Home > News > Production process of silicon nitride products

Production process of silicon nitride products

wallpapers News 2020-05-18
Silicon nitride products can be divided into reaction sintering products, hot pressing products, normal pressure sintering products, isostatic pressing sintering products and reaction refiring products. Among them, reaction sintering is a common method to produce silicon nitride refractory products. 
Reaction sintering method is used to produce silicon nitride products by grinding fine silicon powder (the particle size is generally less than 80 meters) and forming it by machine pressure or isostatic pressure. After the green body is dried, it is heated to 1350 ~ 1400℃ in nitrogen gas and nitriding is produced at the same time in the process of sintering. In this production method, the raw material conditions, firing process and atmosphere conditions have great influence on the performance of the products. 
Silicon powder contains many impurities, such as Fe, Ca, Ai, Ti, etc. Fe is considered a catalyst in the reaction process. It can promote the diffusion of silicon, but at the same time, will also cause defects such as pores. The main role of Fe as an additive: it can be used as a catalyst in the reaction process to promote the formation of SiO2 oxide film on the product surface; The fe - si fusion system was formed, and the nitrogen was dissolved in FeSi2 to promote the production of tany-si3n4. But the iron particle is too big or content is too high, the product also can appear the stomata and so on blemish, reduce the performance. The normal iron content is 0 ~ 5%. Impurities such as Al, Ca and Ti can easily form low eutectic with silicon. Proper addition can promote sintering and improve the properties of the products. 
The finer the silicon powder, the larger the specific surface area, and the lower the firing temperature. The amount of grain-si3n4 in the product increased when compared with the grain-grained grain-silicon powder. Reducing the particle size of silica powder can reduce the microscopic pore size of the product. Appropriate particle size ratio can improve the product density. 
Temperature has a great influence on the rate of nitriding. The oxidation reaction started at 970 ~ 1000℃, and the reaction rate accelerated at about 1250℃. In the high temperature stage, due to the exothermic reaction, if the temperature soon exceeds the melting point of silicon (1420℃), it is easy to flow silicon, which will cause the melt collapse of the silicon powder body. Therefore, the temperature system as shown in FIG. 9-2 is adopted to properly control the heating rate. 
Hot-pressed silicon nitride products are products made by mixing synthetic silicon nitride powder and appropriate sinter agent (MgO, Al2O3, etc.) evenly and placing them in a graphite mold. They are heated to 1600 ~ 1800℃ and pressurized to 20 ~ 40MPa in a hot-pressed furnace according to a certain temperature rise and pressure boost system. 
Atmospheric sintering silicon nitride synthetic silicon nitride powder and sinter agent mixed evenly after molding, drying, in atmospheric nitrogen atmosphere in 1700 ~ 1800℃ sintering products. 
Isobaric sintered silicon nitride products are made by placing synthetic silicon nitride powder or raw blank in a special package in a hot isobaric press, using high-pressure gas as the medium and maintaining 0.5 ~ 3h at 50 ~ 200 MPa and 1500 ~ 2100℃.
Reactive refired silicon nitride products are prepared by reburning pre-burned silicon nitride products at 1700 ~ 1800℃ for 5 ~ 6h.

Say something
  • All comments(0)
    No comment yet. Please say something!
Tag: Silicon nitr