Refractory raw materials In addition to the magnesium-aluminum spinel and high-alumina zircon mentioned above, there are several refractory materials commonly used in refractory bricks. Therefore, in order to obtain better materials, it is necessary to have a better understanding of these raw materials.
3. Silicon carbide
Silicon carbide is widely used in abrasives, heating elements, due to its high hardness, electrical conductivity, high temperature resistance and high strength. Commercially available silicon carbide is divided into black and green. Black silicon carbide is mostly used in refractory raw materials.
Silicon carbide has good high temperature resistance. Under normal pressure, the inconsistent melting temperature of silicon carbide is 2760°C, silicon carbide has high strength, and the flexural strength can reach 625MPa. Silicon carbide has good thermal shock resistance, thanks to its moderately low thermal expansion coefficient (4.7×10-6K-1) and high thermal conductivity [84W/(m·K)]. Therefore, silicon carbide is widely used to make various ceramics and refractory raw materials.
4. Andalusite, kyanite
Both andalusite and kyanite belong to the kyanite group of minerals, and they are referred to as "three stones" together with sillimanite.
Due to the large expansion of kyanite, the high temperature shrinkage of refractory raw materials can be compensated with a small dosage. Due to the low conversion temperature of kyanite, it is suitable for refractory that shrink at lower temperatures. Therefore, kyanite is suitable as an additive for middle and low grade refractoris.
The thermal expansion of andalusite is low, and the dosage is limited. However, larger amounts are required to compensate for the same shrinkage. As the content of andalusite increases, the creep resistance and thermal shock resistance of refractory materials will be greatly improved. However, manufacturing costs also increase significantly. Therefore, andalusite is suitable for medium and high-grade refractories.
5. Silica fume
Silica fume is a by-product obtained from the flue gas overflowing from the recovery furnace during the production of metallic silicon or ferrosilicon alloy. The SiO2 content of silica fume is 90%~98%, the specific surface area is 15~30m2/g, the median particle size is 0.3~0.5μm, and the pH=5.3~7.6. Imported silica fume has higher purity and lower pH value. Domestic silica fume has lower purity and higher pH value. A small amount of MgO and R2O contained in domestic silica fume make it weakly alkaline. Generally, refractory castables prepared with imported silica fume have good fluidity, but the cost of refractory raw materials is also high.
