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The Main Properties of Silicon Nitride

wallpapers Industry 2020-10-10
Silicon nitride is solid, especially hot-pressed silicon nitride, which is one of the most rigid materials in the world. It is incredibly resistant to high temperatures, and its strength can be maintained to a high temperature of 1200°C without falling. It will not melt into a melt after being heated, and will not decompose until 1900°C. It has excellent chemical resistance and can withstand almost all inorganic acids. And caustic soda solution below 30%, it can also resist the corrosion of many organic acids; at the same time, it is a high-performance electrical insulating material.

Silicon Nitride-Nature chemical formula Si3N4. White fine crystal; melting point 1900℃, density 3.44 g/cm (20℃); There are two variants: α type is hexagonal close-packed structure; β type is spar-like structure. Silicon nitride is grey when it has impurities or excess silicon.

Silicon nitride has almost no effect with water; it is slowly hydrolyzed in a robust acid solution to form ammonium salt and silicon dioxide; it is easily soluble in hydrofluoric acid and does not work with dilute acid. The full alkali solution can slowly corrode silicon nitride, and the molten alkali can quickly transform silicon nitride into silicate and ammonia. Silicon nitride can reduce transition metal (see transition element) oxides, lead oxide, zinc oxide, and tin dioxide at temperatures above 600°C, and release nitrogen oxide and nitrogen dioxide. The following reaction occurs between silicon nitride and calcium dinitride Ca3N2 at 1285℃:
Ca3N2+Si3N4─→3CaSiN2

There are several methods for preparing silicon nitride: reacting powdered silicon with nitrogen at 1300~1400℃; reacting pure silicon with ammonia at 1500℃;
The mixture of silicon dioxide and carbon is burnt in nitrogen-containing a small amount of hydrogen; the ammonolysis product Si(NH2)4 of SiCl4 is completely thermally decomposed. Silicon nitride can be used as a catalyst carrier, high-temperature resistant material, coating and abrasive.

Silicon nitride ceramics have the characteristics of high strength and high-temperature resistance. Among the ceramic materials, it has the best comprehensive mechanical properties, thermal shock resistance, oxidation resistance, abrasion resistance, and corrosion resistance. It is the first ceramic used in thermomechanical components—a candidate material. In the machinery industry, silicon nitride ceramics are used as bearing balls, rollers, ball races, moulds, new ceramic tools, pump plungers, mandrel sealing materials, etc.

In the chemical industry, silicon nitride ceramics are used as wear-resistant and corrosion-resistant parts, such as ball valves, pump bodies, combustion vaporizers, filters, etc.
In the metallurgical industry, silicon nitride ceramics are resistant to high temperatures, have low friction coefficients and are self-lubricating. It is stable for most metals and alloy solutions. Therefore, it can be used to make metal material processing tools and dies, such as dial mandrels, extrusion and wire drawing dies, rollers, transfer rollers, heating element fixtures, thermocouple sets, metal heat treatment supports, Crucible, aluminium liquid guide, aluminium lining, etc.


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Tag: Silicon Nitride