How to identify the types of corundum？

Corundum is a polycrystalline aluminum oxide material. Aluminum oxide is one of the main components of the earth’s crust, with abundant resources, relatively cheap and easy to obtain. Corundum has physical and chemical properties such as high temperature resistance, alta resistencia, alta dureza, electrical insulation, y resistencia a la corrosión. Por lo tanto, corundum has become a refractory material with a wide range of uses.

Corundum is a trigonal mineral with NO = 1.768, NE = 1.760, NO-NE = 0.008, a relative density of 4.02, and a hardness of 9. Corundum sometimes contains a small amount of impurities such as Fe, Mn, cr, and Ti. Corundum can be dyed into different colors by these impurities.

Classification of corundum

Corundum can be divided into two categories according to different manufacturing methods: primero, corundum raw materials directly made from bauxite, such as brown corundum and high-aluminum corundum; second, alumina is extracted from bauxite, and then industrial alumina is made into corundum raw materials, such as white corundum, densamente, sintered corundum, etc..

In terms of purity and price, white corundum is high, followed by dense corundum, high aluminum corundum is third, and brown corundum is low. 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 aluminum corundum and brown corundum are both produced from bauxite. The purity of brown corundum is lower than that of high-aluminum corundum, but its true density is higher than that of high-aluminum corundum.
Sintered corundum is a refractory raw material made from industrial alumina, which is ground, ball-pressed, and then sintered at a temperature of about 1800°C. Sintered corundum has a high density and a low apparent porosity. Its volume density is >3.50g/Cm3 and its apparent porosity is <4.5%. Por lo tanto, sintered corundum has properties similar to those of fused corundum: it has good volume stability at high temperature, is not affected by reducing atmosphere, and has a certain resistance to corrosion by molten metal and glass.