Dispersion, slip casting and reaction nitridation of silicon–silicon carbide mixtures

Abstract

The dispersing behaviour of silicon, silicon carbide and their mixtures in aqueous media were monitored by particle size, sedimentation, viscosity and zeta potential analyses as a function of pH of the slurry. The pH values for optimum dispersion were found to be 4 and 8 for silicon, 10 for SiC and 9 for Si+SiC mixtures. Optimum slips of Si+SiC mixtures were slip cast to obtain green compacts which were nitrided once at 1450°C for 2 or 4 h or successively and cumulatively for 8 (2+6) and 10 (4+6) h in a resistively heated graphite furnace. The binding phases in the nitrided products were found to be fibrous/needle like α-Si 3N 4, flaky grains of β-Si 3N 4 and Si 2ON 2. The products containing 19–47% of silicon nitride as bond/matrix possessed flexural strength (three-point bending) values of 50–85 MPa. ©