Silicon nitride and preparation method thereof

Abstract

The invention relates to silicon nitride and a preparation method thereof. The preparation method of the silicon nitride comprises the following steps: performing gas atomization treatment on siliconparticles by using nitrogen to obtain silicon powder subjected to gas atomization; continuously nitrogen under the plasma state and the silicon powder subjected to gas atomization into a reactor, maintaining the temperature of the reactor to 1300 to 1450 DEG C, performing solid and gas separation and retaining solid; and adding alpha-phase silicon nitride, ammonium fluoride and ammonium iodide into the solid, mixing uniformly, vacuumizing, introducing mixed gas of nitrogen and hydrogen until the pressure is increased to the gauge pressure of 0.005 to 0.05 MPa, heating to 1200 to 1250 DEG C, continuously introducing the mixed gas of nitrogen and hydrogen until the pressure is increased to the gauge pressure of 0.01 to 0.1 MPa, maintaining the reaction time for 5 to 10 hours, and cooling after complete reaction to obtain the silicon nitride. The preparation method of the silicon nitride is a composite synthesis method. By the preparation method of the silicon nitride, high alpha-phase silicon nitride can be obtained.

Description

technical field [0001] The invention relates to the field of inorganic non-metallic materials, in particular to a silicon nitride and a preparation method thereof. Background technique [0002] Silicon nitride (Si 3 N 4 ) Ceramics have a series of advantages such as high hardness, high strength, wear resistance, high temperature resistance, small thermal expansion coefficient, large thermal conductivity, good thermal shock resistance and low density. They are used in ceramic engines, machining, microelectronics, and space science. And nuclear power engineering and other fields, has a very broad application prospects. Related products such as silicon nitride ceramic cutting tools, silicon nitride ceramic bearings, automotive engine valves, automotive turbochargers, heaters, various wear-resistant, high-temperature resistant, corrosion-resistant parts, etc. have been used in aviation, electronics, chemical industry, automotive Widely used in other fields. With the continuo...

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Problems solved by technology

[0008] The silicon dioxide carbothermal reduction method is to fully mix silicon dioxide powder and carbon powder, and use carbon to reduce silicon dioxide in a flowing nitrogen or ammonia atmosphere. This method uses silicon dioxide, which is very abundant in nature, as a raw material. Faster reaction rate, especially suitable for large-scale production, and the reaction product is a loose powder after heat treatment, the powder shape is regular, the particle size distribution is narrow, and there is no need for crushing treatment, thereby avoiding the re-introduction of impurities; for example, Germany Bayer reported in JP62241812 that silicon dioxide, carbon and ammonia were used to prepare silicon nitride at high temperature. The disadvantage is that at high temperature, silicon carbide may be generated, which directly affects the yield and purity of silicon nitride.

[0020] Because calcium fluoride and other substances are usually added in this method, the content of calcium and other metal elements in the powder after synthesis increases, which affects the performance of the powder, and the reaction process is under high pressure, which is not safe and requires harsh equipment. , not conducive to mass production

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