SILICON NITRIDE PREPARATION PROCESS Russian patent published in 2005 - IPC

FIELD: industrial inorganic synthesis.

SUBSTANCE: invention is directed to manufacturing very hard thermo- and chemically stable products. In particular, ferrosilicium with 50-95% Si is ground to particle size not greater than 0.1 mm and then mixed with silicon nitride and/or with ammonium chloride, and/or group II metal fluoride, and/or partial ferrosilicium combustion product containing 50-90% silicon nitride, 30-50% iron silicides, 4-16% iron, and up to 5% silicon. When ammonium chloride and group II metal fluoride are used together with each other their ratio will be (1-3):(3-1), respectively. Resulting mix is ground to particle size not greater than 0.1 mm. Powder is placed into reactor, which is filled with nitrogen to pressure 1 to 20 MPa. Burning reaction is the locally initiated and, at the end of it, nitrogen pressure is lowered to 0.1-20 MPa and diazotation reaction is conducted for 0.1-0.5 h. Cooled product is disintegrated and subjected to magnet separation for 0.5-1.0 h to separate iron, after which dissolved in 15-30% HCl. Undissolved precipitate is separated, washed, and dried. Silicon nitride thus obtained represents β-Si₃N₄ or mixture of α- and β-Si₃N₄ with 39.0-39.5% nitrogen and not more than 0.03% iron impurities.

EFFECT: enhanced process efficiency.

13 cl, 1 tbl