O equilíbrio sólido-líquido de sistemas binários de alcoóis graxos e de ésteres graxos foi descrito por meio de modelagem termodinâmica baseada na análise de estabilidade da fase líquida. A metodologia foi aplicada a três tipos de diagramas de fases: (a) sistemas cujos constituintes apresentam miscibilidade completa, em que as substâncias são miscíveis tanto na fase sólida quanto na líquida, (b) sistemas que apresentam ponto eutético simples, (c) sistemas que apresentam ponto eutético e reação peritética. A caracterização da não-idealidade foi feita com o modelo de coeficientes de atividade de Flory-Huggins para descrição dos diferentes comportamentos, que resultou em bom ajuste dos dados. A uniformidade do valor dos parâmetros ajustados mostra que há diferentes interações moleculares comparando-se as funções químicas álcool, éster etílico e éster metílico e a presença de insaturação na cadeia carbônica. Observa-se que os resultados são fortemente afetados pelos valores de entalpia e temperatura de fusão dos compostos puros. A metodologia desenvolvida foi implementada em linguagem Fortran. Do ponto de vista formal, a análise apresentada mostra que a ocorrência de peritéticos pode ser descrita sem que seja necessário postular um modelo de coeficiente de atividade para a fase sólida quando houver imiscibilidade total. / In this work, the modeling of solid-liquid equilibrium of binary systems containing fatty alcohols or fatty esters is presented. Phase equilibrium calculations were carried out using a phase stability analysis which describes the onset of the solid phase formation. The developed methodology was applied to the modeling of three distinct types of phase diagrams: (a) systems wherein the components are miscible in both phases, (b) systems with a single eutectic point, (c) systems with eutectic point and peritectic reaction. The liquid phase non-ideality was accounted for through the Flory- Huggins model for the excess Gibbs energy. It was possible to describe the different types of phase diagrams with excellent agreement with the experimental data. The values of the adjustable parameters are rather low and depend on both the chemical function of the species considered (alcohol, methyl ester or ethyl ester) and the presence of unsaturation in their molecules. The calculated phase diagrams are strongly affected by the experimental values of enthalpy of fusion and temperature of fusion of the pure compounds. Concerning the thermodynamic description of the solid-liquid equilibrium, the presented analysis showed that it is possible to account for the peritectic reaction without assigning a model for the solid phase activity coefficient when the compounds are not miscible in this phase.

Talvez mais que a própria Mecânica, a Termodinâmica possui em seu interior uma grande diversidade de teorias, que se distinguem por motivos vários. Um modo de identificá-las é analisar como se organizam, reflexo da metodologia empregada ao construí-las. Em particular, a organização que Carnot, Thomson e Clausius conferiram à ciência do calor é do tipo sintética, baseada no poder heurístico de ciclos termodinâmicos. Por isso, tal formalismo é chamado de termodinâmica de ciclos. Por outro lado, Gibbs, inspirado na tradição que remonta a Lagrange e a Hamilton, constrói uma teoria analiticamente organizada, conhecida como termodinâmica de potenciais. O estudo comparativo das duas é viável e mostra-se como uma excelente ocasião para verificar e elucidar o poder explicativo e racional de cada uma, com interessantes consequências para a própria Filosofia da ciência. Além disso, contextualizando historicamente cada uma, vê-se que a termodinâmica de Gibbs é uma teoria inspirada no método analítico de Hamilton. / Perhaps more than Mechanical itself, thermodynamics has in its interior a wide variety of theories which differ for various reasons. A way to identify them is analyze how they are organized, which is a reflection of the methodology used to construct them. In particular, the organization that Carnot, Clausius and Thomson have given to the science of heat is the synthetic type, based on heuristic power of thermodynamic cycles. Therefore, this formalism is called thermodynamic cycles. On the other hand, Gibbs, inspired by the tradition going back to Lagrange and Hamilton, builds an analytically organized theory, known as thermodynamics of potentials. The comparative study of the two is possible and shows up as an excellent opportunity to verify and clarify the explanatory and rational power of each, with interesting consequences for the Philosophy of science. In addition, each contextualized historically, it is seen that the Gibbs thermodynamic theory is inspired by the analytical method of Hamilton.

Neste trabalho, realizou-se o estudo que permitiu a otimização termodinâmica das seções binárias pertencentes ao diagrama de fase ternário do sistema LiF-GdF3-LuF3, para tanto o programa FactSage foi empregado na simulação computacional. Assim, o comportamento de fusão das misturas destes compostos foi elucidado, o que representa uma contribuição inovadora para o conhecimento das propriedades físicas e químicas destes materiais. Em particular, determinou-se a faixa de composições nas quais as soluções sólidas de LiGdxLu1-xF4 e GdxLu1-xF3 podem ser obtidas diretamente da fase líquida. Neste trabalho as três secções binárias, LiF-GdF3, LiF-LuF3 e GdF3-LuF3 foram reavaliadas experimentalmente utilizando a calorimetria exploratória diferencial para a obtenção de dados mais precisos de temperatura versus composição, uma vez que foi possível minimizar a contaminação das amostras com compostos de oxigênio. A capacidade calorífica e outros dados calorimétricos foram também determinados experimentalmente e comparados com os existentes na literatura. Os termos da energia livre de Gibbs de excesso para as fases representadas como soluções, os quais descrevem os efeitos de interação não ideal entre os dois fluoretos nestas fases, foram expressos com sucesso pela modelo polinomial Redlich-Kister. Finalmente, o caminho de solidificação no diagrama de fase ternário LiF-GdF3-LuF3 pôde ser extrapolado de acordo com o formalismo de Kohler-Toop. Assim, pela primeira vez, a interação ternária entre os compostos LiF, GdF3 e LuF3 foi determinada. / In this work, it was carried out the study that allowed the thermodynamic optimization of the binary sections belonging to the ternary phase diagram of the LiF-GdF3-LuF3 system, for this purpose the FactSage software was used in the computational simulation. Thus, the melting behavior of the mixture of these compounds has been elucidated, which represents an innovative contribution to the knowledge of the physical and chemical properties of these materials. In particular, it was determined the composition ranges in which the solid solutions of LiGdxLu1-xF4 and GdxLu1-xF3 can be obtained directly from the liquid phase. In this work the three binary sections, LiF-GdF3, LiF-LuF3 and GdF3-LuF3, were evaluated using differential scanning calorimetry to obtain more accurate data of temperature versus composition, since it was possible to minimize the contamination of the samples due to oxygen compounds. The heat capacity and other calorimetric data were experimentally determined and compared with those cited in the literature. The terms of the Gibbs free excess energy for the solution phases, which describe the non ideal interaction effects between the two fluorides at these phases, were expressed by the Redlich-Kister polynomial model. Finally, the solidification path in the ternary phase diagram LiF-GdF3-LuF3 could be extrapolated according to the Kohler-Toop formalism. Thus, for the first time, the interaction between the ternary compounds LiF, GdF3 and LuF3 was determined.

Blendas poliméricas de biopolímeros, além de apresentarem uma melhora das propriedades do material, ainda possuem as vantagens de serem biocompatíveis, biodegradáveis e apresentar baixa toxicicidade, como no caso de blendas de alginato de sódio e fibroína de seda. Membranas confeccionadas a partir desta mistura apresentam grande potencial no desenvolvimento de curativos de alto desempenho, proporcionando condições ótimas de cicatrização. Entretanto, o processo de mistura destes biopolímeros é bastante complexo e resulta na separação de fases, processo que ainda não foi muito explorado. Este trabalho buscou explorar experimentalmente o comportamento do equilíbrio de fases dos sistemas aquosos contendo fibroína de seda e alginato de sódio em diversos valores de pH. Soluções aquosas de fibroína foram previamente preparadas por meio de processo de diálise, e soluções de alginato, por meio de dissolução direta em água. Ambas as soluções eram misturadas em concentrações em que se desejava avaliar o comportamento de fases. Após a separação de fases, a fase líquida sobrenadante era coletada, a fibroína quantificada via espectrofotometria e o alginato, via calcinação. Observou-se que a região monofásica do diagrama de fases é pequena, e a separação de uma segunda fase ocorre em concentrações baixas dos dois biopolímeros. A separação de fases pôde ser descrita como a precipitação da fibroína pela adição de alginato, e a solubilidade da fibroína pôde ser descrita por meio da equação de Cohn. As curvas de solubilidade obtidas não apresentaram diferenças significativas em função do pH. Medidas do potencial Zeta de soluções de alginato e fibroína em diversas faixas de pH não mostraram diferenças significativas quanto à carga superficial das moléculas, o que é compatível com a ausência de influência do pH no equilíbrio de fases. / Polymer blends formed by biopolymers may show an improvement of material properties (compared to the pure biopolymers), and present advantages such as biocompatibility, biodegradability and low toxicity. An interesting biopolymer blend is that formed by sodium alginate and silk fibroin. Membranes prepared with this mixture show great potential in the development of high-performance wound dressing, since it provides optimum healing conditions. However, the mixing process of these two biopolymers is complex and has not been extensively explored. In this work the phase equilibrium behavior of aqueous systems containing silk fibroin and sodium alginate was experimentally studied at different pH values. Fibroin aqueous solutions were previously prepared through dialysis, and alginate solutions were prepared by direct dissolution in water. Both solutions were mixed at the concentration range in which the phase behavior of the system was to be assessed. After phase separation, the supernatant liquid phase was separated, the fibroin was quantified through spectrophotometry. and the alginate was quantified through calcination. The single-phase region of the phase diagram is small, and the separation of a second phase occurs at low concentrations of both biopolymers. The phase separation could be described as the precipitation of fibroin due to the addition of alginate, and the solubility of fibroin was described by the Cohn equation. The solubility was not significantly affected by the pH. The Zeta potential of either alginate or fibroin, measured in solutions of different pH values, did not present any significant difference concerning the surface charges of these macromolecules. This finding agrees with the absence of pH influence upon the phase equilibrium.

A pressão e o volume não podem ser definidos corretamente em um sistema nãohomogêneo. Neste trabalho, definimos variáveis macroscópicas globais para um gás confinado em uma armadilha harmônica, os quais são análogos à pressão e o volume. Um sistema ultra-frio tem variáveis termodinâmicas naturais como o número de átomos e a temperatura. Introduzimos um novo conjunto de variáveis globais conjugadas para caracterizar o sistema macroscopicamente. Construímos diferentes diagramas de fase para um gás de Bose de 87Rb aprisionado em uma armadilha harmônica em termos dessas novas variáveis globais obtidas a partir das frequências da armadilha e a distribuição da densidade dos átomos. Nós construímos estes diagramas de fase, identificando os principais aspectos relacionados à transição da condensação de Bose-Einstein em um gás aprisionado. Este procedimento pode ser usado para explorar aspectos relacionados com a condensação de Bose-Einstein, tais como a compressão isotérmica relacionados com a transição de fase. Por outro lado, estas novas quantidades termodinâmicas nos permitem estudar a natureza dos fenômenos quânticos como a pressão do ponto zero relacionada ao princípio da incerteza. / The pressure and volume can not be defined correctly on a non-homogeneous system. In this work we define macroscopic variables for a gas confined in an harmonic trap, which are analogous to pressure and volume. An ultra-cold system has natural thermodynamic variables as number of atoms and temperature. We introduce a new set of global conjugate variables to characterize the system macroscopically. We measure different phase diagrams of a 87Rb Bose gas in a harmonic trap in terms of these new global variables obtained from frequencies of trap and the density distribution of atoms. We construct these phase diagrams identifying the main features related to the Bose- Einstein condensation transition in a trapped gas. This procedure can be used to explore different aspects related to Bose-Einstein condensation, such as the isothermal compressibility related with the phase transition characteristics. On the other hand, these new thermodynamic quantities allow us to study the nature of quantum phenomena as the zero-point pressure related to the uncertainty principle.

A pressão osmótica é uma das principais propriedades de interesse no estudo da não-idealidade de soluções proteicas, por fornecer diretamente informações sobre a atividade do solvente e, indiretamente, sobre o comportamento da proteína em solução. O presente trabalho objetiva a investigação do uso de equações osmóticas de estado para o cálculo da pressão osmótica em soluções proteicas contendo co-solventes como sais e polímeros. O modelo desenvolvido compreende um termo de esferas rígidas de Carnahan-Starling e um termo atrativo de van der Waals. Para avaliar a adequação do modelo proposto, correlacionaram-se dados de pressão osmótica de soluções proteicas obtidos da literatura para as proteínas lisozima, a-quimotripsina, albumina de soro bovino e imunoglobulina G humana, em soluções aquosas em diversos valores de pH e com diversos co-solventes. O modelo desenvolvido foi capaz de representar adequadamente os dados experimentais na maioria dos casos estudados, com uma correspondência maior do que a equação virial, usualmente empregada no estudo dessas soluções. Para a modelagem de soluções de a-quimotripsina, foi necessário considerar a dimerização da molécula proteica. Em poucos casos, especialmente na modelagem de soluções de albumina de soro bovino contendo polietileno glicol, o modelo mostrou-se insuficiente para correlacionar adequadamente os dados experimentais. Na maioria das vezes, o parâmetro do termo atrativo mostrou uma fraca dependência do pH próximo ao ponto isoelétrico, uma dependência maior com respeito a esse parâmetro em valores de pH mais distantes deste ponto, e uma dependência nítida com respeito à força iônica. De maneira geral, embora a representação dos dados experimentais seja adequada, não foi possível observar tendências inequívocas do parâmetro atrativo com respeito ao pH e a força iônica de modo a permitir o desenvolvimento de um modelo preditivo. / The osmotic pressure is one of the key properties for the assessment of the non-ideality of protein solutions. Its importance is related to the fact that it allows the evaluation of solvent activity and indirectly of the protein behavior in solution. This work presents an investigation on the use of osmotic equations of state for calculating the osmotic pressure of aqueous solutions of proteins containing cosolvents such as salts or polymers. The developed model comprises a repulsive term, corresponding to the hard-sphere equation by Carnahan-Starling, and an attractive term, corresponding to a van der Waals type equation. To assess the suitability of the proposed model, experimental osmotic pressure data obtained from literature for aqueous solutions containing lysozyme, a-chymotrypsin, bovine serum albumin and human immunoglobulin G, at several values of pH and with different cosolvents, were correlated. The model was able to adequately represent the experimental data in most of the cases, with a better agreement than the virial equation, which is the most widely used equation in the study of the osmotic pressure of protein solutions. For the modeling of a-chymotrypsin solutions, it was necessary to consider the dimerization of the protein molecule. Only in a few cases, mainly in the modeling of solutions containing bovine serum albumin and polyethylene glycol, it was not possible to correlate adequately the experimental data. In most cases, the attractive parameter presented a weak dependency on the pH close to the isoelectric point, and a stronger dependency on pH otherwise. The dependency on the ionic strength was almost always strong. To conclude, in spite of the good performance of the model in the correlation of experimental data, definite tendencies of the attractive parameter in relation to pH and ionic strength were not observed, and hence a predictive model could not be developed.

Le développement des équipements portables, des réseaux de capteurs sans fil et systèmes auto-alimentés d'une manière générale génère une forte demande pour les dispositifs de récupération de micro-énergie. Une des voies les plus intéressantes pour auto-alimenter des dispositifs consiste à développer des systèmes recyclant l'énergie ambiante afin de renouveler sans cesse l'énergie consommée par le dispositif. En dehors de la récupération d'énergie électromécanique, il est également intéressant de convertir l'énergie thermique, qui est «disponible» partout, en énergie électrique. Au cours de cette thèse, la conversion d’énergie thermique en énergie électrique fondée sur des variations temporelles de température a été développée et améliorée. Parmi les matériaux ferroélectriques, des monocristaux de PZN-4.5PT et le terpolymère P(VDF-TrFECFE) 61.3/29.7/9 mol % ont été choisis comme matériaux actifs en raison de leurs propriétés remarquables sous champ électrique. En utilisant des cycles thermodynamiques intelligents, par exemple, Ericsson ou à cycle de Stirling, l'efficacité de la conversion de l'énergie pourrait être considérablement améliorée. Dans la première partie, la récupération d'énergie pyroélectrique en utilisant des monocristaux de PZN-4.5PT a été principalement étudiée sous deux aspects: l'effet de fréquence et des transitions de phase sur les cycles d’Ericsson. Il a été montré que l'énergie récupérée diminue de façon non linéaire avec une augmentation de la fréquence. De plus, l’utilisation optimale des transitions de phase pendant le cycle d’Ericsson permet d’améliorer grandement l’énergie récupérée en choisissant une gamme de température de travail appropriée. A partir de ces résultats, deux cycles d’Ericsson asymétriques (LH et HL) ont été réalisés avec succès. Avec les monocristaux de PZN-4.5PT, le cycle HL est le cycle le plus efficace pour la conversion d’énergie thermique en énergie électrique. La deuxième partie traite de la récupération d'énergie électrostatique via la variation non linéaire de la capacité du terpolymère P(VDF-TrFE-CFE) 61.3/29.7/9 mol %. Un cycle d’Ericsson a été réalisé entre 25 et 0°C et comparé à sa simulation à partir de la valeur de la constante diélectrique sous champ électrique DC. La concordance entre la simulation et l’expérience a prouvé la fiabilité de notre évaluation théorique. A partir de la simulation, l'énergie récupérée augmente jusqu'à 240 mJ/cm3 en appliquant un champ électrique de 80 kV/mm. Des cycles de Stirling et d’Ericsson ont également été simulés sous différentes variations de température et champ électriques. L'énergie récupérée augmente avec l’accroissment de la variation de température et de la valeur du champ électrique appliqué et ceci quelque soit le cycle réalisé. Contrairement au cycle d’Ericsson, un cycle de Stirling peut récupérer plus d'énergie pour une même énergie injectée. / The development of portable equipments, wireless sensors networks and self-powered devices in a general manner generates a strong demand for micro-energy harvesting devices. One of the most challenging ways to self power devices is the development of systems that recycle ambient energy and continually replenish the energy consumed by the system. Apart from electromechanical energy harvesting, it is also interesting to convert thermal energy, which is “available” everywhere, into suitable electrical energy. In this thesis, the thermal to electrical energy conversion from temperature fluctuations was developed and improved, and the feasibility of this technique was also confirmed by implementing the experimental experiment. Among different ferroelectric materials, PZN-4.5PT single crystal and P(VDF-TrFE-CFE) 61.3/29.7/9 mol% were chosen as active materials due to their outstanding properties under electric field. By means of some intelligent thermodynamic cycles, e.g., Ericsson or Stirling cycle, which has been presented in previous research, the efficiency of energy conversion could be improved greatly. In the first part, pyroelectric energy harvesting on PZN-4.5PT single crystals with an Ericsson cycle was mainly investigated from two aspects: frequency effect and phase transitions. It was shown that the harvested energy demonstrated a nonlinear decrease with an increase of frequency, and the optimal use of the phase transitions during the Ericsson cycle could greatly improve the harvested energy by choosing the appropriate working temperature range. Based on it, two asymmetric Ericsson models (L-H and H-L cycles) were attempted successfully, and it was confirmed that the H-L cycle is the most effective thermal energy harvesting cycle for this material. The second part concentrated on electrostatic energy harvesting by nonlinear capacitance variation on P(VDF-TrFE-CFE) 61.3/29.7/9 mol% terpolymer. Ericsson cycle was tested experimentally between 25 and 0°C and compared with the simulation from dielectric constant values obtained under DC electric field. The identical result between simulation and experiment proved the reliability of our theoretical evaluation. It was found, from simulation, that the harvested energy increased up to 240 mJ/cm3 when raising the electric field at 80 kV/mm. The further study on Ericsson and Stirling cycle was also made under different temperature and electric field conditions for evaluation. The harvested energy increases with the rising of temperature variation and electric field in both cycles, but in contrast to Ericsson cycle, Stirling cycle can harvest more energy for the same injected energy.

MAX-phase ceramics are a class of ductile ceramic material group with the general molecular formula Mn+1AXn (n = 1, 2, 3….), where M is an early transition element, A is an element from the ‘A’ group of the periodic table and X is either nitride or carbide. One advantage of these materials is that they maintain their strength at high temperatures. In addition these ceramic materials possess the best properties of both ceramics and metals. Some of their important characteristics are low density, high stiffness, machinability, excellent thermal and electrical conductivity and they even exhibit some plasticity at elevated temperature. These amazing combinations of properties have made researchers foresee the technological importance of these materials as a structural ceramic for high temperature application. Since this ceramic is relatively new to the market, only a handful of work has been undertaken on this material and its applications are limited to heating elements. In addition, analysis of the thermodynamic data on this material is incomplete. This PhD work addresses this issue and conducts a complete thermodynamic analysis involved in the formation mechanism of the ternary titanium carbide MAX-phase Ti2AlC ceramic, using Self-propagating High temperature Synthesis (SHS) form of combustion synthesis process, based on the following exothermic reaction: (2+x) Ti + (y) Al + C → Ti2AlC + (x) Ti + (y) Al (i) Where x and y = 0.1. 0.2, 0.3… A thermodynamic model has been formulated to predict the temperature evolution during the reaction (i), for the formation of Ti2AlC using SHS process. In addition the effect of particle size in the elemental reaction has been studied on the formation mechanism of Ti2AlC and methods to control the porosity by fine tuning the particle size has been recognized. Manufacturing processes such as Self-propagating High temperature Synthesis (SHS), foam replication and freeze casting have been developed in this thesis to produce micro and macro porous Ti2AlC ceramic mainly for electrode applications. A systematic material development technique to produce macro porous Ti2AlC ceramic, using a foam replication technique has been established in this research work. The material fabricated by this technique has a uniform pore size (up to 5mm), with open interconnected pores and is ideal for a flow battery application which requires a multifunctional electrode material which is highly porous to allow the flow of electrolyte through it, is corrosion resistant and at the same time being electrically conductive. The mechanical properties of the ceramic produced by this method has been characterised and steps to mitigate the cracks and defects formed during the fabrication process to obtain structurally stable macro porous Ti2AlC ceramic has been reported in this work. This research demonstrates that one of the applications of macro porous Ti2AlC ceramic formed using foam replication technique is as an electrode material in a photo-Microbial Fuel Cell (p-MFC). Graded porosity micro porous Ti2AlC ceramics have also been fabricated using a freeze casting technique, with camphene as the freezing vehicle. A systematic material development process has been tailored for this particular material. A ceramic material with gradient pore size ranging from 27-305µm has been fabricated using this technique. This type of ceramic is a good candidate as an electrode material in micro-redox battery and for sensing applications. A variety of processing parameters such as solid loading (amount of ceramic content in the material), freezing temperature and mould material which affect the pore formation and pore size have been studied in this PhD and the range of porosities achieved by controlling these parameters have been reported.

Proton exchange membrane (PEM) fuel cells are at the forefront among different types of fuel cells and are likely to be important power sources in the near future. PEM is a key component of the PEM fuel cells. The objective of this research is to investigate the fundamental aspects of PEM in terms of thermodynamics and proton transport in the membrane, so that the new proton conducting materials may be developed based on the detailed understanding. Since the proton conductivity increases dramatically with the amount of water in PEM, it is important to maintain a high humidification during the fuel cell operation. Therefore, the water uptake characteristics of the membrane are very important in developing fuel cell systems. Thermodynamic models are developed to describe sorption in proton-exchange membranes (PEMs), which can predict the complete isotherm as well as provide a plausible explanation for the long unresolved phenomenon termed Schroeder¡¯s paradox, namely the difference between the amounts sorbed from a liquid solvent versus from its saturated vapor. The sorption isotherm is a result of equilibrium established in the polymer-solvent system when the swelling pressure due to the uptake of solvent is balanced by the surface and elastic deformation pressures that restrain further stretching of the polymer network. The transport of protons in PEMs is intriguing. It requires knowledge of the PEM structure, water sorption thermodynamics in PEM, proton distribution in PEM, interactions between the protons and PEM, and proton transport in aqueous solution. Even proton conduction in water is anomalous that has received considerable attention for over a century because of its paramount importance in chemical, biological, and electrochemical systems. A pore transport model is proposed to describe proton diffusion at various hydration levels within Nafion¢ÃƒÂ§ by incorporating structural effect upon water uptake and various proton transport mechanisms, namely proton hopping on pore surface, Grotthuss diffusion in pore bulk, and ordinary mass diffusion of hydronium ions. A comprehensive random walk basis that relates the molecular details of proton transfer to the continuum diffusion coefficients has been applied to provide the transport details in the molecular scale within the pores of PEM. The proton conductivity in contact with water vapor is accurately predicted as a function of relative humidity without any fitted parameters. This theoretical model is quite insightful and provides design variables for developing high proton conducting PEMs. The proton transport model has been extended to the nanocomposite membranes being designed for higher temperature operation which are prepared via modification of polymer (host membrane) by the incorporation of inorganics such as SiO2 and ZrO2. The operation of fuel cells at high temperature provides many advantages, especially for CO poisoning. A proton transport model is proposed to describe proton diffusion in nanocomposite Nafion¢ÃƒÂ§/(ZrO2/SO42-) membranes. This model adequately accounts for the acidity, surface acid density, particle size, and the amount of loading of the inorganics. The higher proton conductivity of the composite membrane compared with that of Nafion is observed experimentally and also predicted by the model. Finally, some applications of PEM fuel cells are considered including direct methanol fuel cells, palladium barrier anode, and water electrolysis in regenerative fuel cells.

"Gas carburizing is an important heat treatment process used for steel surface hardening of automotive and aerospace components. The quality of the carburized parts is determined by the hardness and the case depth required for a particular application. Despite its worldwide application, the current carburizing process performance faces some challenges in process control and variability. Case depth variability if often encountered in the carburized parts and may present problems with i) manufacturing quality rejections when tight tolerances are imposed or ii) insufficient mechanical properties and increased failure rate in service. The industrial approach to these problems often involves trial and error methods and empirical analysis, both of which are expensive, time consuming and, most importantly, rarely yield optimal solutions. The objective for this work was to develop a fundamental understanding of the mass transfer during gas carburizing process and to develop a strategy for the process control and optimization. The research methodology was based on both experimental work and theoretical developments, and included modeling the thermodynamics of the carburizing atmosphere with various enriching gasses, kinetics of mass transfer at the gas-steel interface and carbon diffusion in steel. The models accurately predict: 1) the atmosphere gas composition during the enriching stage of carburizing, 2) the kinetics of carbon transfer at the gas-steel surfaces, and 3) the carbon diffusion coefficient in steel for various process conditions and steel alloying. The above models and investigations were further combined to accurately predict the surface carbon concentration and the carbon concentration profile in the steel during the heat treatment process. Finally, these models were used to develop a methodology for the process optimization to minimize case depth variation, carburizing cycle time and total cycle cost. Application of this optimization technique provides a tradeoff between minimizing the case depth variation and total cycle cost and results in significant energy reduction by shortening cycle time and thereby enhancing carburizing furnace capacity."