Generally speaking, there are five major kinds of abrasive for sandpaper on the market: alunimium oxide, silicon carbide, galss, ceramics, and garnet. Aluminium oxide abrasive, also called alumina and corundum, is widely used in polishing industry. Microcrystalline aluminium oxide abrasive is a new kind of abrasive based on alunimium oxide. It maintains the characteristics of high hardness and wear-resistance that ordinary aluminium oxide has. Also, it has high toughness, which changes the shortcoming of crisp and brittleness. It increase the toughness of aluminium oxide ceramics. For these advantages, it has been widely used in the production of bonded abrasive products and coated abrasive tool. The compound of Microcrystalline aluminium oxide abrasive, diamond, cubie boron nitride and other high level abrasive can significantly decrease the cost of abrsive, but the performance is not decreased. It can also be used with other low level abrasive, such as white corundum and brown corundum to improve their performance. So, the Microcrystalline aluminium oxide abrasive has an excellent prospect. Now, various kinds of grinding tools prepared by this abrasive have all ready been widely used in the fields of aerospace, car, machinery, optics, bearing, cutter, mould and so on.
The difference between Microcrystalline aluminium oxide and other aluminium oxide abrasive lies in their forming process and sintering process. The sol-gel forming process ensures the uniformity of its chemical composition. Because it is the sintering process that is used to produce the Microcrystalline aluminium oxide, the uniformity of this crystal is very good. The secondary crystal of this material is sintered by a large amount of micro crystal whose particle size is between 300 and 500 nanometer. Because of this, it possesses the characteristic of anisotropic. Thus, it maintains not only the same high hardness with white corundum but also the high toughness.
The manufacturing process of Microcrystalline aluminium oxide abrasive is not very complicated. First, add hydrogen nitric into Al2O3.nH2O until it becomes sol. Then add modifier and lead crystal agent into the sol to realize gelation. Next, dry up the gel and smash it. Then, by sintering the powder, you will get the microcrystalline aluminium oxide abrasive.
Aluminium oxide is a kind of block compound with sharp edges. The major producer of natural aluminium oxide is South Affrica. But the large quantity of this material used in industry is manmade. It is produced by melting bauxite using the electric arc furnace. Aluminium oxide is an excellent universal abrasive used for woodwork. Among all the abrasive, it is the only mineral abrasive. The white corundum is a kind of abrasive specially used for thermosensitive metal, while the black corundum is used to process casting and steel. In general, corundum will not react chemically with the being polished materials. But it should not be used to polish aluminum and aluminum alloy. Because the aluminium oxide abrasive can make the surface of aluminum dark and leave etch pit on its surface.