Doctor of Philosophy / Department of Chemical Engineering / James H. Edgar / The exceptional radiation resistance, high melting point, and wide energy bandgap (3.2 eV) of icosahedral boron arsenide, B[subscript]12As[subscript]2, make it an attractive candidate for applications in radiation intense environments, for example, in radioisotope batteries. These devices have potential lifetimes of decades rather than days or weeks that are typical of conventional chemical power cells. Solid state neutron detectors are another potential application of this semiconductor, as the boron-10 isotope has a high thermal neutron capture cross-section, orders of magnitude higher than most elements. To produce high quality crystalline B[subscript]12As[subscript]2 for these applications, this research focused on the epitaxy and electrical properties of B[subscript]12As[subscript]2 thin films. The major findings include the following. Twin-free heteroepitaxial B[subscript]12As[subscript]2 layers were obtained on m-plane 15R-SiC and c-plane 4H-SiC inclined 4° and 7° off-axis in the [1-100] direction. These substrates exposed asymmetric step-terrace surface structures that force B[subscript]12As[subscript]2 layers to adopt a single orientation, thus, twins were eliminated. Consequently, the crystal quality was greatly improved over films on on-axis c-plane 6H-SiC, yielding a maximum hole mobility of 80 cm[superscript]2V[superscript]-1s[superscript]-1, nearly 100 times higher than previously reported values. B[subscript]12As[subscript]2 epilayers grown at 1300°C had the lowest defect densities, smallest residual strains, highest mobility and highest deposition rate. Excess AsH[subscript]3 concentration was advantageous to prevent the loss of arsenic from the epilayer. Undoped B[subscript]12As[subscript]2 exhibited a variable-range-hopping conduction, indicating it was a highly disordered system. All films were p-type with a room temperature hole concentration on the order of 10[superscript]12~10[superscript]15cm[superscript]-3. The thermal activation energy of acceptors varied from 0.15 eV to 0.33 eV. The Hall mobility was dominated by impurity scattering at low temperatures and by polar phonon scattering at high temperatures. H, C, O and Si were the major impurities present in the undoped B[subscript]12As[subscript]2 films with concentrations on the order of 10[superscript]18~10[superscript]19 cm[superscript]-3. Si doping and annealing decreased the resistivity by up to two orders of magnitude. The density of localized states was small in the undoped B[subscript]12As[subscript]2 as the intrinsic acceptor levels (IALs) were compensated by the boron interstitials. However, in Si-doped B[subscript]12As[subscript]2, Si may prevent the interstitial boron atoms from compensating the IALs, yielding a decreased density of localized states. The Hall mobility of B[subscript]12As[subscript]2 epilayer was significantly reduced with increasing silicon concentration.

La mise en œuvre des réacteurs nucléaires du futur nécessite des températures de fonctionnement élevées sous flux de neutrons. Parmi les candidats envisagés pour les matériaux de structure et de gainage du combustible, les composites à matrice céramique de type SiCf/SiCm présentent un potentiel élevé. Dans ce cadre, les travaux de thèse ont consisté à étudier un procédé alternatif et innovant pour la réalisation de fibres de carbure de silicium, mettant en jeu le frittage de poudres de taille nanométrique.Une étude sur le frittage sans contrainte du SiC a été réalisée. Celle-ci a permis de définir des systèmes d’ajouts appropriés pour la densification et de maîtriser la microstructure du matériau final à partir (i) de l’analyse de l’influence des paramètres opératoires et (ii) du contrôle de la transition de phase SiC β  SiC α grâce à l’introduction d’éléments extérieurs.Des fibres « crues » SiC/polymère ont ensuite été élaborées par deux procédés de mise en forme : par extrusion d’une solution concentrée en polymère et chargée en nanopoudres et par filage et coagulation d’une suspension aqueuse de poudres nanométriques contenant un polymère hydrosoluble. Le frittage de ces dernières conduit à des fibres céramiques présentant un diamètre de l’ordre de cinquante micromètres. / Silicon carbide ceramic matrix composites (SiCf/SiCm) are of interest for high temperature applications in aerospace or nuclear components for their relatively high thermal conductivity and low activation under neutron irradiation. While most of silicon carbide fibers are obtained through the pyrolysis of a polycarbosilane precursor, sintering of silicon carbide nanopowders seems to be a promising route to explore.For this reason, pressureless sintering of SiC has been studied. Following the identification of appropriate sintering aids for the densification, optimization of the microstructure has been achieved through (i) the analysis of the influence of operating parameters and (ii) the control of the SiC β  SiC α phase transition. Green fibers have been obtained by two different processes involving the extrusion of SiC powder dispersion in polymer solution or the coagulation of a water-soluble polymer containing ceramic particles. Sintering of these green fibers led to fibers of around fifty microns in diameter.

Les réacteurs rapides à gaz font partie des différents concepts étudiés pour la production d’énergie nucléaire. Les composites SiC/SiC sont des matériaux particulièrement intéressant pour le gainage du combustible, grâce entre autres à leur résistance à la corrosion à haute température.Les mécanismes et les cinétiques d’oxydation du carbure de silicium dans les conditions normales de fonctionnement doivent être identifiés et quantifiés, dans la mesure où la corrosion peut dégrader les propriétés mécaniques du composite. Un système expérimental a été développé pour étudier l’oxydation du SiC à hautes températures et faibles pressions partielles d’oxygène. Il apparaît que dans de telles conditions expérimentales, des mécanismes de réaction interfaciale et de volatilisation viennent s’ajouter à l’oxydation parabolique. Les cinétiques de chaque mécanisme sont déterminées en fonction de la température et de la pression partielle en O2, et sont ensuite utilisées dans un modèle numérique de l’oxydation des composites. Le modèle est utilisé pour prédire la durée de vie du composite dans les conditions normales de fonctionnement d’un réacteur. / Gas Fast Reactor (GFR) is one of the different Generation IV concepts under investigation for energy production. SiC/SiC composites are candidates of primary interest for a GFR fuel cladding use, thanks to good corrosion resistance among other properties. The mechanisms and kinetics of SiC oxidation under operating conditions have to be identified and quantified as the corrosion can decrease the mechanical properties of the composite. An experimental device has been developed to study the oxidation of silicon carbide under high temperature and low oxygen partial pressure. The results pointed out that not only parabolic oxidation, but also interfacial reactions and volatilization occur under such conditions. After determining the kinetics of each mechanism, as functions of oxygen partial pressure and temperature, the data are used for the modeling of the composites oxidation. The model will be used to predict the lifetime of the composite in operating conditions.

Le développement des moteurs aéronautiques du futur a permis d’accentuer les recherches concernant les matériaux composites thermostructuraux SiC/SiC. La voie classique d’élaboration de ces matériaux consiste en l’infiltration de la matrice via un procédé par voie gazeuse. Due à leur porosité résiduelle importante, ces matériaux possèdent une faible conductivité thermique. Cette dernière peut générer de forts gradients thermiques pouvant entrainer une rupture prématurée de la pièce. Afin de réduire cette porosité, un procédé alternatif peut être utilisé : l’infiltration par du silicium liquide (procédé MI : Melt Infiltration). L’objectif de ce travail est de comprendre l’ensemble des mécanismes intervenant au cours de l’infiltration du silicium au sein d’une préforme fibreuse composée de fibres SiC Hi-Nicalon S. Ce procédé nécessite une étape en amont de l’imprégnation du silicium consistant en l’introduction de particules de SiC au sein de la préforme.La première partie de ce travail a consisté d’une part, en la définition de l’architecture poreuse des matériaux et, d’autre part, en la réalisation de tests de montée capillaire en utilisant des fluides organiques modèles. A l’aide de l’équation de Washburn, il est ainsi possible d’identifier des tailles de pores caractéristiques au sein de la préforme fibreuse et de la matrice granulaire et de prévoir le courbes d’ascension capillaire du silicium liquide au sein des matériaux. La seconde partie de ce travail décrit la mise en place d’un four permettant de réaliser le suivi in-situ de la prise de masse en silicium au cours du procédé MI. Une comparaison entre les résultats expérimentaux et les courbes prévisionnelles obtenues à l’aide de l’équation de Washburn a ainsi pu être effectuée. La dernière partie de ce travail a consisté en la réalisation d’essai d’imprégnation partielle afin d’identifier les mécanismes de montée capillaire du silicium liquide durant le procédé MI. / The development of aeronautic engines increased the need in high temperature SiC/SiC composite researches. A standard way to proceed is to infiltrate the matrix by chemical vapor infiltration. Due to their high porosity, their thermal conductivity is generally low. This could lead to strong thermal gradients and an early failure in a harsh environment. To reduce porosity, an alternative process can be used: the infiltration of molten silicon (MI: Melt Infiltration). The aim of this work is to understand all mechanisms occurring during the infiltration of silicon in a fibrous preform composed of SiC Hi-Nicalon S fibers. This process needs a first step which consists in the introduction of SiC particles into the preform before the MI process.First, this work focused on the definition of the porous structure of studied materials and capillarity tests using wetting organic solvent. With the use of Washburn’s law, it was possible to identify pore sizes within the fibrous preform and the granular matrix, and so to predict the capillarity ascent graphs of molten silicon into our material. A second part was devoted to the conception of an infiltration furnace which allows in situ following of the samples weight gain. The correlation between graphs obtained with the Washburn model and the experimental process could be established. Finally, the last part of this work presents partial infiltrations of molten silicon into studied materials which permit to identify capillary mechanisms occurring during the MI process.

Aujourd’hui les réacteurs d’irradiations technologiques (MTR) ont un rôle de premier plan pour l’industrie du nucléaire. Dans les réacteurs d’irradiation les niveaux de flux neutroniques et photoniques sont très importants. Un des besoins cruciaux des mesures en MTR est la mise en œuvre d’un dispositif de détection de rayonnement, précis, sélectif, fiable et robuste dans les conditions extrêmes de flux neutroniques et photoniques, et de températures élevées. Les semi-conducteurs à grande bande d’énergie interdite tels que le carbure de silicium (SiC) le diamant et le nitrure de gallium (GaN) possèdent des propriétés remarquables en termes de tenue en température et de résistance aux radiations. Cette thèse a pour principal objectif la comparaison des performances des détecteurs de neutrons dont les parties sensibles sont faites de carbure de silicium (SiC) avec celles des détecteurs basés sur le diamant pour la mesure de neutrons en conditions d’irradiation identiques. Pour cela nous avons réalisé les essais d’irradiation dans le réacteur de recherche de type maquette critique MINERVE au CEA Cadarache. Nous avons également testé les capteurs pour la détection des neutrons rapides de 14 MeV afin d’investiguer la future possibilité de mesurer en ligne des flux de neutrons rapides notamment pour les besoins de la fusion nucléaire (projet ITER). L’ensemble de ces travaux contribue à l’amélioration de la fonctionnalité du détecteur de neutrons en SiC, qui peut être augmentée en intégrant le détecteur à une électronique adaptée et aux outils spécifiques pour l’analyse du signal développés dans le cadre de cette thèse. / Nowadays, the material testing reactors (MTR) are playing a crucial role for nuclear industry. The research reactors allow carrying out the research on material damage and nuclear fuel advanced studies. Harsh radiation environment near the nuclear reactor core requires the radiation detectors to be resistant to high radiation level and high temperature. Neutron radiation detector for nuclear reactor applications plays an important role in getting information about the actual neutron flux. Most suitable semiconductors for harsh environment applications are SiC and diamond thanks to their outstanding properties. The aim of this thesis is to compare the ability of these two semi-conductors to detect neutrons. For this purpose, the neutron irradiation tests of detectors were implemented at MINERVE nuclear research reactor at CEA Cadarache. In this work we also studied the response of both materials to 14 MeV neutron beam with the prospect for future applications for fusion facilities. This work helps to improve the SiC-based detector characterization. The functionality of this detector could be enhanced by integrating it with appropriate radiation resistant electronics and tools for the signal analysis which was developed in the frame of this thesis

Neste trabalho é estudada a viabilidade de produção de dispositivos eletrônicos baseados em filmes semicondutores de carbeto de silício estequiométrico (a-Si0,5C0,5:H) obtidos por deposição química por vapor assistida por plasma, PECVD. A proposta do projeto envolve a realização de uma série de trabalhos que permitam avaliar as potencialidades do a-SiC:H para a fabricação de dispositivos semicondutores simples. Deste modo, desenvolvemos as principais etapas para a construção de dispositivos, as quais envolveram a dopagem elétrica por diferentes técnicas com a utilização de diferentes elementos dopantes, a corrosão seletiva por plasma e a obtenção um dielétrico apropriado e compatível com a tecnologia do SiC, bem como o desenvolvimento de processos de cristalização, que podem se mostrar fundamentais para melhorar as propriedades dos filmes de a-SiC:H. Com tais processos aprimorados, fabricamos estruturas MOSiC (metal-óxidocarbeto de silício) a partir do SiC cristalizado, utilizando como dielétrico de porta o SiO2 crescido por oxidação térmica (seca e úmida) dos próprios filmes de carbeto de silício cristalizados. Essas estruturas apresentaram o comportamento típico de um capacitor MOS, com regiões de acumulação, depleção e inversão bem definidas em todos os casos. Também fabricamos heterojunções de filmes de SiC tipo-p (como depositado e tratado termicamente) sobre substratos de Si tipo-n, os quais mostraram boas caracterísitcas retificadoras para as heteroestruturas formadas pelo a-SiC:H como-depositado e tratado termicamente a 550ºC. Além do mais, também projetamos, fabricamos, modelamos e caracterizamos transistores de filme fino de a-SiC:H. De acordo com as caracterizações elétricas observamos que podemos controlar a condutividade do canal, embora os dispositivos ainda precisem ser aprimorados para se obter melhores níveis de corrente. Vemos, portanto que, embora ainda tenham que ser aperfeiçoados, foram construídos com sucesso dispositivos eletrônicos semicondutores baseados em filmes de a-Si0,5C0,5:H obtidos por PECVD. / In this work we studied the viability to build devices based on stoichiometric amorphous silicon carbide semiconductor films (a-Si0.5C0.5:H), obtained by plasma enhanced chemical vapor deposition technique. The project proposal involves the realization of a series of studies that evaluate the potentialities of the a-SiC:H for the fabrication of simple semiconductor devices. In this way, we developed the main steps for the devices\' fabrication, which involved electric doping, by different doping techniques using different doping sources, selective plasma etching and the obtention of an appropriate and compatible dielectric for SiC technology. Besides, we performed crystallization processes that were essential to improve the properties of the amorphous films. By establishing the processes steps, we manufactured MOSiC (metal-oxidesilicon carbide) structures starting from crystallized SiC and using SiO2 as the gate dielectric, which was obtained by thermal oxidation (wet and dry) of the crystallized silicon carbide films. All the structures presented a typical MOS capacitor behavior, with accumulation, depletion and inversion regions well-defined in all the cases. We also fabricated heterojunctions formed by p-type SiC films (as-deposited and annealed) on n-type silicon substrates that showed good rectifying characteristics for as-deposited and annealed at 550ºC a-SiC:H films. Moreover, we designed, manufactured, modeled and characterized a-SiC:H thin film transistors. The electric characterization demonstrated that it is possible to control the channel conductivity; however, the devices still need to be improved to obtain better current levels. Although some improvement still need to be made, we built successfully electronic semiconductor devices based on a-Si0.5C0.5:H films obtained at low temperatures by PECVD technique.

Nesta tese discorremos sobre crescimento e caracterização de filmes finos de carbeto de silício amorfo hidrogenado (a-Si1-xCx:H) crescidos por deposição química de vapor assistida por plasma (PECVD). Os filmes foram depositados a partir de misturas de silano, metano e hidrogênio, no regime de plasma faminto por silano. Amostras depositadas nessas condições possuem uma maior concentração de ligações Si-C, ou seja, melhor coordenação entre átomos de Si e C, com menor quantidade de ligações C-Hn e Si-H, apresentando um conteúdo de hidrogênio da ordem de 20 at.%, e baixa densidade de poros. Foram analisadas e correlacionadas diversas propriedades dos filmes depositados, explorando-se a potência de rf e a diluição da mistura gasosa em hidrogênio, de forma a melhorar a ordem química, estrutural e morfológica na fase sólida. A composição dos filmes foi determinada por retroespalhamento de Rutherford e espectrometria de recuo frontal. Enfatizou-se a análise dos diferentes tipos de ligações químicas existentes no material por espectrometria no infravermelho por transformada de Fourier, o estudo das propriedades estruturais por espectroscopia de absorção de raios X na borda K do silício, e das propriedades morfológicas analisando-se os perfis de espalhamento de raios X a baixo ângulo para diferentes ligas depositadas. Foram também realizadas medidas de dureza e de microscopia eletrônica para uma amostra estequiométrica, de forma a complementar os demais dados obtidos. Filmes estequiométricos depositados nessas condições apresentam entre 80 e 90% do total de suas ligações entre átomos de Si e C e dureza Vickers de 33 GPa. Tratamentos térmicos entre 600 ºC e 1000 ºC, realizados em atmosfera inerte de N2, mostraram que filmes stequiométricos são mais estáveis frente à absorção de oxigênio. / In this work we discuss the growth and characterization of amorphous hydrogenated silicon carbide thin films (a-Si1-xCx:H) deposited by plasma enhanced chemical vapor deposition (PECVD). It was used a gaseous mixture of silane, methane and hydrogen, at the silane starving plasma regime. Samples grown at these conditions and with a very low silane flow have a larger concentration of Si-C bonds, that is, better coordination among Si and C atoms, with smaller amount of C-Hn and Si-H bonds, presenting a hydrogen content of about 20 at.%, and low density of pores. Material’s properties were correlated for the deposited films, exploring the rf power and hydrogen dilution of the gaseous mixture, aiming to improve the chemical, structural and morphological order in the solid phase. The composition of the films was determined by Rutherford backscattering and forward recoil spectrometry. The Fourier transform infrared spectrometry analysis studied the chemical bonding inside the material, X-ray absorption spectroscopy at the silicon K edge the structural properties in samples as-grown and after thermal annealing, and small angle X-ray scattering was used for the morphological characterization. The hardness was measured and transmission electron microscopy micrographs were taken for a stoichiometric sample, in order to complement the obtained data. Stoichiometric films presented a very high chemical order, having between 80 and 90% of their bonds formed by Si and C atoms and Vickers hardness of 33 GPa. Annealing processes between 600 ºC and 1000 ºC, performed in an inert N2 atmosphere, showed that stoichiometric films are more stable against oxygen absorption.

Atualmente, há uma forte demanda por cerâmicas como materiais estruturais para substituição de metais e ligas de elevada dureza e para uso em ambientes hostis. Dentre as famílias das cerâmicas estruturais, o SiC se destaca devido ao seu conjunto de propriedades: alta resistência à oxidação/corrosão, elevada resistência à abrasão, elevada condutividade térmica, baixa massa específica, elevada dureza, boa resistência ao choque térmico e manutenção da maioria destas propriedades em temperaturas elevadas. O processo Acheson se caracteriza, industrialmente, como o principal processo de síntese do SiC, consistindo em dois eletrodos sólidos, conectados a pó de grafite compactado, circundados por uma mistura de sílica e coque, em que o aquecimento é realizado eletricamente entre temperaturas de 2200 a 2600 oC [SOMIYA, 1991]. A formação do SiC é dependente da pressão parcial dos gases, da temperatura, do tamanho de grão dos reagentes, das propriedades individuais de cada grão, assim como da área de contato e do grau de mistura entre SiO2 e C [LINDSTAD, 2002]. O SiC produzido pelo processo Acheson contém impurezas como Al, Fe, Ti, Na, provindas da matéria-prima, que durante a síntese têm seu comportamento influenciado pela variação de temperatura. Partículas metálicas ou carbetos dessas impurezas estão distribuídos na matriz de SiC, sendo encontrados à medida que a temperatura diminui, com exceção do Al que se encontra em solução sólida com o SiC, substituindo os átomos de Si na rede cristalina [WEIMER, 1997]. Os objetivos deste trabalho se concentraram na caracterização e avaliação da influência da matéria-prima e das condições de processo no SiC obtido pelo processo Acheson. Podendo-se observar, através das análises químicas, mineralógicas e microestruturais, que a distribuição das impurezas, ao longo da secção transversal do SiC, é independente da matéria-prima precursora, sendo que estas se concentram nas regiões mais distantes do núcleo de grafite, porém seus teores são superiores para o SiC sintetizado a partir de uma matéria-prima menos pura, as quais ainda apresentaram temperatura de início do processo de oxidação do SiC pelo menos 50 oC menor, quando comparado ao SiC sinterizados a partir de matérias-primas com maior grau de pureza. / Currently, there is a strong demand for ceramics as structural materials to replace metals and alloys with high hardness for use in hostile environments. Among structural ceramics families, silicon carbide stands out due to its unique properties combination: high corrosion/oxidation resistance, high abrasion resistance, low density, high hardness, high thermal conductivity, good thermal shock resistance and maintenance of the majority of these properties at elevated temperatures. The Acheson process is industrially the main synthesis process of silicon carbide, consisting of two solid electrodes connected to compacted graphite powder, surrounded by a mixture of silica and petroleum coke, wherein the heating is performed electrically between 2200 to 2600 oC [SOMIYA, 1991]. The formation of SiC depends on the partial pressure of gases, temperature, reactants grain size, the properties of each individual grain as well as the contact area and the degree of mixing between SiO2 and C [LIDSTAD, 2002]. The SiC produced by the Acheson process contains impurities from the raw materials, such as Al, Fe, Ti and Na, which during the synthesis are influenced by the temperature gradient. Metal or carbides particles of these impurities are distributed in SiC matrix, being found as the temperature decreases, with exception of Al that forms solid solution with SiC by replacing the Si atoms in the crystal lattice [WEIMER, 1997]. The objectives of this work was the characterization and evaluation of the influence of raw materials and process conditions on the behavior of silicon carbide synthesized by Acheson process. It was observed, through chemical, mineralogical and microstructural analyzes, that the distribution of impurities along the cross section of synthesized SiC is independent of the raw material precursor, and these are concentrated in the most distant regions of the graphite core, but its contents are superior to SiC synthesized from a less pure raw material, which also showed a change in the beginning of the SiC oxidation process, at least 50 ° C lower, than the synthesized SiC from raw material with higher purity.

O carbeto de silício (SiC) é um material que apresenta baixa expansão térmica, altas resistências mecânica e ao choque térmico e alta condutividade térmica. Em razão disto é empregado na confecção de mobília de fornos de sinterização. O SiC no entanto sofre degradação a altas temperaturas quando submetido a atmosferas agressivas. A utilização de recobrimentos protetores evita a exposição direta da superfície do material à atmosfera dos fornos; a mulita pode ser um recobrimento protetor apropriado em razão de sua alta estabilidade em temperaturas elevadas e seu coeficiente de expansão térmica compatível com o do SiC (4x10-6/°C e 5,3x10-6/°C, respectivamente). No presente trabalho foi estudada a obtenção de recobrimento de mulita, para refratário de SiC, a partir da utilização de polímero precursor cerâmico e alumínio particulado. Foram preparadas composições com 10, 20, 30 e 50% (vol.) de alumínio adicionado ao polímero, sendo utilizados pós de alumínio de diferentes distribuições de tamanhos de partículas. As composições foram submetidas a diversos ciclos térmicos para determinação da condição mais adequada à obtenção de alto teor de mulita. A composição que apresentou melhor resultado foi a contendo 20% do pó de Al de menor tamanho de partículas. A partir desta, foi preparada e aplicada suspensão para ser aplicada sobre o refratário de SiC. A suspensão aplicada, após seca, reticulada e tratada termicamente a 1580°C, originou um recobrimento de mulita. Foram realizados ciclos de choque térmico em amostras com e sem recobrimento para comparação, num total de 26 ciclos. As condições foram 600°C/30 min. seguida de resfriamento ao ar até a temperatura ambiente. Após cada choque térmico, as amostras foram caracterizadas por microscopia óptica e eletrônica e determinado o módulo de elasticidade. Os recobrimentos apresentaram boa adesão e não foram detectados danos significativos após os choques térmicos. / Silicon carbide (SiC) presents low thermal expansion, high strength and thermal conductivity. For this reason it is used as kiln furniture for materials sintering. On the other hand, SiC degrades at high temperature under aggressive atmosphere. The use of protective coatings can avoid the right exposition of SiC surface to the furnace atmosphere. Mullite can be a suitable material as protective coating because of its high corrosion resistance and thermal expansion coefficient matching that of SiC (4,7 x10-6/°C e 5,3 x10-6/°C, respectively). In the present work a mullite coating obtained from ceramic precursor polymer and aluminium powder was studied to be applied over SiC refractories. Compositions were prepared with 10, 20, 30 and 50% (vol.) of aluminium powder added to the polymer. They were used aluminium powders with different distributions sizes These compositions were heat treated at different thermal cycles to determine a suitable condition to obtain a high mullite content. The composition with 20% of the smaller particle size Al powder was selected and used to be applied as a suspension over SiC refractory. The applied suspension, after dried, crosslinked and heat treated, formed a mullite coating over SiC refractory. Cycles of thermal shock were performed in coated and uncoated SiC samples to compare each other. They were carried out 26 cycles of thermal shock, in the following conditions: 600°C/30 min. and air cooling to room temperature. After each thermal shock, samples were analised by mean of optical and electron microscopy, elastic modulus was also determined. After thermal shock cycles the coating presented good adhesion and no significant damage were observed.

Este trabalho teve por objetivo obter revestimento de carbeto de silício para esferas combustíveis utilizadas em reatores nucleares do tipo FBNR, através da sinterização de SiC por reação com silício metálico (RBSiC). As matérias-primas foram moídas em moinho de bolas por 24 horas e as temperaturas utilizadas na sinterização foram de 1500° e 2000°C, durante tempos que variaram de 30 a 240 minutos. As amostras foram caracterizadas quanto a fases cristalinas, densidade, microestrutura e resistência mecânica. As peças sinterizadas a 2000°C apresentaram valores de resistência mecânica na faixa de 95 MPa, e densidade de cerca de 90% foram alcançadas, superiores aos valores encontrados para 1500°C.Foram obtidos revestimentos com as técnicas de gel casting e spin coating. A resistência mecânica desses revestimentos foi de, aproximadamente, 50% das amostras sinterizadas a 2000°C. / The aim of this work was to get covering of silicon carbide for use in nuclear fuel reactors of type FBNR, through the sintering of SiC by reaction bonded silicon carbide (RBSiC). The samples were homogenized in a ball mill and the sintering temperatures were 1500°C and 2200°C, during times that varied of 30 until 240 minutes. The product was characterized by crystalline phases, density, microstructure and mechanical resistance. The samples sintering at 2000°C had presented values of mechanical resistance around of 95 MPa, and density around 90%, better that samples sintering at 1500°C. Gel casting and Spin coating techniques had success in coverings process. The mechanical resistance of this coverings were around 50% of the samples sintering at 2000°C.