Al₂O₃ coating for densification of SiC ceramics and sintering kinetics

Incorporation of additives into silicon carbide (SiC) ceramics in low temperature, atmospheric pressure sintering is challenging because uniform mixing of additives and raw SiC powders is quite difficult. Herein, an impregnation coating process in which a precise amount of Al₂O₃ is introduced to raw SiC granules on the nanoscale is described and high-performance SiC ceramics can be processed by atmospheric pressure sintering. The uniform coating promotes densification of SiC via enhanced liquid mass transfer and inhibits grain growth and recombination during sintering. The effects of the doping content on the ceramic structure and mechanical properties are studied. Coating a single layer of Al₂O₃ nano-particles on SiC particles yield the best interfacial activity, sintering density, and mechanical properties. The SiC sample with 7.5 wt% Al₂O₃ possesses the best properties such as a relative density of 97.98%, flexural strength of 434.40 MPa, fracture toughness of 5.23 MPa·m^1/2, and Vickers hardness of 28.21 GPa. The sintering kinetics analyzed by the isothermal sintering method fits the Singh model with an apparent activation energy of 574.64 kJ/mol. The sintering rate is governed by both the interface reaction and diffusion and the model and experimental results provide insights with respect to materials design and commercial batch production.