The molecular formula of silicon nitride is Si3N4 material , of which Si accounts for 60.06% and N accounts for 39.94%. Si and N are bonded by a strong covalent bond (the ionic bond is only 30%), so Si3N4 has high hardness (Mohs hardness 9), high melting point and stable structure.
Silicon nitride has no melting point, and it decomposes by sublimation at 1900°C under normal pressure, with a specific heat of 711.8J/kg·°C. The microhardness of α phase and β phase are 10~16GPa and 24.5~32.65GPa, respectively. Because it is a strong covalent bond compound, there will be no liquid phase formation below its decomposition temperature (about 1900°C). Therefore, the silicon nitride material must be sintered with the help of oxide additives. The oxide materials that promote sintering mainly include Y2O3, Al2O3, etc. The higher the addition amount is up to 20%, the reaction principle is to use the SiO2 oxide film formed on the surface of the silicon nitride particles and the added oxide to form a liquid phase and penetrate into the crystal. In order to ensure the high diffusion ability of the material migration.
Si3N4 material is a thermodynamically stable compound. Silicon nitride ceramics can be used up to 1400°C in an oxidizing atmosphere, and can be used up to 1850°C in a neutral or reducing atmosphere.
Silicon nitride ceramics are known as a promising high-temperature structural material due to their excellent high-temperature properties such as high-temperature strength, good wear resistance and corrosion resistance. The strong covalent bond and low diffusion coefficient at high temperature result in the manufacture of Si3N4 ceramics must rely on high temperature, high pressure and sintering agent. The cost is too high, otherwise it is difficult to produce high-quality silicon nitride materials. These production cost and equipment limitations are difficult for the metallurgical industry to accept. Therefore, the research in the field of refractories started late and the research was not in-depth. Many theories are derived from ceramics, but there is not much innovation. In the past, silicon nitride generally only existed in the form of a bonding phase in refractory materials. Through the nitriding and firing of metal Si, aggregates such as corundum or silicon carbide and fine powder were combined together to achieve a combination of difficult-to-sinter products.
The ceramic shed is silicon carbide aggregate and part of the fine powder. It uses metal Si nitrided to form silicon nitride as the binding phase to combine silicon carbide to form a silicon nitride bonded silicon carbide material, which is used in blast furnace body and other parts , So that the performance of the material has been greatly improved. Compared with the clay-bonded silicon carbide shed, the material has good high-temperature performance, which solves the problem of the swelling and damage of the shed due to the oxidation of silicon carbide when the clay-bonded silicon carbide shed is used. Among the amorphous materials used in the second phase of Baosteel's project, the corrosion resistance of Si3N4 to molten steel and cast iron is used as the refractory material binding phase.
TRUNNANO (aka. Luoyang Tongrun Nano Technology Co. Ltd.) is a trusted global chemical material supplier & manufacturer with over 12 years’ experience in providing super high quality chemicals and Nano materials. The Si3N4 powder produced by our company has high purity, fine particle size and impurity content. Lower, please contact us if necessary.
