Corundum has a variety of colors, it presents different colors due to containing different pigment ions.
Industrially, corundum is divided into brown corundum, white corundum, and black corundum according to the color.
Corundum has colorless, white, golden (pigment ions Ni, Cr), yellow (pigment ions Ni), red (pigment ions Cr), blue (pigment ions Ti, Fe), green (pigment ions Co, Ni, V), Purple (Ti, Fe, Cr), brown, black (pigment ion Fe, Fe), blue-violet under incandescent lamp, red violet effect under fluorescent lamp (pigment ion V).
In addition to the difference in color and the pigment ions contained in it, the differences in the physical and chemical properties of brown fused alumina and white corundum and their use are also considerable.
White corundum is made from high-quality aluminum oxide powder, through smelting and crystallization. It has high purity, good self-sharpening, acid and alkali resistance, high temperature resistance, and stable thermal properties.
Hardness of white corundum is slightly higher than brown corundum, toughness slightly lower than brown corundum.White corundum has high purity, good self-sharpening, good grinding ability, low emitting heat, high efficiency, acid and alkali corrosion resistance, high-temperature resistance and thermal stability. Abrasives made of white corundum grain are suitable for grinding high-carbon steels, high-speed steels, and stainless steels. White corundums can also be used for precision casting and advanced refractory materials.
Typical white corundum chemical indicators: Al2O3 ≥ 99% Na2O ≤ 0.5% CaO ≤ 0.4% magnetic material ≤ 0.003%
Brown corundum is mainly made from bauxite, anthracite and iron filings. It is browned in the electric arc furnace and has good toughness. Its hardness is 1800-2200Kg/mm2,bulk density is ≥ 3.85g/cm3. refractoriness up to 1850 °C, can be made into refractories, can also be used as abrasive.
It has high hardness, toughness, sharp edges, strong grinding force, high temperature resistance, With high efficiency, it is a high-quality abrasive material and high-grade refractories. Abrasive tools made of it are suitable for grinding metals with high tensile strength. They can be used to cut and grind all kinds of general-purpose steels, carbon steels, general alloy steels, forgeable steels, hard steels, etc. As a high-grade refractories, it is widely used in steel, chemical, and other industries.
Typical Brown corundum chemical indicator: AL2O3 95 min.,CaO 0.45% max, Fe2O3 0.3 max, TiO2 range 1.4%-3.8%,SiO2 1.5% max..