METHOD OF PREPARING SILICON NITRIDE WITH ELEVATED CONTENT OF ALPHA-PHASE Russian patent published in 1999 - IPC

FIELD: refractory materials. SUBSTANCE: invention is intended for tool-making industry and can be utilized when manufacturing high-temperature ceramics and refractory materials. Prepared is composition containing, wt %: silicon with particle size up to 30 mcm, 40; ammonium fluoride and chloride at weight ratio (1-7): (7-1), 8; and mixture of fine silicon dioxide with ammonium hydrodifluoride or ammonium hexafluorosilicate with weight ratio of silicon dioxide to either of the two latter 1:(1-5), 2. Silicon tetrafluoride in amounts below 5 vol % can also be added. Mixture is placed in reactor, which is sealed, filled with nitrogen to gage pressure 2 to 8 MPa, and mixture is thermally treated with microwave frequency mediation. Product is characterized by more than 96% alpha-phase content, 80% content of fiber-structured particles with fiber length larger than 10 mcm, 1 mcm in diameter, and specific surface larger than 6 sq.m/g. EFFECT: improved characteristic s of product. 4 cl, 1 tbl