Raw Material of Silicon Nitride Ceramic Bearing Balls in China is In Short Supply

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The main raw material of silicon nitride ceramic bearing ball is silicon nitride ceramic, which is overall in short supply in China.

Silicon nitride ceramic is a kind of inorganic material that does not shrink when sintering. It uses silicon powder as raw material. Firstly, shape into the desired shape using the commonly-used methods of shape-forming, then, conduct preliminary nitridation in nitrogen under the high temperature of 1200°C. Let part of the silicon powder react with nitrogen and form silicon nitride. At this time, the whole body will have already possessed certain strength. Conduct the second nitridation in the 1350°C-1450°C high temperature furnace to react into silicon nitride. By using hot pressed sintering method, the silicon nitride that is of 99% theoretical density can be made.

Due to its high melting point and strong high temperature stability to metal and oxide melts, silicon nitride (Si3N4) ceramic is increasingly being used in various fields of thermal engineering. For example, ceramic refractory slab made by combustion technology, roller, high-temperature bearing, turbine blade, and so on. Presently, silicon nitride ceramic is mostly researched, developed, and applied as high temperature structure and engineering material. Relatively mature products have been formed in machinery, chemical industry, metallurgy, aviation, energy, building materials, semiconductor, and other fields. China’s annual demand of silicon nitride is over 270000 tons. However, its domestic output is only about 100000 tons. Its supply is to a large extent inadequate to meet the demand in the market.

There are many techniques for preparing silicon nitride powder in the world. The representative ones are carbon thermal reduction and nitridation of SiO2 method developed by Dow Chem Co. in America and silica powder direct nitridation method commonly adopted around the globe. Internationally, Starck (Germany), AME (UK), Kemanord (Sweden), Nippon Denko, etc. are big manufacturers. Both of the two crafts need long nitriding time, usually 72 hours each cycle. The silicon nitride powder is also more expensive. The price of silicon nitride made by silicon powder nitridation method is 35USD/kg reported by America. The real average price of silicon nitride powder is 45USD/kg in the international market. Due to the factor of powder performance, the powder widely acknowledged by the international market is still products produced by The Ube in Japan (Ammonolysis method, price is 120USD/kg). In recent years, many companies in China have developed plasma method to prepare nanometer silicon nitride powder domestically. However, big industries are unlikely to be formed so far because of product prices and production scale problems.