The substance of present work is to provide standard thermodynamic functions (STF) of small size molecules for the calculation of the composition and thermodynamic properties of low-temperature plasma, and also method for such a calculation applying obtained STF under non-ideal plasma conditions. With a view to further application in modelling the phenomena in thermal plasma the range of pressures is limited to the region from 0.01 bar to 100 bar, and that of temperature to 298.15–50 kK. To obtain STF the method of partition function resulting from statistical mechanics was proposed. State of art in the given scientific area and theoretical basis of the statistical mechanics required for establishing of the proposed method together with discussion of partition function divergence problem have been reviewed. For the calculation of STF of diatomic molecules the method of direct summation has been employed, whereas, as for the larger size molecules, the rigid rotor and harmonic oscillator model have been generally adopted. The spectral data required for the calculations have been taken from literature, or, in selected cases, these have been computed by quantum chemistry ab initio techniques. The resulting STF have been included into already existing database system of thermodynamic properties and those can serve as input data for subsequent thermodynamic calculations. A general method has been worked out for the purpose of the computation of thermodynamic properties and composition of non-ideal homogenous plasma system in thermodynamic equilibrium. The method is based on minimizing total Gibbs energy to compute at constant pressure or Helmholtz energy to compute at constant volume. The computation algorithm was implemented into computer program and subsequently applied to the computation of the composition and thermodynamic properties of SF6 dissociation and ionization products using obtained STF.

Malgré sa disponibilité, la biomasse de troisième génération est peu utilisée pour la production d’énergie en raison notamment de sa forte contamination en métaux lourds. Afin d’améliorer la compréhension du comportement et de l’éventuel rôle catalytique ou inhibiteur de ces métaux au cours de la pyro-gazéification, et optimiser ainsi la valorisation énergétique de la biomasse contaminée, une approche intégrée expérimentale et thermodynamique a été utilisée. Pour mener à bien ces travaux, une méthode d’insertion dans le bois du métal spécifiquement étudié pour son rôle catalytique, le nickel, a été développée. Cette méthode permet de maîtriser la composition et l’homogénéité des échantillons étudiés, sans altérer la structure du bois. Les essais de pyro-gazéification de bois brut et contaminés dans un réacteur à lit fixe, montrent que, même à faibles teneurs en nickel (entre 0,016 et 0,086 mol/ kg de bois), celui-ci a une activité catalytique importante. Les analyses des phases gaz et solides confirment que l’augmentation de la teneur en Ni dans le bois favorise les réactions de pyro-gazéification qui ont ainsi lieu à des températures plus basses (d’environ 100 °C). En parallèle, une étude thermodynamique a été réalisée afin de conforter les résultats expérimentaux et d’aider à mieux comprendre le comportement des métaux lourds présents dans le bois. Les calculs thermodynamiques, basés sur la minimisation de l’enthalpie libre de Gibbs d’un système constitué de 28 éléments (C, H, O, N et 24 éléments mineurs ou traces), fournissent la spéciation et la répartition dans les différentes phases (gaz, liquides et cendres) des métaux lourds, dont le Ni. Ces calculs, et des analyses spécifiques, ont notamment permis de déterminer la spéciation chimique et physique du nickel au cours de la pyro-gazéification et fournir ainsi une base théorique à son activité catalytique en fonction de la température. / Despite its availability, contaminated biomass is not widely used for energy production due to its high contamination with heavy metals. Understanding the role and behavior of those heavy metals in the pyro-gasification process is a major scientific challenge for optimizing the thermochemical valorization of contaminated biomass. For this purpose, experimental and thermodynamic approaches were used. To carry out this work, a methodology for inserting the studied metal (nickel) in the wood matrix was developed without modifying its structure and controlling the composition and homogeneity of the studied samples. The pyro-gasification tests in a fixed bed reactor have shown that nickel has a catalytic performance even at low concentrations (between 0.016 and 0.086 mol / kg wood). The analysis of gas and solid products confirmed that the increase of Ni content in the wood generated a decrease in the samples pyro-gasification temperature by 100°C. In parallel, a thermodynamic study was conducted to confirm the experimental results and improve the understanding of heavy metals behaviors during pyro-gasification reactions. Thermodynamic calculations based on the Gibbs free energy minimization of a system consisting of 28 elements provide speciation and distribution in the different phases of heavy metals, including Ni. These calculations and specific analyses have made it possible to determine the chemical and physical speciation of nickel during pyro-gasification and thus provide a theoretical basis for its catalytic activity as a function of temperature.

[pt] Devido aos efeitos nocivos dos combustíveis de origem fóssil, cresceu o interesse no uso de fontes sustentáveis de energia, em particular os derivados da biomassa. O presente trabalho consiste no desenvolvimento de uma ferramenta de modelagem computacional da composição da mistura gasosa, chamado gás de síntese ou syngas resultante da gaseificação, baseado no equilíbrio termodinâmico. Assim, são avaliadas a flexibilidade, a confiabilidade e a estabilidade computacional das abordagens de equilíbrio estequiométrico e de minimização da energia livre de Gibbs para determinação das composições do syngas formado no processo. São investigados a influência da umidade relativa da biomassa (0, 20 e 40 por cento em base mássica), da temperatura de gaseificação (800, 1100 e 1400 K), da razão ar combustível em relação a estequiometria (0,2, 0,3 e 0,4) e da quantidade de oxigênio no agente de gaseificação (oxigênio puro, ar ou mistura equimolar dos dois) na composição do syngas, bem como nas eficiências energética e exergética, para biomassas compostas de carbono, oxigênio e hidrogênio. O melhor modelo é usado para otimizar a concentração de agente oxidante e de temperatura que maximizem a eficiência energética para biomassas com 20 por cento de umidade relativa no ar. Esses dados, estão usados para desenvolver modelos matemáticos preditivos usando o conceito de análise de misturas, cuja robusteza é avaliada por análise de variância (ANOVA). Esses resultados estão comparados com as simulações realizadas em um modelo teórico considerando a cinética das reações. Observou-se que o método usando a minimização da energia livre de Gibbs apresentou os melhores resultados para uma aproximação inicial, se tornando uma boa ferramenta para a fase de projeto. No entanto, é necessário desenvolvimento de outros modelos como cinético, CFD ou RNA para análises precisas da gaseificação. / [en] Due to the harmful effects of fossil fuels, interest in the use of sustainable energy sources, in particular those derived from biomass, has grown. The present work consists in the development of a computational modeling tool for the composition of the gas mixture, called synthesis gas or syngas resulting from gasification, based on thermodynamic equilibrium. Thus, the flexibility, reliability and computational stability of the stoichiometric equilibrium and Gibbs free energy minimization approaches are evaluated to determine the compositions of the syngas formed in the process. The influence of biomass relative humidity (0, 20 and 40 percent on mass basis), gasification temperature (800, 1100 and 1400 K), fuel air ratio related to stoichiometry (0.2, 0.3, 0.4) and the amount of oxygen in the gasification agent (pure oxygen, air or equimolar mixture of the two) are investigated in the composition of the syngas, as well as in the energy and exergy efficiencies, for biomasses composed of carbon, oxygen and hydrogen. The best model is used to optimize the oxidizing agent concentration and temperature that maximize energy efficiency for biomass with 20 percent relative humidity in the air. These data are used to develop predictive mathematical models using the concept of analysis of mixtures, whose robustness is assessed by analysis of variance (ANOVA). These results are compared with simulations performed in a theoretical model considering the reaction kinetics. the method using Gibbs free energy minimization presented the best results for an initial approximation, becoming a good tool for a design phase. However, it is necessary to develop other models such as kinetic, CFD or RNA for accurate gasification analysis.

The path explored in this thesis is testing a plasma temperature measurement approach that accounts for interference in a spectrum. The Atomic Emission Spectroscopy (AES) technique used is called Laser Induced Breakdown Spectroscopy (LIBS) and involves focusing a laser pulse to a high irradiance onto a sample to induced a plasma. Spectrally analyzing the plasma light provides a "finger print" or spectrum of the sample. Unfortunately, spectral line broadening is a type of interference encountered in a LIBS spectrum because it blends possible ionic or atomic transitions that occur in plasma. To make use of the information or transitions not resolved in a LIBS spectrum, a plasma temperature method is developed. The basic theory of a LIBS plasma, broadening mechanisms, thermal equilibrium and distribution laws, and plasma temperature methods are discussed as background support for the plasma temperature method tested in this thesis. In summary, the plasma temperature method analyzes the Full Width at Half the Maximum (FWHM) of each spectral line for transitions provided from a database and uses them for temperature measurements. The first implementation of the temperature method was for simulated spectra and the results are compared to other conventional temperature measurement techniques. The temporal evolution of experimental spectra are also taken as a function of time to observe if the newly developed temperature technique can perform temporal measurements. Lastly, the temperature method is tested for a simulated, single element spectrum when considering interferences from all the elements provided in an atomic database. From stimulated and experimental spectra analysis to a global database consideration, the advantages and disadvantages of the temperature method are discussed.

Over the past few decades, a growing interest in the thermal conversion of alternative fuels such as biomass and waste-derived fuels has been observed among the energy-producing companies. Apart from meeting the increasing demand for sustainable heat and power production, other advantages such as reducing global warming and ameliorating landfilling issues have been identified. Among the available thermal conversion technologies, combustion in grate-fired furnaces is by far the most common mode of fuel conversion. In recent years, Fluidized-Bed (FB) technologies have grown to become one of the most suitable technologies for combustion and gasification of biomass and waste-derived fuels.In spite of the benefits, however, some difficulties are attributed to the thermal conversion of the alternative fuels. Ash-related issues could be a potential problem, as low-grade fuels may include considerable concentrations of ash-forming elements such as K, Na, S, Ca, Mg, P, Si and Cl. These elements undergo many undesirable chemical and physical transformations during the thermal conversion, and often cause operational problems such as deposition-related issues, slag formation in furnaces, corrosion of the heat transfer surfaces, and bed agglomeration of the fluidized-beds. Ash-related problems in the utility boilers are a major concern that may result in decreased efficiency, unscheduled outages, equipment failures, increased cleaning and high maintenance costs.This thesis investigated the ash behavior and ash-related problems in two different FB conversion systems: a Bubbling Fluidized-Bed (BFB) boiler combusting solid waste, and a Dual Fluidized-Bed (DFB) gasifier using biomass as feedstock. Full-scale measurements, chemical analysis of fuel and ash, as well as thermodynamic equilibrium modeling have been carried out for the BFB boiler (Papers I-IV), to investigate the impact of reduced-bed temperature (RBT) and also co-combustion of animal waste (AW) on the ash transformation behavior and the extent of ash-related issues in the boiler. For the DFB gasifier (Paper V), a thermodynamic equilibrium model was developed to assess the risk of bed agglomeration when forest residues are used as feedstock.The experimental results showed that the RBT and AW co-combustion could decrease or even resolve the ash-related issues in the BFB boiler, resulting in a lower deposit-growth rate in the superheater region, eliminating agglomerates, and a less corrosive deposit (in RBT case). Thermodynamic equilibrium modeling of the BFB boiler gave a better understanding of the ash transformation behavior, and also proved to be a reliable tool for predicting the risk of bed agglomeration and fouling. The modeling of the DFB gasifier indicated a low risk of bed agglomeration using the forest residues as feedstock and olivine as bed material, which was in good agreement following the observations in a full-scale DFB gasifier.

In this thesis point defects in semiconductors are studied by electronic structure calculations. Results are presented for the stability and equilibrium concentrations of native defects in GaP, InP, InAs, and InSb, for the entire range of doping conditions and stoichiometry. The native defects are also studied on the (110) surfaces of InP, InAs, and InSb. Comparing the relative stability at the surface and in the bulk, it is concluded that the defects have a tendency to migrate to the surface. It is found that the cation vacancy is not stable, but decomposes into an anion antisite-anion vacancy complex. The surface charge accumulation in InAs is explained by complementary intrinsic doping by native defects and extrinsic doping by residual hydrogen. A technical investigation of the supercell treatment of defects is performed, testing existing correction schemes and suggesting a more reliable alternative. It is shown that the defect level of [2VCu-IIICu] in the solarcell-material CuIn1-xGaxSe2 leads to a smaller band gap of the ordered defect γ-phase, which possibly explains why the maximal efficiency for CuIn1-xGaxSe2 has been found for x=0.3 and not for x=0.6, as expected from the band gap of the α-phase. It is found that Zn diffuses via the kick-out mechanism in InP and GaP with activation energies of 1.60 eV and 2.49 eV, respectively. Explanations are found for the tendency of Zn to accumulate at pn-junctions in InP and to why a relatively low fraction of Zn is found on substitutional sites in InP. Finally, it is shown that the equilibrium solubility of dopants in semiconductors can be increased significantly by strategic alloying. This is shown to be due to the local stress in the material, and the solubility in an alloy can in fact be much higher than in either of the constituting elements. The equilibrium solubility of Zn in Ga0.9In0.1P is for example five orders of magnitude larger than in GaP or InP.

For many decades zirconium alloys have been commonly used in the nuclear power industry as fuel cladding material. Besides their good corrosion resistance and acceptable mechanical properties the main reason for using these alloys is the low neutron absorption. Zirconium alloys are exposed to a very severe environment during the nuclear fission process and there is a demand for better design of this material. To meet this requirement a thermodynamic database is useful to support material designers. In this thesis some aspects of the development of a thermodynamic database for zirconium alloys are presented. A thermodynamic database represents an important facility in applying thermodynamic equilibrium calculations for a given material providing: 1) relevant information about the thermodynamic properties of the alloys e.g. amount and composition of phases, oxygen activity, heat capacity etc, and 2) significant information for the manufacturing process e.g. heat treatment temperature. The basic information in the database is first the unary data, i.e. pure elements; those are taken from the compilation of the Scientific Group Thermodata Europe (SGTE) and then the binary and ternary systems. All phases present in those binary and ternary systems are described by means of the Gibbs energy as a function of composition and temperature. Many of those binary systems have been taken from published or unpublished works and others have been assessed in the present work. The elements included in the databse are: C, Fe, Cr, Nb, Ni, Mo, O, Si, Sn, and Zr + H, and the assessment performed under this thesis are: Cr-Sn, Mo-Zr, Sn-Zr, Fe-Nb-Zr and Nb-O-Zr. All the calculations have been made using Thermo-Calc software and the representation of the Gibbs energy obtained by applying Calphad technique with some use of ab initio calculations. / QC 20100902

There is a continuing interest in the subject of arene carbonylation, especially in strong acids and environmentally-benign alternatives are sought to HF/BF3 and to AlCl3 as conversion agents. Ionic liquids offer a powerful solvent for useful conversion agents such as aluminum chloride. The ILs permit AlCl3 to be used at lower HCl partial pressures than with other solvents. The superior reactivity demonstrated by acidic, chloroaluminate ILs is probably due to their enhanced solvation power for HCl and CO. Addition of HCl gas increased reactivity of the system by forming Brnsted acids, and toluene carbonylation is a Brnsted demanding reaction. It was found that reaction is stoichiometric in Al species and only intrinsically acidic ILs are active for toluene carbonylation, therefore it was possible to correlate observed conversion with predicted amounts of Lewis + Brnsted acids. Molecular modeling provided information about the different species present in these ILs and predicted 1H NMR, and 27Al NMR spectrum. Predictions suggested that three types of HCl species are present; and these predictions were confirmed using data of 13C-labeled acetone and its 13C-NMR spectra. These data showed that only one of the three types of HCl in the IL were super acidic. Reactivity towards arene formylation can be tuned by adjusting the ligands R and R in the organic cation and by changing the anion. This reactivity tuning can be exploited in a process where high acidity is required for the conversion of substrate but where separation of product from IL is facilitated by low acidity.

Lorsqu'une impulsion laser est focalisée sur une cible solide immergée dans un liquide, de la matière est vaporisée. La nucléation et la croissance ont lieu dans le liquide et des nanoparticules sont ainsi synthétisées. La méthode est très polyvalente puisqu'une grande variété de matériaux peut être générée. De plus, les nanoparticules sont directement stabilisées dans le solvant. L'ajout d'agent complexant n'est pas nécessaire mais peut tout de même permettre de mieux contrôler la taille des nanoparticules. Cependant, de nombreux processus sont mis en jeu durant la synthèse et l'objectif de ce travail doctoral est de développer la compréhension de ces éléments. Dans la mesure où l'ablation laser déploie une multitude d'´échelle de temps, il a fallu employer différentes méthodes pour élucider ces mécanismes. Pour commencer, je définirai un état de l'art de l'utilisation de l'ablation laser en milieu liquide et nos résultats concernant la synthèse d'aluminium oxyde dopé chrome. Par la suite, je présenterai la spectroscopie des plasmas et les questions sous-jacentes à la notion d'´équilibre dans un plasma moléculaire. Ensuite, je décrirai notre approche atomistique de la nucléation basée sur les techniques de chimie quantique. Enfin, je montrerai l'apport de l'utilisation des méthodes d'ombrographie pour mieux comprendre la thermodynamique du système au temps plus long. Notre étude démontre que la bulle formée suite à l'ablation laser est constituée essentiellement de molécule du solvant dont la quantité n'évolue quasiment pas au cours du temps de vie de la bulle / When a pulsed-laser is focused into a solid target immersed in water, the material is evaporated. Nucleation and growth occur in the liquid and nanoparticles are synthesized. The method can be considered as versatile because one can try to synthesize any kinds of materials. Also, the nanoparticles are directly stabilized by the solvant so there is no need of complexing agents. The nanoparticles are described as ligand-free. However, various processes can occur during the synthesis and the aim of my work is to understand these different components. Since the laser ablation in liquid displays a wide range of timescales, we used numerous methods to address this problem. First, I will present the use of plasma spectroscopy and the questions it raises towards local thermodynamic equilibrium. Then, I will describe our microscopic approach of nucleation based on quantum chemistry techniques. Finally, I will illustrate the advantages of shadowgraphic measurements to reach an hydrodynamic understanding of the system

This thesis presents the derivation of the theory leading to the determination of the governing equations of chemically reacting flows under local thermodynamic equilibrium, which rigorously takes into account effects of elemental (de)mixing. As a result, new transport coefficients appear in the equations allowing a quantitative predictions and helping to gain deeper insight into the physics of chemically reacting flows at and near local equilibrium. These transport coefficients have been computed for both air and carbon dioxide mixtures allowing the application of this theory to both Earth and Mars entry problems in the framework of the methodology for the determination of the catalytic activity of Thermal Protections Systems (TPS) materials.<p>Firstly, we analyze the influence of elemental fraction variations on the computation of thermochemical equilibrium flows for both air and carbon dioxide mixtures. To this end, the equilibrium computations are compared with several chemical regimes to better analyze the influence of chemistry on wall heat flux and to observe the elemental fractions behavior along a stagnation line. The results of several computations are presented to highlight the effects of elemental demixing on the stagnation point heat flux and chemical equilibrium composition for air and carbon dioxide mixtures. Moreover, in the chemical nonequilibrium computations, the characteristic time of chemistry is artificially decreased and in the limit the chemical equilibrium regime, with variable elemental fractions, is achieved. Then, we apply the closed form of the equations governing the behavior of local thermodynamic equilibrium flows, accounting for the variation in local elemental concentrations in a rigorous manner, to simulate heat and mass transfer in CO2/N2 mixtures. This allows for the analysis of the boundary layer near the stagnation point of a hypersonic vehicle entering the true Martian atmosphere. The results obtained using this formulation are compared with those obtained using a previous form of the equations where the diffusive fluxes of elements are computed as a linear combination of the species diffusive fluxes. This not only validates the new formulation but also highlights its advantages with respect to the previous one :by using and analyzing the full set of equilibrium transport coefficients we arrive at a deep understanding of the mass and heat transfer for a CO2/N2 mixture.<p>Secondly, we present and analyze detailed numerical simulations of high-pressure inductively coupled air plasma flows both in the torch and in the test chamber using two different mathematical formulations: an extended chemical non-equilibrium formalism including finite rate chemistry and a form of the equations valid in the limit of local thermodynamic equilibrium and accounting for the demixing of chemical elements. Simulations at various operating pressures indicate that significant demixing of oxygen and nitrogen occurs, regardless of the degree of nonequilibrium in the plasma. As the operating pressure is increased, chemistry becomes increasingly fast and the nonequilibrium results correctly approach the results obtained assuming local thermodynamic equilibrium, supporting the validity of the proposed local equilibrium formulation. A similar analysis is conducted for CO2 plasma flows, showing the importance of elemental diffusion on the plasma behavior in the VKI plasmatron torch.<p>Thirdly, the extension of numerical tools developed at the von Karman Institute, required within the methodology for the determination of catalycity properties for thermal protection system materials, has been completed for CO2 flows. Non equilibrium stagnation line computations have been performed for several outer edge conditions in order to analyze the influence of the chemical models for bulk reactions. Moreover, wall surface reactions have been examined, and the importance of several recombination processes has been discussed. This analysis has revealed the limits of the model currently used, leading to the proposal of an alternative approach for the description of the flow-surface interaction. Finally the effects of outer edge elemental fractions on the heat flux map is analyzed, showing the need to add them to the list of parameters of the methodology currently used to determine catalycity properties of thermal protection materials. / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished