Silicon nitride is very strong, especially hot pressed silicon nitride, which is one of the hardest substances in the world. It is extremely resistant to high temperatures, its strength can be maintained to a high temperature of 1200 °C without falling, it will not melt into a melt after heating, it will decompose until 1900 °C, and it has amazing chemical resistance and can withstand almost all inorganic acids. And less than 30% caustic soda solution can also resist the corrosion of many organic acids; at the same time it is a high-performance electrical insulation material.
Silicon Nitride - Properties Chemical formula Si3N4. White powder crystal; melting point 1900 ° C, density 3.44 g / cm (20 ° C); there are two variants: α type is a hexagonal close packed structure; β type is a spar crystal structure. Silicon nitride is gray when it has impurities or excessive silicon.
Silicon nitride and water hardly act; slowly hydrolyze in a strong acid solution to form an ammonium salt and silica; soluble in hydrofluoric acid, and does not work with dilute acid. The concentrated alkali solution can slowly etch silicon nitride, and the molten strong base can quickly convert silicon nitride into silicate and ammonia. Silicon nitride at 600 ° C can reduce the transition metal (see transition element) oxide, lead oxide, zinc oxide and tin dioxide, and release nitrogen oxides and nitrogen dioxide. At 1285 ° C, the following reaction occurs between silicon nitride and tricalcium carbonate Ca3N2:
Ca3N2+Si3N4─→3CaSiN2
The method for preparing silicon nitride is as follows: reacting powdered silicon with nitrogen at 1300 to 1400 ° C; and reacting pure silicon with ammonia at 1500 ° C;
A mixture of silica and carbon is calcined in nitrogen containing a small amount of hydrogen; the aminolysis product Si(NH2)4 of SiCl4 is completely thermally decomposed. Silicon nitride can be used as a catalyst carrier, a high temperature resistant material, a coating, an abrasive, and the like.
Silicon nitride ceramics have the characteristics of high strength and high temperature resistance. They have the best comprehensive mechanical properties in ceramic materials, and have good thermal shock resistance, oxidation resistance, wear resistance and corrosion resistance. They are the first ceramics for thermal machine parts. A candidate material. In the machinery industry, silicon nitride ceramics are used as bearing balls, rollers, ball races, tooling, new ceramic tools, pump plungers, and mandrel sealing materials.
In the chemical industry, silicon nitride ceramics are used as wear 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 a low coefficient of friction, and are self-lubricating. It is stable to most metals and alloy solutions. Therefore, it can be used to make tooling for metal material processing, such as boring mandrel, extrusion, threading die, roll, transfer roller, heating fixture, thermocouple, metal heat treatment support. , , aluminum liquid guide camp, aluminum lining, etc.
Silicon nitride ceramic materials are also widely used in the electronics, military and nuclear industries.
Silicon nitride material properties
2019 10/28