Silicon nitride-silicon carbide nanocomposites prepared by water processing of commercially available powders

Abstract

Dispersion of nano-sized silicon carbide powders in silicon nitride was examined. Zeta potential was measured over a range of pH values and the aqueous dispersion of nano-sized silicon carbide powders in silicon nitride matrix was optimised. Ultrafine silicon carbide, 30–200 nm, which had agglomerated in organic media leading to a degradation in strength, was well dispersed and acted to reinforce silicon nitride matrix material. Densification of these nanocomposites was also examined. They were densified to 98–99% theoretical density by hot pressing, gas pressure sintering and pressureless sintering. Flexural strengths were measured and nanocomposites densified by the different routes were compared. Gas pressure-sintered nanocomposites had strengths comparable to the hot pressed materials. Gas pressure sintering was identified as a viable densification route for these materials as it does not have the size and shape limitations associated with hot pressing.