The chemical formula for aluminium nitride is AlN. It contains 2 atoms of aluminium and 1 atom of nitrogen.
Aluminum nitride is a ceramic material with high thermal conductivity, high capacity to withstand extreme radiation and exceptional mechanical properties. It is used for a range of applications including as a heat-sink in deep ultraviolet optoelectronics and as a crucible for smelting metals such as iron, aluminium and copper.
Its unique intrinsic properties include spontaneous polarization that is due to the difference in electronegativity between aluminum and nitrogen atoms and the non-centrosymmetric wurtzite crystal structure. This leads to the formation of internal piezoelectric charges under strain.
Due to its low thermal expansion, AlN has excellent room temperature strength and thermal shock resistance. It can be made into a variety of structural ceramics and is often used as a crucible for casting alloys such as gallium arsenide, and as dielectric layers in the production of optical storage media and chip carriers.
The low expansion coefficient of AlN means it can be coated onto substrates such as stainless steel S3400 and Inconel using reactive radio-frequency magnetron sputtering, to produce anticorrosive and wear-resistant coatings with good tribological properties. AlN has also been applied to the surface of acoustic wave sensors, bearings and parts of machine tools.
Aluminium nitride is available as powder or in ceramic form and can be produced through the carbothermal reduction of uniformly mixed Al2O3 or by direct nitridation of aluminium. Carbothermal reduction is a more expensive method, but produces a superior product with lower impurity levels, small particle size and higher purity. Direct nitriding is a cheaper method, but has a much lower conversion rate and produces a product with a higher oxygen content. Both methods require the use of sintering aids and hot pressing to produce dense technical-grade materials.