Application Of Silicon Nitride in Refractory Industry

Application of silicon nitride in refractory industry
Silicon nitride ceramics are considered as promising high-temperature structural materials due to their excellent high-temperature properties, such as high strength, good wear resistance, and corrosion resistance. The strong covalent bonds and low diffusion coefficient at high temperatures necessitate the use of high temperature and high pressure, as well as sintering agents, for the production of silicon nitride ceramics. These production costs and equipment limitations are difficult for the metallurgical industry to accept, which is why research in the field of refractory materials started relatively late and is not in-depth. Many theories are derived from ceramics without much innovation. Currently, silicon nitride exists in refractory materials as a bonding phase, which combines raw materials such as corundum or silicon carbide through nitridation sintering of metals, thus achieving the purpose of bonding refractory materials together. For example, silicon nitride bonded silicon carbide materials used in aluminum electrolytic cells all use Si3N4 generated by nitridation as the bonding phase, and Si3N4 is often introduced into refractory materials in powder form.
(1) Application in ironmaking refractory materials
In recent years, significant advancements have been made in corundum-silicon carbide-silicon nitride-carbon products used in large blast furnaces. Refractory products made of silicon nitride, silicon oxynitride, or sialon-bonded silicon carbide have been widely applied in the middle section of large blast furnaces and load-bearing parts of coke ovens. Additionally, corundum-silicon carbide-silicon nitride-carbon refractory materials are increasingly being used in torpedo cars, demonstrating excellent erosion resistance, wear resistance, and scouring resistance. This has greatly enhanced the service life of the refractory lining in torpedo cars.
Currently, about 61% of blast furnaces abroad have adopted refractory materials containing Si3N4, especially for large blast furnaces with a hearth diameter of 12-15mm, where its adoption rate has reached 68%. According to statistics, over the past 10 years, more than 3,500 tons of such high-quality products have been installed in 127 blast furnaces. The majority of blast furnaces use 270-800 tons each, with applications ranging from tuyeres, bosh, waist to the middle and lower parts of the stack. Silicon nitride bonded products are mainly promoted for use in the middle section of blast furnaces. The Furukawa Steel Plant of Kobe Steel in Japan has experimented by adding a small amount of pure β-Si3N4 to AI2O3-SiC-C bricks on the mixer car. The experiment has shown that its slag resistance and oxidation resistance have been significantly improved.
(2) Application in steelmaking refractory materials
In recent years, silicon nitride has been successively applied to the slide plate materials at the bottom of steel ladles both domestically and internationally. The addition of silicon nitride materials to the slide plate has improved its wear resistance, erosion resistance, and service life, reducing the cost per ton of steel in ladle refining;
(3) Application in refractory materials for smelting non-ferrous metals such as aluminum, copper, and zinc
Silicon nitride ceramics do not wet with metal solutions at high temperatures, making them suitable for use as high-temperature components in non-ferrous metal smelting processes, such as temperature measurement thermocouple casings, smelting furnace linings, various container linings, and crucibles. Silicon nitride ceramic products exhibit good thermal shock resistance and can be stably used for long periods at high temperatures or in high-temperature to low-temperature cycles.
(4) Application in stifling materials
Ceramic shed boards are silicon nitride-bonded silicon carbide materials prepared by reacting and sintering silicon carbide particles and fine silicon powder in a high-temperature nitrogen atmosphere, significantly enhancing the material's performance. Compared to clay-bonded silicon carbide shed boards, these materials exhibit greatly improved high-temperature performance and address the issue of shed board expansion and damage caused by the oxidation of silicon carbide during use.