Aluminum Oxide Color

Aluminum oxide, also known as alumina (uh-LOOM-i-num), is the most common of several aluminium oxides with chemical formula Al2O3. It is a tough and long-lasting material that can be machined and molded into hard wear-resistant materials for use in industrial applications such as wire guides, machinery seals and metering devices. Its extreme strength, wear resistance and ability to withstand high temperatures make it a vital ingredient in high-tech applications such as micro-electric substrates and insulating heatsinks.

Often used as an abrasive, aluminium oxide can be made in different forms for specialized applications. The form of alumina most used in refractories is called alpha alumina with hexagonal crystals, density 4.0 and a Mohs hardness of 9. Alpha alumina converts to gamma alumina at high temperature. Gamma alumina is more finely ground and produces a smoother finish when cutting. It is also heat-stabilized with sodium to give it a high level of corrosion resistance.

The off-white color of this sample can be attributed to impurities in the raw material or sintering additives. Alumina powders are mixed with an organic binder to help them keep their shape before being heated to a very high temperature in a controlled atmosphere until the particles fuse together into chemical bonds (sintering). This process shrinks and hardens the alumina to produce a dense, strong ceramic.

The Occupational Safety and Health Administration classifies aluminium oxide as a nuisance dust, meaning it is not harmful to people when exposed in small amounts, but can cause problems when exposure is prolonged or excessive. Some workers in bauxite refining have developed a condition called Shaver’s disease, a form of pulmonary fibrosis that may be related to breathing in finely divided aluminium oxide.