Inorganic porous materials are widely used in a number of applications, where is a need to functionalize and produce materials with a multiscale porosity. The first part of the thesis describes how a novel and facile powder processing approach, using pulsed current processing (PCP) or, as it is commonly called, spark plasma sintering (SPS), has been employed to produce mechanically stable, hierarchically porous bodies from different porous powders. Surfactant-templated mesoporous spheres were PCP-treated to yield meso/macro porous monoliths. The bimodal pore size can be tailored by choice of templating molecules in the aerosol-assisted synthesis process and by the particle size of the spheres. Diatomite powders were used to produce macro/macroporous monoliths. The densification behaviour of this inexpensive and renewable macroporous raw material was evaluated in detail, and an optimum temperature range was identified where the PCP process yields mechanically strong monoliths. Binder-less, hierarchically porous zeolite monoliths were produced from various zeolite powders, e.g. silicalite-1, ZSM-5 and zeolite Y. Line-broadening analysis of X-ray powder diffraction data by the Rietveld method and electron microscopy showed that the formation of strong interparticle bonds during the PCP process is associated with a local amorphization reaction that is induced by the high contact stress and temperature. Xylene isomerisation studies showed that binder-less ZSM-5 monoliths display a high catalytic selectivity. Direct (in-situ) nanoparticle functionalization of surfactant templated mesoporous silica particles has also been demonstrated. Pre-synthesized TiO2 nanoparticles were dispersed in a precursor solution, containing surfactant and silica source, and processed in an aerosol-generator to produce spherical nanoparticle-functionalized mesoporous particles.

Thermal mismatch between different components of a system could be sources of problems like residual stress induced cracking, thermal fatigue or even optical misalignment in certain high technology applications. Use of materials with tailored thermal expansion coefficient is a counter-measure to overcome such problems. With its negative thermal expansion coefficient zirconium tungstate (ZrW2O8) is a candidate component to be used in synthesis of composites with controlled thermal expansion coefficient (CTE). ZrW2O8 is typically produced by solid-state reaction between zirconium oxide and tungsten oxide at 1200oC. However, it has been demonstrated that ZrW2O8 can also be synthesized using wet chemical techniques, which provide a superior chemical homogeneity that often extents down to the atomic scale, and the convenient means of controlling nucleation and growth of the primary crystallites. With the commonly adopted wet chemical approaches, it is possible to crystallize particles with sizes in the submicrometer range at temperatures as low as 600 oC or even lower. In these studies, precursors are aged either below 100 oC (7 days &ndash / 3 weeks), or at 160-180 oC under hydrothermal conditions (1&ndash / 2 days). Besides the obvious disadvantage in the ageing steps, use of tungsten sources with high cost in all approaches, constitutes the other disadvantage. Production of composites with tunable controlled thermal expansion (CTE) has been achieved by blending negatively and positively expanding materials in different proportions. In majority of these studies composites have been produced by conventional sintering methods. Spark Plasma Sintering (SPS) is a recent technique / in which sintering can be achieved at relatively low temperatures in short durations. There is only one study made by Kanamori and coworkers on the use of SPS in sintering of a composite, in which ZrW2O8 is one of the constituents [1]. This study aims the synthesis of ZrW2O8 particles and composites that possess tunable or zero CTE. A novel precursor recipe for ZrW2O8 synthesis was developed. In preparation of the precursor a total of 2 days of ageing and a temperature less than 100 oC was used. It was developed using a cost-effective tungsten source, namely tungstic acid and its final pH was lower than 1. The particles obtained from &lsquo / unwashed&rsquo / procedure had sizes in micrometer range, while those obtained from &lsquo / washed&rsquo / case had sizes in the range of 400-600 nm. These precursors could readily be crystallized at 600 oC, which in turn provided the desired particle sizes for composite applications. Experimental details on the precursor development are hereby presented with a discussion on the effects of solution parameters (i.e. solubility of tungstic acid, adjustment of the stoichiometry, ageing time) on the phase purity of the fired product. Zirconium oxide (ZrO2) has positive vi thermal expansion, therefore ZrW2O8/ZrO2 was selected as the composite system, and for their synthesis both conventional and spark plasma sintering methods were experimented. Composition ranges that provide composites with almost zero CTE&rsquo / s were determined. The composite having a composition of containing 35% ZrW2O8, 65% ZrO2, and 35 w/o Al2O3 and sintered at 1200 oC for 24 hours had an expansion coefficient of 0.20 x 10-6/K for conventional method, while the one having a composition of 55% ZrW2O8, 45% ZrO2 and sintered at 1000 oC for 5 minutes had an expansion coefficient of 0.94 x 10-6/K for spark plasma sintering method. For characterization of the products X-ray diffraction (XRD), scanning electron microscopy (SEM), photon correlation spectroscopy (PCS), and thermal and dilatometer analyses (DTA/TGA/DMA) were used.

<p>Ionic conductivity of metal oxides is critical for the function of a broad range of different components, such as electrolytes in solid oxide fuel cells and alloys designed for high temperature applications. In both cases the ionic conductivity can be studied by in situ impedance spectroscopy, which is also able to reveal information on the dielectric properties of the metal oxides, and in some cases the influence of their microstructure. The focus of this thesis is on impedance spectroscopy measurements of α-alumina in the temperature range 400-1000 °C. This metal oxide has found extensive use as the protective scale on heat resistant alloys. Some unpublished work on oxygen ion conductivity of yttria-stabilized zirconia is also included.</p><p>The low electrical conductivity of α-alumina can be a source for errors and misinterpretations during impedance spectroscopy measurements. A major disturbance originates from leakage currents that appear in the experimental setup. These leakage currents are due to conduction through the gas phase around the sample, conduction on the sample surface, or poor insulation in the sample holder. It was shown that below 700 °C, conduction on the sample surface could severely distort the measurement. The magnitude of the distortions appeared to be sensitive to the type of electrodes used. The use of a so-called guard electrode was shown to effectively block the surface conduction in the measurements.</p><p>Conductivity of metal oxides is known to be dependent on their microstructure. Generally it is believed that ionic conductivity is favoured along grain boundaries and dislocations. The influence of microstructure on conductivity was studied for α-alumina in the temperature range 400-1000 °C. The conductivity of a series of highly pure and dense samples with narrow grain size distributions was measured by impedance spectroscopy. It appeared that the activation energy for conduction increased with decreasing grain size.</p><p>Results based purely on impendence spectroscopy have some inherently weaknesses. For instance no information on the nature of the charge carrier can be found. Therefore the charge transport in single crystalline α-alumina was simulated by the molecular dynamics method. The results from the simulation were then compared to results from impedance measurements on single crystalline α-alumina. From the simulation it turned out that diffusion of aluminium ions had lower activation energy than diffusion of oxygen. The activation energy of oxygen was close to the measured activation energy, and the mobility of oxygen was higher than for aluminium. Therefore the dominating charge carrier was suggested to be oxygen ions.</p>

找尋新穎的熱電材料是現在許多物理、化學以及材料學家的熱門研究，熱電材料的益處在於可將生活中所產生的廢熱轉化成電能再度利用，可應用在於熱機或是冷凍機之上。 首先，在第一個研究之中，透過布理奇曼法在1050 ℃之下維持10個小時用以製作Cu0.01Bi2Te2.7Se0.3塊材，以及透過水熱法製造出Cu0.01Bi2Te2.7Se0.3奈米粒子，並且將兩種不同尺寸的粒子做不同比例的混合：奈米粒子(粒徑：20~100奈米)重量百分比0、10、20、30和100；接著探討火花電漿燒結法及奈米聚合物對熱電性質之影響。在實驗中發現材料中混入百分之三十的奈米粒子可提升熱電優質係數約一倍，由0.35提升至0.74。若是可以將起初塊材的熱電優質係數提升至較良好的0.7以上，再透過奈米聚合和燒結，其熱電係數在400 K左右是可以超過1的。由這個研究顯示出：火花電漿燒結以及奈米聚合是可以有效的提升熱電優質係數，其主要原因來自於成功的降低熱傳導係數並同時維持住原本所擁有的電阻率以及席貝克係數的提升，而熱傳導降低因於樣品中的奈米結構所造成的粒子邊界增加、晶格的不匹配導致抑制聲子的傳熱所形成的結果。 第二個研究為一樣是透過布理奇曼法在750 ℃之下維持12個小時用以製作BixSb2-xTe3塊材，其中x分別為0.4、0.45、0.5以及0.6，本實驗主要為探討Bi的量對於BiSbTe所造成的影響。由結果中顯示x高於0.5和低於0.5所呈現的熱傳性質的趨勢有些許不同。在x為0.45的塊材中，得到本實驗中在室溫之下，最佳的熱電優質係數1.5，獲得此結果的主要原因來自於相對較低的電阻率，並可觀察到x為0.45的載子濃度高於0.4、0.5和0.6的結果，其將可以佐證x=0.45塊材的低電組率所造成的優質係數提升。 / Physicists, chemists and material scientists at many major universities and research institutions throughout the world are attempting to create novel materials with high thermoelectric (TE) efficiency. It will be beneficial to harvest waste heat into electrical energy. Specialty heating and cooling are other major applications for this class of new TE materials. In the first study, bulk and nanoparticles of Cu0.01Bi2Te2.7Se0.3 were prepared separately. The Cu0.01Bi2Te2.7Se0.3 bulk was fabricated by Bridgeman method at 1050 ℃ for 10 hrs and the nanoparticles were made through hydrothermal method. Two kinds of powders were mixed with the ratios of NPs 0, 10, 20, 30 and 100 wt% and sintered by the SPS technique to form the composite specimens. The ZT value can be enhanced over 100% from 0.35 to 0.74 for specimen with 30 wt% nanoparticles. The consequence indicates that the SPS process and mixing nanocomposite can effectively enhance ZT value. The enhancements were caused mainly by the presence of nanostructured regions existing within the samples which lowered the thermal conductivity. The phenomenon is due to the presence of significant number of grain boundaries, shorten phonon mean free path and lattice mismatch. For another investigation, the BixSb2-xTe3 ingots with x=0.4, 0.45, 0.5 and 0.6. were fabricated by Bridgeman method at 750 ℃ for 12 hrs. We studied the effects of amount of Bi in BixSb2-xTe3 and the SPS process on the ZT enhancement. The experiment showed that for x >0.5, the thermal property changed from a curve to a relatively linear line at the end. The best ZT is 1.5 ingot at 300 K for x=0.45 specimen. The significant ZT improvement arises from the much-reduced electric resistivity. The lowest resistivity for x=0.45 specimen is mainly due to the highest carrier concentration than those with x=0.4, 0.5 and 0.6 ingots.

Fuel for nuclear reactors with an increased thermal conductivity offers the potential for lower fuel operating temperatures and reduced fission gas release rates. Uranium dioxide (UO2) based composites offer a method of achieving a higher thermal conductivity. Silicon carbide (SiC) and molybdenum (Mo) have been identified as potential candidates for use in a composite fuel material. Uranium dioxide composites were manufactured with the inclusion of whiskers and granules of SiC up to a 30 vol% loading. The manufacturing route used was based on the current process employed to commercially manufacture UO2 fuel, by reductive sintering. Composites containing Mo were manufactured via spark plasma sintering and included loadings of up to 10 vol% Mo. The composites were characterised on their microstructural properties and where appropriate the thermal conductivity was determined by laser flash analysis. The composites containing SiC achieved low densities, 95%TD. The microstructure contained channel like structures of Mo, due to the use of an agglomerated UO2 precursor powder. An increased thermal conductivity was determined for the molybdenum composites. At the maximum measurement temperature of 800°C the increase was found to be 68% in the 10 vol% composites compared to UO2.

[pt] O objetivo deste trabalho foi estabelecer uma metodologia de síntese de pós nanométricos a submicrônicos de Y2W3O12, como também relacionar as propriedades óticas, térmicas e mecânicas do Al2W3O12 com métodos distintos de sinterização. As partículas de Y2W3O12 foram obtidas pelo método de co-precipitação reversa modificada mantendo pH constante, com o intuito de manter a supersaturação elevada, garantindo alta taxa de nucleação evitando o crescimento indesejável dos núcleos. As metodologias para cristalização empregadas (tratamento hidrotérmico e calcinação) permitiram obter pós submicrônicos de Y2W3O12 (0.3 ̶ 0.5 Mm) com menor grau de aglomeração em relação ao previamente reportado na literatura. O envelhecimento da dispersão de Y2W3O12 revelou diminuição do tamanho médio de aglomerados em 50 por cento quando comparado à distribuição primária de aglomerados precursores. A dispersão utilizando surfactante CTAB reduziu a aglomeração em 50 por cento. O pó de Al2W3O12 foi sinterizado pelo método de spark plasma sintering (SPS) e comparado com Al2W3O12 sinterizado pelo método de três etapas 1. As propriedades óticas e mecânicas foram estudadas, revelando comportamento distinto entre os materiais consolidados por vias diferentes, evidenciando a importância do método de sinterização sobre a microestrutura final e sobre formação de defeitos pontuais. A espectroscopia de refletância difusa revelou que as amostras obtidas por SPS apresentam absorbância total na faixa da luz visível, sendo coerente com sua coloração preta fosca, assim, a energia de banda proibida dessas amostras situa-se abaixo da energia do espectro visível (EGAP menor que 1,7eV). A amostra sinterizada em três etapas, de coloração branca, possui absorbância parcial no UV-Vis, absorvendo todos os comprimentos de onda até 300nm e conforme o comprimento de onda aumenta e adentra na região visível a absorbância diminui e se torna nula. As amostras de SPS apresentaram ganho expressivo no módulo de Young (80 por cento) e dureza (61-116 por cento) quando comparado com o material obtido por sinterização convencional, previamente descrito na literatura 2, 1. As amostras de SPS quando comparadas com a amostra sinterizada em três etapas 1, apresentou módulo de Young 47 por cento maior e aumento de dureza entre 19-59 por cento, embora, ambas apresentem mesma densidade relativa de 96 por cento, sendo as amostras de SPS com microestrutura de grãos nanométricos proporcionando maior resistência mecânica. O CTE das amostras SPS foi medido, sendo similar ao valor encontrado para a amostra em três etapas 2, constatando que o CTE não foi afetado pela intorução dos defeitos pontuais na Al2W3O12 durante SPS. / [en] The aim of this work is to establish a methodology for the synthesis of submicron nanocomposites of Y2W3O12, as well as to relate the properties, optical and mechanical, of Al2W3O12 with different methods of sintering. The Y2W3O12 particles were obtained by the modified reverse co-precipitation method, maintaining a constant pH along the drip, in order to maintain a high super saturation, ensuring a high nucleation rate, avoiding the undesirable growth of the nuclei. As the methodologies for the crystallization used (hydrothermal treatment and calcination) allowed to obtain post-submicron of Y2W3O12 (0.3 - 0.5 Mm) with lower degree of agglomeration in relation to the report published in the literature. The aging of the dispersion was studied and showed a decrease of 50 percent the average size of agglomerates when compared to the primary distribution of precursor agglomerates. A dispersion using CTAB surfactant reduced 50 percent the agglomeration, as verified by characterization techniques. The Al2W3O12 powder was sintered by the Sintering of Spark Plasma method (SPS) and compared with Al2W3O12 sintered by the three-step method (TSS) 1. The optical and mechanics properties were studied, revealing a differentiated behavior between materials consolidated by different paths, evidencing the importance of the sintering method in a final microstructure. Diffuse reflectance spectroscopy showed that the samples obtained by SPS, it is able to absorb the total wavelengths in the visible light range, being consistent with its black matte color, so the energy gap is below the energy of the spectrum visible (EGAP less than 1.7 eV). The conventional (white) sample absorb all wavelengths up to 300 nm and increasing wavelength decreases absorption and renders it zero. The samples by SPS showed significant gain in the Young s modulus (80 percent) and hardness (61-116 percent) when compared to TSS sample 2, 1. The SPS samples when compared to TSS sample [1], the Young s modulus increased 47 percent and the hardness increased 19-59 percent, although both of them obtained 96 percent relative densities. The reason for the improve of mechanical properties of SPS samples is justified by nanosized grain microstructure providing greater mechanical resistance. The CTE of the SPS samples was measured, being similar to the value found for a three-step sample 2, noting that the CTE was not affected by the introduction of defects in Al2W3O12 after SPS.

L'allègement des structures est devenu un enjeu majeur pour les industries du transport. Afin de répondre à cette demande, une stratégie de recherche d'élaboration de nouveaux matériaux, présentant des propriétés spécifiques égalant a minima les propriétés des matériaux en service, a été mise en place. C'est dans ce contexte général que s'inscrivent ces travaux sur la phase MAX Ti3AlC2. La tenue à l'oxydation et les propriétés en traction et en fluage traction à haute température (800-1000°C) ont été évaluées pour des échantillons élaborés au cours de cette étude par métallurgie des poudres (frittage naturel + frittage flash). Les différents essais menés en oxydation ont montré l'existence de deux comportements (oxydation passivante ou catastrophique suivant la nature des oxydes formés) majoritairement contrôlés par les caractéristiques microstructurales des échantillons (taille de grains, nature des éléments en site A, rugosité et porosité). Les premiers essais de fluage traction réalisés sur la phase MAX Ti3AlC2 ont souligné la bonne ductilité de ces matériaux. De plus, les propriétés spécifiques sont comparables, voire dépassent, celles de superalliages polycristallins et d'aluminures de titane. Une étude multi-échelle a mis en évidence une déformation se produisant par glissement aux joints de grains à 900 et 1000°C et par mouvement de dislocations à 800°C. Un endommagement de type cavitation accompagné par des phénomènes d'oxydation de fissures en surface des fûts a été mis en lumière. / The lightening of structures has become a major challenge for transport industries. New materials with, at least, equivalent specific properties to currently used materials have been designed in order to cope with this challenge. In this regard, Ti3AlC2 MAX phase has been studied. The high temperature (800-1000°C) oxidation resistance and tension and tensile creep properties were assessed for Ti3AlC2 samples elaborated using a powder metallurgy process (pressureless sintering + spark plasma sintering). The various oxidation tests pointed out two different behaviors (protective oxidation or catastrophic one depending on the grown oxides nature) mainly controlled by samples microstructural features (grains size, elements on A site, roughness and porosity). The first tensile creep tests ever performed on Ti3AlC2 MAX phase indicates the high ductility of these materials whose specific properties reach or surpass those of polycrystalline superalloys and titanium aluminides. A multi-scale study highlights deformation mechanisms occurring through intergranular sliding at 900 and 1000°C and through dislocations glide at 800°C. Damage mechanisms occurring through cavitation supported by crack oxidation phenomena on gauge length surface were also underlined.

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No. of bitstreams: 1 teseDSFV.pdf: 5669668 bytes, checksum: 165ca1333f2345e5e1406b40a2c0548c (MD5) Previous issue date: 2016-04-08 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / In the case of composites materials, which presents the magnetoelectric coupling, there are so many questions about the influence of the microstructure on the coupled and uncoupled properties. Thereby, this work proposes the study of the grain size influence, of ferroelectric and magnetic phases, on the magnetic, electric and coupled properties in particulate magnetoelectric composites. In order to study the relationship property/microstructure in volumetric magnetoelectric composites, it was necessary to prepare samples with different average grain sizes, ie, the phases having average grain size in the order of micrometers or nanometers. To perform this study it was used as magnetic phase the CoFe2O4 and, as the ferroelectric phase, the [0,675] Pb(Mg1/3Nb2/3)O3 – [0,325] PbTiO3, mixed in molar ratio 20/80 %, using techniques like micro ball milling (to reduce particle size) and high energy ball milling (to mixture the phases) during the powder syntheses, and Spark Plasma Sintering (SPS) to densify the bulk. Due the presence of secondary phases in sintered composites generated during the application of SPS, a processing protocol was created based on a post sintering thermal treatment, in PbO rich atmosphere, which allowed the reduction of secondary phases without, however, changing the average size of grain. These procedures resulted in composite material suitable for the investigations of the electrical, magnetic and magnetoelectric properties, considering the different microstructures obtained. The magnetoelectric composites showed the self-biased effect arising from the intrinsic strain generated in one phase over the other. It was observed the properties dependence, coupled or uncoupled, with average grain size of both phases. Furthermore, the magnetoelectric composites presented the selfbiased effect that appears due to intrinsic strain generated from one phase over the other. Moreover, the evolution of the magnetoelectric coefficient behavior as a function of temperature and applied magnetic field has been more dependent on the variation of the average grain size of the ferroelectric phase than the ferrimagnetic phase, which can be attributed to the largest amount of ferroelectric phase in the structure compound. / No caso de materiais compósitos, que apresentam o acoplamento magnetoelétrico, existem muitas questões sobre influência da microestrutura nas propriedades independentes e acopladas das fases. Dessa forma, este trabalho propõe o estudo da influência do tamanho médio de grão, tanto da fase ferroelétrica quanto da magnética, nas propriedades elétricas, magnéticas e de acoplamento em compósitos magnetoelétricos particulados. Com o objetivo de estudar a relação propriedade / microestrutura em compósitos magnetoelétricos volumétricos, fez-se necessária a preparação de amostras com tamanho médio de grão distintos, ou seja, as fases possuindo tamanho médio de grão na ordem de micrômetros ou nanômetros. Para a realização deste estudo, foi utilizada como fase magnética o CoFe2O4 e, como fase ferroelétrica, o [0,675] Pb(Mg1/3Nb2/3)O3 – [0,325] PbTiO3, misturados na proporção molar 20/80, utilizando técnicas como micromoagem (para redução de partículas) e moagem de altas energias (para a mistura homogênea das fases) durante a síntese dos pós, e a de Spark Plasma Sintering (SPS) para a densificação dos corpos cerâmicos compósitos. Devido à presença de fases secundárias nos compósitos sinterizados, geradas durante a aplicação de SPS, foi criado um protocolo de processamento baseado em tratamento térmico pós-sinterização, com atmosfera rica em PbO, o qual possibilitou a redução das fases secundárias sem, contudo, alterar os tamanhos médios de grão. Tais procedimentos resultaram em material compósito adequado à realização das investigações das propriedades elétricas, magnéticas e magnetoelétricas, considerando as diferentes microestruturas obtidas. Os compósitos magnetoelétricos apresentaram o efeito self-biased, que aparece devido ao strain intrínseco gerado de uma fase sobre a outra. Foi observada a dependência das propriedades, acopladas ou não, com o tamanho médio de grão de ambas as fases. Além disso, a evolução do comportamento do coeficiente magnetoelétrico em função da temperatura e do campo magnético se mostrou mais dependente da variação do tamanho médio de grão da fase ferroelétrica do que da ferrimagnética, fato que pode ser atribuído à maior quantidade de fase ferroelétrica na estrutura do composto.

Afin d’éviter le relâchement d’iode 129 (déchet de moyenne activité à vie longue) dans l’environnement, un nouveau matériau incorporant l’iodate dans une hydroxyapatite phosphocalcique a été étudié. Deux méthodes de préparation de ce matériau ont été développées : élaboration par précipitation suivi d’un frittage SPS et élaboration par voie cimentaire. Une quantité pondérale d’iode (taux d’incorporation maximal de 10%mass.) est incorporé uniquement sous forme iodate dans la structure apatitique préparée à partir des deux méthodes d’élaboration. Un monolithe ayant un taux de densification de 88,6 % a été obtenu après mise en forme de poudres précipitées par frittage SPS. Ce matériau présente une résistance à la lixiviation satisfaisante, caractérisée par une vitesse d’altération initiale en eau pure à 50 °C de 10-2 g.m-2.j-1 (comparable à celle d’un verre R7T7 lixivié dans les mêmes conditions) et par une vitesse d’altération résiduelle à 50 °C de 10-5 g.m-2.j-1 dans l’eau souterraine d’un site potentiel de stockage. Dans l’ensemble, ce matériau est un candidat potentiel pour un conditionnement de l’iode radioactif. / In order to avoid the release of 129I (long-lived intermediate-level waste) in the environment, we describe a novel material incorporating iodate in a calcium phosphate based hydroxyapatite. This material is prepared by two synthetic processes: a wet precipitation route followed by a spark plasma sintering and a cementitious route. A high iodine content (with a maximum incorporation rate of 10 wt.%) is reached for both processes, by incorporation of the iodate in the apatitic structure. A monolith with relative density of 88.6% was obtained after shaping of the precipitated powders by spark plasma sintering. This material reveals satisfactory leaching properties, with an initial leaching rate in pure water at 50 °C of 10-2 g.m-2.j-1, and a residual leaching rate at 50 °C of 10-5 g.m-2.j-1 in underground water of potential geological repositories. All in all, this material is a potential candidate for the conditioning of radioactive iodine.

Les céramiques polycristallines transparentes de YAG (Yttrium Aluminium Garnet, Y3Al5O12) et de YAG dopé par des lanthanides (Nd, Er, Ho, etc.) ont des propriétés optiques comparables aux monocristaux et peuvent être utilisées comme milieu laser solide dans les lasers solides à haute capacité calorifique. L’utilisation de ces céramiques polycristallines transparentes présente de nombreux avantages comparés aux monocristaux. Ces matériaux ont une meilleure conductivité thermique et sont fabriqués à plus faible coût tout en présentant des propriétés mécaniques améliorées et ce, sur des pièces de plus grandes dimensions. De plus, il est possible d’atteindre de plus forts taux de dopage avec une répartition uniforme du dopant. Le dopage du YAG par l’erbium (0.25 %at.) permet une émission laser « eye-safe » de 1645nm. De plus, un faible taux de dopage permet d’éviter le phénomène d’upconversion lors de l’effet laser.Les conditions pour obtenir la transparence sont, entre autres, l’absence de défauts, une très grande pureté (>99.9%), une répartition de taille de grains homogène et une densité très élevée (>99.9%).Les céramiques transparentes sont obtenues par la voie métallurgie des poudres. La synthèse par voie chimique (co-précipitation, sol-gel, voie hydrothermale…) permet la production de poudres très pures, avec une taille de particules homogène et nanométrique, comparée à la synthèse par voie mécanique (broyage d’oxydes). Le frittage SPS (Spark Plasma Sintering) permet quant à lui une densification rapide, à plus basse température, empêchant ainsi une croissance excessive et anormale des grains lors de la densification. L’application d’un courant électrique de forte intensité associée à une charge uniaxiale permet d’accélerer la cinétique de frittage comparé aux méthodes de frittage conventionelles.Ce travail porte sur l’élaboration de céramiques polycristallines transparentes Er:YAG par la voie métallurgie des poudres. La synthèse de poudre est réalisée par co-précipitation inverse d’une solution de nitrates dans l’hydrogénocarbonate d’ammonium. L’influence des paramètres de synthèse tels que le pH, la concentration, le temps de maturation ou encore le cycle de calcination a été étudiée. Après optimisation des conditions de synthèse, des particules d’Er:YAG pur présentant une taille moyenne de 50nm ont été obtenues. L’étude des mécanismes réactionnels a été menée en associant différentes techniques de caractérisations en température telles que la spectrométrie IR, la diffraction des rayons X, ainsi que des analyses thermo-gravimétriques et différentielles. La formation de la phase YAG à 1050°C passe par la formation d’une phase intermédiaire, le YAP (Yttrium Aluminium Perovskite, YAlO3) à 900°C.Les poudres synthétisées ont ensuite été frittées par frittage flash SPS. L’étude de l’influence du cycle de frittage (température, charge, rampe, maintien) sur la microstructure et son optimisation a été réalisée à partir de poudre commerciale et a permis l’obtention de céramiques transparentes de diamètre 30mm et d’épaisseur 3mm. Un changement d’échelle a également été réalisé permettant la réalisation d’échantillons de diamètre 60mm d’une part, et d’épaisseur 6mm d’autre part / Yttrium aluminium garnet (YAG, Y3Al5O12) transparent ceramics have attracted much attention since it can replace single crystals as host materials in solid state heat capacity lasers. These polycrystalline ceramics present improved mechanical and spectroscopic properties, as well as a better heat conductivity, lower fabrication costs for larger size materials. Furthermore, it is possible to reach higher doping concentrations as well a uniform distribution. Doping YAG with Erbium (Er:YAG) allows eye-safe emission at 1645nm. Moreover, a low doping rate (0.5%at.) enables upconversion process during laser operation. Conditions for transparency are amongst others, the absence of defects, a high purity (>99.9%), an homogeneous grain size as well as a high density (>99.9%).Transparent polycrystalline ceramics can be obtained by powder metallurgy route. Powders, synthesized by chemical reactions such as sol-gel process, co-precipitation or hydrothermal methods, present some advantages like high purity, homogeneity and nano-sized particles compared to those obtained by solid-state reactions. A recent process called Spark Plasma Sintering (SPS) is presented to be a promising technique for the densification of nanostructured materials. Indeed, high current and pressure allow sintering at lower temperatures in shorter sintering time than in regular processes. Besides, rapid heating enables to limit excessive grain growth.In this study, Er:YAG nanopowders have been synthesized by co-precipitation using nitrates as precursors and ammonium hydrogen carbonate as precipitant. The influence of precipitation parameters such as pH, concentration, aging time, or even calcination temperature, has been studied. Er:YAG nanoparticles, with an average grain size of 30nm have been successfully synthesized. The reaction mechanisms have been investigated using different techniques such as infrared spectroscopy, x-ray diffraction, thermal analyses… The YAG phase is formed around 1050°C passing through an intermediate phase called YAP (Yttrium Aluminium Perovskite, YAlO3) at 900°C.Synthesized and commercial powders have been sintered to transparency using SPS device. Optimisation of the sintering conditions (temperature, load, heating rate, dwell time) have been realized using commercial powder. Transparent polycrystalline ceramic specimens with a 30mm diameter and 3mm thickness have been successfully obtained. A scale-up study enabled to produce samples with a diameter up to 60mm and also with 6mm thickness