Silicon nitride and Ferro-Silicon Nitride—Refractories
Early in the 20th century, refractories was developing in the direction of high-purity, high density and ultra-high temperature products, while there had been monolithic refractories and refractory fibers without firing completely and with small power consumption. In the modern times, with the development of atomic energy, space and new energy technologies, the refractories with such comprehensive excellent performance as resistance to high temperature, corrosion, thermal shock and erosion have been applied.
There are a variety of refractories, usually divided into ordinary (1580 ~ 1770 ℃), advanced (1770 ~ 2000 ℃) and top grade (2000 ℃ above) refractories according to the level of refractoriness; or divided into acidic, neutral and basic refractories by the chemical properties. In addition, there are refractories for special occasions.
The neutral refractories are mainly made of alumina, chromium or carbon oxide, as the main ingredients. The corundum products containing more than 95% alumina are high-quality refractory materials with a wider use. The chrome bricks with chromium oxide as the main ingredient have good corrosion resistance on steel slag, but poor thermal shock resistance and relatively low loading deformation temperature. For carbon refractories, there are carbon bricks, graphite products, silicon nitride and ferro-silicon nitride products, with very low coefficient of thermal expansion, high thermal conductivity, good thermal shock resistance, high temperature strength, and resistance to corrosion of acids, alkali and salts, not wetting from the metal or slag, as well as light in weight, so widely used as a high-temperature furnace lining material, and also used as the autoclave liner in petroleum and chemicals.