Low-cost preparation of Si 3N 4–SiC micro/nano composites by in-situ carbothermal reduction of silica in silicon nitride matrix

Abstract

SiC/Si 3N 4 nano/micro composites were prepared from a mixture of α-Si 3N 4, amorphous carbon (carbon black), and Y 2O 3 by carbothermal reduction of SiO 2 present at the surface of Si 3N 4 matrix grains, or added deliberately to the starting mixture. A special heating regime allowed the outgassing of CO(g) (a product of carbothermal reduction) and reduced the residual porosity to less than 2%. The inter- and intragranular SiC inclusions containing the amorphous oxygen-rich layer at the interface between SiC and the Si 3N 4 grains were present, originating from the reaction of free carbon with the silica melt. The reaction consumes silica in the grain boundary phase. The change of the grain boundary chemistry influences both room and high temperature properties of the nanocomposite.