The properties of Si3N4 materials:
Si3N4 material is silicon nitride’s molecular formula. Si comprises 60.06% while N makes up 39.94%. Si and N bond by a strong covalent link (the Ionic bond is just 30%). Si3N4 materials have high hardness (Mohs Hardness 9), high melting points, and a stable structure. Silicon-nitride does not melt and can be sublimated at 1900°C. It has a specific temperature of 711.8J/kg°C and microhardness values of 24.532.65GPa. The strong covalent bond compound means that there is no liquid phase formation below it decomposition temperatures (around 1900°C). It is essential that the silicon nitride materials be sintered by using oxide additives. Most oxide materials which promote sintering are Y2O3, A2O3, and so on. The reaction principle involves using the SiO2 dioxide film that forms on top of silicon nitride particle and adding the oxide to make a liquid phase. This will penetrate the crystal. This is to guarantee the maximum diffusion of the material’s migration.
A thermodynamically stable material, Si3N4 is available. The temperature range for silicon nitride ceramics is 1400 to 1400 degrees Celsius in an oxygenating atmosphere and 1850 to 1850 degrees Celsius in a neutral atmosphere or reducing environment.
Silicon nitride material application in refractory substances:
High-temperature structures made of silicon nitride are very promising because they have excellent properties like high temperatures, wear resistance, and resistance to corrosion. Si3N4 ceramics can only be made due to their strong covalent bond, low diffusion coefficient and high temperature requirements. Otherwise, it would be difficult to produce silicon nitride materials of high quality. This high production cost, along with the limitations of equipment are unacceptable for the metalurgical industry. The research into refractories was not done in depth and began too late. While there are many theories that can be drawn from ceramics, the majority of them do not have much novelty. In the past, silicon Nitride was limited to a bonding stage in refractory materials. The combination of aggregates, such as corundum and silicon carbide with fine powder was used to produce a variety of products that are difficult to sinter.
Part of the fine powder is the ceramic shed, which is made from silicon carbide. The ceramic shed uses silicon carbide aggregate and part of the fine powder to make silicon nitride. It has a better high-temperature performance than clay-bonded Silicon Caride shed. This eliminates problems like swelling and damage from silicon carbide oxidation. Baosteel’s second phase project uses Si3N4 and cast steel as the refractory material binding phases.
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