Corundum is a polycrystalline alpha alumina material. Aluminum oxide is one of the main components of the Earth's crust, with the advantages of abundant resources and relatively inexpensive availability. Corundum has physical and chemical properties such as high temperature resistance, high strength, high hardness, electrical insulation, and corrosion resistance. As a result, corundum has become a widely used refractory material.

Corundum is a mineral with a trigonal crystal system, with no=1.768, ne=1.760, ne no=0.008, a relative density of 4.02, and a hardness of 9. Corundum sometimes contains small amounts of impurities such as Fe, Mn, Cr, and Ti. Corundum can be dyed into different colors by these impurities.

The melting point of corundum is as high as 2050 ℃. The fire resistance of high-quality corundum products is greater than 1900 ℃, the starting temperature for load softening is about 1850 ℃, the ultimate operating temperature is 1950 ℃, and the long-term operating temperature is 1800 ℃. However, the thermal expansion coefficient of corundum is 8.6 × 10-6 ℃ -1, which belongs to the material with moderate to low thermal shock resistance.

The hardness of corundum is 9, which is only lower than diamond and a few artificially synthesized high hardness minerals. Aluminum oxide products have high strength, with a room temperature compressive strength of up to 2000MPa; The flexural strength at room temperature can reach over 250MPa, and the flexural strength at 1000 ℃ is still 150MPa. High density alumina products can be

Effectively resist the erosion of molten metals such as iron, aluminum, nickel, and vanadium; At room temperature, it is not corroded by sulfuric acid, hydrochloric acid, nitric acid, or hydrofluoric acid, but at high temperatures, sodium fluoride and concentrated sulfuric acid have a certain degree of corrosion on aluminum oxide. Aluminum oxide has a certain resistance to the erosion of glass and slag.

According to different manufacturing methods, corundum can be divided into two categories: first, corundum raw materials directly manufactured from bauxite, such as brown corundum and high alumina corundum; Secondly, alumina is extracted from bauxite, and then industrial alumina is made into corundum raw materials such as white corundum, dense corundum, sintered corundum, etc. Various types of fused alumina

The performance comparison is shown in the table:

Comparison of properties of various fused alumina materials

As shown in the table above, in terms of purity and price, white corundum has the highest purity, followed by dense corundum, high alumina corundum, and brown corundum has the lowest purity. White corundum and dense corundum are both produced from industrial alumina. The purity of dense corundum is lower than that of white corundum, but its density is higher than that of white corundum. High alumina corundum and brown corundum are both made of alumina

Produced. The purity of brown corundum is lower than that of high alumina corundum, but its true density is higher than that of high alumina corundum.

Sintered corundum is a refractory material made from industrial alumina as raw material, which is finely ground, pressed into balls, and then sintered at an ultra-high temperature of about 1800 ℃. Sintered corundum has high density and low apparent porosity, with a bulk density of ≥ 3.50g/cm3 and an apparent porosity of ≤ 4.5%. Therefore, sintered corundum has properties similar to fused corundum

Quality: It has good volume stability at high temperatures, is not affected by reducing atmosphere, and has a certain resistance to the erosion of metal and glass liquids. The following table shows the properties of sintered corundum:

Properties of sintered corundum