Dehydration sequence of hydrated alumina in air
Aluminium oxide appears in nature as
(=Corundum). The hexagonal a-Al2O3
is the only thermodynamically stable modification. Besides there is the
cubic face-centered g-Al2O3,
which develop from aluminium hydroxide at 400-800°C and is finaly converted
at 1100°C. Chemical data of
calcinated aluminas are given on a separate page.
Technically corundum is manufactured
today by electric melting of bauxite, which is the starting material for
refractory products. Thus, for example crucibles, protective tubes and
refractory bricks are produced as sintered corundum by pressing a-Al2O3
with bonding agents such as clays, which are fired at approx 1300°C.
Alumina coatings are available as Aluminium-Oxide-Coating
AA and Aluminium-Oxide-Coating AW.