Silicon nitride products can be divided into reaction sintering products, hot pressing products, atmospheric pressure sintering products, isostatic pressing sintering products and reaction re sintering products. Among them, reactive sintering is a common method to produce silicon nitride refractory products. Silicon nitride products produced by reaction sintering method are formed by grinding fine silicon powder (particle size is generally less than 80m), forming by mechanical pressing or isostatic pressing, drying the green body, heating it to 1350 ~ 1400 in nitrogen, and sintering by nitriding at the same time. With this production method, the raw material conditions, firing process and atmosphere conditions have a great influence on the properties of the product.

 

 

 

There are many impurities in silicon powder, such as iron, calcium, titanium, etc. Iron is considered as a catalyst in the reaction process. It can promote the diffusion of silicon, but it will also cause defects such as pores. The main functions of Fe as an additive: it can be used as a catalyst in the reaction process to promote the formation of silica oxide film on the product surface; The iron silicon melt system is formed, and nitrogen is dissolved in liquid ferrosilicon to promote the formation of - Si3N4. However, if the iron particle is too large or the content is too high, defects such as pores will appear in the product and reduce the performance. The addition amount of iron is generally 0 ~ 5%. Impurities such as aluminum, calcium and titanium are easy to form eutectic with silicon. Proper addition can promote sintering and improve product properties.

 

 

 

The finer the particle size of silicon powder, the larger the specific surface area and the lower the sintering temperature. The content of - Si3N4 in the products with finer grains is higher than that in the products with coarser grains. Reducing the particle size of silicon powder can reduce the micropore size of the product. The appropriate particle size ratio can improve the product density.

 

 

 

Temperature has a great influence on nitriding rate. The nitriding reaction began at 970 ~ 1000, and the reaction rate accelerated at about 1250. In the high-temperature stage, due to the exothermic reaction, if the temperature rapidly exceeds the melting point of silicon (1420), silicon flow is easy to occur, and in serious cases, silicon powder will melt and collapse. Therefore, the above technologies are shared by everyone. In recent years, silicon nitride products have developed rapidly with good application and performance, and are widely used by many people.

 

 

 

Silicon nitride products are one of the very hard materials in the world. Silicon nitride is an inorganic material with the characteristics of low density, high strength and good high temperature resistance. Silicon nitride products have high strength and hardness, and the hardness of hot pressed silicon nitride is very high.