Dispersion, slip casting and reaction13; nitridation of silicon-silicon carbide mixtures

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 1450xB0;C for 2 or 4h or successively and cumulatively for 8 (2 + 6) and 10 (4 + 6) h in a resistively heated graphite furnace. The binding13; phases in the nitrided products were found to be 13; fbrous/needle like a-Si 3N4 , faky grains of (3-Si3N413; and Si2ON2 . The products containing 19-47% of silicon nitride as bond/matrix possessed fexural strength (three ppoint bending) values of 50-85 MPa. 1999 Elsevier Science Limited. All rights reserved