|M.Sc Student||Eran Gross|
|Subject||The Influence of Additives on Sintering and Microstructural|
Evolution of SiC
|Department||Department of Materials Science and Engineering||Supervisor||Full Professor Kaplan Wayne D.|
|Full Thesis text|
A pressureless solid phase sintering process for silicon carbide (-SiC 6H) was developed and optimized using boron and carbon as sintering additives. The as-received powder was ball-milled with the sintering additives and a deflocculant. After drying and sieving, the powder was compacted using uniaxial pressing followed by cold isostatic pressing. The green bodies were sintered in a carbon resistance furnace under flowing He at 2100°C. The influence of the sintering additives and sintering conditions on the density and microstructure were evaluated using scanning electron microscopy, transmission electron microscopy and density measurements. Undoped samples did not sinter, and the microstructure was characterized by particle coarsening and a film of SiO2. Samples sintered with only boron or carbon did not sinter. The carbon-doped samples had a microstructure which was similar to the undoped samples; containing coarsened particles, a porous microstructure, and an amorphous film containing silicon, carbon and oxygen. Samples doped with 0.5 wt.% boron and 3 wt.% carbon sintered to a density of 96% with a microstructure of mostly uniaxial grains.
The role of carbon in reducing SiO2 during solid-state sintering of SiC was directly shown using a model experiment, where transmission electron microscopy was used to follow oxidation and reduction of the surface of SiC single crystal. The lack of densification for undoped samples is explained by the low surface energy of SiO2 compared to the grain boundary energy of SiC, which reduces the driving force for densification.