Dissertations / Theses on the topic 'Sulfuric material'

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Thesis (Ph. D.)--University of Missouri-Columbia, 2007.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed Feb. 27, 2008). Vita. Includes bibliographical references.

In this work, the crystallization of alpha-calcium sulfate hemihydrate in sulfuric acid solution and the correlation between its properties and preparation conditions by reaction of sulfuric acid with lime (CaO) have been thoroughly investigated. The research involved the study of conversion-dissolution of calcium sulfate dihydrate in H2SO4 solution, the measurement of solubilities, thermo-dynamic calculations and the preparation of alpha-CaSO4 ·0.5 H2O via different methods of reactive mixing of H2SO4 and CaO. It was found that the calcium sulfate solids can saturate the sulfuric acid solutions in only 5 minutes. The solubility of calcium sulfate hemihydrate in 0--3.0M H 2SO4 solution at 100°C was experimentally determined and thermodynamic calculations with the aid of FactSage and OLI have led to establishment of the phase diagram for the CaSO4-H2SO 4-H2O system. An operating window has been determined in terms of H2SO4 concentration, temperature and time within which alpha-hemihydrate can be produced by reaction of lime with H 2SO4. This window is defined as 0.6--1.1M H2SO 4 (steady-state concentrations), 98--105°C and 1 hour retention time. Dihydrate was found to form as intermediate phase quickly converting to hemihydrate. The kinetics of conversion depends on the acidity level.
For the standard preparation procedure of adding lime into hot sulfuric acid, alpha-hemihydrate grows in the c-axis direction much more rapidly than in other directions ending in the form of fine needle crystals. Also, independent of the shape of the seed particles, the resultant crystals of hemihydrate are needle-shaped, which suggests a "dissolution-recrystallization" mechanism. Upon prolonged equilibration in their acid-preparation solution hemihydrate needle-shape crystals become fibrous and eventually convert to anhydrite. It is believed that uptake of SO42- instead of Ca2+ is the rate-determining step in the hemihydrate crystallization process. The hot SO42--rich environment rendered most of the additives (particularly organic) tried ineffective. Trivalent cations such as Fe3+ and Al3+, are the only ones found to modify the crystal morphology from needle-shape to small "grain" type morphology.
Slow addition of H2SO4 solution to slaked lime - reverse procedure was found to favor the production of alpha-hemihydrate with column-shaped as opposed to needle-shaped crystal morphology within otherwise the same operating window, 0.6--1.1M H2SO4. Preliminary assessment of the properties of the alpha-hemihydrate materials synthesized in this work showed them to compare satisfactorily with other materials produced by conversion of dihydrate to hemihydrate.

The pyrometallurgical processing of copper concentrates produces SO₂-bearing offgas. SO₂ in the offgas is catalytically oxidized to SO₃ and absorbed into a ∼98.5% H₂SO₄-H₂O mixture in a sulfuric acid plant. This research provides an analysis of a copper smelter sulfuric acid plant and discusses the control and optimization necessary to attain the following goals: (a) minimize smelter SO₂ emissions; (b) maximize acid plant capacity and availability. The objectives of this work are to: (a) prepare mathematical descriptions of sulfuric acid plant operations; compare the mathematical predictions with plant data; (c) use the mathematical descriptions to: (i) predict acid plant behavior with varying feed SO₂ strengths and gas flow rates; (ii) determine control strategies to minimize smelter SO₂ emissions; (iii) evaluate requirements for an existing acid plant to accommodate future increased feed gas flows and SO₂ strengths.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2005.
Includes bibliographical references (p. 276-279).
Eight heats of material with base alloy chemistries of Alloys 800 HT or 617 with platinum additions of 2, 5, 15, or 30 wt% have been characterized according to their microstructural features. The goals of characterization were to determine metallurgical stability for service as self-catalytic structural materials. The results presented herein will be useful to the development of a material for the construction of a heat exchanger designed for sulfuric acid decomposition. This type of heat exchanger is a key component to hydrogen generation by the thermochemical sulfur-iodine water-splitting process, a future technology that promises efficient hydrogen production if coupled to a Generation IV nuclear reactor heat source. Characterization of each material was carried out in the cast and wrought conditions with optical and SE microscopy, electron dispersive spectrometry, chemical composition analysis, and thermodynamic modeling. Materials have been characterized according to grain size and morphology, precipitate features, twinning characteristics, and platinum composition effects. Results indicate that platinum and carbon compositions have the greatest effect on the development of microstructural features.
(cont.) Increasing platinum compositions in both base alloy chemistries fosters the presence of annealing twins, which indicates that platinum additions reduce stacking fault energy within the alloy systems. Platinum additions appear to cause the development of larger grain structures as well as increase corrosion resistance. With the exception of the Alloy 800 HT - 30 wt% Pt system, the alloy systems characterized herein were melted with carbon contents between 1.2 - 3.6 times higher than the maximum specified compositions for the base chemistries. Excessive inter and intra-granular carbide precipitation resulted, which leads to compromised corrosion resistance and mechanical properties. Inter-granular attack due to sensitization is observed in the Alloy 800 HT - 2, 5 wt% Pt systems. SEM micrographs of the Alloy 617 - Pt systems show that these systems are less prone to inter-granular attack. The grain structures of each base alloy - Pt system are much finer than those of the respective base alloy systems included for comparison. Fine grain structures are detrimental to overall ductility and high temperature creep strength. On average, the Alloy 800 HT - Pt systems developed larger grains than the Alloy 617 - Pt systems.
(cont.) A two phase microstructure that resembles pearlite developed in the Alloy 617 - 30 wt% Pt system. This alloy system will be excluded from further characterization for self catalytic structural application due to expected poor mechanical and corrosion resistance properties. The most important microstructural improvements for the development of a self-catalytic structural material include a reduction of carbon content and an increase in grain size. Further characterization of catalytic, corrosion resistance, and mechanical properties are required for selection of the optimum platinum addition to the base chemistries of Alloys 800 HT and 617 for sulfuric acid decomposition service.
by David Andrés Rigual.
S.M.

Developing next generation secondary batteries has attracted much attention in recent years due to the increasing demand of high energy and high power density energy storage for portable electronics, electric vehicles and renewable sources of energy. This dissertation investigates sulfur based advanced electrode materials in Lithium/Sodium batteries. The electrochemical performances of the electrode materials have been enhanced due to their unique nano structures as well as the formation of novel composites. First, a nitrogen-doped graphene nanosheets/sulfur (NGNSs/S) composite was synthesized via a facile chemical reaction deposition. In this composite, NGNSs were employed as a conductive host to entrap S/polysulfides in the cathode part. The NGNSs/S composite delivered an initial discharge capacity of 856.7 mAh g-1 and a reversible capacity of 319.3 mAh g-1 at 0.1C with good recoverable rate capability. Second, NGNS/S nanocomposites, synthesized using chemical reaction-deposition method and low temperature heat treatment, were further studied as active cathode materials for room temperature Na-S batteries. Both high loading composite with 86% gamma-S8 and low loading composite with 25% gamma-S8 have been electrochemically evaluated and compared with both NGNS and S control electrodes. It was found that low loading NGNS/S composite exhibited better electrochemical performance with specific capacity of 110 and 48 mAh g-1 at 0.1C at the 1st and 300th cycle, respectively. The Coulombic efficiency of 100% was obtained at the 300th cycle. Third, high purity rock-salt (RS), zinc-blende (ZB) and wurtzite (WZ) MnS nanocrystals with different morphologies were successfully synthesized via a facile solvothermal method. RS-, ZB- and WZ-MnS electrodes showed the capacities of 232.5 mAh g-1, 287.9 mAh g-1 and 79.8 mAh g-1 at the 600th cycle, respectively. ZB-MnS displayed the best performance in terms of specific capacity and cyclability. Interestingly, MnS electrodes exhibited an unusual phenomenon of capacity increase upon cycling which was ascribed to the decreased cell resistance and enhanced interfacial charge storage. In summary, this dissertation provides investigation of sulfur based electrode materials with sulfur/N-doped graphene composites and MnS nanocrystals. Their electrochemical performances have been evaluated and discussed. The understanding of their reaction mechanisms and electrochemical enhancement could make progress on development of secondary batteries.

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The floodplain soils of Pernambuco state - Brazil have been widely used to agriculture and their improperly management has promoted, in those with sulphidric materials, the sulfurization process, generating acidity in the soil, and release of heavy metals such iron. The aim of this study was to characterize Gleysol in areas of coastal wetlands along the shoreline of Pernambuco state cultivated with sugar cane, trying to understand genesis and occurrence of acid sulphate soils. Thus, we studied three floodplain soils along the shoreline of Pernambuco: floodplain soil in Goiana river (profile 1), floodplain soils in Sirinhaém river (profiles 2, 3 and 4) and floodplain soils in Ipojuca river (profiles 5, 6 and 7). Were realized a morphological characterization of soils, chemical analyzes for the purpose of soil classification, sequential extraction and total content of iron, and mineralogical analysis using XRD. Was observed predominance of the clay fraction in all profiles, which is consistent with the depositional environment in waters with low kinetic energy. The profiles 2, 3 and 4 showed extremely acidic reaction, with pH values below 2.5, indicating the presence of sulfuric horizon. The presence of sulphidric materials in the profiles 2, 3 and 4, confirmed the presence of sulfuric horizon. The sulfuric horizons in the profiles 2, 3 and 4 had high EC values between 9 and 21 dS m-1, being consistent with the high concentrations of sulphate generated by sulfurization process. The higher levels of iron were found associated with forms of poorly crystalline oxyhydroxides, values between 0.03 and 1.56 mmol kg-1. The assembly mineralogical soil had become very influenced by the geology of the basin of the rivers that bathe the floodplains. In the clay fraction were identified illite, kaolinite, goethite and smectite (beidellite/montmorillonite and nontronite), the silt fraction were: Illite, kaolinite, quartz and feldspar, in the sand fraction were: quartz, feldspar, mica and kaolinite. The floodplain soils showed morphological, physical, chemical and mineralogical related to the origin of the sediments and their position in the landscape. The occurrence of acid sulphate soils was detected only in the floodplain of Sirinhaem river.
Os solos de várzeas do litoral Pernambucano têm sido bastante utilizados na agricultura e o seu manejo inadequado tem promovido, naqueles que apresentam materiais sulfídricos, o processo de sulfurização, gerando acidez no solo, além de liberação de metais a exemplo do ferro. O objetivo deste trabalho foi caracterizar Gleissolos em áreas de várzeas litorâneas ao longo do litoral Pernambucano cultivadas com cana-de-açúcar, buscando compreender sua gênese e a ocorrência de solos Tiomórficos. Para tanto, foram avaliados solos de três várzeas ao longo do litoral Pernambucano: várzea do rio Goiana (perfil 1), várzea do rio Sirinhaém (perfis 2, 3 e 4) e várzea do rio Ipojuca (perfis 5, 6 e 7). Foi realizada a caracterização morfológica dos solos, análises químicas para fins de classificação do solo, extração sequencial e total do ferro, além de análise mineralógica utilizando DRX. Observou-se predominância da fração argila em todos os perfis, que condiz com o ambiente de deposição em águas com baixa energia cinética. Os perfis 2, 3 e 4 apresentaram reação extremamente ácida, chegando a atingir valores de pH inferiores a 2,5, evidenciando a presença de horizonte sulfúrico. A presença de materiais sulfídricos nos perfis 2, 3 e 4, confirmou a existência de horizonte sulfúrico. Os horizontes sulfúricos dos perfis 2, 3 e 4 apresentaram alta C.E., com valores variando entre 9 e 21 dS m-1, estando condizente com as altas concentrações de sulfato gerado pelo processo de sulfurização. Os maiores teores de ferro foram encontrados associados às formas de oxihidróxidos de baixa cristalinidade, apresentando valores entre 0,03 e 1,56 mmol kg-1. A assembléia mineralógica dos solos apresentou-se bastante influenciada pela geologia da bacia dos rios que banham as várzeas. Na fração argila os minerais identificados foram: ilita, caulinita, goethita e esmectita (beidelita/nontronita e montmorilonita); na fração silte foram: Ilita, caulinita, quartzo e feldspato; na fração areia foram: quartzo, feldspato, mica e caulinita. Os solos de várzeas apresentaram propriedades morfológicas, física, químicas e mineralógicas relacionadas à origem dos sedimentos e sua posição na paisagem. A ocorrência de Gleissolos Tiomórficos foi constatada somente na várzea do rio Sirinhaém.

Lithium-sulfur (Li-S) batteries have been considered as an attractive alternative to current Li-ion batteries due to their large theoretical capacity (1672 mA-h/g) and theoretical energy density (2600 Wh/kg) while having a low cost, an abundance of the material, and relatively non-toxic properties. However, the low cyclability and significant capacity fading during the first several cycles prevent Li-S rechargeable batteries from being commercialized. During discharge, elemental sulfur is reduced to the final product Li2S through a series of soluble intermediate species, lithium polysulfides (Li₂S _x, 2 ≤ x ≤ 8). Lithium polysulfides dissolved into the electrolyte in the separator can no longer participate in redox reductions, resulting in a loss of active materials, as well as a “shuttling effect” that causes capacity fading and low coulombic efficiency. Despite the fact that decades of research have attempted to solve this, the problem is still not resolved due to a lack of fundamental understanding of the system. This includes how lithium polysulfides are produced during discharge interactions with other components in the cell and the reaction mechanisms (the electrochemical and chemical processes) during cycling. The objective of this dissertation is to provide a fundamental understanding of lithium polysulfides produced during discharge of a Li-S cell. This is an essential piece of knowledge when designing and identifying the issues associated with Li-S batteries.

To begin, the morphology, thermal properties, and ionic conductivity of an ether-based nanostructured block copolymer containing lithium polysulfides were investigated. Previous work has shown that nanostructured block copolymer electrolytes containing an ion-conducting block and modulus-strengthening block has the potential of enabling solid-state lithium metal rechargeable batteries. This is of particular interest for a lithium-sulfur battery to fully explore its high energy density and capacity. Understanding the thermal and electrochemical properties of these block copolymer electrolytes containing lithium polysulfides is essential for evaluating their potential use in Li-S batteries. A systematic study of polystyrene-b-poly(ethylene oxide) (SEO) block copolymer mixed with Li₂S_x with an average x value of 4 and 8 was conducted. Small angle X-ray scattering, differential scanning calorimetry, and ac impedance spectroscopy were used to measure the morphology, thermal properties, and ionic conductivities of all samples. The ionic conductivity of SEO/Li₂S_x mixtures were compared with those of poly(ethylene oxide) (PEO) mixed with Li₂S_x to quantify the effect of nanostructuring on ion transport. The conductivities of both SEO and PEO samples containing polysulfides with a longer average chain length higher than the same polymer containing polysulfides with a shorter average chain length at all salt concentrations, indicating that dissociation of long-chain polysulfides occurs more readily than short-chain polysulfides. Normalized conductivity was used to quantify the effect of morphology on ion transport. The results showed that SEO suppressed the migration of polysulfides relative to PEO. However, this suppression is inadequate for practical applications. In other words, cathode architectures that prevent polysulfides from entering the electrolyte are necessary for enabling Li-S batteries with block copolymer electrolytes. Nevertheless, the results obtained in this study are important as they enable quantification of polysulfide migration in Li-S batteries with imperfect polysulfide encapsulation, a limitation that applies to all known Li-S batteries.

Next, UV-vis spectroscopy with radiation wavelength in the range 200 - 800 nm was used to study different polysulfides in ether. Ex-situ UV-vis spectra were measured for chemically synthesized lithium polysulfides in TEGDME, Li₂ S_{x_mix} | TEGDME solutions for x_mix values of 4, 6, 8, and 10 and sulfur concentrations of 10, 50, and 100 mM. The peaks are generally more resolved at lower concentrations than at higher concentrations for all x_mix values, suggesting a concentration dependence of spectra shape. The peak at 617 nm was used to confirm the existence of S₃ ^•- radical anion, which supports the argument that polysulfide radical anions are stable in ether-based electrolytes, and may play an important role in Li-S reaction mechanism. Using in-situ UV-vis method was discussed and challenges for Li-S reaction mechanism study were evaluated. A new fluorinated-ether based electrolyte was explored. Its low polysulfide solubility makes it a good candidate to be used in in-situ Li-S reaction studies because UV-vis radiations do not have a large penetration path through high concentration of polysulfide-containing materials. However, the main challenge in using UV-vis spectroscopy to study Li-S reaction mechanism is the ambiguity in peak assignments arised both from a lack of spectra standards for different polysulfides. It is difficult to experimentally obtain polysulfide spectra standards because polysulfides cannot be separated. (Abstract shortened by ProQuest.)

CORREIA, L. M. Fe2O3 ou Co3O4 suportados em sílicas mesoporosas modificadas com NH4F e Ti para adsorção de benzotiofeno e reação de oxidação catalítica seletiva parcial de H2S a S. 2017. 233 f. Tese (Doutorado em Engenharia Química)-Centro de Tecnologia, Universidade Federal do Ceará, Fortaleza, 2017.
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The presence of sulfur (S) in automotive fuels must be retrain, once it generates air pollution and promotes damage to the motor (corrosion), affecting the health of living beings. The conventional process of hydrodesulfurization (HDS) for sulfuric compounds removal, used by petrochemical industries, generates large amount of H2S, which can be used in selective partial oxidation reaction of H2S to S. The HDS treatment process is not effective to remove refractory compounds at low concentrations of S, making polish techniques, such as adsorption, necessary due to environmental constraints increase. This situation has led to a need of deeper research in the area of sulfur compounds removal in fossil fuels (gas and diesel). Thus, the development of methodologies to prepare and characterize new adsorbents with high sulfur removal are necessary. The adsorption of BT (standard organic molecule contained in gas and diesel) was investigated using a regular mesoporous silica SBA-15 type and modified with NH4F, and impregnated with Fe and Co respectively. The experiments were done in batch, with different initial BT concentrations (3-15 mmol.L-1) at different temperatures (30 °C, 40 °C and 50 °C). In the second part of the research, the H2S was partially oxidized to S and SO2 using a tubular fixed bed catalytic reactor, containing mesoporous silica HMS, SBA-15, and MCM-41 modified with NH4F and Ti, and respectively Fe2O3 and Co3O4. The catalytic tests were conducted at 180 °C and 170 oC. Reactional conditions were a catalyst mass of 100 mg (40-60 mesh), operating with a 125 mL.min-1 total flow, with molar ratio H2S/Air/He (1/5/94). The brackets, adsorbents and active phases of mesoporous catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), adsorption and desorption isotherms at -196°C, x-ray photoeletronic spectroscopy (XPS), Fourier transform infrared (FTIR), Elemental analysis (CHNS) and spectroscopy of UV-visible region. The results show that mycotoxin adsorbents are promising for the hydrodesulfurization process for BT removal, especially, the sample (15Co/SBA-15/NH4F). All the prepared catalysts are active and promising for the elementary S production. The most stable catalyst was 15Fe/MCM-41, obtaining conversion values of H2S (89.72%), selectivity of S (96.19%), and selectivity of SO2 (3.81%) at 180 °C and 360 min of reaction time in the H2S to S selective oxidation partial reaction in gas phase
A presença de enxofre (S) nos combustíveis automotivos deve ser combatida, uma vez que gera a poluição atmosférica e traz prejuízos ao motor (corrosão), afetando também à saúde dos seres vivos. O processo convencional de hidrodessulfurização (HDS) para remoção dos compostos de S, utilizado pelas indústrias petroquímicas, gera elevada quantidade de H2S, o qual pode ser utilizado na reação de oxidação seletiva parcial de H2S a S. O processo de tratamento por HDS não é eficaz para remoção de compostos refratários em baixas concentrações de S, o que torna necessário a técnicas de acabamento como a adsorção, devido a um aumento nas restrições ambientais. Essa situação tem levado a uma necessidade de maiores pesquisas na área de remoção de sulfurados nos combustíveis (gasolina e diesel). Assim, busca-se desenvolver metodologias para preparar e caracterizar novos adsorventes com elevada capacidade de remoção de enxofre. A adsorção de BT (molécula orgânica modelo contida na gasolina e diesel) foi investigada utilizando-se sílicas mesoporosas do tipo SBA-15 e modificadas com NH4F, e impregnadas respectivamente com Fe e Co. Os experimentos foram feitos em batelada, com diferentes concentrações iniciais de BT (3-15 mmol/L) e temperaturas distintas (30 oC, 40 oC e 50 oC). Na segunda parte da pesquisa o H2S foi parcialmente oxidado a S e SO2 utilizando um reator catalítico de leito fixo do tipo tubular, contendo sílica mesoporosa do tipo HMS, SBA-15, e MCM-41 modificadas com NH4F e Ti, e respectivamente Fe2O3 e Co3O4. Os testes catalíticos foram conduzidos a uma temperatura de reação de 180 ºC e 170 oC. As condições reacionais foram massa do catalisador de 100 mg (40-60 mesh), operando com uma vazão total de 125 mL min-1, com razão molar H2S/Ar/He (1/5/94). Os suportes, adsorventes e as fases ativas dos catalisadores mesoporosos foram caracterizados por difração de raios-X (DRX), microscopia eletrônica de transmissão (MET), isotermas de adsorção e dessorção a -196 oC, espetroscopia fotoeletrônica de raios-X (XPS), infravermelho com transformada de Fourier (FTIR), análise elementar (CHNS) e espectroscopia da região do UV-visível. Os resultados demonstram que os adsorventes são promissores para o processo de hidrodessulfurização para a remoção da molécula de BT, especialmente, a amostra (15Co/SBA-15/NH4F). Todos os catalisadores preparados são ativos e promissores para produção de S elementar. O catalisador mais estável foi 15Fe/MCM-41, obtendo-se valores de conversão de H2S (89,72%), seletividade a S (96,19%), e seletividade a SO2 (3,81%) na temperatura de 180 oC e tempo reacional de 360 min na reação parcial de oxidação seletiva de H2S a S em fase gás

This dissertation is composed of seven chapters, detailing advances within the area of sulfur polymer chemistry and processing, and highlights the relevance of the work to the fields of polymer science, energy storage, and optics that are enabled through the development of novel high sulfur-content copolymers as discussed in the following chapters. The first chapter is a review summarizing both the historical forays into utilization of elemental sulfur in high sulfur-content materials and the current research on the incorporation of sulfur into novel copolymers and composites for high value added applications such as energy production/storage, polymeric optical components, and dynamic/self-healing materials. Although recent efforts by the materials and polymer chemistry communities have afforded innovative sulfur containing materials, many studies fail to take advantage of the low cost and incredible abundance of sulfur by incorporating only minimal quantities into the end products. A fundamental challenge in the preparation of sulfur-containing polymers is simultaneous incorporation of high sulfur-content through facile chemical methods, to truly use the element as a novel feedstock in copolymerizations. Contributing to the challenge are the intrinsic limitations of sulfur (i.e., low miscibility with organic solvents, high crystallinity, and poor processability). The emphasis in chapter 1 is the critical development of utilizing sulfur as both a reagent and solvent in a bulk reaction, termed inverse vulcanization. Through this methodology we can directly prepare materials which retain the advantageous properties of elemental sulfur (i.e., high electrochemical capacity, high refractive index, and liable bond character), obviate the processing challenges, and enable precise control over composition and properties in a facile manner. The second chapter focuses on advancement in colloid synthesis, specifically an example mediated by in-situ reduction of organometallic precursors (ClAu^IPPh₃) by elemental sulfur at high temperatures. In chapter 2, elemental sulfur is employed both as a reactant and novel solvent, generating composite composed of well-defined gold nanoparticles (Au NPs) fully dispersed in a sulfur matrix. While the synthesis of Au NPs in molten sulfur was a novel development the challenge of analyzing the particles directly within the sulfur composite matrix by microscopy techniques required improvement of the composites mechanical properties. To overcome this issue, a one-pot reaction in which the Au NPs were initially synthesized, was vulcanized through an ambient atmosphere-tolerant bulk copolymerization by the addition of a difunctional comonomer (divinylbenzene). The improved composite integrity enabled microtoming and transmission electron microscopy analysis of the particles within the crosslinked reaction matrix. Due to the facile capabilities of directly dissolving the comonomers within the molten sulfur the inverse vulcanization methodology provides a simple route to prepare stable, high sulfur-content copolymers in a single one-pot reaction. The third chapter expands upon the methodology for direct dissolution of difunctional comonomers into molten elemental sulfur to afford chemically stable copolymer. A major challenge associated with the high temperature (i.e., 185 °C) bulk copolymerization reactions between sulfur and vinyl comonomers (i.e., divinylbenzene, DVB) is the high volatility of the organic monomers at elevated temperatures (BP of DVB = 195 °C). To obviate this problem required a novel monomer with an increased boiling point for successful scaling of the inverse vulcanization methodology. The work presented in chapter 3 details the employment of 1,3-diisopropenylbenzene (DIB, BP = 231 °C) to enable larger scale bulk inverse vulcanization reactions, allowing facile control over thermomechanical properties by simple variation in copolymer composition (50–90-wt% S₈, 10–50-wt% DIB). Poly(Sulfur-random-1,3-diisopropenylbenzene) ((poly(S-r-DIB)) copolymers prepared via the inverse vulcanization methodology possess substantially improved processing capabilities compared with elemental sulfur. A facile demonstration of improved processability is the generation of free-standing micropatterned structures using a high sulfur content liquid pre-polymer resin that can be poured into a mold and cured into the desired final form. The highest weight percentage copolymer (i.e., 90-wt% S₈) was also demonstrated to improve cycle lifetimes and capacity retention (823 mAh•g⁻¹ at 100 cycles) of a Lithium-Sulfur (Li-S) cell when the copolymer was utilized as the active material instead of elemental sulfur. Chapter four focuses on the optimization of Li-S cell performance as a function of copolymer composition and provides a more thorough understanding of the means by which copolymer active material improves battery performance. A substantial challenge associated with Li-S cells is the fast capacity fade and short cycle lifetimes that result from loss of the active material (i.e., sulfur) during normal cycling processes. The field has generally addressed these issues by encapsulation of the sulfur in a protective shell (e.g., polymeric, carbonaceous, or metal oxide in nature) in an attempt to sequester the active material. However, encapsulation of sulfur is non-trivial and leads to low loadings of sulfur, resulting in a low energy density within the final cell. To address the challenges associated with maintaining high capacity and long cycle lifetimes while employing an active material which is low cost, generated in a facile manner, and has a high sulfur content required a novel approach. In the work presented in chapter 4 we prepared high sulfur content copolymers via the inverse vulcanization methodology, which meet all the requirements necessary of an active material, and investigated the performance of Li-S batteries as a function of the copolymer composition. A survey of several poly(S-r-DIB) copolymer compositions were prepared with DIB compositions ranging from 1-50-wt% DIB (i.e., 50-99 wt% sulfur) and screened to determine optimal compositions for optimal Li-S battery performance. From this analysis it was determined that copolymers with 10-wt% DIB (90-wt% S₈) were optimal for producing Li-S batteries with high capacity and long cycle lifetimes. 10-wt% DIB copolymers batteries ultimately achieved long cyclic lifetimes and maintained high capacity (>600 mAh/g at 500 cycles). Chapter five details the optimization of conditions necessary to generate large scale (>100 g) inversely vulcanized sulfur copolymers and their application towards Li-S batteries. As previously stated a significant challenge in the Li-S battery field is the production of a Li-S active material with improved performance that is low cost, synthesized in a facile manner, and possesses high sulfur content. To date poly(S-r-DIB) copolymers prepared via the inverse vulcanization methodology afford some of the longest cycle lifetimes and highest capacity retention for polymeric active materials. However, initial inverse vulcanization reactions investigated for preparing active materials were performed on 10 gram scales. The goal of the work presented in chapter 5 was to prepare materials on a scale applicable to fabrication of several prismatic Li-S cells, each of which requires several grams of active material. However, scaling up of the reaction to a kilogram and utilizing the traditional inverse vulcanization conditions (i.e., 185 °C) results in catastrophic degradation as a consequence of the Trommsdorf effect. To address this challenge required decreasing the radical concentration within the bulk copolymerization, which necessitated performing the kilogram scale inverse vulcanization reactions at lower temperatures (i.e., 130 °C) over a longer reaction period. Decreasing the temperature generates materials that are nearly identical in thermomechanical properties to smaller scale samples and the battery performance is likewise comparable (>600 mAh/g at 500 cycles). The key advantage of performing the inverse vulcanization reaction at lower temperatures is that additional monomers, with lower boiling points or degradation issues, can be utilized and the increased gelation time, enables facile incorporation of additives (e.g., carbon black or nanoparticles) into the reaction. Chapter six focuses on the development of poly(S-r-DIB) copolymers as novel mid-infrared (mid-IR) transmitting materials and the analysis of the optical properties as a function of copolymer composition. A challenge in the optical science community is the limited number of materials applicable to the development of innovative optical components capable of functioning in the mid and far-IR regions. Semi-conductor and chalcogenide glasses have been widely applied as device components in infrared optics due to their high refractive indices (n ~2.0–4.0) and high transparency in the infrared region (1–10 μm). However, such materials are also expensive, difficult to fabricate, and toxic in comparison to organic polymers. On the other hand organic polymers are easily processed, low cost, and generated from easily accessible raw materials. Unfortunately, polymeric materials generally have low refractive indices (n<1.65) and are prepared from monomers with functional groups that are highly absorbing at mid-IR and longer wavelengths. Chapter 6 details the realization through the inverse vulcanization methodology of the first example of a material that is high refractive index and low mid-IR absorption, but also low cost and easily processable. Critical to achieving a polymeric material which was appropriate for mid-IR applications was the high sulfur content and the absence of functional groups, both of which are afforded by the facile copolymerization process. By simply controlling copolymer composition the optical properties of the material were tailorable; allowing adjustment of the refractive index from ~1.75 (50-wt% DIB) to ~1.875 (20-wt% DIB). Finally, through facile techniques, high quality copolymers lenses were prepared and we demonstrated the high optical transparency over several regions of the optical spectrum, from the visible (400–700 nm) all the way to the mid-IR (3–5μm). Poly(S-r-DIB) copolymers demonstrated high transparency to mid-IR light, but still maintain the processing capabilities of an organic polymer, the first example of such a material to possess both qualities. Ultimately the inverse vulcanization methodology offers a novel route to low cost, high refractive index, IR transparent materials, opening up unique opportunities for polymeric optical components within the optical sciences field. The seventh chapter discusses utilization of the inverse vulcanization methodology as a means to prepare and control the dynamic behavior of sulfur copolymers for potential applications towards self-healing materials. The incorporation of dynamic covalent bonds into conventional polymer architectures, either directly within the backbone or as side-chain groups, offers the stability of covalent bonds but with the ability of stimuli-responsive behavior to afford a change in chemical makeup or morphology. Traditionally the installation of such functionality requires the use of disparate, orthogonally polymerizable functional groups (i.e., vinyl) and discrete design of the comonomers utilized to generate a responsive copolymer. Therefore, a challenge in developing novel dynamic copolymers is the ability to install stimuli-responsive functionality directly as a result of the copolymerization without the need for rigorous synthetic monomer design and complex copolymerization techniques. In chapter 7 we discuss the analysis of poly(S-r-DIB) copolymers with rheological techniques to assess the composition dependent dynamic behavior. Aided by the bulk nature of copolymerization, the feed ratio of S₈ and DIB directly dictates copolymer microstructure; thus the sulfur rank between the organic groups (i.e., DIB) was tailorable from a single sulfur (thioether) to multiple sulfurs (pentasulfide). Control over sulfur content and number of S–S enables control over the dynamic behavior, as monitored via in-situ rheological techniques. The highest sulfur-content copolymers (80-wt% S₈, 20-wt% DIB) showed the fastest response when under shear stress due to the large number of S–S bonds. On the other hand when no dynamic bonds were present in the copolymer (i.e.; 35-wt% S₈, 65-wt% DIB) there is no dynamic behavior and full recovery of the pristine mechanical properties was not observed. The facile synthesis and simple control over copolymer microstructure affords the inverse vulcanization methodology an advantage over other dynamic materials, and provides potential secondary qualities (i.e., high refractive index) built directly into the structure.

This PhD project aims to address the low energy storage issues of electrode materials for supercapacitors through morphological and defect engineering. The key scientific contribution in this thesis includes: revealing the superior intrinsic electrochemical properties of NiCo-sulfide to hydroxide/oxides, demonstrating a facial defect engineering to enhance electrochemical properties of CoxNi1-xS2 by low temperature plasma, developing a new method for synthesis of high-performance carbon material derived by biomass.

Les travaux présentés dans cette thèse portent sur la synthèse et la caractérisation structurale et physico-chimique de composés sulfures à propriétés thermoélectriques. Un intérêt a été porté sur plusieurs familles de composés sulfures avec pour objectif le développement et/ou l’optimisation des performances thermoélectriques de ces composés.Un premier composé binaire, TiS2, a été élaboré par mécanosynthèse suivi d’une étape de densification par Spark Plasma Sintering (SPS). Les caractérisations structurales ont démontré un effet du processus d’élaboration sur la microstructure ainsi que sur la stœchiométrie du composé. Ce procédé induit une réduction considérable de la conductivité thermique mais aussi électrique du matériau ne permettant pas d’optimiser la figure de mérite du composé. Un second composé a ensuite été développé selon deux voies de synthèses (conventionnelle et mécanosynthèse), le composé ternaire Cu4Sn7S16. Il a été mis en évidence que ce composé semi-conducteur possède une structure complexe qui favorise une conductivité thermique intrinsèquement faible. Les propriétés thermoélectriques ainsi que l’influence de la non-stœchiométrie sur ce composé ont été rapportées. Enfin les composés CuCoxTi2-xS4 et Cu26V2Sn6S32 ont été au cœur des derniers résultats présentés. Ces composés présentent des propriétés de transport plus métalliques propices à l’obtention de facteurs de puissance plus élevés que dans composé Cu4Sn7S16. D’une part, l’élaboration du matériau et l’influence du taux de Co sur le transport électronique ont été discutées sur le composé CuCoxTi2-xS4. D’autre part, l’élaboration par la mécanosynthèse ainsi que les conditions de densification ont été reliés aux propriétés de transport du composé Cu26V2Sn6S32. Une amélioration significative des performances thermoélectriques de ce dernier a été rapportée.Ces différentes études ouvrent des perspectives intéressantes dans l’élaboration et l’optimisation des composés sulfures en vue d’applications industrielles
The work presented in this thesis focuses on the synthesis and the structural/physicochemical characterizations of sulfide compounds with thermoelectric properties. Several families of sulphide compounds have been studied with the aim of developing and/or optimizing their thermoelectric performances.A binary compound, TiS2, was synthesized by mechanical alloying followed by a densification using Spark Plasma Sintering (SPS). The structural characterizations have revealed the effect of the elaboration on the microstructure and stoichiometry of the compound. This process induces a considerable reduction in the thermal and electrical conductivity of the material which hindered the optimization of the figure of merit. The ternary compound Cu4Sn7S16 was then developed according to two synthetic routes (conventional and mechanical alloying). It has been demonstrated that this semiconductor compound has a complex structure which promotes an intrinsic low thermal conductivity. The influence of the non-stoichiometry on the thermoelectric properties has been reported. Finally, the CuCoxTi2-xS4 and Cu26V2Sn6S32 compounds were the last interesting results presented. These compounds show metallic transport properties with high power factors. The synthesis and the influence of the Co content on the electronic transport properties have been discussed on the CuCoxTi2-xS4 compound. The effect of mechanical alloying and densification conditions were related to the transport properties of the Cu26V2Sn6S32 compound. Substantial improvement of the thermoelectric performances as reported.These various studies open interesting perspectives for the development and optimization of sulfide compounds for industrial application

This dissertation is comprised of five chapters detailing advances in the synthesis and preparation of polymers and materials and the application of these materials in lithium-sulfur batteries for next-generation energy storage technology. The research described herein discusses progress towards overcoming three critical challenges presented for optimizing Li-S battery performance, specifically, addressing the highly electrically insulating nature of elemental sulfur, extending the cycling lifetime of Li-S batteries, and enhancing the charge discharge rate capability of Li-S cathodes. The first chapter is a review highlighting the use of polymers in conventional lithium-sulfur battery cathodes. Li-S battery technology presents a grand opportunity to realize an electrochemical energy storage system with high enough capacity and energy density capable of addressing the needs presented by electrical vehicles and base load storage. Polymers are ubiquitous throughout conventional Li-S batteries and their use has been critical in overcoming the challenges presented for optimizing Li-S cathode performance towards practical implementation. The high electrical resistivity of elemental sulfur requires the incorporation of conductive additives in order to formulate it into a functional cathode. A polymer binder must be utilized to integrate the elemental sulfur as the active material with the conductive additives into an electrically conductive composite affixed to a current collector. The electrochemical action of the Li-S battery results in the electroactive sulfur species converting between high and low order lithium polysulfides as the battery is discharged and charged. These lithium polysulfides become soluble at various stages throughout this cycling process that lead to a host of complications including the loss of electroactive material and slow rate capabilities. The use of polymer coatings applied to both the electroactive material and the cathode as a whole have been successful in mitigating the dissolution of lithium polysulfides by confining the redox reactions to the cathode. Elemental sulfur is largely intractable in conventional solvents and suffers from poor chemical compatibility limiting synthetic modification. By incorporating S-S bonds into copolymeric materials the electrochemical reactivity of elemental sulfur can be maintained and allow these polymers to function as the electroactive cathode materials while enabling improved processability and properties via the comonomeric inclusions. The use of inverse vulcanization, which is the direct copolymerization of elemental sulfur, is highlighted as a facile method to prepare polymeric materials with a high content of S-S bonds for use as active cathode materials. The second chapter focuses on the synthesis and polymerization of a novel bifunctional monomer containing both a styrenic group to access free radical polymerization and a propylenedioxythiophene (ProDOT) to install conductive polymer pathways upon an orthogonal oxidative polymerization. The styrenic ProDOT monomer (ProDOT-Sty) was successfully applied to a two-step sequential polymerization where the styrenic group was first leveraged in a controlled radical polymerization (CRP) to afford well defined linear homo- and block polymer precursors with pendant electropolymerizable ProDOT moieties. Subsequent treatment of the these linear polymer precursors with an oxidant in solution enabled the oxidative polymerization of the pendant ProDOT groups to install conductive polythiophene inclusions. Although the synthesis and CRP of ProDOT-Sty was novel, the key advance in this work was successful demonstration that sequential radical and oxidative polymerizations could be carried out to install conductive polymer pathways through an otherwise nonconductive polymer matrix. The third chapter expands upon the use of ProDOT-Sty to install conductive polymer pathways through a sulfur copolymer matrix. The highly electrically insulating nature of elemental sulfur precludes its direct use as a cathode in Li-S batteries and thus the use of ProDOT-Sty in the preparation of a high sulfur content copolymer with conductive inclusions was targeted to improve electrical properties. Inverse vulcanization of elemental sulfur with ProDOT-Sty and a minimal amount of 1,3-diisopropenylbenzene (DIB) was first completed to afford a sulfur rich copolymer with electropolymerizable side chains. Subsequently, the improved processability of the sulfur copolymer was exploited to prepare thin polymer films on electrode surfaces. The poly(ProDOT-Sty-𝑐𝑜-DIB-𝑐𝑜-sulfur) (ProDIBS) films were then subjected to oxidizing conditions via an electrochemical cell to invoke electropolymerization of the ProDOT inclusions and install conductive poly(ProDOT) pathways. Evaluation of the electrical properties with electrochemical impedance spectroscopy (EIS) revealed that the charge transfer resistance was reduced from 148 kΩ to 0.4 kΩ upon installation of the conductive poly(ProDOT) corresponding to an improvement in charge conductance of more than 95%. This also represented a key advance in expanding the scope of the inverse vulcanization methodology as the first example of utilizing a comonomer with a functional side chain. The fourth chapter focuses on expanding the scope of the inverse vulcanization polymerization methodology to include aryl alkyne based comonomers and the application of new these new sulfur copolymers as active cathode materials in Li-S batteries. The early work on developing inverse vulcanization relied heavily on the use of DIB as one of the few comonomers amenable to bulk copolymerization with elemental sulfur. One of the principal limitations in comonomer selection for inverse vulcanization is the solubility of the comonomer in molten sulfur. Generally it has been observed that aromatic compounds with minimal polarity are miscible and thus common classes of comonomers such as acrylates and methacrylates are immiscible and preclude their compatibility with inverse vulcanization. It was found that aryl alkynes are a unique class of compounds that are both miscible with molten sulfur and provide reactivity with sulfur centered radicals through the unsaturated carbon-carbon triple bonds. Additionally, it was found that internal alkynes were best suited for inverse vulcanization to preclude abstraction of the somewhat acidic hydrogen from terminal alkynes. 1,4-Diphenylbutadiyne (DiPhDY) was selected as a prototypical comonomer of this class of compounds for preparing high sulfur content copolymers via inverse vulcanization. Poly(sulfur-𝑐𝑜-DiPhDY) was prepared with various compositions of S:DiPhDY and these copolymers were formulated into cathodes for electrochemical testing in Li-S batteries. The poly(S-𝑐𝑜-DiPhDY) based cathodes exhibited the best performance reported at the time for a polymeric cathode material with the figure of merit of the first inverse vulcanizate to enable a cycle lifetime of up to 1000 cycles. The fifth chapter details the preparation of composite materials composed of a sulfur or copolymeric sulfur matrix with molybdenum disulfide (MoS₂) inclusions and the use of these materials for Li-S cathodes with rapid charge/discharge rate capabilities. The higher order lithium polysulfide redox products (e.g., Li₂S₈ Li₂S₆) generated during Li-S cycling are soluble in the electrolyte solution of the battery. The rate capability of the Li-S battery is thus fundamentally limited by mass transfer as these electroactive species must diffuse back to the cathode surface in order to undergo further reduction (discharge) or oxidation (charge). In order to limit the effective diffusion length of the soluble lithium polysulfides and therefore mitigate the diffusion limited rate, composite materials with fillers capable of binding the lithium sulfides were prepared. MoS₂ was selected as the filler as simulations had indicated lithium polysulfide had a strong binding interaction with the surface of MoS₂. Furthermore, it was demonstrated for the first time that metal chalcogenides such as MoS₂ readily disperse in molten sulfur which enabled the facile preparation of the composite materials in situ. The composites were prepared by first dispersing MoS₂ in liquid sulfur or a solution of liquid sulfur and DIB below the floor temperature of S₈ (i.e.<160 °C). The dispersions were then heated above the floor temperature of S₈ to induce ring opening polymerization of the sulfur phase and afford the composites. The composites were found to be potent active cathode materials in Li-S batteries enabling extended cycle lifetimes of up to 1000 cycles with excellent capacity retention. Furthermore, the composite materials were successful in enhancing the rate capability of the Li-S cathodes where reversible capacity of >500 mAh/g was achieved at the rapid rate of 5C (i.e. a 12 min. charge or discharge time).

III-V compound Gallium Antimonide (GaSb), with a low bandgap of 0.72 eV at room temperature, is an attractive candidate for a variety of potential applications in optoelectronic devices. Ion implantation, among non-epitaxial methods, is a common and reliable doping technique to achieve local doping and obtain high-performance ohmic contacts in order to form a pn junction in such devices. An advantage of this technique over the diffusion method is the ability to perform a low-temperature process leading to accurate control of the dopant profile and avoiding Sb evaporation from GaSb surface occurring at 370 C. In this work, the effect of protons and sulfur ions as two implant species on the electrical behavior of MBE-grown undoped GaSb on semi-insulating (SI) GaAs was investigated via the Hall Effect. Protons and sulfur ions were implanted at room temperature (27 C) and 200 C, respectively, and rapid thermal annealing (RTA) was implemented at various temperatures and durations upon encapsulated GaSb. The damage induced by protons enhanced the hole density of GaSb up to around 10 times, whereas mobilities showed both increase and decrease compared to the un-implanted one, depending on the dose. While the activation of sulfur donors at an elevated temperature was anticipated after annealing sulfur implanted GaSb, instead it led to increase in p-type concentration, as the residual damage originated from sulfur implantation dominated substitutional doping. Furthermore, GaSb p/n photovoltaic devices were fabricated by applying sulfur implantation through silicon nitride layer at RT into an n-GaSb wafer (n-type base, p-type emitter). The device showed a rectifying current and photovoltaic characteristic. The J-V plot under AM1.5G illumination conditions, before and after an etch-back optimizing process, indicated lower short circuit current density J_sc, the same open circuit voltage V_oc, and higher fill factor FF, compared to the photovoltaic device with a p-type base. Also, both normalized series R_s and shunt R_p resistances in p/n diode indicated lower and higher values, respectively, as opposed to a GaSb p++/p diode, indicative of higher quality and lower manufacturing defects.
Master of Science
Generally, the photovoltaic effect is a process by which voltage or electric current is generated in a photovoltaic cell when exposed to light. A solar cell is a photovoltaic device, typically consisting a pn junction, that converts incident photon power into electrical power and delivered to a load to do electrical work for variety of applications. There are variety of methods to form a pn junction and fabricate such devices, among which ion implantation is a reliable doping technique. In this process, dopant ions are accelerated and smashed into a perfect semiconductor lattice, creating a cascade of damage that may displace a thousand atoms for each implanted ion and become activated after an annealing process. The ions themselves can act as either electron donors, make the semiconductor n-type, or electron acceptors, make it p-type. In this work, sulfur ions and protons, as two implant species, were implanted into separate Gallium Antimonide (GaSb) substrates and the effect of each on the electrical behavior of GaSb was investigated by Hall effect experiment. Both species raised hole carrier concentration. This behavior was not expected for sulfur ions as they would be assumed to act as electron donors after activation and convert the GaSb surface to an n-type semiconductor. It was identified that this behavior is due to the domination of created defects during implantation over the number of activated sulfur donors. The same characteristics were predicted and verified for proton implantation as well, the effect of which is just leaving damage in the lattice. Furthermore, to verify this method for converting n-type GaSb to p-type and fabricating a pn junction in GaSb for photovoltaic application, sulfur implantation into an n-type GaSb wafer was performed and optimized by removing the excess surface damage away from the device's metal contacts using wet etching. The device showed a diode-like rectifying current and photovoltaic characteristic. Some parameters such as short circuit current density J_sc, open circuit voltage V_oc, fill factor FF, and resistances (shunt and series) were measured and calculated using J-V plot under dark and illuminated conditions.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 139-150).
Sulfur is a promising positive electrode for lithium batteries with the potential to create the step-change improvement in energy density and cost needed for the widespread adoption of electric vehicles and renewable energy. However, lithium-sulfur batteries suffer from a number of challenges, among them poor rate capability resulting in part from a complex dissolution-precipitation mechanism which produces electronically insulating end members S₈ and Li₂S. Few studies have heretofore been performed on rate-limiting mechanisms in Li-S batteries, which must be elucidated in order to inform rational design of electrodes with high capacity and rate capability. Polysulfide solutions, intermediates in the electrochemical reduction of sulfur, are used for the first time to make an efficient, high energy density flow battery, enabled by a novel flow battery architecture using a percolating network of nanoscale conductive carbon. An extensive experimental study of exchange current density for redox of higher order polysulfide solutions and their ionic conductivity has been conducted. The type and amount of electrolyte solvent has been found to influence both of these. The second portion of this thesis characterizes the kinetics of Li₂S electrodeposition, which is responsible for three-quarters of the theoretical capacity of the sulfur cathode. Kinetics are found to be highly dependent on solvent choice in a manner similar to exchange current density. Furthermore, electrodeposition kinetics are found to slow considerably at the low electrolyte/sulfur ratios which are needed for high energy density and low cost. Materials such as conductive oxides can serve as nucleation promoters and help solve this challenge. The morphology of precipitates is found to be dependent on discharge rate, with large, discrete particles forming at low rates. A model was for describing 3-D electrodeposition of Li₂S under the influence of a soluble redox mediator which enables efficient utilization of conductive surface area and prevents passivation of conductive carbon with insulating Li₂S.
by Frank Yongzhen Fan.
Ph. D.

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Tese (Doutoramento)
IPEN/T
Instituto de Quimica, Universidade de Sao Paulo - IQ/USP

京都大学
新制・課程博士
博士(人間・環境学)
甲第23286号
人博第1001号
京都大学大学院人間・環境学研究科相関環境学専攻
(主査)教授 内本 喜晴, 教授 田部 勢津久, 教授 高木 紀明
学位規則第4条第1項該当
Doctor of Human and Environmental Studies
Kyoto University
DFAM

One of the major technical challenges towards a viable H2S//Air SOFC is to identify and develop anode materials that are electronically conductive, chemically and electrochemically stable, and catalytically active when exposed to H2S-rich environments. The corrosive nature of H2S renders most traditional state-of-the-art SOFC anode materials (Ni, Pt, Ag) useless for long-term cell performance even at very low sulfur concentrations. In my doctoral thesis work, a new class of perovskite-based anodes was developed for potential use in SOFCs operating with H2S and sulfur-containing fuels. Cermets from this family of materials have shown excellent chemical stability and electrochemical performance at typical SOFC operating conditions. As an added benefit, they appear to preferentially oxidize H2S over hydrogen, as suggested by open circuit voltage, impedance spectra, and cell performance measurements obtained using various H2S-H2-N2 fuel mixtures. Cell power output values were among the highest reported in the literature and showed no significant deterioration during 48-hour testing periods. Impedance measurements indicated overall cell resistances decreased with increasing temperature and H2S content of the fuel. This behavior is starkly different from that of contemporary SOFC anodes, where the presence of H2S usually increases overall polarization resistance and ultimately destroys the cell. Results are promising due to the drastic improvement in sulfur tolerance compared to the current generation of SOFC power systems.

Les sulfures alcalino-terreux sont des materiaux tres prometteurs pour la polychromie en electroluminescence de couches minces. Nous avons travaille sur la matrice cas. Nous avons prepare des couches minces de cas et cas:eu#2#+ par pulverisation cathodique radio-frequence reactive. Nous avons defini les conditions optimales de depot, pour lesquelles les couches obtenues ont une tres bonne qualite cristalline, ne sont pas deficientes en soufre, ce qui empeche la formation de composes oxygenes, et presentent une cathodoluminescence dans le rouge tres intense. La resistivite et la densite d'etats pieges de ces couches ont ete determinees. Les dispositifs electroluminescents a structure metal-isolant-cas:x-isolant-metal ont une luminance tres faible, liee a une charge transferee insuffisante. Nous avons donc realise des dispositifs a structure plus complexe: metal-isolant-zns-cas:x-zns-isolant-metal. Les couches de zns ameliorent les performances de ces dispositifs et influent sur les mecanismes de fonctionbnement. Nous avons realise des dispositifs dans lesquels l'interface zns/cas est de bonne qualite; ceci nous a permis de comprendre les mecanismes responsables de l'electroluminescence

Sulfur-species in geological materials have detrimental consequences for geoenvirormental engineering. The research considers aspects of sampling, testing and assessment that were identified as in need of further investigation. Field and laboratory studies show that the distribution of sulfur-species with depth below ground level can be divided into three zones: an upper sulfate leached zone, an intermediate zone with sulfate-horizons and a lower sulfate-poor, sulfide-rich zone. Based on this zonation, a targeted sampling strategy for sulfur-species is presented and permits application of existing classifications for aggressive ground. Petrographic studies of mudrock aggregates reveal the variations in sulfur-species morphology. It is shown that both framboidal and euhedral pyrite can oxidise extensively and that expansion due to gypsum growth may comprise several stages. Dehydration of hydrous sulfate minerals during sample drying was found to be insignificant for typical sulfur-species concentrations. Where high levels of accuracy are required, air-drying (<40ºC) is suitable, however vacuum drying may be required to remove all water from clay soils. The UK gravimetric method for acid-soluble sulfate determination was found to suffer from numerous error sources, with ±0.1% S042- error possible. Use of ICP-OES/AES to quantify sulfate in an acid-extract improved accuracy by an order of magnitude, to an acceptable level for sulfate contents around the tolerance for geo-materials. ICP-OES/AES is recommended as the standard method, with gravimetry to be used only if the sample mass is increased ten-fold. A review of the limitations associated with derived chemical terms such as equivalent pyrite shows that each term relies heavily on assumptions that may not be valid under certain conditions, particularly in the presence of insoluble sulfates and organic sulfur. The geoenvirorunental implications of the research findings are discussed in the context of various ground engineering scenarios and best-practice recommendations are made.

xv, 132 p. : ill. A print copy of this title is available from the UO Libraries, under the call number: SCIENCE TK7871.15.F5 H325 2007
The effects of sulfur alloying on the electronic properties of CuIn(SeS) 2 and CuInGa(SeS) 2 materials has been investigated using sophisticated junction capacitance techniques including drive-level capacitance profiling and transient photocapacitance and photocurrent spectroscopies. CISSe and CIGSSe materials are used as absorber layers in thin-film photovoltaic devices. By characterizing the electronic properties of these materials we hope to understand how these materials can be improved to make thin-film devices with better conversion efficiencies. Sulfur widens the bandgap of these materials by moving the valence band to lower energies and the conduction band to higher energies. This significantly affects the electronic structure of these devices by increasing the activation energies of dominant acceptor levels and lowering room temperature free hole carrier densities. Using optical spectroscopies we observe a large, broad defect that also changes its apparent energetic depth with sulfur alloying. The occupation of this defect was controlled both optically and thermally, and showed a striking temperature dependence. This temperature dependence was measured by recording the relative defect signal, the ratio of the TPC signal in the defect regime to the above bandgap regime, as a function of temperature. As the temperature of the measurement was decreased, steps in the relative defect signal were observed, indicating the turning off of the thermal pathway that emptied trapped charge from the defect. Remarkably, such steps were seen at the same temperature in CISSe and CIGSSe devices with similar sulfur content. In addition, no steps were seen in CMS devices. This points to a defect state specific to the incorporation of sulfur in the absorber material. We hope that a better understanding of the electronic structure of these materials will assist in the creation of improved wide-bandgap thin-film photovoltaic devices.
Adviser: J. David Cohen

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1995.
Vita.
Includes bibliographical references (leaves 171-179).
by Filippos Patsiogiannis.
Sc.D.

Dans la perspective de la réalisation de luminophores pour écrans cathodiques, une étude de la luminescence de l'europium dans des réseaux-hôtes soufres caracterisés par une large bande interdite a été réalisée. La première partie porte sur l'élaboration des sulfures MS et la détermination des facteurs influençant leurs rendements de photoluminescence et de cathodoluminescence. La seconde est consacrée a l'étude des systèmes MS-Al2S3 et MS-SiS2. De nouveaux thioaluminates ont ete isoles; les donnees cristallographiques sur les thiosilicates ont été complétées. La dernière partie rassemble les résultats d' une étude comparative de la luminescence de Eu2+ dans les thioaluminates, thiogallates et thiosilicates alcalino-terreux: distribution spectrale, rendements, extinction thermique...

Ce travail de recherche porte sur la synthèse, la mise en forme et la caractérisation de matériaux à base de sulfures ou oxysulfure pour des applications optiques passives ou actives. Différentes techniques de synthèse, notamment la précipitation en milieu aqueux ou la synthèse par combustion, ont été utilisées pour préparer les nanopoudres précurseurs, ZnS, CaLa₂S₄, BaLa₂S₄ ou La₂O₂S. Il a été constaté qu'un traitement sous H₂S/N₂ permet de purifier ces précurseurs tout en conservant la phase cubique (ZnS) nécessaires pour la préparation de céramiques transparentes. Des céramiques ZnS, avec une transmission maximale d'environ 70% à la longueur d'onde de 10 µm, ont été élaborées par compaction à chaud en utilisant les techniques Hot Pressing ou Spark Plasma Sintering pour des applications optiques dans la fenêtre 8-12 µm. Des poudres de ZnS dopées au Fe²⁺ ont été synthétisées et étudiées avec une bande d'émission très large entre 3 µm et 4,5 µm. Des effets laser ont été obtenus à des longueurs d'ondes entre 3,4 µm et 3,6 µm en fonction de la température. Des poudres d'oxysulfure de lanthane co-dopées à l'Er³⁺ et l'Yb³⁺ ont été étudiées comme matériaux fluorescents pour modifier le spectre solaire avec l'objectif d'augmenter le rendement des cellules solaires photovoltaïques. Un rendement quantique supérieur à 100% a été obtenu avec un pompage à 523 nm pour des émissions dans le visible et le proche infrarouge. Ces résultats montrent que ces matériaux sont des matrices très efficaces pour le dopage des terres rares.

Electrodes from lead-acid batteries were studied using scanning electron microscopy and energy dispersive spectroscopy. This to observe the effects of cycling on the batteries and how a capacity recovery process, known as Macbat regeneration, affected the active material with focus on hard sulphation. First, two new batteries were cycled for two months and electrodes from them were studied when the batteries were new, cycled, fully charged after cycling and regenerated after cycling. Then electrodes from a separate battery that had been used in industry was studied prior to and after Macbat regeneration. On the cycled batteries it was found that after the cycling of the batteries no hard sulphation were present on the electrodes. The study of the separate battery showed that the battery had hard sulphation in its electrodes and that the Macbat regeneration was able to remove hard sulphation both on the surface of the electrodes and also inside the active material.
Elektroder från bly syra batterier studerades med hjälp av svepelektronmikroskopi och energidispersiv spektroskopi. Detta för att observera effekterna av cykling på batterierna och hur en process för kapacitet återhämtning, kännd som Macbat regenerering, påverkade det aktiva materialet med fokus på hård sulfatering. Först blev två nya batterier cyklade i två månader och elektroder från dem studerades när batterierna var nya, cyklade, fulladdade efter cykling och regenererade efter cykling. Sedan studerades elektroder före och efter Macbat regenerering från ett separat batteri som hade använts i industri. På  de cyklade batterierna fann man att efter cyklingen av batterierna fanns ingen hård sulfatering på elektroderna. Studien av det separata batteriet visade att batteriet hade hård sulfatering i elektroderna och att Macbat regenereringen kunde ta bort hård sulfatering både på ytan och även inne det aktiva materialet.

Orientador: Iakov Veniaminovitch Kopelevitch
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
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Resumo: Evidências experimentais e teóricas recentes de que a supercondutividade nas várias formas alotrópicas do carbono pode ocorrer em temperaturas próximas ou até acima da temperatura ambiente, desencadearam um grande interesse científico. Resultados do presente trabalho demonstraram a ocorrência de supercondutividade em compósitos de carbono vítreo-enxofre (CV-S) a T = 3 K. Nossas medidas revelaram que a supercondutividade ocorre em uma pequena fração da amostra, e que a grafitização do carbono amorfo parece ser uma condição necessária para disparar a supercondutividade. Apresentamos também evidências de supercondutividade à temperatura ambiente em sanduíches de grafite/Si, e demonstramos que a supercondutividade está associada à interface grafite/silício. O comportamento encontrado é semelhante ao conhecido para estruturas supercondutoras de baixadimensionalidade. Em particular, observamos oscilações do tipo Josephson em curvas características de corrente-tensão (I-V), bem como sua supressão pela aplicação de campo magnético. Além disso, o campo magnético perpendicular transforma as curvas características I-V do tipo supercondutor para tipo isolante, assemelhando-se à transição supercondutor-isolante induzida por campo magnético em redes de junções Josephson. Todos estes resultados indicam que a interface grafite/silício pode ser um material promissor para o desenvolvimento de dispositivos microeletrônicos sem dissipação à temperatura ambiente
Abstract: Recent both experimental and theoretical evidence that superconductivity in various allotropic forms of carbon can occur at temperatures near or even above room temperature, triggered a broad scientific interest. Results of the present work demonstrated the occurrence of superconductivity in carbon glassy-sulfur composites (CV-S) at T = 3 K. Our measurements revealed that the superconductivity occurs in a small fraction of the sample, and that the graphitization of the amorphous carbon seems to be a necessary condition to trigger the superconductivity. We also present evidence for the room temperature superconductivity in graphite/Si sandwiches and demonstrate that the superconductivity is associated with the graphite/silicon interface. The found behavior is similar to that known for low-dimensional superconducting structures. In particular, we have observed Josephson-type oscillations in current-voltage (I-V) characteristics as well as their suppression by applied magnetic field. Moreover, the perpendicular magnetic field transforms the superconducting-like to insulating-like I-V characteristics resembling the magnetic-field-driven superconductor-insulator transition in Josephsonjunction-arrays. All these results indicate that graphite-silicon interface can be a promising material for the development of microelectronic devices without dissipation at room temperature
Mestrado
Supercondutividade
Mestre em Física

Unlike polymer electrolyte fuel cells, solid-oxide fuel cells (SOFCs) have the potential to use a wide variety of fuels, including hydrocarbons and gasified coal or different types of ample carbonaceous solids. However, the conventional anode for an SOFC, a composite consisting of nickel and yttria-stabilized-zirconia (YSZ), is highly susceptible to carbon buildup (coking) and deactivation (poisoning) by contaminants commonly encountered in readily available fuels. Further, the low ionic conductivity of the electrolyte and the poor performance of the cathode at lower temperatures require SOFCs to operate at high temperatures (>800°C), thereby increasing costs and reduce system operation life. Thus, in order to make SOFCs fully fuel-flexible, cost-effective power systems, the issues of anode tolerance to coking and sulfur poisoning as well as the slow ionic conduction in the electrolyte and the sluggish kinetics at the cathode need to be addressed. In this thesis, a novel electrolyte was shown to have the highest ionic conductivity below 750°C of all known electrolyte materials for SOFCs applications, which allowed for fabrication of a thin-electrolyte cell with high power output at lower temperatures. The detailed electrochemical analyses of BZCYYb conductor revealed that the conductivities were sensitive to doping and partial pressure of oxygen, hydrogen, and water. When used in combination with Ni as a composite anode (Ni-BZCYYb), it was shown to provide excellent tolerance to coking and sulfur poisoning. Extensive investigations on surfaces of BZCYYb and Ni by Raman Spectroscopy and Scanning Auger Nanoprobe disclosed that its unique ability appears linked to the mixed conductor's enhanced catalytic activity for sulfur oxidation and hydrocarbon cracking/reforming, as well as enhanced multilayer water adsorption capability. In addition, the nanostructured oxide layers on Ni from dispersion of BZCYYb traces during high-temperature calcinations may effectively suppress the formation of carbon from dehydrogenation. Based on the fundamental understanding on surface properties, a new and simple modification strategy was developed to hinder the carbon-induced deactivation of the state-of-the-art Ni-YSZ anode. Compared to the complex Ni-BZCYYb anode, this modified Ni-YSZ anode could be readily adopted in the latest fuel cell systems based on YSZ electrolyte. The much-improved power output and tolerance to coking of the modified Ni-YSZ anode were attributed to the nanostructured BaO/Ni interfaces observed by synchrotron-based X-ray and advanced electron microscopy, which readily adsorbed water and facilitated water-mediated carbon removal reactions. Density functional theory (DFT) calculations predicted that the dissociated OH from H₂O on BaO reacted with C on Ni near the BaO/Ni interface to produce CO and H species, which were then electrochemically oxidized at the triple-phase boundaries of the anode. Also, some new insights into the sulfur poisoning behavior of the Ni-YSZ anode have been revealed. The so-called "second-stage poisoning" commonly reported in the literatures can be avoided by using a new sealant, indicating that this poisoning is unlikely the inherent electrochemical behavior of a Ni-YSZ anode but associated with other complications. Furthermore, a new composite cathode with simultaneous transport of proton, oxygen vacancies and electronic defects was developed for low-temperature SOFCs based on oxide proton conductors. Compared to the conventional oxygen ion-electron conducting cathode, this cathode is very active for oxygen reduction, extending the electrochemically active sites and significantly reducing the cathodic polarization resistance. Towards the end, these findings have great potential to dramatically improve the economical competitiveness and commercial viability of SOFCs that are driven by cost-effective and renewable fuels.

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Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq
Low lands in Brazil have a great potential for agriculture, however, they have some limitations due to the presence of high water table and severe risk of flooding. When located near by the sea cost, these floodplains can have influence of the sea water, resulting in the presence of sulfide soils, which, if drained, can develop sulfuric horizons. The sulfuric horizons are mainly characterized by high levels of acidity and exchangeable aluminum, which can result in serious environmental impact to the ecosystem. The agriculture use of these soils requires a deep knowledge of soil physical, chemical and mineralogical properties, in order to support the development of sustainable management practices. The objective of this work was to study chemical and mineralogical properties of acid sulfate soils formed in the floodplain of Camocim river, Caaporã municipality, state of Paraíba. The main aim was to support decisions on the viability of sugarcane cropping in these areas. Soils were characterized morphologically and samples were collected along a transect from the high land towards the river channel. Besides the routine physical, chemical and mineralogical analysis, other determinations were carried out involving total sulfur, incubation pH, soluble anions, electrical conductivity of the saturation extract and sequential iron extraction. The soils were classified as: Argisolic,Dystric Tb Haplic Gleysol (P1) Typic Sapric Sulfide Organosol (P2), Organosolic Orthic Sulfide Gleysol (P3 and P4). Soil distribution in the landscape of the Camocim river floodplain is mainly related to the relief, which determines drainage, water table and, consequently, the soil forming processes related to water excess. The presence of sulfuric horizons occur at the surface, in the very poorly drained soil profiles, and at 43 cm depth in the poorly drained soils close to the river channel. The studied acid sulfate soils do not have salinity at present time, and the high electrical conductivity is determined by the formation sulfuric acid (H+ + SO4 2-) from pyrite oxidation. Sugarcane crop decay in the floodplain of Camocim River, after one year of cultivation was a consequente of the sulfuric horizon formation after the implementation of the drainage system in soils with sulfide materials. The main soil minerals, indentified by X-ray diffraction, in the clay fraction were jarosite quartz, feldspars, kaolinite, smectite (essentially montmorillonite), illite and gibbsite. Quartz and feldspars were the minerals identified in sand and silt fractions. The results of the iron sequential extraction showed predominance of non crystalline iron oxides and very low amounts or absence of iron associated with pyrite, reflecting the advanced oxidation stage determined by the drainage system.
As áreas de várzeas no Brasil apresentam um grande potencial para a agricultura, no entanto, estas áreas apresentam algumas limitações ao uso agrícola devido à presença de lençol freático elevado e risco freqüente de inundação. Quando localizadas em áreas litorâneas, estas áreas podem sofrer influência marinha podendo apresentar solos tiomórficos que, quando drenados, formam horizonte sulfúrico, caracterizados principalmente pela elevada acidez, elevados teores de alumínio trocável, podendo causar sérios impactos ambientais no ecossistema onde ocorrem. A incorporação destas áreas no processo produtivo depende de um profundo conhecimento das propriedades físicas, mineralógicas e principalmente químicas, de forma a subsidiar o desenvolvimento de técnicas sustentáveis de manejo. Neste contexto, foi realizada a caracterização física, química, mineralógica, além da extração sequencial de ferro de solos tiomórficos desenvolvidos na várzea do rio Camocim, no município de Caaporã, PB. O objetivo do estudo foi identificar a ocorrência de solos tiomórficos e caracterizá-los, com o fim de obter subsídios para a tomada de decisão de incorporar estas áreas ao cultivo de cana-de-açúcar ou mantê-las nas condições naturais. Para tanto foi feito um transecto perpendicular ao canal principal do rio, a partir das terras altas, onde foram descritos e coletados quatro perfis de solo. Em campo foi realizada a caracterização morfológica dos perfis e coletadas amostras para as análises físicas, químicas e mineralógicas de rotina, além de análises específicas para determinação do enxofre total, pH de incubação, ânions solúveis, CE do extrato da pasta saturada e extração sequencial de ferro. Os solos foram classificados como Gleissolo Háplico Tb Distrófico argissólico (P1), Organossolo Tiomórfico Sáprico típico (P2) e Gleissolo Tiomórfico Órtico organossólico (P3 e P4). A distribuição dos solos na várzea do rio Camocim guarda estreita relação com o relevo, que condiciona a drenagem e, consequentemente, os processos de formação relacionados com o excesso de água. A presença de horizonte sulfúrico foi constatada a partir do horizonte superficial nos perfis muito mal drenados da planície de inundação, e a partir de 43 cm, nos solos mal drenados da ombreira. Os solos tiomórficos estudados não apresentam salinidade, sendo a alta condutividade elétrica resultante da formação de ácido sulfúrico proveniente da oxidação da pirita (H+ e SO4 2-). A degradação do canavial em grandes áreas da várzea do rio Camocim, após um ano de cultivo, foi consequência da formação do horizonte sulfúrico com a drenagem da área, tendo em vista que os materiais sulfídricos ocorrem desde a superfície. Os minerais identificados por DRX foram: jarosita, quartzo, feldspatos, caulinita, esmectita (essencialmente montmorilonita), ilita e gibbsita, na fração argila. Quartzo e feldspatos foram os minerais identificados nas frações areia e silte. Os valores da extração sequencial de ferro mostraram predomínio de formas não cristalinas de óxidos de ferro e baixíssimos teores ou ausência de ferro associado à pirita, indicando que os solos tiomórficos estudados apresentam avançado estágio de oxidação, promovido pela drenagem realizada na área de estudo na tentativa de viabilizar o cultivo da cana-de-açúcar.

This master's thesis deals with a topic of determination of the most suitable ratio of cathode materials for the lithium-sulfur systems. The first two chapters provide a general introduction to the topic of electrochemical energy sources and present the commonly used primary and secondary battery systems with emphasis on their characteristics and applications. The core of the theoretical part is dedicated to lithium-ion and lithium-sulfur batteries, their working principles along with the benefits or drawbacks related to the particular systems, and widely used materials. The experimental part briefly comments on determining the suitable electrode paste preparation method, the subsequent main part is focused on evaluation of electrochemical performance of cells using different ratios of cathode materials. Five samples of cathode materials were prepared, where the sulfur ratio is in range from 64 to 88 wt. %. Finally, the comparison of all prepared ratios in terms of their electrochemical properties is provided.

In 2013, the worldwide production of renewable electricity accounted for 22.1% of the total energy production with 0.9% coming from solar photovoltaics (PVs). Recently, there has been a growing interest for Cu2ZnSnS4 (CZTS) quaternary semiconductor due to the abundance and low cost of its precursors. Moreover, this chalcopyrite material has an ideal direct band gap around 1.5 eV, high absorption coefficient (α >104 cm-1) and high conductivity, making it suitable for nanostructured and dye-sensitized solar cell (DSSC) applications. Here, CZTS nanoparticles have been synthesized by pulsed laser deposition (PLD) and simultaneously deposited in the interstitial space of ZnO nanowire arrays to form bulk heterojunction 3D nanostructured solar cells. Secondly, vertically oriented CZTS nanoplates have been synthesized by PLD and used as counter electrode in platinum-free dye-sensitized solar cells. These CZTS nanostructures proved to be suitable in achieving workable solar cells, which could significantly cut down the cell cost and provide environmentally friendly photovoltaic devices. Alternately, hybrid organic–inorganic perovskite solar cells have become one of the most attractive photovoltaic technologies with easy solution fabrication and high conversion efficiencies. However, the devices remain unstable under certain processing and environmental conditions. Herein, formamidinium lead tri-halide perovskite (FAPbI3) planar heterojunction solar cells have been fabricated under a controlled environment. The fabrication parameters (precursor concentration, annealing, etc) and the effect of humidity on the structural, optical, and electrical properties of FAPbI3 thin films and devices have been investigated and proved to be critical in the processing of efficient devices. Solar cells with conversion efficiency of 16.6% have been obtained. Furthermore, in-situ techniques such as in-situ (scanning) transmission electron microscopy and in-situ XRD were performed to understand the crystallization and degradation mechanisms of FAPbI3 thin films.The in-situ data were correlated with planar heterojunction FAPbI3 devices efficiency data in order to improve the device fabrication process.

Les propriétés photocatalytiques de catalyseurs commerciaux et synthétiques ont été étudiées pour la décomposition sous flux d'un composé odorant modèle, le sulfure d'hydrogène (H2S), sous irradiation UV-A et visible. Un modèle simplifié qualitatif pour la visualisation de la désactivation du catalyseur est proposé. En outre, les catalyseurs ont été incorporés dans des films multicouches en utilisant différents polyélectrolytes. Ces films ont été caractérisés par ellipsométrie, AFM, spectroscopie UV-visible et SEM sur des surfaces modèles. Ces films sont homogènes et transparents, et leur porosité permet un transport de masse quasiment libre des composés volatiles dans le film. Afin de tester l'activité photocatalytique des films LbL contenant des catalyseurs, ces films ont été assemblés sur des réacteurs tubulaires en verre (avec un diamètre de 2,7 cm et une longueur de 40 cm) et soumis à un flux de H2S sous irradiation UV-A. L'activité des films s’est montrée proportionnelle au nombre de couches de catalyseur constitutif du film et dépendante de la nature chimique du polyélectrolyte constitutif du film. Après optimisation de la structure du film par rapport à la composante catalytique et au composant polyélectrolyte, les films les plus efficaces ont été déposés sur des textiles en coton et leur activité photocatalytique a été mesurée pour la décomposition en flux de H2S sous irradiation à la lumière visible. De plus, les applications potentielles de ces textiles revêtus par LbL pour l'élimination d'autres polluants intérieurs communs ont été illustrées par la décomposition d’acétaldéhyde, de méthyl éthyl cétone et d’ammoniac gazeux sous irradiation à la lumière visible
The photocatalytic properties of commercially available and synthesized catalysts were studied for on-stream decomposition of a model odorous compound hydrogen sulphide (H2S) under UV-A and visible light irradiation. A simplified qualitative model for visualization of the catalyst deactivation is proposed. Further, catalysts were incorporated into multilayer films using different polyelectrolytes. Such films were characterized by ellipsometry, AFM, UV-visible spectroscopy and SEM on model surfaces. These films are homogeneous and transparent, and their porosity allow for almost free mass transport of the volatile compounds within the film. In order to test the photocatalytic activity of LbL films containing catalysts, such films were assembled on tubular glass reactors (with the diameter of 2. 7 cm and the length of 40 cm) and subjected to H2S flow under UV-A irradiation. The activity of films was found to be proportional to the number of film constituent layers of catalyst and dependent on the chemical nature of the film constituent polyelectrolyte. After the film structure was optimized with respect to catalytic component and polyelectrolyte component, the most efficient films were deposited on cotton textiles, and their photocatalytic activity was measured for on-stream decomposition of H2S under visible light irradiation. Further, the potential applications of such LbL-coated textiles for the removal of other common indoor pollutants were exemplified by decomposition of acetaldehyde, methyl ethyl ketone and ammonia gas under visible light irradiation

Em ambientes poluídos como a região metropolitana de São Paulo é imprescindível o conhecimento da natureza da poluição para que sejam estabelecidos procedimentos de minimização ou de controle das emissões. O estudo da poluição atmosférica já vem sendo realizado há muitos anos, sendo os componentes inorgânicos estudados a partir da determinação em amostras coletadas em filtros, soluções, entre outros meios. Neste trabalho é apresentado um método de determinação da razão isotópica de enxofre utilizando a técnica da Espectrometria de Massas com Plasma de Argônio como fonte de íons. O uso de um espectrômetro de massas de dupla focalização com fonte de íons por plasma de argônio, HR-ICPMS, o qual atinge resoluções (m/Δm) de até 8000, permitiu a resolução dos pfcoS dos isótopos 32S e 34S das interferência isobáricas mais comuns e/ou intensas, assim as medições foram realizadas utilizando-se diretamente as m/z dos isótopos do enxofre: A discriminação de massa foi avaliada analisando-se o material de referência NIST 8555 Sulfeto de Prata. A discriminação de massa em elementos leves como é o caso do enxofre é mais acentuada do que para os mais pesados. Assim, uma solução do material de referência era analisada a cada seqüência de 5 ou 6 soluções das amostras. A razão isotópica do enxofre foi determinada em amostras de ar atmosférico coletadas em Sâo Paulo, Ilha Rei George; na Península Antártica e diretamente do escapamento de um carro movido a gasolina e a diesel, utilizando-se um amostrador de grandes volumes e um conjunto de filtros composto de: um filtro de fibra de vidro para a coleta da fração grossa seguido de dois filtros de celulose impregnados com uma mistura de KOH e trietanolamina para a coleta do SO2 e sua oxidação a SO42-. Dois procedimentos de extração dos compostos de enxofre foram utilizados: uma somente com água e outra mais enérgica com ácido nítrico em forno de microondas. Os resultados obtidos indícaram que os dois procedimentos de extração resultam em soluções com composição isotópica diferentes. Além disso, a razão isotópica entre as soluções provenientes dos filtros de fibra de vidro e de celulose são também diferentes. Provavelmente, devido ao fracionamento existente em função da forma química do enxofre presente preferencialmente numa fração ou noutra. A análise quantitativa dos metais revelou uma presença de Fe em concentrações altas (5000-20000 ng/m3), enquanto que os demais (Mn, Cu, Cr, Ni, V, Sr, Cd, Co, Nd, Gd, Ir, Rh, Zr, Re e Ag) estavam presentes em concentrações mais baixas (< 300 ng/m3). Pelas características da amostragem, o Fe foi associado à ressuspensão do solo. O Nd, Gd, Ir, Rh, Re e Ag puderam ser tanto associados à ressuspensão do solo quanto à emissões por automóveis. O Mn, Cu, Cr, Ni, V e Sr foram associados à emissões devido à queima de combustíveis fósseis.
Polluted areas like the Great São Paulo nave a compltex pollution composition. The knowledge of this composition is essential in order to minimize or controt tne dífferent sources. Several atmospheric pollution studies have been done analyzing the inorganic fraction in samples collected in filters, solutions and other media. In this study, the sulfur isotopic ratio determination by using the mass spectrometry with an argon plasma as a source of ions is presented. A double focusing sector field mass spectrometer with an argon plasma, HR-ICPMS, was used. Since 8000 resolution (m/Δm} can be achieved, the 32S and 34S sulfur isotopes can be directly measured with no interferences from the common isobaric interferences (oxygen compounds). Tne isotopic ratio was determined in materials collected by using a high volume sampler. These samples were collected in São Paulo, in the King George Island; Antarctic and directly from the gases exhaust of agasoline and diesel vehicles. Two different filters were used : an external glass fiber filter was used to collect the gross fraction followed by two KOH-Triethanolamine impregnated cellulose filter to collect S)2. Two extraction procedures were used. The first one is an energetic extraction with nitric acid and micro-wave heating and the second one only with water being the soluble sulfur compounds extracted from the filters after had left 24 hours in a beaker with water. Mass discrimination was evaluated by analyzing the NlST 8555 Silver Sulphide Reference Material. As the mass discrimination is more prominent in light elements, the reference material solution was analyzed within a sequence of 5 or 6 samples. The results indicated dífferent isotopic ratio between the solutions obtained with these two extraction procedures. Different isotopic ratios were also observed in the sulfur isotopic composition in the gross and the fine fraction. This is probably due to different sulfur species present preferentially in a given fraction. The quantitative analyses of metals revealed a high Fe concentration (5000-20000 ng/m3) and lower concentrations (<300 ng/m3) to the others (Mn, Cu, Cr, Ní, V, Sr, Co, Co, Ncf, Go, Ir, Rh, Zr, Re and Ag). lron was associated to the soil dust. Neodymium, Gd, Ir, Rh, Re and Ag were associated to the soil dust and to the vehicles emissions. Manganese, Cu, Cr, Ni, V and Sr were associated to the vehicles emissions.

La lixiviación en pilas es uno de los métodos mineros utilizados para extraer cobre desde la roca chancada en minerales de baja ley. El método consiste en formar pilas de gran extensión, y en algunos casos de gran altura, con el mineral chancado que contiene cobre, las que son regadas en su parte superior con soluciones cuyo compuesto principal es ácido sulfúrico. El flujo descendente genera así una solución rica en cobre en la parte inferior de la pila, la que es extraída mediante un sistema de tuberías previamente instaladas para estos efectos. La práctica ha mostrado que existen cambios de permeabilidad de estos depósitos durante el proceso de lixiviación, lo cual afecta la colección de las soluciones y la estabilidad estática y sísmica de las pilas. En este contexto, la presente investigación se ha centrado en los aspectos asociados a la evaluación de la permeabilidad para lograr un buen desempeño de las pilas desde el punto de vista de flujo de las soluciones. Se realizaron ensayos de permeabilidad en laboratorio a tres diferentes materiales provenientes de tres obras mineras, incluyendo ensayos con soluciones compuestas de ácido sulfúrico y agua, a fin de analizar los efectos de éstas en la permeabilidad de los depósitos. Para realizar estos ensayos se construyó un permeámetro de pared flexible cuyos componentes son resistentes a la acción del ácido sulfúrico. Los resultados de los ensayos permiten concluir que no existen significativas variaciones en la permeabilidad al utilizar soluciones ácidas respecto a los ensayos convencionales realizados con agua. Resultados deficientes o contradictorios que pudieran haberse obtenido en experiencias anteriores en este tipo de suelos, se estima están asociadas a la utilización de equipos inadecuados construidos con piezas de metales lixiviables al contacto con ácido sulfúrico. Por otra parte, dos de los materiales estudiados presentan granulometrías que propician inestabilidad interna frente al flujo. Consistentemente, en los ensayos realizados sobre estas muestras se ha observado migración de partículas. Estos resultados permiten concluir que la mayoría de los cambios globales de permeabilidad en las pilas se debe a la localización de partículas finas en determinados planos, constituyendo subestratos de menor permeabilidad dentro de los depósitos.

This study was undertaken to understand the effect of applied pressure on the performance of the lithium sulfur cathode. Compressible carbon based cathodes and novel nickel based cathodes were fabricated. For each cathode, pore volume and void volume were quantified and void fraction was calculated, compression under 0 to 2MPa was measured, and lithium-sulfur cells were assembled and cycled at pressures between 0 and 1MPa. The cathodes studied had void fractions in the range of 0.45 to 0.90. Specific discharge capacities between 200 and 1100 mAh/g under 1MPa were observed in carbon-based cathodes. Nickel-based cathodes showed increased specific discharge capacity of up to 1300 mAh/g, with no degradation of performance under pressure. The high correlation of specific discharge capacity and void fraction, in conjunction with previous work, strongly suggest that the performance of lithium-sulfur cathodes is highly dependent on properties that influence ionic mass transport in the cathode.

Cette thèse porte sur l'étude des deux étapes principales des procédés de transformation de la chalcopyrite (CuFeS2) en cuivre, le grillage et la fusion scorifiante, pour répondre à un problème archéologique. Pour chaque étape, des simulations expérimentales sont effectuées en laboratoire en modélisant les conditions d'un réacteur protohistorique. D'une part, la cinétique de grillage est étudiée par thermogravimétrie couplée à l'analyse physicochimique des produits intermédiaires. D'autre part, les simulations de fusion scorifiante sont principalement menées pour mesurer l'influence respective de deux sources d'oxygène sur la microstructure des produits obtenus : la quantité initiale d'oxyde et la pO2 de l'atmosphère régnant dans le système. Ces simulations expérimentales aboutissent à : - La caractérisation des réactions chimiques mises en jeu lors du procédé, et la proposition de leur mécanismes réactionnels. - L'élaboration de référentiels expérimentaux qui mettent en évidence les correspondances entre conditions opératoires et produits obtenus. Ces référentiels sont reproduits en conditions protohistoriques afin de vérifier leur pertinence. Ces données physico-chimiques sont ensuite exploitées pour répondre à une problématique archéologique en particulier : la métallurgie extractive du cuivre dans les Alpes et le Sud de la France au Chalcolithique et à l'âge du Bronze Ancien.

Dans un contexte de diversification des fonctionnalités sur silicium (more than Moore), les sulfures de transition sont actuellement activement étudiés pour la réalisation de dispositifs optiques originaux. Dans cette famille, certains matériaux présentent une structure lamellaire structurellement semblables au graphène. C'est le cas de certains sulfures de vanadium. La synthèse de ces films lamellaires reste activement dominée par les procédés CVD à haute température (>550°C). Cependant, pour espérer le développement d'une synthèse fiable, il est important de diminuer cette température de dépôt qui conduit à des films souvent peu uniforme et conforme. Dans ce travail nous avons étudié la potentialité d'une approche de dépôt par voie chimique en phase vapeur à basse température (200°C). Cette synthèse a permis l'obtention d'un film de sulfure de vanadium amorphe sur un substrat de 300mm et a montré la capacité de ce film à se réorganiser pour obtenir un film lamellaire de V7S8 après recuit thermique. Un film de 5,2nm présente des propriétés optiques et électriques intéressantes ; ce film est conducteur il possède une densité de porteur de 1,1.1023 cm-3, les porteurs majoritaires sont les trous (type p), une mobilité de 0,2 cm2.(V.s) -1, une conductivité de 1063 S.cm-1, un travail de sortie de 4,8 eV tout en préservant une bonne transparence (transmittance de 75% pour une longueur d’onde de 550nm)
In the context of functional diversification (“More than Moore”), transition sulfides are currently being actively studied for original optical devices production. Some materials in this family have a lamellar structure, similar to graphene like vanadium sulfides. The synthesis of these lamellar films remains actively dominated by high-temperature CVD processes (> 550 ° C). However, in order to hope the development of a reliable synthesis methods, it's important to reduce this deposition temperature which leads to a poor uniformity and a poor conformity. In this work we have studied the potential of a chemical vapor deposition approach at low temperature (200 ° C). This method allow us to obtain an amorphous vanadium sulfide film on a 300 mm wafer and point out theirability to self-reorganize in order to obtain a lamellar film of V7S8 after thermal annealing. A 5.2nm film has interesting optical and electrical properties; this film is conductive with a carrier density of 1.1.1023 cm-3, the holes are the main charges carriers (type p), a mobility of 0.2 cm2. (Vs) -1, a conductivity of 1063 S.cm -1, an output work of 4.8 eV while preserving good transparency (transmittance of 75% for a wavelength of 550nm)

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and, (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2006.
Includes bibliographical references (p. 63).
The Sulfur-Iodine Cycle for the thermochemical production of hydrogen offers many benefits to traditional methods of hydrogen production. As opposed to steam methane reforming - the most prevalent method of hydrogen production today - there are no carbon dioxide emissions. Compared to other methods of hydrogen production, the efficiency of the cycle is excellent. Due to the high temperatures necessary for the cycle, which are generally greater than 8500C, several of the Generation IV nuclear reactor concepts are attractive thermal energy sources. However, the high temperature and corrosive reaction conditions of the cycle, involving reactions including the decomposition of H2SO4 at 400-9000C, present formidable corrosion challenges. The conversion of sulfuric acid to sulfur dioxide was the focus of this study. The alloying of structural materials to platinum has been proposed as a solution to this problem. A catalytic loop to test the materials was constructed. Sulfuric acid was pumped over the material at 903+20C. The sulfur dioxide production of the catalyst was measured as a means of quantifying the efficiency of the system as a function of temperature.
(cont.) The maximum possible production of the material was calculated by using a mass balance. A gas chromatograph was used to calculate the actual production of sulfur dioxide. The results of the experiment show that an molecular conversion efficiency of 10% is attained when operating at 900C while using 800H + 5%Pt as a catalyst. The research confirms the catalytic activity of the material.
by Kevin Miu.
S.B.

L'utilisation de matériaux originaux, à forts indices de réfraction linéaires et non-linéaires et à faibles énergies de phonon, tels que les verres de sulfures, permet d'envisager des applications comme l'amplification large bande (1,3-1,5 µm), la régénération et la commutation tout-optique en télécommunication. Les travaux de recherche présentés ici concernent l'étude de fibres optiques et verres de chalcogénures transmettant dans l'infrarouge. La fenêtre optique des verres appartenant au système de référence GeGaS a été élargie dans le domaine du visible par addition de chlorures de métaux et d'alcalino-terreux. Les caractérisations physico-chimiques en termes de propriétés thermiques, optiques, de durabilité chimique et l'étude de l'organisation structurale des compositions mettent en lumière l'impact de l'insertion d'halogènes dans les verres de sulfures. Les verres de sulfures du système Ge-Ga-Sb-S présentent une potentialité pour l'amplification optique entre 1,3 et 1,47 µm par dopage terre-rare. La loi du gap, établissant la probabilité de relaxation multiphonon à l'écart d'énergie entre un niveau excité et un niveau immédiatement inférieur, a été démontrée dans les verres de sulfures du système GeGaSbS. L'étude des propriétés spectroscopiques de Yb3+ dans différentes matrices sulfures et halogéno-sulfures a permis d'établir le diagramme d'énergie de l'ytterbium dans chacune de ces matrices et de choisir celle la plus adaptée aux études de refroidissement optique. Les verres du système GeGaSbS ont fait l'objet d'études de mise en forme. Une fibre monomode, d'ouverture numérique 0,44 et de diamètre de mode 2 µm a été obtenue et caractérisée à la longueur d'onde de 1,55 µm. La fluorescence infrarouge du dysprosium et du thulium sur des fibres multimode a été étudiée. La bonne aptitude de ces verres au fibrage a conduit à la réalisation de fibres microstructurées, de types bande interdite photonique et à trous. La caractérisation optique de ces fibres a révélé le caractère quasi-monomode d'une des fibres à trous à la longueur d'onde de 1,55 µm.