Processes
Alumina is the most widely used oxide in advanced ceramics. It is extracted from bauxite ore using a hot solution of caustic soda (Bayer process), then purified using various chemical methods until the purity levels reach 99.99% (the characteristics of the material increase with the purity of the product).
The ceramics are shaped using traditional processes, then sintered between 1,400°C and 1,700°C, according to the reactivity of the powder. They are often modified with MgO, to limit granular growth, or with chrome, which produces a red colour and slightly increases hardness (often referred to as polycrystalline rubies).
Properties
Alumina is particularly used for its very high hardness, more than 18GPa (Vickers), which makes it the hardest natural material after diamond, and therefore very resistant to wear. It is also used for its resistance to corrosion, high temperatures, electrical insulation properties, thermal conduction and biocompatibility properties.
Applications
Alumina is widely used in the following applications: electronics (insulating substrates), biomedical prosthetics, cutting tools, wear-resistance components (thread guides, bearings, nozzles, etc.), ballistic protection, fluid management (filling pumps, ball valves, anti-abrasion and anti-corrosion coatings).