Abstract: High-purity .alpha.-type silicon nitride comprised of a granular crystal having an .alpha.-phase content of at least 95%, a nitrogen content of at least 38% by weight and an average particle size of not larger than 3 .mu.m is provided. This high-purity .alpha.-type silicon nitride is prepared by heating a nitrogen-containing silane compound at a temperature of at least about 1,300.degree. C. in a heating furnace comprised of a material containing a metal having a melting point exceeding 1,600.degree. C. and capable of being bonded with oxygen at the heating temperature.

Abstract: A noncurable sealing material from a hydroxyl end-blocked polydiorganosiloxane, a filler and a silane or siloxane with two hydrolyzable groups having silicon-nitrogen bonds or silicon-oxygen-nitrogen bonds. The material when mixed and stored under substantially anhydrous conditions remains fluid but when exposed to the moisture in air increases in viscosity to form a sealing material which is uncured.