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In this paper, the influence of the starting powder characteristics for five commercial Si 3 N 4 powders on sintering behavior, microstructure and mechanical properties of hotpressed Si 3 N 4 ceramics with and without the addition of La 2 O 3 -Yb 2 O 3 -MgO sintering additives was investigated. For the system without sintering additives, the high amount of the impurities in the starting powders could facilitate the densification process and promote β-Si 3 N 4 grain growth. However, large whisker-like particles (α phase) present in the initial powders inhibited the sintering process, which led to a lower density of Si 3 N 4 ceramics. On the other hand, when the sintering additives were introduced in the beginning stage of the powder processing step, the effects of impurities content and particle morphology in the initial powders on the densification and microstructure were not apparent. There was tendency that finer powder size resulted in finer microstructure. However, a high α-phase ratio in the initial powders could accelerate the abnormal grain growth and thus lead to better mechanical properties.

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