Ceramic components containing up to almost 100% alumina are made by firing a preprepared and shaped “green” part at temperatures in excess of 1500°C. By carefully controlling the intrinsic shrinkage that takes place, the highly densified product offers high mechanical strength and hardness with resistance to wear and chemical corrosion. Additionally, alumina ceramics exhibit very favourable thermal and electrical resistance properties.
An important group of applications has been established through exploiting the superior wear resistance that alumina provides, specifically:
- Grinding media (alumina balls, beads, cylinders etc)
- Thread guides for the textle industry
- Wear resistant linings
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.
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.
Low soda alumina
This alumina has very low soda content: between 300 and 500ppm. Carefully controlling calcination using the proprietary Reynolds process also allows a wide range of primary crystal size to be offered.