Corundum is the most frequently used abrasive. The purer the corundum, the harder it also is, which can be determined from the colour. The toughness can be increased by adding various metal oxides and by shortening the cooling process in production.
The following distinctions are made:
Brown fused alumina
with more than 94% Al2O3 (aluminium oxide) is e.g. used to treat steel castings and cast iron. Its toughness permits especially high pressing forces.
White fused alumina consists of more than 99.9% Al2O3
Due to its hardness and thermal resistance up to 2,000°C, white fused alumina is suitable for tough steel types (tool steel), for grinding and polishing glass as well as for all steel types requiring cool grinding.
A very important field of application for the ultrapure white fused aluminas are varnishes and coatings, particularly powder and UV coatings, in which they enhance the scratch-resistance of furniture surfaces, worktops and floors. Fused alumina is most effective in ramps and highly wear-resistant industrial floors.
Semi-friable fused alumina with approx. 97% Al2O3 (aluminium oxide) is classified between brown fused alumina and white fused alumina due to its technical properties. It is less tough than brown fused alumina, but has a higher cutting quality.
Pink fused alumina gets its characteristic colour when chromium oxide is added to melt. It has a slightly higher grain toughness. Its higher edge stability makes it possible for use in form and profile grinding; otherwise it is identical to white fused alumina. Due to its hardness, fused alumina is often added to surfaces to protect them against wear (e.g. in varnishes and laminates).
Ruby fused alumina has further metal oxides added to it, particularly Cr2O3 (chromium(III) oxide). This results in maximum toughness making ruby fused alumina suitable for the grinding of high-alloy steel types.
Silicon carbide is heat-resistant up to approx. 1,600°C and contains hard, sharp-edged crystals. One abrasive grain usually only consists of a single or a few crystals. Compared with fused alumina, SiC is harder and more brittle. There are many fields of application, ranging from conventional blasting agents to hard concrete aggregates which make industrial floors abrasion-resistant and conductive and vaults particularly durable. It is used in engineering ceramics due to its low weight and low thermal expansion. In addition, SiC is a semiconductor and is used in the manufacture of blue LEDs, for example. SiC also produces a very pronounced glitter effect in dark colours (e.g. façades, plaster).
Higher-quality green silicon carbide is primarily used to treat glass, china, marble, gemstone, artificial stone, for precision treatment of light and non-ferrous metals as well as leather.