Microwave sintering of Si3N4 based composites

The aim of this PhD dissertation is to investigate possible techniques for improvement of the limited dielectric properties of Si3N4-based ceramics through susceptor use and sintering aids, with the target of making them more suitable for microwave applications. To this end, the best susceptor (SiC-Silicon Carbide) is found from Comsol and FDTD simulations, using the dimensions of the rectangular cavity of the single mode microwave furnace used for the experiments. In the first stages of the experiments, sintering aids were not used; however, in later experiments TiN was added with the addition of 2.5 wt.%, 5 wt. %. and 17 wt. %. Furthermore, some experiments were made for Si3N4 powder with the additive of 5 wt% ZrO2. Dielectrical measurement has shown that using TiN as a sintering additive have, to some extent, demonstrably enhanced the dielectric properties of SiAlON, and allowed it to reach higher temperatures during the microwave processing, whereas, pure ZrO2 affected slightly the dielectric properties of Si3N4. The effect of microwaves on the phases, microstructure and mechanical properties were studied. Microwave and conventionally produced composite materials are compared, and the importance of this study is particularly emphasised in terms of energy and time saving.