane crop has a high potential for carbon sequestration and increase of productivity under elevated CO2 concentrations<br>Mestrado<br>Biologia Celular<br>Mestre em Biologia Celular e Estrutural
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Balestra, Luigi <1994>. "Models and Simulations of Diamond-like Carbon for large-area high voltage power diodes." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2022. http://amsdottorato.unibo.it/10110/1/FINAL_VERSION_300.pdf.
Testo completoAbstract (sommario):
Silicon-based discrete high-power devices need to be designed with optimal performance up to several thousand volts and amperes to reach power ratings ranging from few kWs to beyond the 1 GW mark. To this purpose, a key element is the improvement of the junction termination (JT) since it allows to drastically reduce surface electric field peaks which may lead to an earlier device failure. This thesis will be mostly focused on the negative bevel termination which from several years constitutes a standard processing step in bipolar production lines. A simple methodology to realize its counterpart, a planar JT with variation of the lateral doping concentration (VLD) will be also described. On the JT a thin layer of a semi insulating material is usually deposited, which acts as passivation layer reducing the interface defects and contributing to increase the device reliability. A thorough understanding of how the passivation layer properties affect the breakdown voltage and the leakage current of a fast-recovery diode is fundamental to preserve the ideal termination effect and provide a stable blocking capability. More recently, amorphous carbon, also called diamond-like carbon (DLC), has been used as a robust surface passivation material. By using a commercial TCAD tool, a detailed physical explanation of DLC electrostatic and transport properties has been provided. The proposed approach is able to predict the breakdown voltage and the leakage current of a negative beveled power diode passivated with DLC as confirmed by the successfully validation against the available experiments. In addition, the VLD JT proposed to overcome the limitation of the negative bevel architecture has been simulated showing a breakdown voltage very close to the ideal one with a much smaller area consumption. Finally, the effect of a low junction depth on the formation of current filaments has been analyzed by performing reverse-recovery simulations.
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Dul, Sithiprumnea. "Carbon-based polymer nanocomposites for 3D-printing." Doctoral thesis, University of Trento, 2018. http://eprints-phd.biblio.unitn.it/3038/1/PhD_Thesis_Dul_2018.pdf.
Testo completoAbstract (sommario):
In this PhD project, novel polymer nanocomposites are developed with the aim to increase the performances of 3D-printed parts obtained by fused deposition modeling (FDM). The attention is focused on carbon-based nanomaterials incorporated into an acrylonitrile–butadiene–styrene (ABS) polymer by a solvent-free process. ABS-based nanocomposites were prepared by incorporating different kinds and amounts of graphene nanoplatelets (GNP), carbon nanotubes (CNT) and hybrid (GNP/CNT) systems. In order to understand the effect of the manufacturing process on the material’s properties, the samples were produced into two different processing routes: (i) melt compounding and compression molding, and (ii) melt compounding, following by filament extrusion, and fused deposition modelling (FDM). Several characterization techniques were employed in order to evaluate the flowablity, morphology, mechanical and functional properties of the materials.
In the first part of work, ABS-graphene nanocomposites are described. Two ABS matrices having different viscosity were compared with the addition of various types of commercial graphene nanoplatelets (xGnP® M5, C300, C500, and C750 by XG Sciences) in the range 2-8 wt%. The better processability and higher stiffening effect on compression molded plates were achieved by utilizing the low viscosity ABS. The effects of GNPs on the thermal, electromagnetic shielding (EMI SE), electrical and mechanical behaviour of an ABS matrix were investigated. Melt flow index (MFI) values almost linearly decreased with all the type of GNP, especially with the highest surface area nanofiller (GNP-C750). Due to large size of graphene, nanocomposites filled with GNP-M5 showed the better properties of in electromagnetic interference shielding efficiency (EMI SE) and stiffness. Consequently, GNP-M5 were selected and incorporated at 4 wt% in ABS filaments used to feed a FDM machine to obtain specimens with various build orientations. The elastic modulus and dynamic storage moduli of 3D printed parts along three different build orientations were increased by the presence of GNP-M5 in the ABS matrix. At the same time, a decrease in both strength and strain at break was observed when GNP-M5 is added to ABS. Moreover, higher thermal stability was induced on 3D printed parts by GNP, as indicated by a reduction in both coefficient of linear thermal expansion and creep compliance. A comparison between 3D printed and compression molded parts highlighted the importance of the orientation effects induced by the FDM process.
In the second part of work, the results of the investigation on ABS-carbon nanotubes nanocomposites are reported. ABS-CNT nanocomposites plate production by compression molding and their characterization was a preliminary step. Nanocomposite ABS/CNT filaments at 1-8 wt % were obtained by using direct melt compounding and extrusion. The optimal CNT content in the filaments for FDM was found to be 6 wt %; for this composite, a detailed investigation of the thermal, mechanical and electrical properties was performed. The presence of CNT in ABS filaments and 3D-printed parts resulted in a significant enhancement of the tensile modulus and strength, accompanied by a reduction of the elongation at break. As documented by dynamic mechanical thermal analysis, the stiffening effect of CNT in ABS is particularly pronounced at high temperatures. Besides, the presence of CNT in 3D-printed parts accounts for better creep and thermal dimensional stabilities of 3D-printed parts, accompanied by a reduction of the coefficient of thermal expansion. 3D-printed nanocomposite samples with 6 wt% of CNT exhibited a good electrical conductivity, even if lower than pristine composite filaments. In addition, the strain sensing capabilities of the conducting 3D-printed samples with 6 wt% of CNT with two different infill patterns (HC, and H45) were studied. Upon the strain applied, the resistance change and damage in the conductive FDM parts were detectable. Fatigue and creep loading on FDM products were also carried out.
In last part of work, ABS-GNP-CNT hybrid nanocomposites are described. ABS nanocomposites plates with addition GNP-M5 and CNT at 2-8 wt% were compared. A significant higher reduction in MFI value by the addition of CNT compared to GNP was observed. The ABS/GNP nanocomposites showed the slightly higher stiffness and the creep stability compared to the ABS/CNT nanocomposites, but showed the lower tensile strength. Also, the ABS/CNT samples showed significant higher electrical properties in comparison to ABS/GNP. The total nanofiller content of CNT/GNP hybrid plates was fixed at 6 wt%. The hybrid nanocomposites showed a linear increase in modulus and strength as a function to CNT/M5 ratio. Moreover, conductive hybrid nanocomposite plates were obtained by the addition of CNT. The composition of 50:50 of CNT/GNP at 6 wt% was selected for FDM process due to the good compromise between processability and properties (e.g. mechanical and electrical). In agreement with electrical resistivity, EMI SE of 6 wt% ABS/CNT and 50:50 hybrid ABS nanocomposites resulted to be -46 dB and -31.7 dB for plate samples. EMI SE of FDM parts is about for -14 dB HC and H45 build orientation and –25 dB for PC build orientation printing from ABS/CNT nanocomposites, while parts had EMI SE about -12 dB for HC and H45 and -16 dB for PC from hybrid nanocomposites.
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MAFFEIS, VIVIANA. "Carbon nano-onions for biomedical applications." Doctoral thesis, Università degli studi di Genova, 2018. http://hdl.handle.net/11567/928946.
Testo completoAbstract (sommario):
The biomedical applications of carbon nanomaterials are under intensive investigation for the development
of next-generation therapeutics. Although much focus has been placed on carbon nanotubes (CNTs) and
graphene, other carbon nanomaterials including carbon nanohorns (CNHs), nanodiamonds (NDs) and
fullerenes have emerged as suitable candidates for biomedical applications. Among these multi-shell
fullerenes, also known as carbon nano-onions (CNOs), are the less studied carbon nanomaterials in
biomedicine. The unique properties of carbon nano-onions, such as high surface area-to-volume ratio,
thermal conductivity, electrical conductance, mechanical stiffness and ease of chemical functionalization
render them fascinating materials for diverse applications including drug-delivery, diagnostics, biological
imaging and tissue engineering. Carbon nanomaterials are emerging as smart nanostructures for
biomedicine due to the possibility to incorporate multiple functionalities and moieties internally or externally.
They can be modified at a precise physicochemical level to optimize targeting in the complex in vivo
environment and also engineered for fluorescence detection, magnetic resonance imaging and ablation of
tumor cells. Herein, robust and versatile synthetic strategies for the modification of carbon nano-onions
(CNOs) are reported. The development of novel CNO conjugates represent a promising platform for the
realization of novel technology scaffold for molecular imaging, photodynamic therapy and molecular
transporter of fully synthetic carbohydrate-based vaccines for immunotherapy due to the large specific
surface area and unique optical and electrochemical properties of CNOs. Through the methodologies
described, these smart nano-materials can envisage the realization of multi stimuli-responsive and dynamic
architectures capable of changing their physicochemical behavior upon encountering specific microenvironmental
signals becoming relevant for diagnosis, imaging and therapies of specific disease
applications.
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IMBRAGUGLIO, DARIO. "Nanostructured carbon/silicon composite opto-electrochemical devices for sensing and energy harvesting applications." Doctoral thesis, Politecnico di Torino, 2013. http://hdl.handle.net/11583/2506359.
Testo completoAbstract (sommario):
My research activity deals with fabrication, characterization and functionalization techniques of silicon-based nanostructures and systems, such as silicon nanowires and nanostructured porous silicon. In particular, I focused my final dissertation thesis on the synthesis and study of a new class of carbon/silicon nanocomposites, produced by a recently discovered carbonization chemistry of porous silicon. Such a new chemistry has been optimized in order to obtain samples amenable for applications into a liquid dynamic environment. The employed carbon nanocasting process provides both a stable and conductive hybrid nanomaterial, allowing the carbonized porous silicon film to act as working electrode in aqueous media. The electrode stability has been tried out in different liquids as well as under voltage applied. Moreover, the optical properties of the nanostructure enable its use as a sensor for electrically charged species in buffer solutions, such as biomolecular complexes. By application of an electrical potential difference between the working and a counter electrode, the sensor is able to simultaneously attract and detect both positively than negatively charged targets. In the case of electroadsorbed biomolecules, indications on the retention of their functional activity after releasing from the electrode surface are also provided. Furthermore, an electrical measurement system has been added to the optical one in order to monitor, in real-time with the optically transduced signal, the current flowing between the two electrodes during the sensing experiments. A few prototypes which synchronize the optical and electrical responses of the sensor have been fabricated and their performances tested by varying the electrical parameters. These new combined opto-electrochemical devices can potentially find applications both in future label-free sensing than in next-generation energy harvesting technologies.
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De, Genua Francesca. "Engineered Alumina / Silicon Carbide Laminated Composites." Doctoral thesis, Università degli studi di Trento, 2014. https://hdl.handle.net/11572/368173.
Testo completoAbstract (sommario):
High-melting temperature oxides, carbides and nitrides are superior in hardness and strength to metals, especially in severe conditions. However, the extensive use of such ceramics in structural engineering applications often encountered critical problems due to their lack of damage tolerance and to the limited mechanical reliability. Several ceramic composites and, in particular, laminated structures have been developed in recent years to enhance strength, toughness and to improve flaw tolerance. Significant strength increase and improved mechanical reliability, in terms of Weibull modulus or minimum threshold failure stress, can be achieved by the engineering of the critical surface region in the ceramic component. Such effect can be realized by using a laminated composite structure with tailored sub-surface insertion of layers with different composition. Such laminate is able to develop, upon co-sintering, a spatial variation of residual stress with maximum compression at specific depth from the surface due to the differences in thermal expansion coefficient of the constituting layers.
In the present work silicon carbide has been selected as second phase to graduate the thermal expansion coefficient of alumina due to its relatively low specific density that could allow the production of lighter components with improved mechanical performance, also for high temperature applications. Ceramic laminates with strong interfaces composed of Al2O3/SiC composite layers were produced by pressureless sintering or Spark Plasma Sintering (SPS) of green layers stacks prepared by tape casting water-based suspensions. Monolithic composites containing up to 30 vol% silicon carbide were fabricated and thoroughly characterized. Five engineered ceramic laminates with peculiar layers combination that is able to promote the stable growth of surface defects before final failure were also designed and produced. By changing the composition of the stacked laminae and the architecture of the laminate, tailored residual stress profile and T-curve were generated after co-sintering and successive cooling in each multilayer.
The results of the mechanical characterization show that the engineered laminates are sensibly stronger than parent monolithic composite ceramic and exhibit surface damage insensitivity, according to the design. Such shielding effect is especially observed when macroscopic cracks are introduced by high load Vickers indentations. Some designed multilayers exhibit reduced strength scatter and higher Weibull modulus, which implies superior mechanical reliability. Fractographic observations on fracture surfaces of the engineered laminates show a graceful crack propagation within the surface layers in residual compressive stress which can be attributed to the stable growth of superficial cracks before final failure as it is predicted by the apparent fracture toughness curve. Such fracture behaviour is considered to be responsible for the peculiar surface damage insensitivity and the improved mechanical performance.
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SOTO, ALICIA. "Carbon capture, utilization, and storage (CCUS) and how to accelerate the development and commercialization of carbon base products in the European and US market." Doctoral thesis, Politecnico di Torino, 2021. http://hdl.handle.net/11583/2942140.
Testo completo
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SHAHZAD, MUHAMMAD IMRAN. "Growth, Characterization & Applications of Carbon Nanomaterials." Doctoral thesis, Politecnico di Torino, 2014. http://hdl.handle.net/11583/2551359.
Testo completoAbstract (sommario):
The purpose of this research is to develop and improve the process of massive growth of carbon nanotubes (CNTs) via chemical vapor deposition (CVD). Beside the growth of CNTs and their potential applications, CNTs based polymer composites properties were also explored. The thesis may be divided into two major sections.
In the first section a comprehensive introduction to carbon nanomaterials specifically CNTs (which includes the structure, types, growth mechanism and techniques, characterization techniques and properties) is described. Then the CVD growth procedure adopted in our lab to grow different carbon nanomaterials in particular Multiwall Carbon nanotubes (MWCNTs) under differential experimental conditions is discussed. We have grown upto 3mm thick MWCNTs carpet on Si substrate with MWCNTs diameter in the range 20nm-80nm. The individual length of MWCNTs is as long as few hundreds of micrometer. MWCNTs based structures were also grown on patterned surfaces. The patterning of the surfaces is performed by soft photolithography. These MWCNT structures have very interesting applications e.g. a). The vertical cylinders were use to produce SiC hollow cylinders, and b). CNT based fins grown on Si substrate were used to enhance the convective heat transfer properties. Several treatments (thermal annealing, acid treatment and plasma treatment) were also performed on MWCNTs in order to modify their characteristics. These procedures are useful for purification, functionalization and graphitization of MWCNTs.
The second section about CNT based polymer composites starts with the brief introduction to polymer composites, processing techniques, major issues in mixing the CNTs in different polymers and finally the mixing tools used for better dispersion. The optical characterization of PDMS based MWCNTs composites films are studied. These films can have application in optical limiting devices. Furthermore, the transparency of these films is also used to calculate a unique parameter absorption cross section of a single MWCNT. The absorption cross section of individual MWCNTs having widely different aspect ratios scales with their volume. The approximation of absorption cross section per carbon atom is also in close agreement with that of graphite.
The electrical conductivity phenomena in epoxy based carbon nanomaterials (CNMs) composites are also discussed. A total number of 16 types of different CNMs were used. Several conduction behaviors have been found e.g. from highly conductive CNTs which showed linear Ohmic curve, to non-linear diode-like trend to completely insulating one. The best performances have been reached by the shortest and thinner MWCNTs (both as grown and slightly functionalized with COOH groups), which can underline that small fillers can be better dispersed inside the composite and create a better conductive net within the matrix. We have also applied physical models such as the percolation theory and the fluctuation mediated tunnelling theory to the most conductive nanocomposites, with poor agreement between experimental data and theoretical prediction. Finally, we applied a recently revised model based on tunnelling-percolation theory and obtained a good fit between experimental and theoretical results.
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AUDASSO, EMILIO. "Simulation of High Temperature Fuel Cells for Carbon Capture." Doctoral thesis, Università degli studi di Genova, 2021. http://hdl.handle.net/11567/1038604.
Testo completoAbstract (sommario):
The aim of this doctoral thesis is to develop and apply a kinetic model for the simulation of High Temperature Fuel Cells for energy conversion and Carbon Capture applications. In particular, the work will focus on the analysis and the modeling of a newly discovered mechanism in Molten Carbonate Fuel Cells that sees the net migration of H2O from the cathode to the anode side in competition with the usually encountered migration of CO2. This mechanism was never reported in the literature and was named "dual-anion mechanism" to underline the parallel migration of carbonate and hydroxide ions. It is important because it can greatly affect the cell’s performance in terms of both energy conversion and CO2 sequestration.
The work was performed in collaboration with ExxonMobil that first observed this phenomenon during a campaign to test the use of molten carbonate fuel cells as Carbon Capture devices. The work was also done in partnership with FuelCell Energy, who through an agreement with ExxonMobil obtained all of the experimental data of this phenomenon.
The analysis of the mechanism and the development of a model to simulate cells working at such conditions were conducted in a series of different steps. To start, based on experimental data, the mechanism was studied as a function of the reactant gases to understand the main dependences of the occurring phenomena. Consequently, as more data became available, additional dependences to improve the knowledge of the mechanism and the modeling were studied. In particular, the work was focused on the analysis of the effects that the diffusion resistance has on the extent on which one anionic path evolves over the other. Successively, the operating temperature and the carbonate/hydroxide equilibrium were studied and included in the model. The analysis of the experimental data also allowed to observe the effects that the gas atmosphere can have on the cell ohmic resistance as it was determined that the electrolyte melt can change based on equilibria between melt and gas phase. The developed kinetic formulation was implemented into the SIMFC code, a home-made Fortran program realized by the group PERT of the University of Genoa for the simulation of High Temperature Fuel Cells (Molten Carbonate and Solid Oxide). In this way, the model was successfully tested by simulating the experimental data.
Additionally, a formulation to consider the direct internal steam reforming of CH4 on the performance of cells was also included into the SIMFC code. The formulation considers the reaction locally with dependence on catalyst loading. As such, it allows the study of the effect of catalyst distribution and degradation. This part of the thesis was developed on Solid Oxide Fuel Cells instead of Molten Carbonate. This choice was dictated by the fact that I spent a period of 8 months during the first year of the Ph.D. program at the Korea Institute of Science and Technology studying solid oxide fuel cells materials, specifically focused on the use of perovskite (a possible solid oxide fuel cells anode material) as catalysts for the CH4 reforming reaction which will be presented.
The overall model developed and implemented into the SIMFC code was demonstrated to be very promising in simulating High Temperature Fuel Cells performance under a great range of operating conditions.
11
SHEIKH, ABUBAKR AYUB. "Advanced carbon dioxide thermodynamic cycles for power production." Doctoral thesis, Università degli studi di Brescia, 2022. http://hdl.handle.net/11379/563080.
Testo completoAbstract (sommario):
I cicli termodinamici dell'anidride carbonica per la produzione di energia sono una nuova tecnologia in fase di ricerca e sviluppo in vari gruppi di ricerca in tutto il mondo. Le principali caratteristiche attrattive dei cicli ad anidride carbonica sono una maggiore efficienza del ciclo, un ingombro ridotto e la loro capacità di integrazione con diverse fonti di calore. Tuttavia, ci sono alcune sfide specifiche dell'applicazione di tali cicli di alimentazione, tra cui una minore efficacia di recupero del calore, un lavoro specifico per il ciclo inferiore e la necessità di schemi di ciclo complessi per il recupero del calore di scarto. In secondo luogo, la sensibilità dell'efficienza del ciclo all'aumento della temperatura minima del ciclo ne limita anche il funzionamento per condizioni in cui è disponibile solo un mezzo di raffreddamento freddo. Per affrontare le suddette sfide dei cicli energetici dell'anidride carbonica, questo lavoro propone nuovi cicli avanzati transcritici dell'anidride carbonica che funzionano con miscele binarie a base di CO2 come fluidi di lavoro per la produzione di energia.
Il calcolo accurato delle proprietà termofisiche dei fluidi di lavoro è fondamentale per l'analisi termodinamica dei cicli di alimentazione utilizzando miscele binarie a base di CO2 come fluidi di lavoro. Di conseguenza, uno degli obiettivi primari di questa ricerca è quello di esaminare vari modelli di proprietà termodinamiche al fine di selezionarne uno in grado di calcolare proprietà termodinamiche accurate nell'intervallo di temperatura di interesse. Inoltre, i punti critici vapore-liquido in varie composizioni molari della miscela vengono calcolati combinando i criteri dei punti critici di Gibbs con Peng-Robinson EoS.
Al fine di esplorare il potenziale termodinamico delle miscele di CO2 che lavorano fluidi su un'ampia gamma di temperature della sorgente di calore, vengono considerate due applicazioni: recupero del calore di scarto ad alta temperatura (Tmax=350℃) e energia solare concentrata (Tmax=550℃ e 700℃). Nel campo del recupero di calore ad alta temperatura, la miscela CO2-R134a (70% CO2 molare) nel ciclo di alimentazione transcritico mostra un'efficienza totale di 4 punti superiore rispetto al ciclo di alimentazione ad anidride carbonica (14,3% in caso di CO2-R134a e 10,8% in caso di CO2) con la stessa disposizione del ciclo e pressione massima di esercizio.
Cinque miscele di CO2 sono considerate fluidi di lavoro per cicli energetici accoppiati a una torre solare concentrata (CSP) e il guadagno in efficienza del ciclo è studiato con riferimento al ciclo di ricompressione di sCO2 e al ciclo di recupero semplice di sCO2. Con un semplice layout del ciclo di recupero, il fluido di lavoro CO2-TiCl4 [80% CO2 molare] mostra un'efficienza del ciclo del 50,7%, che è vicina all'efficienza del ciclo ottimale del ciclo di ricompressione sCO2 (cioè 50,8%) alla temperatura massima del ciclo di 700 ℃ . Inoltre, quando la temperatura massima del ciclo è 550 ℃, CO2-TiCl4, CO2-C6F6, CO2-CF3I e CO2-SO2F2 determinano anche un guadagno nell'efficienza del ciclo rispetto al semplice ciclo di recupero sCO2.
Considerando l'enorme potenziale delle miscele di CO2 nel migliorare l'efficienza termodinamica del ciclo, viene effettuata un'analisi dettagliata per un blocco di potenza da 100 MW integrato con una torre solare a concentrazione che adotta il fluido di lavoro della miscela CO2-SO2. L'analisi a diversa composizione molare della miscela suggerisce una miscela di CO2 molare all'85% come scelta ottimale a causa della maggiore efficienza del ciclo indipendentemente dal layout del ciclo. Sulla base dei vantaggi termodinamici ed economici, i cicli di alimentazione transcritici operanti con una miscela di CO2-SO2 risultano essere una scelta migliore per le centrali elettriche CSP.<br>Carbon dioxide thermodynamic cycles for power production is a new technology under research and development in various research groups around the globe. The main attractive features of carbon dioxide cycles are higher cycle efficiency, lower size footprint and their integration capability with different heat sources. However, there are some application-specific challenges of such power cycles including lower heat recovery effectiveness, lower cycle specific work and necessity of complex cycle layouts for waste heat recovery. Secondly, the sensitivity of cycle efficiency to rising cycle minimum temperature also limits its operation for conditions where only cold cooling medium is available. To address the aforesaid challenges of carbon dioxide power cycles, this work proposes new transcritical advanced carbon dioxide cycles operating with CO2-based binary mixtures as working fluids for power production.
The accurate calculation of thermophysical properties of working fluids is critical for thermodynamic analysis of power cycles using CO2-based binary mixtures as working fluids. As a result, one of the primary goals of this research is to examine various thermodynamic property models in order to select one that is capable of computing accurate thermodynamic properties in the temperature range of interest. Furthermore, vapor-liquid critical points at various molar compositions of mixture are calculated by combining Gibbs critical point criteria with Peng-Robinson EoS.
In order to explore thermodynamic potential of CO2 mixtures working fluids over wide range of heat source temperatures, two applications are considered: high temperature waste heat recovery (Tmax=350℃) and concentrated solar power (Tmax=550℃ and 700℃). In the field of high temperature heat recovery, CO2-R134a mixture (70% molar CO2) in transcritical power cycle shows 4 points higher total efficiency compared to carbon dioxide power cycle (14.3% in case of CO2-R134a and 10.8% in case of CO2) with the same cycle layout and maximum operating pressure.
Five CO2 mixtures are considered as working fluids for power cycles coupled with a concentrated solar power (CSP) tower, and the gain in cycle efficiency is studied with reference to sCO2 recompression cycle and sCO2 simple recuperative cycle. With a simple recuperative cycle layout, CO2-TiCl4 [80% molar CO2] working fluid shows cycle efficiency of 50.7%, which is close to the optimum cycle efficiency of the sCO2 recompression cycle (i.e. 50.8 percent) at cycle maximum temperature of 700℃. Moreover, when cycle maximum temperature is 550 ℃, CO2-TiCl4, CO2-C6F6, CO2-CF3I and CO2-SO2F2 also brings about gain in cycle efficiency compared to sCO2 simple recuperative cycle.
Considering the huge potential of CO2 mixtures in improving thermodynamic efficiency of the cycle, a detailed analysis is carried out for a 100 MW power block integrated with concentrated solar power tower adopting CO2-SO2 mixture working fluid. Analysis at different molar composition of mixture suggests 85% molar CO2 mixture as optimum choice owing to higher cycle efficiency irrespective of cycle layout. Based on thermodynamic and economic advantages, transcritical power cycles operating with CO2-SO2 mixture turns out to be a better choice for CSP power plants.
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De, Genua Francesca. "Engineered Alumina / Silicon Carbide Laminated Composites." Doctoral thesis, University of Trento, 2014. http://eprints-phd.biblio.unitn.it/1219/1/PhD_Thesis_DE_GENUA_FRANCESCA.pdf.
Testo completoAbstract (sommario):
High-melting temperature oxides, carbides and nitrides are superior in hardness and strength to metals, especially in severe conditions. However, the extensive use of such ceramics in structural engineering applications often encountered critical problems due to their lack of damage tolerance and to the limited mechanical reliability. Several ceramic composites and, in particular, laminated structures have been developed in recent years to enhance strength, toughness and to improve flaw tolerance. Significant strength increase and improved mechanical reliability, in terms of Weibull modulus or minimum threshold failure stress, can be achieved by the engineering of the critical surface region in the ceramic component. Such effect can be realized by using a laminated composite structure with tailored sub-surface insertion of layers with different composition. Such laminate is able to develop, upon co-sintering, a spatial variation of residual stress with maximum compression at specific depth from the surface due to the differences in thermal expansion coefficient of the constituting layers.
In the present work silicon carbide has been selected as second phase to graduate the thermal expansion coefficient of alumina due to its relatively low specific density that could allow the production of lighter components with improved mechanical performance, also for high temperature applications. Ceramic laminates with strong interfaces composed of Al2O3/SiC composite layers were produced by pressureless sintering or Spark Plasma Sintering (SPS) of green layers stacks prepared by tape casting water-based suspensions. Monolithic composites containing up to 30 vol% silicon carbide were fabricated and thoroughly characterized. Five engineered ceramic laminates with peculiar layers combination that is able to promote the stable growth of surface defects before final failure were also designed and produced. By changing the composition of the stacked laminae and the architecture of the laminate, tailored residual stress profile and T-curve were generated after co-sintering and successive cooling in each multilayer.
The results of the mechanical characterization show that the engineered laminates are sensibly stronger than parent monolithic composite ceramic and exhibit surface damage insensitivity, according to the design. Such shielding effect is especially observed when macroscopic cracks are introduced by high load Vickers indentations. Some designed multilayers exhibit reduced strength scatter and higher Weibull modulus, which implies superior mechanical reliability. Fractographic observations on fracture surfaces of the engineered laminates show a graceful crack propagation within the surface layers in residual compressive stress which can be attributed to the stable growth of superficial cracks before final failure as it is predicted by the apparent fracture toughness curve. Such fracture behaviour is considered to be responsible for the peculiar surface damage insensitivity and the improved mechanical performance.
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Di, Giacomo Raffaele. "Carbon nanotube based networks, bio-nano-composites and sensors." Doctoral thesis, Universita degli studi di Salerno, 2013. http://hdl.handle.net/10556/1326.
Testo completoAbstract (sommario):
2011 - 2012<br>The formation of a photosensitive device due to the local breakdown in an MOS structure with an impurity containing oxide layer has been observed. A stepwise breakdown of the oxide layer resulted in the formation of a transistor like characteristics with further on stable current-voltage characteristics. A high value of the photosensitivity of the resulting structure has been found, when illuminated with white or blue light. This can be explained by the formation of a local p-n junction during electrical breakdown due to out-diffusion of dopants from the oxide into the underlying silicon substrate. The development of the photocurrent has been monitored during breakdown formation. This monitoring procedure can be used for the optimization of the photosensitive device.
After these experiments a defect-free oxide was produced and tested. Multi walled carbon nanotubes (MWCNTs) have been deposited by casting electrophoresis on top of this SiO2 layer.
Using three different microscopy techniques: namely Atomic Force Microscopy, Secondary Electron Microscopy and Focused Ion Beam Microscopy, the geometry of the interconnection of a single junction between the deposited MWCNTs has been investigated in detail. A very particular twisted interconnection geometry has been observed. Furthermore a strong stability of the sample in time has been observed proving a strong adhesion of the tubes to the SiO2 surface.
Furthermore, MWCNTs were deposited from two different solutions leading to different results regarding their morphology: an almost bi-dimensional “carpet” of MWCNTs, and a network composed of a very limited number of MWCNTs. The “carpet” was obtained using a solution with 1% of sodium dodecyl sulfate in de-ionized water, saturated with MWCNTs. This solution was very stable in time and reproducible carbon nanotube networks could be obtained. All the pure nanotube networks were deposited by di-electrophoresis inside an aluminium contact gap with a contact
distance of 3μm. After the deposition the temperature dependent conductivity of the MWCNTs “carpet” inside the aluminum contact gap has been determined. The temperature behavior of the conductivity shows a good qualitative agreement with the fluctuation induced tunneling model for disordered materials. A rapid reduction of the random telegraph noise present in the virgin devices has been observed after relatively short application of a constant voltage. This increases the possibilities to use aluminum contacts for electronic CNT devices like sensors, where device stability is more important than high current levels. When a different solvent has been used, that resulted in a much lower concentration of CNTs within the micro-gap, a stable electrical behavior has not been achieved.
Successively using the same technique for the solution of MWCNTs a Candida albicans/multi walled carbon nanotube (Ca/MWCNTs) composite material has been produced. It can be used as a temperature-sensing element operative in a wide temperature range (up to 180 °C). The Ca/MWCNTs composite has excellent linear current-voltage characteristics when combined with coplanar gold electrodes. Growing cells of C. albicans were used to structure the carbon nanotube-based composite. The fungus C. albicans combined with MWCNTs co-precipitated as an aggregate of cells and nanotubes that formed a viscous material. Microscopic analyses showed that Ca/MWCNTs formed an artificial tissue. Slow temperature cycling was performed for up to 12 days showing a stabilization of the temperature response of the material. As another application of this new bio-nano-composite layer, the realization of a flexible transparent conductive film has been demonstrated.
A more general procedure in order to obtain novel artificial materials has been proposed and realized using isolated tobacco cells in combination with carbon nanotubes. The electrical, mechanical, optical, thermo-electrical properties of these materials have been determined. Using tobacco cells, a material with low mass density and mechanical properties suitable for structural applications, along with high values of the electrical conductivity has been obtained. Measurements of the mechanical and electrical behavior have been combined with theoretical modeling. These findings indicate a procedure for next generation cyborg nano-composite materials. [edited by authors]<br>XI n.s.
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LASIO, BARBARA. "Fabrication of Cu-based metal matrix composites reinforced with carbon nanofillers." Doctoral thesis, Università degli Studi di Cagliari, 2019. http://hdl.handle.net/11584/260760.
Testo completoAbstract (sommario):
The thesis takes inspiration from the worldwide issues related to the shortage of critical raw materials (CRMs) and the need of finding sustainable alternatives to CRMs within fields and sectors strategic to the well-being and economy of industrialized countries.
The research activity has been focused on the fabrication of Cu-matrix composites reinforced with carbon nanofillers, nano-graphite and graphene in particular. This class of composites attracts considerable interest as a consequence of the broad spectrum of applications Cu-MCs could find due to their thermal and electric conductivities, self-lubricating properties of graphite, cost-effectiveness and availability.
Ball milling (BM) and spark plasma sintering (SPS) have been combined to provide an innovative methodology to fabricate Cu-MCs reinforced with carbon nanofillers enabling the fine dispersion of nanoparticles into the Cu matrix. Specifically, a two-stage cycle involving BM first and, then, SPS has been shown to result in the dispersion of graphite particles in relatively large Cu grains. The iteration of cycles allows the refinement of graphite nanoparticles and their dispersion in Cu powders on the microscopic scale, mostly at grain boundaries, and the subsequent incorporation of nanoparticles into Cu grains due to grain growth mechanisms activated and promoted by high temperatures during SPS.
Molecular level mixing has been also tested to obtain Cu-MCs reinforced with graphene starting from liquid solutions of Cu nanoparticles and graphene. In particular, graphene was dispersed during the redox synthesis to obtain Cu nanopowder, subsequently consolidated by SPS.
Despite the intrinsic different between the two methods, it has been possible to prepare Cu-MCs with graphite nanoparticles and graphene as dispersoids. Structural and microstructural characterization indicate that dispersoids are finely dispersed into the Cu matrix. Nanoindentation measurements clearly demonstrate the significant enhancement of mechanical properties, thus providing an important clue to the validity of the methodology developed.
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Piovani, Mônica Regina. "Balanço de carbono em fotobiorreato com cultivo de Chlorella bulgaris em excesso de 'C 'O IND.2'." [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/266663.
Testo completoAbstract (sommario):
Orientador: Telma Teixeira Franco<br>Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química<br>Made available in DSpace on 2018-08-21T16:33:14Z (GMT). No. of bitstreams: 1
Piovani_MonicaRegina_D.pdf: 3018875 bytes, checksum: fd8c35c2204ec9208757e570785a6b90 (MD5)
Previous issue date: 2012<br>Resumo: As microalgas são microrganismos que vem sendo utilizados na bioconversão de carbono em produtos com interesse comercial como, por exemplo, biocombustíveis, corantes, suplementos alimentares e cosméticos. Elas podem ser cultivadas em sistemas autotróficos e heterotróficas sendo que as fontes de carbono, gasosas ou líquidas, podem ser provenientes de resíduos industriais reduzindo os custos de sua produção. Para identificar quais os possíveis produtos gerados durante o cultivo o objetivo deste trabalho foi avaliar a bioconversão de dióxido de carbono em fotobiorreatores identificando os principais bioprodutos gerados nas fases sólida, líquida e gasosa do sistema. Os experimentos foram conduzidos em fotobiorreatores de coluna de bolhas, alimentados com meio de cultivo sintético, com microalga C. vulgaris em fase exponencial de crescimento. Foi utilizado reator isotérmico, intensidades luminosas de 150?.molm-2.s-1, e injeção de ar com dióxido de carbono na vazão de 1Lmin-1. Além da conversão de carbono foram avaliados métodos de extração de lipídeos baseados no método de Bligh & Dyer e métodos gravimétricos para determinação do teor de umidade. A conversão de CO2 nos sistemas utilizados foi avaliada nas fases sólida, líquida e gasosa e foi expressa em termos de produção de biomassa (6%), em compostos solúveis na fase líquida, e composta orgânicos voláteis (88%) liberados para fase gasosa do sistema. O teor de umidade da biomassa das microalgas foi de 85% para os métodos avaliados e para os métodos para extração de lipídeos foi possível observar a influência do teor de umidade na biomassa na porcentagem de lipídeos que teve variação de 3% a 24%<br>Abstract: Microalgae are microorganisms that have been used for bioconversion of carbon into products of commercial interest such as, biofuels, pigments, food supplements and cosmetics. They can be grown in autotrophic and heterotrophic systems and the carbon sources, gaseous or liquid, can be derived from industrial wastes, reducing the costs of production. To identify the possible products generated during the culture the objective of this study was to evaluate the bioconversion of carbon dioxide in photobioreactors identifying key byproducts in solid, liquid and gaseous phases the generated in system. The experiments were conducted in bubble column photobioreactors, fed synthetic growth medium, and C. vulgaris cultures in exponential growth phase. The reactor was operated isothermically with 150?molm-2s-1 of light intensities and injection of air with carbon dioxide in the flow 1Lmin-1. Besides the carbon conversion, were evaluated lipid extraction methods based on the Bligh & Dyer's method and gravimetric methods for determination of moisture content. The conversion of CO2 systems will be evaluated in phases solid, liquid and gaseous systems, expressed in terms of biomass (6%), production in soluble compounds in the liquid phase and volatiles organic compounds released into the gaseous phase. The moisture content of microalgae biomass was 85% for the evaluated methods and for the extraction of lipids methods was possible to observe the influence of moisture content in the percentage of lipids that ranged from 3% to 24%<br>Doutorado<br>Desenvolvimento de Processos Químicos<br>Doutora em Engenharia Quimica
16
Schulte, Emily Christine <1993>. "Streamlining explanatory variables for household decision-making of low-carbon technologies (LCT) into a coherent decision framework." Master's Degree Thesis, Università Ca' Foscari Venezia, 2020. http://hdl.handle.net/10579/16651.
Testo completoAbstract (sommario):
Around the world, strategies are put in place to facilitate the adoption of low-carbon technologies (LCT) on the household level, yet, individual decision-making is complex. Despite information about driver and barrier related to adoption decisions for specific LCTs is abundant, its usefulness for understanding household adoption decisions is limited, because studies lack theoretical coherence and results are fragmented. This thesis aims to develop a decision framework by deriving universal mechanisms governing household adoption behavior from literature.
First, related theoretical concepts are merged to a theoretical decision framework. Following an inductive approach, explanatory variables utilized in studies on decision-making concerning exemplary LCTs are clustered to superordinate explanatory variables (SEV) in the framework structure. Focussing on behavioral studies only, key SEVs, their interrelations and dynamics are analysed and combined in a practical decision framework.
In the framework, the expression of general dispositions in a decision unit, and the expression of LCT traits in a technology are combined to explain behavioral driver and barrier which are predictive of behavior. A construct of hypothesis proposes explicit effects of specific general dispositions and LCT traits on behavioral driver and barrier in a functional (personal-functional), normative (environmental) and symbolic (social interaction) dimension.
From a practical viewpoint, the framework offers a starting point for consumer-specific intervention strategies directly targeting general dispositions or LCT traits to enhance drivers or reduce barriers for adoption. Yet it doesn’t offer explanations as to why decision units enter the decision process, and future confirmatory research is needed to empirically test the proposed decision framework.
17
CAMISASCA, ADALBERTO. "Carbon nano-onions as promising nanomaterial for biomedical and electrochemical applications." Doctoral thesis, Università degli studi di Genova, 2019. http://hdl.handle.net/11567/940927.
Testo completo
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Scaburri, Raffaele <1974>. "The incomplete ionization of substitutional dopants in Silicon Carbide." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3924/1/scaburri_raffaele_tesi.pdf.
Testo completoAbstract (sommario):
This thesis analyzes theoretically and computationally the phenomenon of partial ionization of the substitutional dopants in Silicon Carbide at thermal equilibrium. It is based on the solution of the charge neutrality equation and takes into account the following phenomena: several energy levels in the bandgap; Fermi-Dirac statistics for free carriers; screening effects on the dopant ionization energies; the formation of impurity bands. A self-consistent model and a corresponding simulation software have been realized. A preliminary comparison of our calculations with existing experimental results is carried out.
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Scaburri, Raffaele <1974>. "The incomplete ionization of substitutional dopants in Silicon Carbide." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3924/.
Testo completoAbstract (sommario):
This thesis analyzes theoretically and computationally the phenomenon of partial ionization of the substitutional dopants in Silicon Carbide at thermal equilibrium. It is based on the solution of the charge neutrality equation and takes into account the following phenomena: several energy levels in the bandgap; Fermi-Dirac statistics for free carriers; screening effects on the dopant ionization energies; the formation of impurity bands. A self-consistent model and a corresponding simulation software have been realized. A preliminary comparison of our calculations with existing experimental results is carried out.
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Mousavi, Sayed Alireza. "Randomized Network of Single Walled Carbon Nanotubes Thin Film Transistor: Fabrication, Simulation and Application as Biosensor." Doctoral thesis, Universita degli studi di Salerno, 2014. http://hdl.handle.net/10556/1465.
Testo completoAbstract (sommario):
2011 - 2012<br>Nanoelectronic devices based on nanomaterials, such as carbon
nanotubes (CNTs) have attracted remarkable attention as a promising
building block for future nanoelectronic circuits due to their
exceptional electrical, mechanical and chemical characteristics. The
electrical characteristics of CNTs, such as high mobility, quasiballistic
conductance and resistance against electromigration, allow to
surpass the properties of current Si based complementary metal oxide
semiconductor (CMOS) devices. In particular, the large surface area
and nanoscale structure makes SWCNTs promising candidates for
chemical and biological sensing applications as well. Current research
covers broad scientific fields, such as study of materials properties at
nanoscale, development, fabrication and simulation of nanoscale
structures, for electronics and biomedical applications. However, there
is ample space for advancements in both theoretical studies and
practical applications for CNT-based systems.
This thesis addresses the design and manufacture of thin film
transistor (TFT) based on randomized network of single walled carbon
nanotubes (SWCNTs) that exploit the unique properties of such
materials to create a label-free biosensor for detection of variety
biomolecules, particularly proteins. In addition, in order to analyze the
electric transport of SWCNTs network in the TFT channel a numerical
3-dimensional (3D) model for the thin film layer is developed.
The SWCNTs-TFTs are fabricated by using microfabrication to
obtain a micro-interdigitated electrode (μ-IDE) as drain-source
electrode. The sizes vary between 2 to 50 μm. Thin-film transistors
(TFTs) are fabricated by using SWCNTs thin film as the
semiconducting layer and SiO2 thin film as the dielectric layer. The
high purity semiconducting network of SWCNTs layer is deposited
with an effective technique that combines the silanization of the
substrate with vacuum filtration process from dispersed SWCNTs in
surfactant solution. . The adopted technique provides a low-cost, fast,
simple, and versatile approach to fabricate high-performance
SWCNTs-TFTs at room temperature. The morphological arrangement
of SWCNTs forming the active layer in the channel of the transistor is
checked with scanning electron microscopic (SEM). The TFTs
obtained exhibit p-type transistor characteristics and operate in
2
accumulation mode. The results are interpreted by considering the
percolation theory. The exponent a of the power law describing the
conductivity can be linked to the structural complexity of the SWCNT
network. In particular an exponent = 1.7 was found experimentally,
showing that the obtained thin film is relatively dense and near
percolation. In addition, the experimental data have been compared
with the results of the 3D model simulating the charge transport in the
SWCNT structures formed in the TFT channel. The simulation results
lead to an exponent = 1.8 that is in good agreement with the
experimental data. The proposed model seems to be able to reliably
reproduce the transport characteristics of the fabricated devices and
could be an effective tool to improve the SWCNTs-TFTs structure.
Moreover, the fabricated SWCNTs-TFT devices provide a suitable
platform for high-performance biosensors in label-free protein
detection. The sensing mechanism is demonstrated on a proof of
principle level for the interaction of biotin and streptavidin on the
SWCNTs surface. It is used as a research model for biosensor
application. The SWCNTs thin-film biosensor has high sensitivity and
it is capable of detecting streptavidin at concentration of 100 pM. [edited by author]<br>XI n.s.
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DE, ANGELIS ELENA. "Integrated Assessment Modelling to support decision makers in planning air quality and low carbon win-win policies. A socio-economic and health perspective." Doctoral thesis, Università degli studi di Brescia, 2021. http://hdl.handle.net/11379/550298.
Testo completoAbstract (sommario):
Integrated Assessment Modelling to support decision makers in planning air quality and low carbon win-win policies. A socio-economic and health perspective.<br>Integrated Assessment Modelling to support decision makers in planning air quality and low carbon win-win policies. A socio-economic and health perspective.
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LUCCI, MASSIMILIANO. "Gas sensor based on single wall carbon nanotubes." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2008. http://hdl.handle.net/2108/601.
Testo completoAbstract (sommario):
Single-walled carbon nanotubes (SWNTs) are nowadays one of the most investigated materials and the realization of
ordered SWNT structures is of fundamental importance for the improvement of many technological fields, from the
non-linear optics to the realization of transistor, to the assembly of gas sensing devices.
A SWNT is formed by rolling a graphene sheet into a seamless cylinder with a diameter on the nanometer scale. The
individual SWNTs are joined each other and assembled into bundles by Van der Waals forces. Guest molecules can
potentially interact with SWNTs via the outer surfaces of bundles, the inside of the tubes and /or the interstitial channels
between the tubes in a bundle. These different situations are expected to play an important role in tuning the guest
molecule/SWNT interaction during gas adsorption and/or desorption, and have been investigated theoretically and
experimentally using different approaches.
In particular, the interaction between gaseous molecules and SWNTs has been investigated from different point of
view, including gas storage and gas detection through modification of electronic and thermal properties or through
modification of the field emission properties. Compared with conventional solid-state sensors, that typically operate at
temperatures over 200 °C, and conducting polymers-based sensors, that provide only limited sensitivity, sensing
devices assembled with single-wall nanotubes can exhibit high sensitivity and fast response time at room temperature.
Due to the high surface area of nanotubes, a little amount of nanotube material can provide many sites for gas
interaction. The accessibility of these sites depends on the status of aggregation of the nanotubes. Our preliminary
studies suggested that the sensitivity of a nanotube-based device can be optimized controlling the organization of the
SWNTs. Ordered bundles of SWNTs exhibit indeed a sensitivity double with respect to that of a disordered deposit.
This is likely due to the enhancement of surface area for organized SWNT systems with respect to randomly placed
SWNT bundles.
Hence, aligned nanotubes can serve as a very efficient material for use in gas detection. Directionality of SWNT can be
obtained directly during the synthesis process, or after manipulation of dispersed nanotubes, by mean of several
methods, such as filtration/deposition from suspension in strong magnetic fields, field emission, electrophoresis or
dielectrophoretical processes. In particular the use of electric fields to move, position and align SWNTs has been
reported in recent papers and the results indicate that both the electrophoresis (EP) and dielectrophoresis (DEP) routes
have potential advantages for arranging nanotubes in controlled systems.
Beyond the sensitivity, another severe constraint for gas detection is the time either for the reset of the sensor after
exposure to the gas, either for the acceleration of the response itself.
Since practical applications can be severely limited by slow absorption/desorption processes, we felt it worthwhile to
investigate in a systematic way some physical parameters affecting the sensor response.
In this thesis we present a study of NH3 ,NOx and H2 detection using organized SWNTs as sensing material and an
innovative procedure to improve the time response of the sensor by applying a back gate voltage. Moreover study
on gas detection and gas storage were done using QCM sensor.
23
Graziani, Gabriela <1986>. "New Phosphate-Based Treatments for Carbonate Stone Consolidation and Protection." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7560/4/Graziani__PhD_thesis.pdf.
Testo completoAbstract (sommario):
Carbonate stones on site undergo severe weathering processes, that make consolidation and protection necessary. However, currently available consolidants and protectives are far from being satisfactory when applied to this kind of materials. For this reason, in this thesis an innovative hydroxyapatite-based treatment was developed for limestone consolidation, marble consolidation and marble protection.
Firstly, a new treatment protocol was set up for limestone and marble consolidation: solution precursor, concentration and pH, application method and possible additions were investigated to improve the treatment performance. Then, efficacy, compatibility and durability of the treatment were evaluated on these two lithotypes, in comparison with the products currently used for the same aim (ethyl silicate and ammonium oxalate). For marble, the treatment protocol developed in laboratory was also tested on a real historic artefact and on site.
Moreover, a surface treatment for protecting marble against acidic rain was formulated, investigating how different parameters (starting solution pH and concentration, organic and inorganic additions) affect the morphology, composition and acid resistance of the treated surface.
Excellent results were achieved: hydroxyapatite resulted an effective, compatible and durable consolidant for carbonate stone. Moreover, ethanol addition allowed to obtain a uniform, acid resistant protective hydroxyapatite layer on marble.
24
Graziani, Gabriela <1986>. "New Phosphate-Based Treatments for Carbonate Stone Consolidation and Protection." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7560/.
Testo completoAbstract (sommario):
Carbonate stones on site undergo severe weathering processes, that make consolidation and protection necessary. However, currently available consolidants and protectives are far from being satisfactory when applied to this kind of materials. For this reason, in this thesis an innovative hydroxyapatite-based treatment was developed for limestone consolidation, marble consolidation and marble protection.
Firstly, a new treatment protocol was set up for limestone and marble consolidation: solution precursor, concentration and pH, application method and possible additions were investigated to improve the treatment performance. Then, efficacy, compatibility and durability of the treatment were evaluated on these two lithotypes, in comparison with the products currently used for the same aim (ethyl silicate and ammonium oxalate). For marble, the treatment protocol developed in laboratory was also tested on a real historic artefact and on site.
Moreover, a surface treatment for protecting marble against acidic rain was formulated, investigating how different parameters (starting solution pH and concentration, organic and inorganic additions) affect the morphology, composition and acid resistance of the treated surface.
Excellent results were achieved: hydroxyapatite resulted an effective, compatible and durable consolidant for carbonate stone. Moreover, ethanol addition allowed to obtain a uniform, acid resistant protective hydroxyapatite layer on marble.
25
LUDMERCZKI, ROBERT. "Carbon-based nanostructures in hybrid materials for detection and removal of water pollutants." Doctoral thesis, Università degli Studi di Cagliari, 2020. http://hdl.handle.net/11584/294538.
Testo completoAbstract (sommario):
The thesis is mainly focused on the better understanding of carbon dots (C-dots) formation in bottom-up syntheses, by identifying the key chemical processes and correlating them to the observed fluorescence. Therefore, several types of C-dots were studied, by systematically varying the used (molecular) precursor ratios and reaction times. Selected samples were surface functionalized by organosilanes to reveal the role of the C-dots surface functional groups in the overall photoluminescence. As better understanding of the ongoing processes finally achieved, the synthesized C-dots were applied in photocatalysis experiments by combining them with titania and an appropriate C-dot was tested as a nitrite ion sensor.
26
Srisuriyachai, Falan <1980>. "Evaluation of alkali flooding combined with intermittent flow in carbonate reservoir." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/857/1/Tesi_Srisuriyachai_Falan.pdf.
Testo completoAbstract (sommario):
The majority of carbonate reservoir is oil-wet, which is an unfavorable
condition for oil production. Generally, the total oil recovery after both primary and
secondary recovery in an oil-wet reservoir is low. The amount of producible oil by
enhanced oil recovery techniques is still large. Alkali substances are proven to be able
to reverse rock wettability from oil-wet to water-wet, which is a favorable condition
for oil production. However, the wettability reversal mechanism would require a noneconomical
aging period to reach the maximum reversal condition. An intermittent
flow with the optimum pausing period is then combined with alkali flooding
(combination technique) to increase the wettability reversal mechanism and as a
consequence, oil recovery is improved.
The aims of this study are to evaluate the efficiency of the combination
technique and to study the parameters that affect this method. In order to implement
alkali flooding, reservoir rock and fluid properties were gathered, e.g. interfacial
tension of fluids, rock wettability, etc. The flooding efficiency curves are obtained
from core flooding and used as a major criterion for evaluation the performance of
technique.
The combination technique improves oil recovery when the alkali
concentration is lower than 1% wt. (where the wettability reversal mechanism is
dominant). The soap plug (that appears when high alkali concentration is used) is
absent in this combination as seen from no drop of production rate. Moreover, the use
of low alkali concentration limits alkali loss. This combination probably improves oil
recovery also in the fractured carbonate reservoirs in which oil is uneconomically
produced.
The results from the current study indicate that the combination technique is
an option that can improve the production of carbonate reservoirs. And a less quantity
of alkali is consumed in the process.
27
Srisuriyachai, Falan <1980>. "Evaluation of alkali flooding combined with intermittent flow in carbonate reservoir." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/857/.
Testo completoAbstract (sommario):
The majority of carbonate reservoir is oil-wet, which is an unfavorable
condition for oil production. Generally, the total oil recovery after both primary and
secondary recovery in an oil-wet reservoir is low. The amount of producible oil by
enhanced oil recovery techniques is still large. Alkali substances are proven to be able
to reverse rock wettability from oil-wet to water-wet, which is a favorable condition
for oil production. However, the wettability reversal mechanism would require a noneconomical
aging period to reach the maximum reversal condition. An intermittent
flow with the optimum pausing period is then combined with alkali flooding
(combination technique) to increase the wettability reversal mechanism and as a
consequence, oil recovery is improved.
The aims of this study are to evaluate the efficiency of the combination
technique and to study the parameters that affect this method. In order to implement
alkali flooding, reservoir rock and fluid properties were gathered, e.g. interfacial
tension of fluids, rock wettability, etc. The flooding efficiency curves are obtained
from core flooding and used as a major criterion for evaluation the performance of
technique.
The combination technique improves oil recovery when the alkali
concentration is lower than 1% wt. (where the wettability reversal mechanism is
dominant). The soap plug (that appears when high alkali concentration is used) is
absent in this combination as seen from no drop of production rate. Moreover, the use
of low alkali concentration limits alkali loss. This combination probably improves oil
recovery also in the fractured carbonate reservoirs in which oil is uneconomically
produced.
The results from the current study indicate that the combination technique is
an option that can improve the production of carbonate reservoirs. And a less quantity
of alkali is consumed in the process.
28
ABDUL, KARIM MUHAMMAD RAMZAN. "Metal matrix composites reinforced with SiC long fibers and carbon nanomaterials produced by electrodeposition." Doctoral thesis, Politecnico di Torino, 2015. http://hdl.handle.net/11583/2591591.
Testo completoAbstract (sommario):
The research work of this PhD thesis was done on the study, production and characterization of two types of metal matrix composites: 1) fiber reinforced metal matrix composites and, 2) carbon nanomaterials reinforced metal matrix composites.
In fiber reinforced metal matrix composites, a metal or an alloy is reinforced with continuous or discontinuous fibers in order to improve the specific strength and stiffness at high temperatures. For example superalloys are the typical materials for the hot parts of aeronautic engines. They are very important in the aerospace field as they offer high temperature mechanical strength together with a good resistance to oxidation and corrosion. But due to high temperatures involved in the service conditions, buckling of the material may occur. In order to avoid this high temperature buckling phenomena, a reinforcement of the superalloy could be needed to maintain the mechanical properties. For this reason it was thought to investigate the possibility of realizing continuous fibers reinforced metal matrix composites over the superalloys that can further improve the high temperature properties. Due to its simplicity and viability, electrochemical deposition was chosen as the production technique to produce this kind of composite materials. The selected substrate for electrodepositing the nickel matrix composite was nickel based superalloy Inconel-718, and monofilament continuous silicon carbide fibers were chosen as reinforcement.
First of all chemical compatibility was studied between the nickel matrix, superalloy and silicon carbide fibers, both in the uncoated form, and coated with carbon or carbon/titanium diboride. Both theoretical calculations and experiments were conducted, suggesting the use of a carbon coating over fibers and a buffer layer of nickel to increase the interface quality as well as to avoid unwanted reactions between substrate and silicon carbide fibers. After studying the chemical feasibility of all the related components, electrodeposition of the composites was performed in order to demonstrate the practical feasibility of the process. Then final composites were deposited on the dog-bone shaped specimens of Inconel-718. The produced composites were subjected to mechanical tests in order to evaluate the mechanical properties at room temperature and at high temperatures (400 °C and 600 °C). Evaluation of the results shows improvement in the yield strength of the produced composites with respect to the superalloy alone at room temperature. There is a decrease in the yield strength at high temperatures due to the failure of the interface between the superalloy and the composite layer but it is demonstrated that if a hot pressing treatment is done, then the interface strength is retained at high temperature and thus yield strength values will also increase.
Fracture analysis and EDS analysis were also performed on the fractured surfaces of the samples with the help of field emission scanning electron microscope in order to study the fracture mechanisms involved and the composition of the interface after their testing at high temperatures. The fracture mechanisms in Ni/SiC composite layer was of debonding and pull out type which is typical characteristic of the fiber reinforced composites. The superalloy fractures with ductile behavior at room temperature. At temperatures of 400 °C and 600 °C, the superalloy fails with more ductile character after extensive amount of plastic deformation before its fracture.
Carbon nanomaterials are widely being used to reinforce the metallic materials in order to improve their electrical, thermal, corrosion, wear and friction resistance for particular applications. In this part of the research work, graphene nanoplatelets (GNPs) and graphene oxide (GO) were chosen as nano reinforcements to produce nickel matrix nanocomposites with the intention to evaluate their wear and friction behavior. Graphene nanoplatelets and graphene oxide consist of few layers of graphene and graphene oxide respectively and their layered structure coupled with the small size of these materials can be helpful reducing the wear rate of the composites. Crystallite size, hardness and roughness of the coatings were also studied in order to understand the effect of nano phases on these properties.
Again the production technique employed consists of electrodeposition of the composites over a conducting steel substrate. A lot of work has been done in producing metal matrix composites reinforced with carbon nano fibers, carbon nanotubes and graphene. But graphene nanoplatelets and graphene oxide are not much evaluated for reinforcing the metallic matrices especially with the electrodeposition technique. To produce these types of composites by electrodeposition, a uniform and stable dispersion of the carbon nanomaterials in the nickel deposition baths is necessary. So particular attention was given to this aspect and uniform and stable dispersions were obtained by using a suitable dispersant, chosen after a wide screening, namely poly sodium styrene sulphonate (PSS). The dispersing technique employed the ultrasonication of the deposition bath with the help of an ultrasonic probe. The obtained coatings were strong and well adherent to the steel substrate, and presented rather well dispersed graphene oxide or graphite nanoplatelets, even if some agglomerates were still present in samples obtained from highly concentrated suspensions.
The nanocomposites were characterized in terms of microhardness, crystallite size, roughness and wear and friction behaviors. The composites with GO show very little effect on the microhardness whereas Ni/GNP composites show slight increase in the hardness. The effect on the crystallite size is not significant. Low concentration of the nano phase gives the composites a good smooth surface with less roughness whereas, by increasing the concentration of the carbon nanomaterials, the composites produced presents a rougher surface. Pin-on-disk tests were chosen to evaluate the wear behavior of the composites. The obtained results demonstrated a significant decrease in the wear rate, percent mass loss and volume loss of the composites as compared to the pure nickel one. The worn tracks observations suggest that the nanocomposites were worn by adhesive wear mechanism.
29
Bassan, Fabio. "Optimization of industrial processes for forging of carbon and stainless steels." Doctoral thesis, Università degli studi di Padova, 2015. http://hdl.handle.net/11577/3423990.
Testo completoAbstract (sommario):
The possibility to produce stainless steel components at limited cost and characterized by elevated mechanical properties, has gained more importance in the last years. Nowadays, the cold and warm forging processes of carbon steels are widely used to form industrial parts due to their economic advantages, but there is still lack of extensive research on industrial process design and evaluation of the microstructural properties of cold-warm forged stainless steel parts.
In the last few decades, the environment concerning the recent forging industry has been rapidly changed. Now, near-net-shape or net-shape manufacturing processes are becoming a useful practice in metal forming, resulting in saving material and energy.
Many parts produced with machining can be manufactured at lower cost by cold and warm forging. Traditionally, forging design is carried out using mainly empirical guidelines, experience, and trial-and-error, which results in a long process development time and high production costs.
In order to avoid this, in recent years, computer-aided simulation approaches have proved to be powerful tools to predict and analyze material deformation during a metal forming operation. There are now many commercial finite-element (FE) packages to simulate forging and bulk metalworking processes. To date, most have focussed on predicting the shape of the final product after simple or complex single- or multi-stage forming operations. On the other hand, other aspects are being included in these numerical models, such as an improved understanding of the constitutive material behaviour, friction and lubrication conditions, and the properties of the final product, in order to predict more complicated phenomena such as tool life prediction, ductile fracture and microstructure evaluation.
The focus of this PhD thesis is the development of an innovative approach based on the design of integrated experimental procedures and modelling tools, in order to accurately re-design a range of industrial single-stage cold-warm forming processes to form stainless steel components and investigate the microstructural evolution of forged parts obtained at different forging temperatures. In addition, the design of a multi-stage cold forging process of a low-carbon steel and the prediction of surface defects that occur in each stage of the forming-sequence have been carried out.
To this aim, a series of tensile tests were conducted to evaluate the influence of temperature and strain rate on the materials elasto-plastic properties.
Futhermore, an innovative experimental setup was used to reproduce the realistic friction conditions at the tool-workpiece interface, in order to accurately predict metal flow during forging cycles.
Experimental data were subsequently validated and implemented in a commercial 3D-FE software and accurately calibrated to perform fully coupled numerical simulations for the reference processes.
Finally, the forged parts obtained were characterized by macro- and microstructural inspections in order to evaluate the presence of underfilling problems and surface defects, which were consistent with the numerical FE results coming from both simulated processes (i.e. single- and multi-stage forging), and to analyze the microstructural evolution of α- and γ-phase during single-stage tests both at room temperature and from 400 to 700 °C.
The materials investigated in this work are low-carbon AISI 1005 ferritic-pearlitic steel (Wr. N. 1.0303), AISI 304L austenitic (Wr. N. 1.4307) and commercially named Duplex 2205 ferritic-austenitic stainless steel (Wr. N. 1.4462). The developed experimental tests are suitable to proper evaluation of steels behaviour in terms of mechanical properties, and to precisely calibrate coupled numerical models when they are applied to conventional and re-design forging processes.
The techniques used in this work include: tensile tests, T-shape compression tests, visual inspections (i.e. supported by vernier calliper and micrometer measurements), hardness and micro-hardness tests, LOM (Light Optical Microscopy), FEG-ESEM (Field-Emission Gun Environmental Scanning Electron Microscope), EDS (Energy Dispersive X-ray Spectroscopy), EBSD (Electron Back Scattering Diffraction) and numerical models carried out with FORGE2011®-3D.<br>La possibilità di produrre componenti in acciaio inossidabile a costo limitato e caratterizzati da elevate proprietà meccaniche, ha assunto notevole importanza negli ultimi anni. Al giorno d'oggi, i processi di stampaggio a freddo e a semicaldo di acciai al carbonio sono ampiamente usati per produrre componenti industriali, grazie ai loro vantaggi economici, ma è ancora assente in letteratura un'ampia ricerca di nuovi metodi di progettazione industriale di processi di deformazione plastica a freddo e a semicaldo di prodotti in acciaio inossidabile, con la successiva valutazione delle proprietà microstrutturali.
Negli ultimi decenni, l'industria dei processi di stampaggio è cambiata rapidamente. Ora i processi produttivi near-net-shape o net-shape stanno diventando una pratica utile nella formatura dei metalli, garantendo notevoli risparmi di materiale ed energetici. Molti componenti, ottenuti con lavorazioni per asportazione di truciolo, possono essere prodotti a basso costo mediante stampaggio a freddo o a semicaldo. Tradizionalmente, la progettazione dei processi di forgiatura avviene utilizzando linee guida empiriche, basate sull'esperienza e su tentativi trail-and-error da parte dei progettisti, che si traducono poi in tempi di sviluppo del processi e costi di produzione elevati.
Per evitare ciò, negli ultimi anni, gli approcci di simulazione numerica si sono dimostrati strumenti potenti per prevedere e analizzare la deformazione del materiale mediante processo di formatura. Attualmente sul mercato sono presenti molti pacchetti commerciali adatti a simulare i processi di forgiatura dei metalli e la maggior parte di essi sono concentrati sulla previsione della forma del prodotto finale dopo operazioni di formatura semplici o complesse, mono- o multi-stadio. Altri aspetti vengono inclusi in questi modelli numerici, quali una migliore comprensione del comportamento del materiale, delle condizioni di attrito e lubrificazione e delle proprietà del prodotto finale, per poter prevedere fenomeni più complicati come la stima della vita dell'utensile, delle condizioni di frattura duttile e la valutazione della microstruttura.
Lo scopo della presente tesi di dottorato è lo sviluppo di un approccio innovativo basato sulla progettazione di procedure sperimentali integrate con strumenti di modellazione numerica, per riprogettare accuratamente una serie di processi di forgiatura industriali mono-stadio adatti alla produzione di componenti in acciaio inossidabile a diverse temperature.
Inoltre è stata effettuata la riprogettazione di un processo di formatura multi-stadio a freddo di un acciaio a basso tenore di carbonio, con la successiva previsione dei difetti superficiali che si verificano in ogni fase della sequenza di formatura.
A tale scopo sono stati condotti una serie di test di trazione, per valutare l'influenza della temperatura e della velocità di deformazione sulle proprietà elasto-plastiche dei materiali considerati. Inoltre è stato realizzato un innovativo apparato sperimentale per riprodurre le condizioni di attrito reali all'interfaccia tra lo spezzone e l'utensile, al fine di prevedere con precisione il flusso del metallo in fase di deformazione plastica.
I dati sperimentali sono stati validati e implementati in un software commerciale agli elementi finiti 3D-FE e successivamente calibrati con precisione, per effettuare accurate simulazioni numeriche dei processi di riferimento.
I componenti forgiati ottenuti sono stati oggetto di indagini macro e microstrutturali, per valutare l'eventuale presenza di difetti superficiali, e analizzare l'evoluzione microstrutturale della fase α e γ a diverse temperature di forgiatura (i.e. 20, 400, 500, 600, 700 °C). I risultati sperimentali sono stati successivamente validati mediante simulazione numerica.
I materiali studiati in questo lavoro sono: acciaio ferritico-perlitico AISI 1005 a basso tenore di carbonio (Wr. N. 1.0303), AISI 304L austenitico (Wr. N. 1.4307) e ferritico-austenitico Duplex 2205 (Wr. N. 1.4462). Le prove sperimentali sviluppate sono adatte ad una corretta valutazione del comportamento degli acciai in termini di proprietà meccaniche, calibrando con precisione i modelli numerici se applicate a processi industriali di forgiatura tradizionali e riprogettati.
Le tecniche utilizzate in questo lavoro prevedono: test di trazione, test di compressione T-shape, controlli visivi (mediante calibro cinquantesimale e micrometro), misure di durezza e microdurezza, microscopia ottica (LOM), microscopia elettronica a scansione ad emissione di campo (FEG-ESEM), spettroscopia a dispersione di energia (EDS), diffrazione da retrodiffusione elettronica (EBSD) e modelli numerici sviluppati in FORGE2011®-3D.
30
Lencina, Rodrigo. "Optimization of high carbon austenitic manganese steels for comminution processes." Doctoral thesis, Università degli studi di Padova, 2014. http://hdl.handle.net/11577/3424542.
Testo completoAbstract (sommario):
Austenitic manganese steels are widely used in mineral comminution processes due to their good wear resistance and high toughness. The classical chemical composition for austenitic manganese steel in these applications is about 12%Mn and 1.2%C, steel first produced by R. Hadfield more than a century ago. Ever since, many efforts to improve its mechanical properties and wear resistance have been made, mostly driven by the continuous demand of the mining industry for bigger crushing equipment and lower production costs.
In this work, two types of austenitic manganese steels containing a relative high content of carbon are investigated. The high carbon content provided the steels good wear resistance, but compromises their mechanical properties. An important deleterious effect observed due to high carbon content was embrittlement due to the precipitation of carbides at grain boundary.
Another important feature of the steels under study was their difference in manganese content, which played an important role in stabilizing carbon in the austenitic matrix. Furthermore, both steels contained titanium, which contributed to increase wear resistance through the formation of a hard phase of stable carbides.
Heat treatments were performed, aimed to solubilize precipitated carbides and to improve quenching conditions, in order to avoid reprecipitation of these carbides, especially in thick castings. The results presented showed a correct selection of the temperature for austenitization and, additionally, a characterization of the kinetics of the re-precipitation phenomenon.
After the improvements of the microstructure, the steels were tested in pilot scale crushers to assess their wear properties. Additionally, field tests were performed as well in industrial applications: in a cone crusher, a horizontal shaft impactor and a hammermill.
The results of the metallurgical and tribological studies demonstrated the need for improvements in the chemical composition of the steels. For this reason, different elements, such as Nb, Al, Ni, Mo, were added to the composition of the steels. Finally, a cost estimation of the industrial production of these new steels was performed, in order to assess their economic feasibility.
The results showed that the phenomenon of carbide re-precipitation is the main reason for embrittlement. Manganese content was the most important variable to stabilize the microstructure. The addition of Ni to this steel resulted in an improvement of mechanical properties, while maintaining the good wear resistance.
Two appendixes are included with original research work that was secondary to the scope of the thesis project. The first, presents a mathematical model that simulates the granulometric curve of the product from a crusher, but taking in consideration the wear in the liners of the machine. The other, presents an ultrasound treatment, which had comminution effects in different types of mineral particles. Ultrasound was tested as well in a leaching process to investigate their kinetic enhancement effects.<br>Gli acciai austenitici al manganese sono largamente utilizzati nell’industria mineraria poiché hanno un’elevata resistenza all’abrasione e un altissima tenacità. La composizione chimica più diffusa nell’attività mineraria è di circa 1.2% C e 12% Mn, composizione che è stata prodotta per prima volta da R. Hadfield più di un secolo fa. Da questo momento, molte ricerche sono state eseguite per migliorare le proprietà meccaniche e la resistenza all’usura di questi acciai. Soprattutto perché la industria mineraria attuale richiede costi di produzione più bassi e frantoi con più grande capacità.
In questo studio, sono presentati due acciai austenitici al manganese, i cui contenuti di carbonio sono considerevolmente alti. Questo contenuto di carbonio fornisce agli acciai buona resistenza all’ usura, ma diminuisce le proprietà meccaniche. Un effetto non desiderato del alto contenuto di carbonio è il infragilimento dovuto alla re-precipitazione di carburi a bordo grano.
Un'altra caratteristica importante degli acciai studiati è il loro contenuto di manganese, che ha avuto un ruolo preponderante nella stabilizzazione del carbonio nella matrice austenitica. Anche, entrambi acciai contenevano del titanio, elemento che ha contribuito a incrementare la resistenza all’usura tramite la formazione di carburi duri e stabili.
Sono stati eseguiti dei trattamenti termici allo scopo di solubilizzare delle fasi precipitate e anche a migliorare la condicione di tempra in modo di evitare la re-precipitazione di questi carburi, specialmente nei getti di grosso spessore. I resultati ottenuti forniscono una temperatura ottimale per la austenitizazione degli acciai e anche, caratterizzano la cinetica di re-precipitazione dei carburi a bordo grano.
Dopo le procedure di miglioramento della microstruttura, i due acciai sono stati testati a scala pilota utilizzando dei piccoli frantoi. Anche, sono stati eseguiti test sul terreno, in diverse machine a livello industriale: frantoio a cono, mulino a asse orizzontale e mulino a martelli.
I resultati delle studi metallurgici e tribologici hanno dimostrato la necessita di miglioramenti nella composizione chimica degli acciai. Quindi, diversi elementi sono stati aggiunti agli acciai (Nb, Al, Ni, Mo). Alla fine, è stata eseguita una stimazione dei costi di produzione per gli nuovi acciai, allo scopo di valutare la loro fattibilità economica.
Pertanto, è stato dimostrato che il fenomeno di re-precipitazione è la causa più importante del infragilimento. Il contenuto di manganese è stato la varabile più importante per stabilizzare la microstruttura. La aggiunta di nichel a questo acciaio a permesso la migliora delle proprietà meccaniche, e allo stesso tempo di mantenere la resistenza all’usura.
Se inseriscono due appendici contenenti lavori di ricerca che non apparteneva allo scopo principale della tesi. La prima appendice tratta un modello matematico che simula la curva granulometrica del prodotto appartenete a un frantoio. Il modello prende in considerazione la perdita di qualità dovuta alla usura dei rivestimenti. L’altra appendice parla di un trattamento di ultrasuono eseguito allo scopo di macinare delle diverse particelle di rocce. Anche, questo trattamento è stato impiegato in uno sperimento idrometallurgico allo scopo di verificare l’incremento della cinetica di lisciviazione.
31
Angiola, Marco. "Gas sensing properties of carbon nanostructures." Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3424809.
Testo completoAbstract (sommario):
This work is aimed to evaluate the optical gas sensing properties of carbon nanomaterial. In particular it is focused on two materials, Carbon Nanotubes (CNTs) and Graphene Oxide
(GO).
The comprehension of the mechanisms of interaction of these materials with the gas molecules is fundamental for a future application of these materials as sensors targeted to a
specific specie or capable to distinctly detect several dangerous species. On this purpose nanostructures based on GO and CNTs have been produced and tested as optical gas sensors toward oxidizing/reducing gases (H2, CO, NO2) and aromatic volatile Organic Compounds (benzene, toluene, xylene).
Gold nanoparticles (Au NPs) have been used as optical probe thanks to the peculiar Localized Surface Plasmon Resonance feature in the visible range, which is extremely
sensitive to the variation in optoelectronic properties of the surrounding media, such as refractive index and the variation in charge carrier involved in plasmonic excitation in the Au NPs.
Not only amplify the Au NPs the variation in optoelectronic properties of the layer of carbon nanomaterial, but also the electromagnetic coupling with carbon nanomaterials may induce
an enhancement in response and a lowering of the limit of detection of the sensors to the target species.
Moreover, the GO and CNTs are provided of a large possibility of functionalization, which can be used to tailor the gas sensing properties of the nanostructures toward specific species.
CNTs have been combined with the Au NPs, Pd NPs, Ni NPs and fullerenes. Pd and Au NPs increase the response toward H2
, meanwhile Ni NPs and fullerenes appear specific to CO. It
is also suggested the opportunity to monitor the features of the absorbance plot of fullerenes and CNT in the NIR as optical probes, with the carbon nanomaterials playing both the role
of sensing element and optical probe.
The presence of the different functional groups in GO was investigated. The increase in sp2conjugation has a profitable effect for the sensing of H2. Instead, the removal of the oxidized
functional groups hinder the response of the films toward CO and NO2.
The reduction and functionalization of the GO with para- Phenylene Diamine induces the detection of NH3without Au NPs as optical probe. The sensors produced are characterized by high transparency in the visible range and may be incorporated as non-invasive sensors on transparent surfaces.
Most of the sensors worked at 150°C and 300°C. Test of gas sensing have been conducted at low temperatures, at 80°C for CNTs in fullerene matrix and good results were achieved. The
possibility of sensors active at room temperature is suggested by the positive tests conducted with CMG, paving the way for future developments in active optical material sensitive to
gases at room temperature.<br>Il presente lavoro è focalizzato sullo studio di sensori ottici basati su nanomateriali di carbonio, nell’ottica di un’applicazione di questi materiali come sensori di gas. Il lavoro prende in analisi due materiali, i nanotubi di carbonio (CNTs) e il grafene ossido (GO).
La comprensione dei meccanismi di interazione di questi materiali con le molecole di gas è fondamentale per le applicazioni future di questi materiali nel rilevamento di diverse specie nocive di gas. A tal proposito, nanostrutture a base di GO e CNTs sono state sviluppate e studiate come sensori ottici verso gas ossidanti-riducenti (H2, CO, NO2) e nei contronti di
composti volatili organici aromatici (benzene, toluene, xylene).
Le nanoparticelle di oro sono state utilizzate come sonde ottiche grazie alla loro peculiare caratterista di risonanza plasmonica di superficie localizzata, la quale è estremamente sensibile alle variazioni di proprietà ottico-elettroniche del mezzo che le circonda, come l’indice di rifrazione, e alle variazione di densità di portatori di carica che sono coinvolti nell'eccitazione plasmonica nelle nanoparticelle di oro.
Quindi, le nanoparticelle di oro, non solo amplificano le variazioni optoelettroniche del film di nanomateriali di carbonio a cui sono state accoppiate, ma interagiscono con questi
inducendo un miglioramento della risposta ai gas e un abbassamento del limite di rilevamento ai gas in analisi.
Inoltre, GO e CNTs presentano una vasta gamma di possibili funzionalizzazioni, che, possono essere sfruttate per una progettazione mirata delle proprietà di gas sensing delle nanostrutture di carbonio.
I CNTs sono stati abbinati a nanoparticelle di Au, Pd, Ni e a fullereni. Pd e Au portano ad un miglioramento delle prestazioni dei sensori verso il gas H2, nanoparticelle di Ni e fullereni
sembrano avere un’azione specifica verso il gas CO.
In questo lavoro viene anche suggerita la possiblità di monitorare le proprietà di assorbanza di fullereni e CNTs nel range del vicino IR. I CNTs, in tal caso, avrebbero la duplice
funzione di sonde ottiche e di materiale sensibile.
Oltre all'effetto delle nanoparticelle di oro sulle proprietà di gas sensing del GO, è stata valutata l’influenza dei diversi gruppi funzionali. L’estensione dei domini sp2 sembra
favorire il rilevamento di H2, mentre una forte rimozione di gruppi funzionali inibisce la risposta del GO verso CO e NO
2.
32
Candian, Valentina Andrea <1992>. "Utilizzo della metodologia LCA per la valutazione di interventi di efficientamento energetico e calcolo della carbon footprint su una piscina pubblica." Master's Degree Thesis, Università Ca' Foscari Venezia, 2020. http://hdl.handle.net/10579/16763.
Testo completoAbstract (sommario):
Questo caso di studio tratta di un’analisi di efficientamento energetico e dell’impronta di carbonio della piscina pubblica Acquarena di Bressanone/Brixen, cittadina situata nella regione a statuto autonomo Trentino Alto Adige. Acquarena è la prima piscina italiana ad avere aderito a EMAS (Eco-Management and Audit Scheme), sistema comunitario di ecogestione a audit a cui possono aderire volontariamente le imprese e le organizzazioni che vogliono raggiungere l’obiettivo di fornire un servizio sostenibile. Per verificare le performance dell’impianto si è ricorso all’utilizzo della metodologia LCA confrontando due anni, rispettivamente il 2015 e il 2018, nell’arco dei quali sono stati apportati miglioramenti nella piscina per aumentare le prestazioni della struttura. Un ulteriore obiettivo è stato quello di confrontare due differenti software per l’analisi del ciclo di vita, l’open source OpenLCA e SimaPro.
33
CARADONNA, ANDREA. "Carbon-based polymer nanocomposites with enhanced conductive properties." Doctoral thesis, Politecnico di Torino, 2018. http://hdl.handle.net/11583/2703852.
Testo completoAbstract (sommario):
Nowadays the development of new technologies requires materials with unconventional combination of properties. Polymers are classified as electrical and thermal insulating materials, which limits their use for several important technological applications. However, conductive polymers could be used in order to overcame drawbacks in the use of metals, metal alloys and ceramic materials as conductive media. Thermal conductive polymers could be profitably exploited in heat management applications (e.g. heat sink, heat exchangers), while electrical conductive polymers could be used in different fields depending on their electrical conductive values. To enhance the conductive properties of polymers, several approaches has been reported in literature. However, the most established way to achieve this goal consists in the development of suitable composite materials by means of the incorporation of conductive fillers within the polymeric matrix. The choice of the conductive filler is a crucial point in the development of the final material. Due to their extremely high thermal and electrical conductivity, coupled with the low density, the nano-metric scale and the outstanding mechanical properties, carbon-based nanomaterials are the most promising fillers suitable for processing conductive polymers. Since graphene nanoplatelets (GNPs) are considered young materials with potentials not yet fully exploited, multiwall carbon nanotubes (MWCNTs) are nowadays the most established materials used as conductive filler.
In this thesis work thermally and electrically conductive polymer composites, filled with carbon-based nanomaterials were investigated.
In the first part of the experimental work, particular attention was devoted to the development of GNPs-based thermally conductive polymers. By properly selecting several polymeric matrices and comparing several available processing techniques it was possible to outline a guideline in the use of GNPs as thermally conductive fillers. A strong filler characterization reveals that, in spite to the amount of defects and to the filler purity, the main GNPs properties able to enhance the thermal conductivity of polymers is the lateral dimension.
With the aim of developing metal-free circuits integrated in nanocomposite, a laser printing process was successfully exploited in order to obtain electrical conductive paths on the surface of a polymeric materials containing MWCNTs. Starting from the literature knowhow and new experimental results, a complete comprehension of the parameters that affect the laser printing process was achieved by applying a statistical approach. By analysing the experimental outcomes with a statistical approach, it was possible to focus the attention on the main laser parameters that govern the process, thus obtaining multifunctional and multidirectional conductive materials with surface electrical resistance per unit length (inside the tracks) lower than 1 kΩ/cm at 0.5 wt.% of MWCNTs loading content.
Finally, by combining outcomes obtained as described above, hybrid carbon-based nanocomposites were developed, with the purpose of enhancing contemporaneously thermal and electrical conductivity. Hybrid materials, obtained starting from a commercial masterbatch containing MWCNTs, demonstrated the possibility to partially replace the high amounts of carbon nanotubes with low cost carbon based materials without worsening the good conductive properties.
Not only conductive properties were investigated, but all the studied materials were also characterized by means of mechanical and thermal stability tests, thus demonstrating the possibility of adopting carbon-based polymer nanocomposites as multifunctional materials.
34
RICCITELLI, RICCARDO. "Fabrication and characterization of carbon nanotube-based vacuum triode." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2009. http://hdl.handle.net/2108/919.
Testo completoAbstract (sommario):
Il lavoro svolto in questi anni di dottorato si è focalizzato sulla realizzazione e
caratterizzazione di un triodo su scala micro/nanometrica. Il dispositivo in
questione, in cui il fascio elettronico è ottenuto a partire da un catodo
freddo realizzato con nanotubi, fonde in se le caratteristiche e le proprietà
sia dei dispositivi a stato solido, sia dei dispositivi valvolari, offrendo da un
lato un’elevata resistenza fisico‐termica, la capacità di miniaturizzazione, gli
elevati tempi di vita e il peso ridotto, dall’altro alte frequenze e potenze di
uscita. In questa attività sono stati messi a punto i passi tecnologici e di
processo relativi alla realizzazione del dispositivo, è stato studiato ed
analizzato il comportamento fisico dei catodi freddi realizzati con nanotubi
di carbonio (CNTs), nanowires di silicio (SiNWs), o nanorods di Ossido di
Zinco (ZnO). Sono state inoltre valutate le problematiche relative al
funzionamento del dispositivo in frequenza e sono state proposte soluzioni a
tal proposito. I risultati ottenuti in questo lavoro si sono concretizzati in 2
pubblicazioni su rivista, un articolo di review, 6 proceedings e 2 brevetti. Le
competenze acquisite durante questo lavoro di dottorato hanno inoltre
consentito di implementare il Progetto Europeo FP7 OPTHER, (Optically
Driven TeraHertz Amplifiers), finanziato dalla comunità Europea nel periodo
2008‐2011 di cui il nodo di Roma risulta essere coordinatore.<br>This three years work dealt with the fabrication and characterization of
carbon nanotube‐based vacuum triode. By reporting the manufacturing
aspects and the related problems of the most widely investigated field
emission devices, Spindt‐type arrays, innovative materials like Carbon
Nanotubes (CNTs), Silicon Nanowires (SiNWs) and some promising Metal
Oxide Nanostructures (namely ZnO, CuO, WO3, SnO2) have been shown and
described as potential materials for the realization of field emission
cathodes. As a result, their relative figures of merit in diode characterization
in terms of turn‐on electric field, threshold electric field, current densities,
emission stability and field enhancement factor have been carried out.
Technological processes for the design and the fabrication of carbon
nanotube‐based nanotriode with high field enhancement factor have been
investigated.
Problems correlated to the behavior of the device in high frequency
characterization have been evaluated and possible solutions devised to
overcome them have been analyzed and proposed.
Results obtained in this work contributed to two publications, a review
chapter, six proceedings and two patents and it has permitted at our group
to participate as coordinator at the project OPTHER (Optically Driven
TeraHertz Amplifiers), financed by FP7 in 2008.
35
VITALI, MATTEO. "Thermodynamic and fluid-dynamic challenges associated with the transport of CO2 via pipelines." Doctoral thesis, Università Politecnica delle Marche, 2022. http://hdl.handle.net/11566/299669.
Testo completoAbstract (sommario):
The emissions related to the human activities that led to greenhouse effect can be related, but not limited to, the carbon dioxide emissions. Carbon Capture Utilization and Storage (CCUS) is claimed as a solid climate mitigation strategy in particular for the most challenging missions. The development of an international CO2 transportation network is considered a necessary cross-cutting topic in the Carbon Capture and Storage sector. Indeed, the development of large-scale CCUS projects will require the management and transport of CO2 in the presence of impurities and with lower costs. The accuracy of modelling CO2 in the presence of other components needs to be further assessed and lots of thermodynamic aspects of CO2 management are still object of debate and research. In this work the thermodynamic and fluid-dynamic challenges associated with the transport of CO2 via pipelines have been investigated. A complete and critical review of the main thermodynamics aspects involved during the transport of CO2 at high-pressure has been presented. The aspects related to risk and safety of CO2 pipelines have been deeply analysed with specific focus on the modelling of accidental releases with computational fluid dynamic and simplified models. Furthermore, an assessment of the most suitable equations of state for the accurate modelling of CO2 in presence of impurities is also proposed with quantitative and qualitative conclusions. Moreover, the transient transport phenomena involved for the transport of dense-phase CO2 have been analysed experimentally and numerically. Horizontal depressurization behaviour have been modelled with numerical thermofluid-dynamic simulations and validated against experimental data obtained from high-resolution measurements on a state-of-the-art large scale laboratory. This work includes also some experimental activity performed for the study of vertical flows in CO2 pipes for injection and the development of a data extraction and processing tool. Finally, the simulation of running shear fracture and its implication in CO2 have been also discussed and a tool for the simulation of decompression in CO2-rich mixtures has been developed and validated.<br>Le emissioni legate alle attività umane che hanno portato all'effetto serra sono attribuibili alle emissioni di anidride carbonica. La cattura, utilizzo e stoccaggio dell’anidride carbonica (CCUS) è considerata una solida strategia di mitigazione del clima, in particolare per le missioni più impegnative. Lo sviluppo di una rete di trasporto internazionale di CO2 è considerato un tema trasversale necessario nel settore della cattura e dello stoccaggio del carbonio. Infatti, lo sviluppo di progetti CCUS su larga scala richiederà la gestione e il trasporto di CO2 in presenza di impurità e con costi inferiori. L'accuratezza della modellazione della CO2 in presenza di altri componenti deve essere ulteriormente valutata e molti aspetti termodinamici della gestione della CO2 sono ancora oggetto di dibattito e ricerca. In questo lavoro sono state studiate le sfide termodinamiche e fluidodinamiche associate al trasporto di CO2 tramite condotte. È stata presentata una rassegna completa e critica dei principali aspetti termodinamici coinvolti nel trasporto di CO2 ad alta pressione. Gli aspetti relativi al rischio e alla sicurezza delle condotte di CO2 sono stati approfonditi con focus specifico sulla modellazione dei rilasci accidentali con modelli fluidodinamici computazionali e semplificati. Viene inoltre proposta, con conclusioni quantitative e qualitative, una valutazione delle equazioni di stato più idonee per la modellizzazione accurata della CO2 in presenza di impurità. Sono stati altresì analizzati sperimentalmente e numericamente i fenomeni di trasporto transitorio coinvolti nel trasporto di CO2 in fase densa. Il comportamento della depressurizzazione orizzontale è stato modellato con simulazioni termofluidodinamiche numeriche e convalidato rispetto a dati sperimentali ottenuti da misurazioni ad alta risoluzione su un laboratorio all'avanguardia su larga scala. Questo lavoro comprende anche alcune attività sperimentali svolte per lo studio dei flussi verticali nei tubi di CO2 per l'iniezione e lo sviluppo di uno strumento di estrazione ed elaborazione dati. Infine, è stata discussa anche la simulazione della frattura duttile e la sua implicazione nella CO2 ed è stato sviluppato e validato uno strumento per la simulazione della decompressione in miscele ricche di CO2.
36
STRONGONE, VALENTINA. "Preparation and characterization of UV-LED curable composite systems based on carbon fillers." Doctoral thesis, Politecnico di Torino, 2021. http://hdl.handle.net/11583/2875751.
Testo completo
37
FOGLIA, ALESSIA. "From anaerobic membrane bioreactors to water resource recovery facility: experimental validation and sustainability assessment." Doctoral thesis, Università Politecnica delle Marche, 2022. http://hdl.handle.net/11566/295203.
Testo completoAbstract (sommario):
La transizione dal concetto di ‘’impianto di trattamento delle acque reflue’’ a quello di ‘’impianto di recupero di risorse dalle acque reflue a bassa impronta di carbonio’’ è stata indirizzata affrontando i seguenti temi: il riutilizzo dell'acqua depurata, il recupero di risorse e la valutazione dell'impronta di carbonio. In particolare, per quanto riguarda il riutilizzo dell'acqua depurata sono stati analizzati e confrontati trattamenti convenzionali di affinamento del refluo e soluzioni innovative che prevedono trattamenti anaerobici a membrana. In questo contesto, è stata operata per circa due anni una filiera di trattamento a scala pilota, composta da un reattore anaerobico UASB combinato con una membrana di ultrafiltrazione (AnMBR). Operando con un carico organico (OLR) di 1 kg COD/m3/giorno, la produzione di biogas era di circa 0.39 ± 0.2 L/giorno. L'aumento dell'OLR a 2 kg COD/m3/giorno ha determinato un aumento della produzione di biogas fino a 4.11 ± 3.1 L/giorno. Le condizioni di elevata salinità (1500 mgCl/L) hanno influito negativamente sulla produzione di biogas senza creare fenomeni di sporcamento aggiuntivi alla membrana. L'effluente finale trattato soddisfa gli standard di qualità della CLASSE A del nuovo regolamento UE 741/2020 per il riutilizzo dell'acqua ed è adatto per scopi di fertirrigazione in agricoltura. Un'unità aggiuntiva è stata combinata al trattamento AnMBR per la rimozione dei contaminanti emergenti (CECs), utilizzando polimeri a impronta molecolare (MIPs). È stata avviata una colonna di adsorbimento e il diclofenac è stato utilizzato come composto target. L'efficienza di rimozione è risultata pari al 50%. Sono state inoltre indagate la presenza di microplastiche (MPs) nelle acque reflue. Dai risultati sperimentali lo schema a fanghi attivi convenzionali, in scala reale, ha rimosso l'86% di MPs, mentre la filiera anaerobica su scala pilota ha ottenuto una rimozione del 94%. In questo scenario è stato anche progettato e realizzato un prototipo per il campionamento di volumi di refluo significativi al fine di rilevare concentrazioni rappresentative di MPs. Sono stati affrontati, inoltre, l’aspetto dell’inquinamento dovuto ai sovraflussi di piena della fognatura mista e i problemi relativi alla balneazione delle acque validando in campo filiere di trattamento modulari composte da filtro rotativo dinamico, adsorbimento su carbone attivo granulare e disinfezione UV. I risultati del pilota hanno mostrato rimozioni di TSS, COD ed E.Coli rispettivamente pari al 90%, 69% e 99%. Inoltre, sono stati condotti studi di fattibilità su impianti in piena scala che prevedono l’integrazione di soluzioni di recupero delle risorse quali fosforo, acidi grassi volatili e biopolimeri. In particolare, sono state valutate, utilizzando metodi quali CBA, S-LCA ed SRL, soluzioni eco-innovative, sviluppate nell'ambito del progetto H2020 Smart-Plant da integrare agli impianti esistenti ai fini di chiudere il ciclo dell’acqua. Complessivamente, gli impianti di depurazione integrati con le SMARTechs mostrano benefici ambientali e sociali, con un valore economico totale (TEV) massimo superiore di un 23% rispetto allo scenario di base, mentre i valori di SRL sono risultati nel range 6-7, dimostrando una buona accettazione sociale e un buon potenziale di adattamento delle SMARTechs. Infine, è stato approfondito il tema del Carbon Footprint per il servizio di depurazione, proponendo un nuovo approccio metodologico. La maggior parte dei fattori di emissione considerati è stata validata da campagne di misura in 12 impianti. I valori specifici dell’impronta di carbonio sono pari a 0.04-0.20 tonCO2eq/AE/anno, variabili in base alle dimensioni dell'impianto. Le categorie più impattanti sono state individuate nelle emissioni indirette associate ai GHG disciolti, scaricati nel corpo idrico superficiale e al consumo energetico, che contribuiscono rispettivamente per il 13-70% e il 10-40%.<br>Technical solutions for the transition from ‘wastewater treatment plant’ (WWTP) to the concept of ‘low-carbon water resource recovery facility’ (WRRF) were assessed, addressing i) water reuse, ii) resource recovery and iii) carbon footprint assessment. Specifically, in terms of water reuse, conventional ‘’fit-for-purpose’’ treatments and innovative solutions as anaerobic treatments were analysed and compared. A pilot scale system, placed in a hotspot of seawater intrusion, composed of an upflow granular anaerobic sludge blanket (UASB) reactor coupled with AnMBR (Anaerobic Membrane Bioreactor) was set-up and operated for more than 2 years. At an organic loading rate (OLR) of 1 kg COD/m3/d, biogas production was around 0.39 ± 0.2 L/d. The increase of the OLR to 2 kg COD/m3/d resulted in increase of biogas production to 4.11 ± 3.1 L/d with fermented cellulosic sludge addition. High saline conditions of 1500 mgCl/L adversely affected the biogas production without deteriorating the membrane operation. The final effluent met quality standards of CLASS A of the new EU regulation741/2020 for water reuse and resulted suitable for fertigation purposes in agriculture. An additional unit was coupled with the AnMBR treatment for removing contaminants of emerging concern (CECs), using Molecurarly Imprinted Polymers (MIPs) as adsorbent filler. An adsorption column was started-up and diclofenac was used as target compound. Removal efficiency was up to 50%. Additionally, microplastics (MPs) occurrence and removals in wastewater treatments were investigated. The full-scale conventional activated sludge scheme removed 86% of MPs, while the pilot-scale UASB+AnMBR configuration achieved 94% MPs removal. The results highlighted an accumulation phenomenon of MPs in the sludge and this affected negatively the methanogenic activity of anaerobic biomass. In this scenario also a prototype system for collecting significant wastewater sampling volumes to detect more representative MPs concentrations was designed and realized. On the other hand, water pollution in stormwater and related water bathing issues were addressed assessing combined sewer overflows (CSOs) management strategies and validating advanced compact treatments, composed of dynamic rotating belt filter, adsorption on granular activated carbon and UV disinfection, to minimize their impacts. The results of pilot treatment showed great potential for TSS, COD and E. coli removal efficiencies with more than 90%, 69% and 99%, respectively. Moreover, feasibility studies in full-scale WWTPs, addressing resource recovery solutions, including phosphorous salts, volatile fatty acids and biopolymers recovery were carried out. In particular, real environment eco-innovative solutions, developed within the H2020 Smart-Plant project to renovate existing WWTPs and close the circular value chain, were assessed using Cost-Benefit Analysis (CBA), Social Life Cycle Assessment (S-LCA) and Social Readiness Level (SRL) methods. Overall, the SMARTechs created benefits both from an environmental and social point of view, with a maximum total economic value (TEV) up to +23% compared to baseline scenario. In terms of social assessment SMARTechs fell in SRL range of 6-7, which implies a good societal acceptance and adaptation potential. Finally, Carbon Footprint Assessment for the wastewater treatment service was deeply investigated, proposing a new methodological evidence-based approach. Most of the considered emissions factors for carbon footprint assessment were validated by site-specific measurements campaigns in 12 WWTPs. Specific carbon footprints resulted in the emissions of 0.04-0.20 tonCO2eq/PE/y, varying according to the size of the plant. The most impactful categories were identified for indirect emissions associated with dissolved GHGs discharged in the surface water body and due to energy consumption, which accounted for 13–70% and 10–40%, respectively.
38
CARLINO, Francesco. "Influenza degli elementi di lega nei bagni di zincatura sulla formazione delle fasi intermetalliche e sulla resistenza a flessione dei rivestimenti a caldo." Doctoral thesis, Università degli studi di Cassino, 2021. http://hdl.handle.net/11580/83827.
Testo completoAbstract (sommario):
In almost all industrial applications metallic materials are the most widely used and they are employed in a wide range of applications. These materials work in continuous contact with the surrounding environment; in fact, in this environment they fulfil the functions for which they are designed and manufactured.
The interaction between the metallic material and the environment in which it operates is a chemical one and it is known as corrosion. Hot-dip galvanising is the most effective and widely used protection technique against corrosion. This technique is valuable because it has a dual action: firstly, a barrier is created that insulates the metal from the aggressive environment, and secondly, the zinc in the coating has a lower electrochemical potential than iron; therefore, the substrate is protected by the Zn-based coating even if this latter is damaged. The relationship between the mechanical properties of the coating and the parameters of the hot dip galvanising process can be understood by analysing the kinetics of coating developments. Indeed, the mechanical characteristics can be profoundly modified by intermetallic phases. For this reason, to supervise the phases present in the composition of the coating is necessary for improving the mechanical properties. In the scientific literature, there are some models that consider the kinetic development of intermetallic phases. Considering both the phenomena of interdiffusion between zinc and iron atoms, and the stability of the phases for a precise chemical composition, to anticipate the thickness of the phase is substantial. The formation and propagation of cracks can be anticipated through a damage model, which should be developed by analysing the damage micro-mechanisms of the intermetallic phases.
In this activity, the hot dip galvanizing process was applied to low carbon steel samples, considering different bath compositions. Then, the obtained coatings were studied by optical microscopy, analysing and identifying the formation of different intermetallic phases, depending on the composition of the bath. After, bending tests were carried out in the laboratory using the Duncan mechanism, which was suitably mounted on a 100 kN electromechanical machine. Five different protective zinc coatings were characterised and compared, which derived from immersion in different baths. Specifically, the five baths used were: pure Zn, Zn - Pb 1%, Zn - Al 5%, Zn - Sn 3% and Zn - Ti 0.5%; moreover, five different immersion times were considered: 15, 60, 180, 360 and 900 seconds. The temperature used in the galvanizing phase was instead kept constant at about 460 °C for all the investigated conditions. The obtained thicknesses and the various damage caused by the stress were then compared and analysed, through various comparisons carried out by means of optical microscope observations on the sections of the different galvanised specimens. Therefore, through this study, it was possible to identify the various damage mechanisms of the intermetallic phases as a function of the dipping time and the bath composition. It was found that the damage mechanisms were mainly represented by nucleation and growth of radial cracks in correspondence of the hardest and most fragile phases of the coating. It was also possible to evaluate the importance of ductile phases presence and how their thickness growth tended to stop the propagation of defects. Finally, replacing toxic elements such as Lead in favour of elements such as Tin, Aluminium and Titanium was preliminary evaluated; however, further studies are necessary in order to improve the homogeneity and uniformity of the zinc coating for avoiding possible problems of coating adhesion and detachment.
39
GIGLIO, EMANUELE. "Carbon dioxide methanation for synthetic natural gas (SNG) production." Doctoral thesis, Politecnico di Torino, 2017. http://hdl.handle.net/11583/2674176.
Testo completoAbstract (sommario):
This work deals with the coupling between high temperature steam electrolysis and carbon dioxide methanation (hydrogenation) to produce a synthetic gas directly injectable in the natural gas distribution grid. This system concept is one of the existing possibilities related to a pathway named Power-to-gas. According to this strategy, low-priced surplus electric energy coming from renewable energy sources (RES) or nuclear plants can be converted into chemical energy of a fuel in order to store it for a longer time. Another purpose is to compensate the unbalances of the electric grid due to the daily and seasonally fluctuations of electricity production from RES (especially wind and solar). The integration between solid oxide electrolysis cell (SOEC) technology and methanation seems to be promising due to the possible thermal integration between exothermal hydrogenation and thermal energy required within the water splitting unit. Hydrogen generated through steam electrolysis can react with carbon dioxide producing methane and water (4 H2 + CO2 ↔ CH4 + 2 H2O).
A preliminary screening of nickel-based catalysts has been carried out at atmospheric pressure in order to identify the catalyst(s) with higher activity. During this experimental activity seven samples have been tested: a standard NiO on γ-Al2O3 catalyst (Ni/A); three Ni-based samples (Ni/C5, Ni/C10 and Ni/C15) with a composite support containing a mixture of γ-Al2O3 and other promoters (CeO2, ZrO2 and TiO2); two nickel-aluminum hydrotalcites (Ni-Al 8.7 and Ni-Al 12, prepared at a pH of 8.7 and 12, respectively) and a commercial NiO/γ-Al2O3 catalyst (CRG-F). Hydrotalcites and commercial catalyst present better performance than oxides-supported nickel samples and are more active especially at low temperature (below 300 °C). The different activity far from equilibrium can be put in relation with some physic and chemical properties. Hydrotalcites and commercial catalyst presented higher nickel content than the other samples. Moreover, also the metal dispersion seems to play a role in order to enhance the catalytic performance. Concerning oxide-supported Ni-based catalysts, the addition of promoters (CeO2, TiO2 and ZrO2) to γ-Al2O3 within the support showed a beneficial effect on the activity due to the increased catalyst reducibility.
A new test rig has been designed and set up in order to perform an experimental activity at high pressure (up to 30 bar). Samples at both small (0.25-0.5 mm) and pellet (3 mm) size have been tested at different pressure, temperature and inlet gas composition. As a preliminary activity, a commercial catalyst at pellet size was tested at 300 °C and different residence times with two different inlet mixtures (in order to reproduce a series of two reactors with an inter-condensation of the produced water). This experimental activity enabled the production of synthetic gas with hydrogen content lower than 5%, which is the maximum acceptable H2 amount considered in this work for the direct injection of SNG into the natural gas distribution grid. Thus, the feasibility of the process in terms of overall conversion into methane was verified. Then, a test campaign has been carried out by varying several operating parameters in order to describe the methanation kinetics for a commercial catalyst (NiO/γ-Al2O3) at small particles size (250-500 μm). Total and reactants partial pressures and temperature were varied during the experimental activity. The obtained experimental points have been used into an ideal PFR model for the kinetic parameters estimation. Both power law and Langmuir-Hinshelwood (LHHW) rate equations were considered. Concerning LHHW-type equations, the one leading to the best fitting of experimental data is based on the dissociative chemisorption of both hydrogen and carbon dioxide as reaction mechanism.
The obtained kinetics was used as a basis for a 1D plug flow reactor model applied to a series of two cooled multi-tube fixed bed reactors for methane synthesis: the main goal is to estimate temperature and conversion profiles along the axial coordinate. Evaporating water at 240 °C (i.e. at ≈ 33 bar) has been considered as a coolant: this strategy ensures a high heat transfer coefficient on the shell side. Both micro and macro kinetics equations are solved. Thus, transport phenomena between gas and solid catalyst have been taken into account. In addition, the evaluation of the effectiveness factor for isothermal particles enabled the estimation of the mass transfer inside the porous catalyst. In order to moderate the temperature increase (i.e. to prevent the hot spot risk) especially within the first reactor, part of the reacting CO2 is conveyed directly to the second reactor by-passing the first one. A carbon dioxide split ratio of 0.7 (meaning that the 30% of the total CO2 flow by-passes the first reactor) ensures that the maximum temperature reached within the solid catalyst is lower than 600 °C (this value has been fixed at the maximum acceptable temperature). The length of the second reactor was adjusted in order to ensure a methane fraction in the outlet gas equal to 95% (on dry basis), enabling the production of a synthetic gas with a H2 content lower than 5% (i.e. injectable in the NG pipeline). Inlet pressure has been set equal to 15 bar.
The obtained results from the 1D model have been used for the design of the methanation unit consisting in a series of two cooled reactors with steam inter-condensation. Then, the process modeling of a plant coupling high temperature electrolysis and methanation is presented: the main goal of this analysis is the calculation of an overall plant efficiency (in terms of electricity-to-SNG chemical energy). The plant size has been set considering a 10 MWel SOEC-based electrolysis unit. It has been assumed that the heat produced from the exothermal methanation is entirely used for the water evaporation; the as generated steam is the key reactant of the electrolysis unit. Through the pinch analysis, a further thermal integration between hot and cold streams was performed. The external heat requirement obtained through the minimization of thermal needing was equal to 121 kW (≈1% of the electrolyser duty). However, such integration requires a too high number of heat exchangers, resulting in increasing costs and higher system complexity. Thus, the heat exchangers network has been re-designed in order to reduce the number of components. Hot and cold streams of electrolysis section have been coupled; a similar procedure has been applied to the methanation unit. Thus, the only integration between the two sections is represented by the reaction heat used for the water evaporation. The reduced complexity results in a higher external heat requirement (272 kW): this new value has been considered acceptable (≈3% of the electrolysis power).
Efficiency was calculated as the ratio between the SNG chemical power and the overall electric input (including electrolysis power, compression duties and external heating). The SOEC-based power-to-gas system presented an HHV-based efficiency equal to ≈ 86 % (≈ 77 % on LHV basis).
40
LUPONE, FEDERICO. "Additive manufacturing of carbon fiber reinforced thermoplastic polymer composites." Doctoral thesis, Politecnico di Torino, 2022. http://hdl.handle.net/11583/2966347.
Testo completo
41
VACCARIELLO, ENRICO. "Synthetic models of distribution gas networks in low-carbon energy systems." Doctoral thesis, Politecnico di Torino, 2021. http://hdl.handle.net/11583/2912988.
Testo completo
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MARCHISIO, SILVIA. "Composite Materials reinforced by Carbon Nanotubes." Doctoral thesis, Politecnico di Torino, 2013. http://hdl.handle.net/11583/2506164.
Testo completoAbstract (sommario):
The work of this Ph.D. thesis has been realised in the field of a promising and largely studied technological material: the carbon nanotubes (CNTs). Since 1991 a large number of attempts have been conducted, trying to exploit the outstanding potential of this carbonaceous material, in order to improve the properties of several matrices. The most important application is the production of polymer matrices composites (PMCs), but in last decades an increasing number of metal matrix ones (MMCs) have been presented and recently also ceramic matrix (CMCs) applications have been attempted. Despite massive efforts focused on CNTs-composites, the potential of employing this reinforcement materials has not yet been fully exploited. This lack is substantially due to the difficulties associated with the dispersion of entangled carbon nanotubes during processing and poor interfacial interaction between CNTs and matrix materials. Because of these reasons the very first aspect of this work has been the study of the dispersion state of nanotubes. The aim of the experiments was not only to obtain a good dispersion and distribution of the CNTs, but also to evaluate their dispersion grade. Indeed, due to their nanosize and to their carbonaceous nature, few simple experimental techniques result suitable for this purpose. The second part of the work consisted in the application of the carbon nanotubes to the production of new materials for technological applications, with improved mechanical properties. Three composite materials with different matrices have been designed, developed and produced: a polymer matrix composite, a ceramic matrix and a metal matrix one. For PMCs a polyvinyl butyral matrix has been used and the composites were obtained by a deeply studied technique: the tape casting technology. The same approach was also used in the case of CMCs: tape casted silicon carbide matrix composites reinforced by carbon nanotubes have been produced. Finally a third matrix has been experimented: MMCs were investigated starting from pure aluminium powders. For Al matrix composites a particular technique was used: the sintering was obtained starting from a powder metallurgy approach and exploiting electric current and pressure (Electric Current Assisted Sintering approach). For all the three different composite materials, after the development of the production route and the preparation of several specimens, a characterization step followed. The materials were characterized in terms of physical properties, morphology and microstructure, and mechanical behaviour.
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TRAVAGLIA, PAOLO. "Dielectric and EM properties of carbon filled epoxy resin." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2009. http://hdl.handle.net/2108/859.
Testo completoAbstract (sommario):
Questa tesi riguarda le proprietà dielettriche e di assorbimento alle microonde della resina epossidica caricata di nanocariche. Tre differenti nanocariche a base di carbonio sono state usate in questa tesi: Carbon black (CB) nanofibre di carbonio (CNF) e nanotubi di carbonio (CNT). Inoltre,sono stati provati vari processi di dispersione delle nanocariche nella resina, per analizzare gli effetti della distribuzione delle nanocariche sulle proprietà dielettriche dei composti che ne risultavano. È stata misurata la permettività usando un sistema VNA nella banda-X (8,2-12,4 GHz) usando il metodo della guida d’onda. La morfologia dei campioni è stata studiata con un sistema FEG-SEM. usando il modello del circuito equivalente è stata tentata una connessione tra la morfologia dei campioni e la permettività. Infine si è giunti alla conclusione se questi materiali sono adatti ad essere usati come materiali che assorbenti le microonde elettromagnetiche.
Nei campioni di CB, realizzati usando cariche con differenti aree di superficiali specifiche la distribuzione delle cariche nella resina é differente, quando si usano cariche di alta area di superficiale producendo piccoli corti clusters ramificati, e nell’altro caso aggregati lunghi spessi e serpeggianti. In entrambi i casi i clusters sono vicini a una forma cilindrica e possono essere visti come condensatori a cilindri paralleli, immersi nella resina. Di conseguenza, i campioni di alta area di superficie presentano valori più bassi di permettività reale (misura la capacita del sistema), dovute alla minore lunghezza dei clusters (armature dei condensatori), ma una maggiore permettività immaginaria (legata agli effetti della conduttività e della dispersione) perché come è stato fatto notare precedentemente i clusters sono disposti in maniera molto ravvicinata permettendo l’attivazione di modelli di conduzione hopping and tunnelling. i campioni CB hanno dimostrato buoni risultati come assorbitori di EM raggiungendo un picco di 38dB usando un campione spesso 4mm.
Nei campioni caricati con cariche con alto aspect ratio (CNF e CNT) il parametro principale è la loro dispersione nella resina,nelle prove con campioni caricati con CNF, nonostante l’uso di metodologie differenti,è stata raggiunta una dispersione non soddisfacente,con la microstruttura risultante composta di aggregati. Le misurazioni EM hanno messo in luce che maggiore il numero e più piccola la dimensione degli aggregati,maggiori sono ε’ e ε” per la stessa ragione trovata nel caso dei campioni caricati con CB. Nel caso dei campioni CNT, invece una dispersione veramente buona stata raggiunta con l’aiuto di un surfactante ed un sonicatore più potente. I risultati dimostrano di nuovo che la permettività è legata alla microstruttura, con la stessa tendenza stabilita con altri tipi di nanocariche, tuttavia,in questo caso è stata rinvenuto un nuovo caso che mette in luce che c’è un ottimo livello di dispersione sopra quale i CNT non interagiscono tra di loro risultando in un ε’ molto alto e in un ε” molto basso visto che la dispersione attraverso l’effetto Joule è limitata. Le prestazioni di assorbimento di CNF e CNT dimostra che sia una percentuale troppo elevata sia la troppa dispersione porta ad un materiale soprattutto riflettente, con basse prestazioni di assorbimento. Un buon compromesso, perciò ,deve essere trovato per ogni sistema come compromesso tra la composizione del materiale, la microstruttura e lo spessore.
Parte del lavoro sperimentale e stata condotta presso l’università di Monash (Clayton, Victoria Australia) sotto la supervisione del Prof. George Simon.<br>This thesis deals with the dielectric and absorbing properties at microwaves (x-band) of epoxy resin filled nanocomposites. Three different carbonaceous nanofillers were used in the experimental: carbon black (CB), carbon nanofibers (CNF) and carbon nanotubes (CNT). Moreover, various dispersion processes of nanofiller in the resin were tried, in order to analyze the effect of filler distribution on the dielectric properties of the resulting composites. Permittivity was measured using a vector network analyzer in x-band (8,2-12,4 GHz) using the waveguide method. Samples morphology was studied by FEG-SEM. Using the equivalent circuit analogy, a link between samples morphology and permittivity was attempted. The suitability of these materials as electromagnetic microwaves absorbers was finally assessed.
In carbon black samples, realized using fillers with different specific surface areas, the filler distribution within the resin is very different, producing small short branched clusters when using high surface areas filler, and long thick and meandering aggregates in the other case. In both samples the clusters are close to cylindrical shape and may be seen as parallel cylinders capacitors in the resin. As a consequence, high surface area samples present lower values of real permittivity (that takes into account capacity of the system), due to the smaller length of capacitor plates, but higher imaginary permittivity (linked to conductivity and dissipations effects) because, as noted above, the clusters are closely spaced, permitting the activation of hopping and tunnelling conduction modes. CB samples showed good performances as EM absorbers, reaching a peak of -38 dB using a sample 4 mm thick.
In samples loaded with high aspect ratio (CNF and CNT) the key parameter is their dispersion in the resin. In CNF experimentation, despite the use of different methodologies, an unsatisfying dispersion was achieved, with the resulting microstructure made of aggregates. The EM measurements highlighted that the higher the number and the smaller the dimension of the aggregates, the higher are ε’ and ε”,for the same reason found in the case of CB. With CNT, instead, very good dispersions were achieved, by means of the aid of surfactants and of a more powerful sonicator. The results demonstrate again that permittivity is linked to microstructure, with the same trend established with the other type of nanofillers. Nevertheless, in this case, a new evidence was found highlighting that there is an optimum level of dispersion, above which the CNT do not interact each other, resulting in very high ε’ and very low ε”, since dissipation through Joule effect is limited.
The absorbing performance of CNF and CNT demonstrate that too much filler, or too much dispersion of it (i.e. Low ε”), bring to a mostly reflective medium, with low absorbing performance. An optimum formulation needs, therefore, to be found for every system as a compromise among material composition, microstructure and thickness.
Part of the experimental work (most of chapter 6 ) was carried out during the author secondment to Monash University (Clayton, Victoria Australia) under the supervision of Prof. George Simon.
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MANCINELLI, ENRICO. "Trace metals and dissolved organic carbon in biochar varying with feedstock type and pyrolysis temperature." Doctoral thesis, Università Politecnica delle Marche, 2018. http://hdl.handle.net/11566/252872.
Testo completoAbstract (sommario):
La presenza nel biochar di carbonio labile (e.g. carbonio organico disciolto (DOC)) e di sostanze inorganiche (e.g. metalli pesanti) potenzialmente dannosi può limitare o impedire l’utilizzo del biochar per interventi di risanamento ambientale. Sono stati prodotti biochar da pirolisi lenta a diverse temperature (i.e. 300, 450 e 700 °C) da diversi tipi di feedstock (i.e. cippato da residui di lavorazione del legno (WC), lignina (LG), digestato da fanghi di depurazione (DSS), corteccia di pino (PB)). Il contenuto totale, la lisciviazione e la biodisponibilità di metalli, quali Cd, Cr, Cu, Ni, Pb e Zn, sono stati analizzati nei biochar da WC (BCWC), LG (BCLG) e DSS (BCDSS). Sono stati condotti test in colonna con flusso ascendente per valutare il rilascio di DOC da BCLG, BCWC e BCPB. La temperatura (450 oppure 700 °C) di pirolisi più efficace per ridurre la lisciviazione e la biodisponibilità dei metalli dipende dal metallo considerato. La temperatura di 450 °C si è dimostrata adatta a stabilizzare Cr e Ni nei biochar analizzati, in quanto questi metalli non hanno dimostrato alcuna tendenza alla lisciviazione né biodisponibilità. Un incremento di temperatura di pirolisi ha reso Zn e Cu più stabili nella matrice carboniosa, diminuendone la frazione biodisponibile, impedendo il rilascio di Zn e riducendo la lisciviazione di Cu a valori <1 % del contenuto totale di Cu. Un chiaro trend non è stato osservato per metalli quali Cd e Pb, diminuendo o incrementando nella frazione soggetta a lisciviazione o biodisponibilità con la temperatura di pirolisi a seconda del tipo di feedstock considerato. Il rilascio di DOC da BCWC e BCLG, valutato per mezzo di test in colonna, ha mostrato un andamento influenzato dalla temperatura adottata nella produzione dei suddetti biochar. BCWC e BCLG, prodotti a 700 °C, hanno rilasciato quantità cumulate di DOC (0.02–0.07 % di contenuto di carbonio totale (TC)) più basse dei rispettivi biochar prodotti a 450 °C (0.06–0.09 % di contenuto di TC). Sono state osservate variazioni nella lisciviazione di DOC da biochar prodotto da corteccia di pino (BCPB) in funzione della temperatura di pirolisi e del tipo di percolante (i.e. acque meteoriche di dilavamento in ambiente urbano (USWR)). BCPB, prodotto a diverse temperature, ha rilasciato simili quantità cumulate di DOC (0.01 % del contenuto di TC) con le acque meteoriche di dilavamento prelevate da un’area pedonale. BCPB, prodotto a 700 °C, ha rilasciato più basse quantità cumulate di DOC (0.02 % contenuto di TC) con le acque meteoriche di dilavamento prelevate da un tetto.<br>The content of carbon in labile forms (e.g. dissolved organic carbon (DOC)) and potentially hazardous inorganic substances (e.g. trace metals) in biochar (BC) may limit or prevent the utilization of BC for environmental remediation purposes. BCs were produced from slow pyrolysis at different temperatures (i.e. 300, 450 and 700 °C) from different types of feedstock (i.e. wood chips (WC), lignin (LG), digested sewage sludge (DSS), and pine bark (PB)). Total trace metal (Cd, Cr, Cu, Ni, Pb, and Zn) concentration, leachability, and bioavailability were investigated for BCs from WC (BCWC), LG (BCLG), and DSS (BCDSS). DOC leachability from BCs was investigated via up-flow percolation test method. The most suitable pyrolysis temperature (450 or 700 °C) for reducing trace metal leachability and bioavailability depends on the trace metal considered. The temperature of 450 °C was effective in stabilizing Cr and Ni in the analyzed BCs as these trace metals were not prone to leaching or present in bioavailable forms. In the tested BCs, an increase in pyrolysis temperature made trace metals such as Zn and Cu more stable in the char matrix, decreasing in the bioavailable fractions, hindering leachability of Zn, and decreasing leachability of Cu to <1 % of the total Cu concentration. Trace metals such as Cd and Pb did not show a clear temperature trend, increasing or decreasing in the bioavailable or leachable fractions depending on the feedstock. Analysis of the up-flow percolation test showed the same temperature related trend in DOC leachability from BCWC and BCLG, with high temperature (700 C) BCs releasing lower cumulative amounts of DOC compared with low temperature (450 C) BCs, which were in the range 0.02–0.07 % and 0.06–0.09 % of total carbon (TC) content, respectively. DOC leaching from BCPB varied with pyrolysis temperatures and types of leachant (i.e. urban storm-water runoff (USWR)). Irrespective of the pyrolysis temperature, BCPB released cumulative amount of DOC up to 0.01 % of the TC content with pathway USWR. High temperature (i.e. 700 °C) BCPB released lower cumulative amount of DOC (up to 0.02 % of the TC content) with roof USWR. It is likely that the leachant (i.e. pathway USWR) with relatively higher pH and DOC concentration limited the release of DOC from the BC matrix, whereas the types of leachant (i.e. deionized water, and roof USWR) with relatively lower pH and DOC concentrations enhanced the release of DOC from the BC matrix.
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Corradetti, Stefano. "Study and development of high release refractory materials for the SPES project." Doctoral thesis, Università degli studi di Padova, 2013. http://hdl.handle.net/11577/3422608.
Testo completoAbstract (sommario):
Throughout the last century, theoretical and experimental research made by the international nuclear physicists community has led to important advancement in the knowledge of the mechanisms that govern the behavior and stability of the nuclei. The technological improvements necessary to support this research has often opened the way to new applications in other field of science and industry which directly reflects in our common life experience.
Nowadays, Europe is becoming more and more a leader in both theoretical and experimental nuclear physics, as testified by the presence on its territory of several institutes and laboratories dedicated to this field of research, like CERN (Organisation Européenne pour la Recherche Nucléaire), the world’s largest particle physics laboratory. Italy, represented mainly by INFN (Istituto Nazionale di Fisica Nucleare), is one of the main members of this community.
One of the most important projects supported by INFN is SPES (Selective Production of Exotic Species), which aim is to develop a facility for the production of radioactive ion beams (RIBs) in one of the four national laboratories of INFN, LNL (Laboratori Nazionali di Legnaro).
The facility is designed to produce and deliver to users both proton-rich and neutron-rich nuclei (range of mass 80-160 amu) to be used for nuclear physics research, as well as other applications in different fields of science. The generation of the aforementioned isotopes will occur inside a properly designed target, which represents the core of the whole project. The choice of the proper material for the target, both in terms of composition and properties, is of vital importance in determining the quantity and type of the produced isotopes.
In this work, the synthesis and characterization of different types of target materials are presented. The results of experimental tests performed on some of the produced materials, in configurations very similar to those intended for the final SPES facility are also reported.
Chapter 1 gives a general overview of the SPES project and its context whereas chapter 2 introduces the main topics related to the on-line behavior of the SPES target, relative to both its layout and to the properties of the material constituting it. Chapter 3 is focused on uranium carbide, which will be used at SPES to produce neutron-rich isotopes; after a description of its main physicochemical properties, the results of two on-line tests performed on target prototypes made of this material is reported and discussed into detail. In chapter 4 the synthesis methods and release-related properties of two potential materials to be used as SPES targets for the production of proton-rich isotopes, boron and lanthanum carbides, are presented<br>Nel corso dell’ultimo secolo, la ricerca teorica e sperimentale condotta dalla comunità internazionale in fisica nucleare ha portato ad importanti passi avanti nella comprensione dei meccanismi che governano il comportamento dei nuclei e della loro stabilità. In molti casi, le innovazioni tecnologiche che si sono rese necessarie per supportare tali ricerche hanno aperto la strada verso nuove applicazioni scientifiche ed industriali con ripercussioni dirette nella vita di tutti i giorni.
Attualmente, l’Europa è sempre più leader nel campo della fisica nucleare, teorica e sperimentale, come testimoniato dalla presenza nel suo territorio di svariati istituti e laboratori dedicati a questa specifica area di ricerca, come ad esempio il CERN (Organisation Européenne pour la Recherche Nucléaire), il più grande laboratorio al mondo per la fisica delle particelle. L’Italia, principalmente rappresentata dall’INFN (Istituto Nazionale di Fisica Nucleare), è uno dei principali membri di questa comunità.
Uno dei progetti più importanti finanziato dall’INFN è SPES (Selective Production of Exotic Species), la cui finalità è la costruzione di una facility per la produzione di fasci di ioni radioattivi, in uno dei quattro laboratori nazionali dell’INFN, LNL (Laboratori Nazionali di Legnaro).
La facility è progettata per produrre e fornire agli utenti isotopi proton-rich e neutron-rich (massa compresa fra 80 e 160 amu) utilizzabili per esperimenti di fisica nucleare, ma anche per altre applicazioni in diversi settori scientifici. La formazione di tali isotopi avverrà all’interno di uno specifico bersaglio (target), che rappresenta il cuore dell’intero progetto. La scelta dell’opportuno materiale per il target, sia in termini di composizione che di proprietà è di vitale importanza nel determinare la quantità e tipo di isotopi prodotti.
In questo lavoro, vengono descritte nel dettaglio la sintesi e caratterizzazione di diversi tipi di materiali proposti come target, ed inoltre vengono riportati i risultati di test sperimentali condotti su alcuni di essi, ottenuti in modalità molto simili a quelle a cui saranno sottoposti nella facility SPES.
Il capitolo 1 fornisce una presentazione generale del progetto SPES e del contesto scientifico ad esso legato, mentre nel capitolo 2 viene descritto nel dettaglio il comportamento operativo del target SPES, con particolare riferimento alla sua geometria e alle proprietà del materiale che lo costituirà. Nel capitolo 3 vengono presentate le proprietà del materiale scelto come bersaglio per produrre isotopi neutron-rich, ovvero il carburo di uranio; vengono inoltre presentati i risultati di un test sperimentale di produzione di isotopi da parte di un prototipo di target SPES costituito di tale materiale. Il capitolo 4 descrive la sintesi e caratterizzazione di carburi di boro e lantanio, con particolare riferimento alle proprietà riconducibili alla capacità di rilascio di isotopi; tali materiali rappresentano dei potenziali target SPES per la produzione di isotopi proton-rich
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BAYAT, AHMAD. "RF characterization and applications of carbon based composites." Doctoral thesis, Politecnico di Torino, 2018. http://hdl.handle.net/11583/2715629.
Testo completoAbstract (sommario):
Graphene is a monolayer of carbon atoms with remarkable electronic and mechanical properties. The attractive electronic properties of thin and thick films made of carbon nanotubes (CNTs) and graphene are increasingly being exploited for environmental and biological sensors. In particular, their sensitivity, selectivity, fast response time, ability to operate at room temperature, and their passive nature (no power consumption) provide competitive advantages of CNTs in sensor applications. However, their design as RF wireless sensors requires the integration of an antenna with the sensor element. Moreover, while the plasmonic nature of graphene at terahertz frequency has been widely reported, investigations on the practical utility of graphene at the microwave frequencies used in wireless sensor nodes are sparse which is indicated in this thesis.
First, an ink comprising graphene thick films of different concentrations (12.5%, 25% and 33% in weight) is prepared for deposition, by screen printing. Detailed investigation of the surface morphology of the films using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) reveals that the graphene films present a homogeneous dispersion of the filler with a comparatively lower surface roughness at higher concentrations, and negligible agglomerates. The films are then printed in between copper electrodes on FR-4 substrate, commonly used in RF circuits, and the measured scattering parameters analyzed. A measurement-based RF equivalent circuit model of the graphene film is developed using a microstrip transmission line with a gap loaded by the film.
Second, investigation on various patch antennas with different substrates using Multi-Walled Carbon Nanotube (MWCNT) thin film deposition is addressed. Screen printing technique is used to insert a CNT film in a loading stub connected to the antenna patch. The variation of the CNT surface impedance modifies the resonant frequency from the reference value, as revealed by comparison of return loss measured with and without the CNT loading. This CNT stub loaded patch antenna can be used as a bio sensor.
Third, a printed RF slot ring resonator is configured with a graphene thin-film for sensor application. The conductive losses in the graphene film are characterized by dielectric spectroscopy and considered in the design. The graphene sensing element comprising the slot ring can be integrated with control electronics as a passive wireless sensor node. The novelty of this research is that RF losses are minimized by capacitively loading the ring at selective locations along its periphery. Dielectric spectroscopy is used to study variation in surface impedance of the film for various graphene loadings, and RF simulations are corroborated with measurements on graphene loaded slot ring resonators used in ammonia gas sensor application. The measurement steps are taken into consideration. As mentioned, the ring resonant frequency shift in presence of the ammonia gas is the factor used to sense the gas.
Fourth, a novel design of an aperture coupled antenna which is weakly coupled to an interdigitated capacitor (IDC) is presented that serves the dual purpose of antenna impedance matching and the sensing function, the latter enabled by a thick film of CNTs deposited on the IDC surface. Simulations using CNT films of varying conductivity (or surface impedance) reveal that a strong antenna resonance can be produced. Furthermore, a study of the patch antenna radiation pattern with and without the CNT film shows weak coupling between the film and the antenna (loss of 0.5 dB or less relative to patch alone). Thus, the sensor film and geometry can be independently optimized without affecting radiation pattern.
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LAVAGNA, LUCA. "Carbon materials and their role as reinforcement in composite materials." Doctoral thesis, Politecnico di Torino, 2019. http://hdl.handle.net/11583/2729657.
Testo completo
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MALEKIMOGHADAM, REZA. "Study on the Mechanical Properties of Carbon Nanotube Coated‒Fiber Multi-Scale (CCFM) Hybrid Composites." Doctoral thesis, Politecnico di Torino, 2022. http://hdl.handle.net/11583/2970995.
Testo completo
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SISCA, LORENZO. "Structural Health Monitoring based on Piezoelectric transducers: a Carbon Fiber Automotive Component Application case." Doctoral thesis, Politecnico di Torino, 2021. http://hdl.handle.net/11583/2907018.
Testo completo
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PROIETTO, Federica. "STUDY OF ELECTROCHEMICAL PROCESSES FOR THE CONVERSION OF CARBON DIOXIDE TO ADDED-VALUE PRODUCTS." Doctoral thesis, Università degli Studi di Palermo, 2020. http://hdl.handle.net/10447/395119.
Testo completo