PURPOSE: To produce a powdery silicon nitride capable of stably producing a silicon nitride ceramic having a high strength at high temperature with excellent reproducibility by specifying the weight ratio of β phase to α phase and the size of the crystallite.
CONSTITUTION: This powdery silicon nitride having 0.018 to 0.032 weight ratio of β phase to α phase and ≤0.2μm size of the crystallite can be produced, e.g. by calcining and crystallizing amorphous silicon nitride which is a thermal decomposition product of silicon imide while controlling the calcination conditions (packing density, rate of temperature rise, maximum holding temperature, holding time, etc.) to control the properties of the powder according to the imide decomposition method capable of arbitrarily controlling the properties of powder, e.g. ratio of crystal phases, content of internal oxygen, secondary particle size, primary particle size and specific surface area or by admixing 5 to 20wt.% powdery silicon nitride of ≥92% ratio of α phase and 2≥10m2/g specific surface area with powdery silicon metal having ≥10m2/g specific surface area and ≤1.0wt.% oxygen content, calcining the resultant mixture in an atmosphere of a mixture gas of H2 and N2 at 1400 to 1500°C while elevating the temperature at 10 to 50°C/h according to the direct nitriding method.
YAMAO TAKESHI
WATANABE KEIICHIRO
BESSHO HIROKI
NGK INSULATORS LTD