The Aluminium ion takes the place of the Si ion in the crystalline network. This enables the make up of the glaze to be varied without modifying the mechanical properties.
Aluminas with intermediate to relatively high specific surface areas (BET 3- 75m²/g) with alpha alumina contents varying between 20% and 95%.These are produced by controlled rotary calcination of aluminium trihydroxide.
Coarse alumina hydrate
Aluminium trihydroxide (ATH) is produced by the Bayer Process in Gardanne. These ATH grades are used for the production of a variety of aluminium salts and in glass production.
Hard calcined alumina
These aluminas have low specific surface area (BET < 1m²/g) and are almost entirely alpha alumina. Standard soda content is 3000-4000 ppm and intermediate soda content is 2000-3000 ppm. Hard calcined aluminas are produced in rotary kilns.