Dans le domaine du photovoltaïque, le composé Cu2ZnSnS4 (CZTS) serait une solution alternative aux composés classiques en couches minces qui sont à base d'éléments chers ou toxiques. Mise à part un gap de 1.5 eV et un coefficient d'absorption de 10-4 cm-1, il est constitué d'éléments bénins et abondants, ce qui réduira le coût de revient de la cellule finale. Il connaît un intérêt particulier et bien qu'il ait atteint un rendement de 12.6%, il demeure méconnu quant à l'effet de ses propriétés intrinsèques sur ses performances photovoltaïques. En raison de la volatilité du soufre, des déviations à la stoechiométrie peuvent être enregistrées rendant la synthèse d'un monophasé très difficile. Les phases secondaires sont difficilement inévitables, elles constituent une barrière à la formation de la phase CZTS, ce qui rend difficile la fixation du gap et augmente le taux de recombinaison des porteurs de charges. Dans le cadre de cette thèse, une série de composés CZTS a été synthétisée par réaction à l'état solide et liquide avec des excès en soufre pour compenser les pertes liées à la décomposition chimique et l'évolution de la composition dans le diagramme de phase Cu-Zn-Sn-S. L'effet du souffre sur la cristallinité, la pureté et l'ordre dans la maille a été mis en évidence. Le domaine monophasé a été déterminé et il a été montré qu'il est possible d'obtenir des composés de grande pureté. La morphologie par microscopie optique a révélé des polycristaux granulaires avec rejet des phases secondaires dans les joints de grains. Le composé Cu2ZnGeS4 (CZGS) pourrait trouver des applications dans le photovoltaïque et l'optoélectronique. L'ajout de l'étain pourrait sensiblement améliorer la cinétique réactionnelle et la cristallinité d'où l'intérêt d'étudier le composé Cu2ZnGexSn(1-x)S4 ( x=0 à 1). L'analyse cristallographique par DRX a montré une transition structurale d'une kesterite pour CZTS vers une orthorhombique pour CZGS. Le composé Cu2Zn(Ge,Sn)S4 est une solution solide avec gap de miscibilité entre 0 et 20% de germanium / In the photovoltaic field, Cu2ZnSnS4 (CZTS) compound is an alternative solution to substitute solar thin film based on toxically and expensive conventional materials. The gap of this material is around 1.5eV and absorption coefficient 10-4 cm-1, in addition this material is composed of abundant and harmless elements which will strongly decrease the price of the final cell. This material present a particular interest and in spite of the efficiency which reached 12.6%, till now this material is not well known especially the effect of its intrinsic properties on its photovoltaic performances. Because of the sulfur volatility, it is difficult to prepare single phase compound. Also, it is difficult to surmount the formation of secondary phases which are a barrier to CZTS complete reaction allowing difficulties to fix the gap and increase the recombination of carrier. In the frame of this PhD thesis, a serial of CZTS compounds has been synthetized from solid and liquid state using an excess of sulfur to compensate its volatility and the composition change in the Cu-Zn-Sn-S equilibrium diagram. We have determined the monophased field and we have shown that it is possible to obtain a compound with high purity. By optical microscopy we have observed a granular morphology composed of polycrystalline grains and the secondary phases were rejected in the grains boundary. The Cu2ZnGeS4 (CZGS) compound can be used for photovoltaic and optoelectronic applications. The addition of tin can be a good way to improve the kinetic reaction and the crystallinity of this materials, So, it is interesting to study Cu2ZnGexSn(1-x)S4 ( x=0 to 1) compound . By X ray diffraction we have shown a structure transition from Kesterite (CZTS) to orthorhombic (CZGS). The Cu2Zn(Ge,Sn)S4 compound is a solid solution with a gap miscibility between 0 and 20% of germanium

<p dir="ltr">Nanoparticles have seen immense development in the past several decades due to their intriguing physicochemical properties. The modern chemist is interested not only in methods of synthesizing nanoparticles with tunable properties but also in the chemistry that nanoparticles can drive. While several methods exist to synthesize nanoparticles, it is often advantageous to put nanoparticles on a variety of conductive substrates for multiple applications (such as energy storage and conversion). Despite enjoying over 200 years of development, the electrodeposition of nanoparticles suffers from a lack of control over nanoparticle size and morphology. Understanding that structure-function studies are imperative to understand the chemistry of nanoparticles, new methods are necessary to electrodeposit a variety of nanoparticles with control over macro-morphology but also microstructure. When a nanodroplet full of a metal salt precursor is incident on the electrode biased sufficiently negative to drive electroplating, nanoparticles form at a shocking rate (on the order of microseconds to milliseconds). We start with the general nuts-and-bolts of the experiment (nanodroplet formation and methods for electrodeposition). The deposition of new nanomaterials often requires one to develop new methods of measurement, and we detail new measurement tools for quantifying nanoparticle porosity and nanopore tortuosity within single nanodroplets. Owing to the small size of the nanodroplets and fast mass transfer, the use of nanodroplets also allows the electrodeposition of high entropy alloy nanoparticles at room temperature. Electrodeposition in aqueous nanodroplets can also be combined with stochastic electrochemistry for a variety of interesting studies. We detail the quantification of the growth kinetics of single nanoparticles in single aqueous nanodroplets. Nanodroplets can also be used as tiny reactors to trap only a few molecules, and the reactivity of those molecules can be electrochemically probed and evaluated with time. Overall, this burgeoning synthetic tool is providing unexpected avenues of tunability of metal nanoparticles on conductive substrates. Moreover, there is little understanding of how ion transfer can affect the fundamental of nanoparticle synthesis with nanodroplet-mediated electrodeposition. This thesis details different experiments performed to study the role of ion transfer during the nucleation and growth of nanoparticles.</p>

No description available.

Commercial alloys are continuously developed to improve their performance. Therefore it is important to develop new optimisation software, which could be used in development of new materials or in materials selection. In this study the mechanical properties which are important in materials selection in mechanical design are investigated. Two types of materials are analysed, aluminium alloys and stainless steels but focus will be on the aluminium alloys. Thermodynamic analysis has been used to evaluate the effect of the microstructure. Solid solution hardening has been successfully modelled for both aluminium alloys and stainless steels and follows the theories by Labusch and Nabarro. The precipitation hardening is most dominant for the hardenable aluminium alloys, but the non-hardenable alloys also increase their strength from precipitation hardening. The non-hardenable alloys are divided into tempers, which differ in the amount of strain hardening. This has also been modelled successfully. Combining these fundamental results with multiple regression, models for mechanical properties have been created. Separate models are developed for wrought aluminium alloys and stainless steels. For the aluminium alloys this includes the solid solution hardening and the precipitation hardening. For the stainless steels the thickness, nitrogen content and ferrite content are included together with the solid solution hardening. / QC 20101122

La compréhension et la maîtrise des mécanismes qui pilotent le vieillissement des aciers en présence d’une sursaturation de lacunes est un défi dans de nombreux domaines industriels, et particulièrement dans le cas des réacteurs nucléaires. Ces aciers contiennent invariablement des solutés interstitiels en tant qu’éléments d’alliage ou impuretés, et des lacunes (V) qui sont des défauts structuraux d’équilibre. Nous avons choisi le système Fe-V –X (X = C, N ou O) comme matériau modèle d’un acier ferritique. Au sein de ce système, des amas lacunes-solutés interstitiels sont susceptibles de se former car, malgré les concentrations très faibles de leurs constituants, ces amas présentent une énergie de liaison importante. Dans cette étude, nous avons tout d’abord cherché à calculer les propriétés intrinsèques d’équilibre de ces amas traités individuellement, à la fois leur propriétés thermodynamiques (énergie libre de liaison) et cinétiques (mobilité, taux de dissociation, ainsi que leur lien avec une description continue de la diffusion). Cette caractérisation effectuée à l’échelle atomique a ensuite permis de mettre en évidence différents effets de ces amas sur un système macroscopique contenant simultanément différents types d’amas : augmentation des limites de solubilité des solutés et de la concentration totale des lacunes en solution solide, couplage de flux entre lacunes et solutés, accélération des cinétiques de précipitation des solutés et dissolution des précipités par une stabilisation de la solution solide par les lacunes. Ces résultats ont été obtenus grâce au développement et/ou à l’extension de méthodes analytiques de physique statistique qui décrivent les constituants de ces amas et leurs interactions à l’échelle atomique. Enfin, nous nous sommes également intéressés aux cavités dans le fer-α, dont l’étude nécessite une approche différente de celle des petits amas. Entre autres, nous avons étudié les effets d’un réseau discret sur la forme d’équilibre d’une cavité, et décrit différents mécanismes d’évolution de ces objets à l’échelle atomique. / Understanding and monitoring the aging of steels under vacancy supersaturation is a challenge of great practical interest for many industrial groups, and most of all for those related to nuclear energy. These steels always contain interstitial solutes, either as alloying elements or as impurities, and vacancies (V) that are equilibrium structural defects of materials. We have chosen the Fe-V -X system (X = C, N or O) as a model system for ferritic steels. Vacancy-solute clusters are likely to form in such systems because, despite the very low concentrations of their components, these cluster show very high attractive bonding. First of all, we have been working on the computation of intrinsic equilibrium properties of individual clusters, both thermodynamic (free binding energies) and kinetic (mobilities, dissociation coefficients, and their relationship with continuum diffusion) properties. Thanks to this atomic-scale characterization procedure, we have been able to highlight various effects of these clusters on a macroscopic system containing different cluster types : increase of solute solubility limits and total vacancy concentrations, flux couplings between interstitial solutes and vacancies, acceleration of solute precipitation kinetics and precipitate dissolution by solid solution stabilization due to vacancies. These results would not have been obtained without the development and/or extension of analytical methods in statistical physics which are able to describe cluster’s components and their interactions at the atomic scale. Finally, we have also been working on cavities in α-iron, the study of which requires a different approach. Our study highlights the impact of the atomic discrete lattice on the equilibrium shape of cavities, and describes various kinetic mechanisms of these objects at the atomic scale.

Le recyclage des résidus organiques (RO) en agriculture pourrait permettre de limiter l’utilisation des ressources minérales de phosphore (P), à condition de déterminer leur efficacité pour fournir du P aux cultures. L’objectif de ce travail était donc d’étudier les mécanismes déterminant l’effet des RO apportés au sol sur la biodisponibilité du P pour la plante (phytodisponibilité). Ce travail a été basé sur cinq essais de terrain à La Réunion, fertilisés sur une décennie avec des fertilisants organiques ou minéraux, et sur des expérimentations d’incubations en conditions contrôlées et de cultures de plantes en pot. Le P inorganique (Pi) et organique (Po) disponible du sol a été déterminé par des extractions (eau, Olsen), la technique des diffusive gradients in thin films (DGT) et la dilution isotopique associée à des membranes échangeuses d’ions. La capacité de sorption en Pi des sols a été évaluée avec des courbes de sorption. Le P phytodisponible a été déterminé en mesurant le P prélevé par la plante. Dans les différents types de sol (andosol, andique cambisol, nitisol et arenosol), l’apport de RO a augmenté le Pi disponible relativement au Po, suggérant que la minéralisation du Po issu des RO n’est pas un facteur limitant la disponibilité du Pi. Les RO ont augmenté le Pi disponible principalement par l’augmentation du pH du sol et par conséquent la diminution de sa capacité de sorption de Pi. Le P phytodisponible a augmenté avec le Pi disponible du sol, mais a diminué avec l’augmentation du pH du sol. Au-delà de la dose de P, l’effet de l’apport de RO à long-terme sur la phytodisponibilité du P semble principalement contrôlé par l’évolution induite du pH du sol. / Application of organic residues (OR) on agricultural soils could reduce the use of mineral phosphorus (P) fertilizers, but this implies to determine the efficiency of OR to meet crop requirements. We thus aimed to study mechanisms determining the effects of OR on P bioavailability to plants (phytoavailability). Our work was based on five field trials with decadal organic or mineral fertilization located in Réunion island, and on incubations and plant growth experiments under controlled conditions. Available inorganic P (Pi) and organic P (Po) was determined using extractions (water, Olsen), the diffusive gradients in thin films technique (DGT) and the isotopic dilution associated to anion exchange membranes (EAEM). Phytoavailable P was determined as the plant P uptake. Soil Pi sorption capacity was determined using sorption curves. For all soil types studied (andosol, andic cambisol, nitisol, and arenosol), RO increased mainly available Pi and had few effects on available Po, which suggests that mineralization of Po applied with RO does not limit Pi availability. Application of RO increased available Pi mainly by increasing soil pH and consequently by decreasing soil Pi sorption capacity. Phytoavailable P increased with soil available Pi, but decreased with increasing soil pH. Our work suggests that except the dose of P applied, effect of RO on P phytoavailability depends mainly on soil pH changes induced.

No description available.

[1] Four specimens of zoned tourmaline from granitic pegmatites are characterised in detail, each having unusual compositional and/or morphologic features: (1) a crystal from Black Rapids Glacier, Alaska, showing a central pink zone of elbaite mantled by a thin rim of green liddicoatite; (2) a large (~25 cm) slab of Madagascar liddicoatite cut along (001) showing complex patterns of oscillatory zoning; and (3) a wheatsheaf and (4) a mushroom elbaite from Mogok, Myanmar, both showing extensive bifurcation of fibrous crystals originating from a central core crystal, and showing pronounced discontinuous colour zoning. Crystal chemistry and crystal structure of these samples are characterised by SREF, EMPA, and 11B and 27Al MAS NMR and Mössbauer spectroscopies. For each sample, compositional change, as a function of crystal growth, is characterised by EMPA traverses, and the total chemical variation is reduced to a series of linear substitution mechanisms. Of particular interest are substitutions accommodating the variation in [4]B: (1) TB + YAl ↔ TSi + Y(Fe, Mn)2+, where transition metals are present, and (2) TB2 + YAl ↔ TSi2 + YLi, where transition metals are absent. Integration of all data sets delineates constraints on melt evolution and crystal growth mechanisms. [2] Uncertainty has surrounded the occurrence of [4]Al and [4]B at the T-site in tourmaline, because B is difficult to quantify by EMPA and Al is typically assigned to the octahedral Y- and Z-sites. Although both [4]Al and [4]B have been shown to occur in natural tourmalines, it is not currently known how common these substituents are. Using 11B and 27Al MAS NMR spectroscopy, the presence of [4]B and [4]Al is determined in fifty inclusion-free tourmalines of low transition-metal content with compositions corresponding to five different species. Chemical shifts of [4]B and [3]B in 11B spectra, and [4]Al and [6]Al in 27Al spectra, are well-resolved, allowing detection of very small (< ~0.1 apfu) amounts of T-site constituents. Results show that contents of 0.0 < [4]B, [4]Al < 0.5 apfu are common in tourmalines containing low amounts of paramagnetic species, and that all combinations of Si, Al and B occur in natural tourmalines.

In South Africa, being the second largest global coal exporter, coal mining plays a pivotal role in the growth of our economy, as well as supplying our nation’s ever increasing electricity needs; while also accounting for more than 10% of the 20 x 109 m3 water used annually in the country. Coal mining may thus be classified as a large-scale water user; known to inevitably generate wastewater [acid mine drainage (AMD)] and other waste material, including fly ash (FA). Current and conventional AMD treatment technologies include precipitation–aggregation (coagulation/flocculation) – settling as hydroxides or insoluble salts. The process stream resulting from these precipitation processes is still highly saline, therefore has to undergo secondary treatment. The best available desalination techniques include reverse osmosis (RO), electro dialysis (ED), ion exchange and evaporation. All available treatment methods associated with raw AMD and its derived process stream fall prey to numerous drawbacks. The result is that treatment is just as costly as the actual coal extraction. In addition, remediation only slows the problem down, while also having a short lifespan. Research conducted into converting fly ash, an otherwise waste material, into a marketable commodity has shown that direct mixing of known ratios of FA with AMD to a pre-determined pH, erves a dual purpose: the two wastes (AMD and FA) could be neutralized and produced a much cleaner water (secondary co-disposal [FA/AMD]-process water), broadly comparable to the process water derived from precipitation-aggregation treated AMD. The collected post process solid residues on the other hand, could be used for production of high capacity ion exchange material (e.g. zeolite A, faujasite, zeolite P, etc.). The produced ion exchange material can subsequently be utilized for the attenuation of metal species in neutralized FA/AMDprocess waters. / Magister Scientiae - MSc

[1] Four specimens of zoned tourmaline from granitic pegmatites are characterised in detail, each having unusual compositional and/or morphologic features: (1) a crystal from Black Rapids Glacier, Alaska, showing a central pink zone of elbaite mantled by a thin rim of green liddicoatite; (2) a large (~25 cm) slab of Madagascar liddicoatite cut along (001) showing complex patterns of oscillatory zoning; and (3) a wheatsheaf and (4) a mushroom elbaite from Mogok, Myanmar, both showing extensive bifurcation of fibrous crystals originating from a central core crystal, and showing pronounced discontinuous colour zoning. Crystal chemistry and crystal structure of these samples are characterised by SREF, EMPA, and 11B and 27Al MAS NMR and Mössbauer spectroscopies. For each sample, compositional change, as a function of crystal growth, is characterised by EMPA traverses, and the total chemical variation is reduced to a series of linear substitution mechanisms. Of particular interest are substitutions accommodating the variation in [4]B: (1) TB + YAl ↔ TSi + Y(Fe, Mn)2+, where transition metals are present, and (2) TB2 + YAl ↔ TSi2 + YLi, where transition metals are absent. Integration of all data sets delineates constraints on melt evolution and crystal growth mechanisms. [2] Uncertainty has surrounded the occurrence of [4]Al and [4]B at the T-site in tourmaline, because B is difficult to quantify by EMPA and Al is typically assigned to the octahedral Y- and Z-sites. Although both [4]Al and [4]B have been shown to occur in natural tourmalines, it is not currently known how common these substituents are. Using 11B and 27Al MAS NMR spectroscopy, the presence of [4]B and [4]Al is determined in fifty inclusion-free tourmalines of low transition-metal content with compositions corresponding to five different species. Chemical shifts of [4]B and [3]B in 11B spectra, and [4]Al and [6]Al in 27Al spectra, are well-resolved, allowing detection of very small (< ~0.1 apfu) amounts of T-site constituents. Results show that contents of 0.0 < [4]B, [4]Al < 0.5 apfu are common in tourmalines containing low amounts of paramagnetic species, and that all combinations of Si, Al and B occur in natural tourmalines.