Low temperature densification of silicon nitride materials

Thin layers of oxides, corresponding to additions of up to 5 w/o Na2O have been deposited on the surface of grains of a commercial silicon nitride powder using alcoholic solutions containing appropriate amounts of the metal alkoxide. The resulting powders have been densified by hot pressing and pressureless sintering techniques, and their sintering characteristics identified in comparison with equivalent materials produced by adding the oxide in particulate form. In every case, a better sintering performance was observed at all temperatures for the oxide-coated materials, with ∼97% dense sintered materials being obtained at temperatures as low as 1400-1500 °C. Microstructures were observed using a S-2400 Hitachi Scanning Electron Microscope (SEM) and final microstructure was more uniform than that obtained by conventional method. It is concluded that the powder coating technique is an excellent method of homogeneously incorporating minor amounts of sintering additive into a powder.