Preparation of SiC@Al2O3-Y2O3 core-shell nanoparticles by a slow precipitation method for dense SiC sintering

High sintering temperatures and high pressures are often needed for the densification of SiC. The sintering of SiC can be facilitated by adding Al2O3-Y2O3 oxides as the sintering additives. In the present study, the SiC@Al2O3-Y2O3 composite nanoparticles with a core-shell structure were designed and prepared using a slow co-precipitation method in the presence of urea. It was found that by slowing down the hydrolysis rate of the metal ions, Al(OH)(3) and Y(OH)(3) could be co-precipitated and uniformly coated on the surface of the SiC nanoparticles by a heterogeneous nucleation mechanism. After subsequent heat treatment, SiC@Al2O3-Y2O3 nanoparticles with amorphous Al2O3-Y2O3 layers of 2-3 nm were obtained. SiC ceramics with different oxides aids were prepared by sintering the core-shell nanoparticles at 1800-1900 degrees C under a pressure of 30 MPa. For SiC with higher additives of 20 wt%, evident volatilization of the oxide aids occurred at high temperatures with the segregation of the oxides. For the sample sintered at 1800 degrees C, dense SiC ceramics with uniform sintering aids distribution were obtained with the Al2O3-Y2O3 content as low as 5 wt% and a surface Vickers hardness of 31.5 GPa was obtained.