<p>Pages that are darker in colour were scanned one at a time to produce a high quality image.</p> / <p>Following a review of the gas nitriding process, of the Fe-N system and of the formation of the compound layer, this study investigates the interaction between the diffusing nitrogen and the material to be nitrided.</p> <p>The formation of the compound layer and diffusion case is discussed for pure iron. AISI 1070 low alloy steel is investigated using different microstructures and the resulting effect on the nitrided microstructure is presented. The interaction of a nitride forming element is studied with a Fe/Fe-5Cr diffusion couple specimen. The strengthening mechanisms resulting from the nitriding process for all these materials are discussed using standard models from the literature. The scale of the precipitates produced in pure iron as well as in the 1070 steel pearlitic and spheroidized microstructure is found to provide marginal hardening. The interaction between N and carbides obtained during the nitriding of the 1070 martensitic microstructure gives rise to a significant hardness increase up to 130HV. The most significant hardening effect (up to 900HV) is obtained with the formation of a high density of fine CrN precipitates in the Fe-Cr specimens.</p> / Master of Applied Science (MASc)

[pt] O nitreto de gálio (GaN) é um dos mais interessantes e promissores materiais para aplicação em dispositivos óptico- eletrônicos. GaN pode ser usado para a fabricação de diodos e lasers azuis. O desenvolvimento deste tipo de material está relacionado com três campos principais: 1) deposição de camadas de GaN cristalino; 2) produção de nano- filamentos a partir de reações confinadas no interior de nanotubos de carbono; 3) síntese de GaN em pó por diferentes métodos químicos. Recentemente, novas técnicas de deposição adotaram a sublimação de pós de GaN como fonte de gálio para a produção de nanofilamentos de GaN, filmes finos ou cristais. Estes métodos de sublimação mostram a necessidade do emprego de pós de GaN. No presente trabalho, é apresentada uma nova rota para a produção de pós de GaN a partir da reação gás-sólido entre Ga2O3 e NH3(g) utilizando o carbono como agente redutor no interior de um novo tipo de reator, disposto verticalmente. A partir desta rota obteve-se pós de GaN com conversões aproximadamente de 100% e com estrutura cristalina hexagonal. A quantidade de GaN obtida variou de acordo com os parâmetros experimentais adotados. Através de uma análise estatística foi possível determinar a influência da temperatura, razão molar de carbono/Ga2O3 e do tempo experimental sobre a taxa de produção de GaN. / [en] It is well known that gallium nitride (GaN) is one of the most interesting and promising materials for optoelectronic devices. GaN can be used for manufacturing blue light- emitting diodes and lasers. Development of this material is concerned with three main areas 1) deposition of GaN crystalline layers onto different substrates; 2) manufacturing of GaN nanorods from chemical reactions in the confined spaces provided by carbon nanotubes; 3) synthesis of GaN powders by different chemical methods. Recently, new deposition techniques have adopted sublimation of GaN powders as gallium source to produce GaN nanorods, thin films or bulk crystals. These sublimation methods rely on the supply of GaN powders. This thesis presents a new route to produce GaN powder from gas-solid chemical reaction between Ga2O3 and NH3 using carbon as reducing agent in a new reactor design. The GaN powder obtained from this route possesses a hexagonal crystal structure and was found to correspond to almost 100% conversion of Ga2O3. The amount of GaN present in the powders varied with experimental parameters. A statistical analysis showed the influence of temperature, carbon/Ga2O3 ratio and experimental time on the production of GaN powder.