Silicon Nitride Ceramic Preparation And Application
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Update time : 2021-11-22 09:41:51
Silicon nitride ceramic is an inorganic material ceramic that does not shrink during sintering. Silicon nitride is very strong, especially hot-pressed silicon nitride, which is one of the hardest materials in the world. It has high strength, low density, high temperature resistance and other properties.
Silicon Nitride Ceramic Preparation
The preparation process of Si3N4 ceramics is mainly concentrated in the reaction sintering method, hot pressing sintering method, atmospheric sintering method, air pressure sintering method and other types.
Reaction sintering method (RS)
It adopts the general forming method. First, the silicon powder is pressed into a green body of the required shape, and it is put into a nitriding furnace and subjected to pre-nitriding (partial nitriding) sintering. The pre-nitrided green body already has a certain strength. Various mechanical processing (such as turning, planing, milling, drilling) can be carried out. Finally, the temperature above the melting point of silicon; the green body is fully nitrided and sintered again to obtain a product with little dimensional change.
Hot Press Sintering (HPS)
It uses Si3N4 powder and a small amount of additives (such as MgO, Al2O3, MgF2, Fe2O3, etc.) at a pressure above 1916 MPa and a temperature above 1600 ℃ for hot press molding and sintering. The mechanical properties of Si3N4 ceramic produced by hot pressing sintering method are better than that of reaction sintered Si3N4, with high strength and density.
Atmospheric pressure sintering method (PLS)
In terms of increasing the pressure of the sintering nitrogen atmosphere, it uses the properties of Si3N4 to increase the decomposition temperature (usually at N2 = 1atm, starting from 1800°C). After atmospheric sintering in the temperature range of 1700-1800°C, then, air pressure sintering is carried out in the temperature range of 1800-2000°C.
Air pressure sintering method (GPS)
Air pressure sintering of silicon nitride is carried out at a pressure of 1 to 10 MPa and a temperature of about 2000°C. The high nitrogen pressure suppresses the high temperature decomposition of silicon nitride. Due to the use of high temperature sintering, with less sintering aids, it is sufficient to promote the growth of Si3N4 grains, and obtain a high toughness ceramic with long columnar grains with in-situ growth with a density of> 99%.
Silicon Nitride Ceramic Application
Silicon nitride ceramics have excellent mechanical properties, wear resistance, corrosion resistance and other excellent properties, which make it widely used in many industrial fields such as metallurgy, machinery, energy: semiconductor, chemical industry, aerospace, and so on.
In mechanical engineering, silicon nitride ceramics can be used to manufacture bearings, cutting tools, high-temperature bolts, drawing dies, ball valves, plungers, sealing materials, nozzles, etc.
Compared with cemented carbide tools, hot-pressed sintered silicon nitride ceramic tools have 5-15 times higher durability and 3-10 times higher cutting speed. By compounding TiC, ZrC, etc., dispersion strengthening can further improve the performance and life of silicon nitride tools.
Silicon nitride ceramic has excellent mechanical properties, both wear resistance and self-lubricating. It is an excellent bearing material and has a longer life than other ceramic bearings. It is resistant to high temperature and corrosion, and can work in harsh environments.
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