A new sintering additive for silicon carbide ceramic

Silicon carbide (SiC) ceramic with nanoscale silicon carbide powder and oxide (MgO+Al2O3+Y2O3) or nitrate salt [Mg(NO3)2+Al(NO3)3+Y(NO3)3] additives was hot-pressed at 1800 °C, 25 MPa, for 30 min. All the samples had fine, equiaxed microstructures with an average grain size less than 1 μm. The addition of nanoscale SiC did not effectively improve the relative density. Whether nano-SiC was added or not, the samples with nitrate salt additives had a higher relative density than their counterparts with oxide additives, and the maximum values were as high as 98.1 and 97.7%, respectively. Crystalline YAG phase was detected by XRD only in samples with nitrate salt additives, and the major phases in the oxide additive samples were the same 3C and 4H polytypes as those in the starting powders. Compared with the previous study, the elemental distribution of Y, Al, and Mg was more homogeneous in the oxide additive samples.