METHOD OF OBTAINING CHARGE MATERIAL FOR SYNTHESIS OF SILICON NITRIDE Russian patent published in 2012 - IPC C01B21/68 C04B35/58 C04B35/628 

FIELD: chemistry.

SUBSTANCE: invention relates to powder technology and is meant for producing, via self-propagating high-temperature synthesis, silicon nitride with high content of basic substance, fine particle size of the basic mass with considerably narrow grain-size distribution. The method involves mixing powdered silicon and silicon nitride as a diluent, wherein a filling layer of silicon powder is first formed, silicon is then activated by autogenous grinding of particles in a high-speed jet of compressed gas, e.g., nitrogen or air, at excess pressure of not less than 6 kg/cm² for not less than 2 recycles of the charge mass with movement thereof by an ascending gas stream from the filling layer to the zone of centrifugal forces generated by the rotor of a centrifugal classifier; the powdered material is recycled by outputting the coarse fraction from the zone of centrifugal forces and returning to the filling layer; air-centrifugal separation of particles smaller than 5 mcm is carried out, after which in the nitrogen jet, activated silicon is mixed with powdered silicon nitride having average particle size δ₅₀ smaller than 1 mcm and distribution function width Span=(δ₉₀-δ₁₀)/δ₅₀ of not more than 2, in amount of 10-25% of total weight, for 7-8 recycles at excess nitrogen pressure of not less than 4 kg/cm², where δ₅₀ is the size where particles of smaller size account for weight ratio of 50% (average particle size), δ₁₀ is the size where particles of smaller size account for weight ratio of 10% and δ₉₀ is the size where particles of smaller size account for weight ratio of 90%. As a result, silicon nitride is obtained in form of a fragile sinter from fine particles while significantly cutting the amount of inert diluent in the charge material and increasing output of the end product.

EFFECT: method enables to increase efficiency and carryout synthesis with low nitrogen pressure, which makes SHS technology safer.

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