Preparation of Dense SiC Ceramics by Aqueous Gelcasting

Concentrated SiC slurry with Y2O3 and Al2O3 as sintering assistants was prepared, by using the medium of gelcasting premix solution and pH adjusting reagent of TMAH (tetramethylammonium hydroxide). The measurements of Zeta potential, sedimentation and viscosity show that SiC, Y2O3 and Al2O3 can disperse well in premix solution at basic region. Rheological study clarifies that concentrated SiC gelcasting slurry has low viscosity and shear stress after adding 0.5wt% TMAH, which is suitable to cast into the mold. The green body formed by gelcasting was pressureless sintered at 2000℃for 1h. SEM image of SiC ceramic indicates that the structure of SiC sintered body is homogeneous and no obvious defects existing. The relative density, flexural strength, hardness and toughness of SiC sintered body are (98.1±0.2)%, (722±70)MPa, (20.18±0.75)GPa and (4.00±0.20)MPa·m1/2, respectively.