Alumina functions in pigments:
- Precipitated micronic alumina trihydrate isused with cobalt to obtain the colour blue.
- Soft calcined alumina is used with manganese to obtain the colour red
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.
Fine alumina hydrate
Aluminium trihydroxide (ATH) produced by the Gardanne Bayer process is subject to controlled grinding to obtain a range of particle size distributions and low viscosity grades.
Ground calcined alumina
These aluminas are ground in continuous ball-mills or air-jet mills to median particle sizes (d50) 3, 4, 5 or 6 µm.