aluminum oxide

Aluminium oxide is an excellent thermal and electrical insulator. In its crystalline form, called corundum, its hardness makes it suitable for use as an abrasive and as a component in cutting tools. Aluminium oxide is responsible for metallic aluminium's resistance to weathering. Metallic aluminium is very reactive with atmospheric oxygen, and a thin passivation layer of alumina quickly forms on any exposed aluminium surface. This layer protects the metal from further oxidation. The thickness and properties of this oxide layer can be enhanced using a process called anodising. A number of alloys, such as aluminium bronzes, exploit this property by including a proportion of aluminium in the alloy to enhance corrosion resistance. China produced 8.51 million tons of alumina in 2005, up 21.9 percent year on year. But it also had to import 7 million tons of alumina, a 19.4 percent rise from a year earlier, to meet the ballooning domestic demand. Despite the growth in alumina production in the two months, Chinese enterprises had to import alumina at a record high price of 650 U.S. dollars per ton, indicating a strong market demand (especially aluminum oxide) in the country, according market observers.