2006 Volume 114 Issue 1327 Pages 247-252
A SiC powder of median size 0.8 μm was mixed with polyacrylic acid (PAA, dispersant) in a 0.3 mol/l-R(NO3)3 solution (R=Yb, Y, Gd, Sm, Nd and La) at pH 5 to adsorb uniformly the sintering additive (R3+ ion) on the SiC surface. The aqueous 30 vol% SiC suspension with 0.52 mass% PAA and 1.50 mass% R2O3 (as R(NO3)3), relative to SiC, was consolidated by filtration through a gypsum mold to form green compacts of 50-52% of theoretical density. The consolidated green compacts were densified with grain growth to 76-99% relative density by hot-pressing under a pressure of 39 MPa at 1950°C for 2 h in an Ar flow. The addition of R2O3 of smaller R3+ ion was effective to enhance the sinterability of SiC and also to achieve smaller grain size of SiC. This result was discussed based on the additional experiment result on the chemical interaction between SiC compact and the SiO2-R2O3 liquid. The average flexural strength and Weibull modulus of dense SiC were 612 MPa and 5.1, 719 MPa and 6.7, and 731 MPa and 9.8 for Gd2O3, Y2O3 and Yb2O3 addition, respectively.