Calcined Alumina

Calcined alumina provides the highest hardness (Mohs 9), exceptional wear resistance, high-temperature mechanical strength, excellent chemical inertness, and good electrical insulation properties. These properties are essential for technical ceramic components operating in high-temperature, high-wear, or electrically demanding environments.

Calcined alumina is used in high-voltage electrical insulators, refractory bricks and kiln furniture, wear-resistant ceramic components (grinding media, liners), spark plugs, cutting tools, electronic substrates, and advanced technical ceramics where other materials lack the required hardness and thermal stability.

Higher purity (>99% Al₂O₃) alumina produces ceramics with better mechanical strength, higher dielectric performance, lower porosity, and more consistent sintering behaviour. Lower-purity grades contain more impurities (SiO₂, Fe₂O₃) that can form secondary glass phases, reducing high-temperature mechanical performance.

High-purity alpha-alumina ceramics typically require sintering temperatures of 1550–1700°C to achieve full densification (>99% theoretical density). Sintering aids such as MgO (0.1–0.5%) are added to promote grain boundary mobility and densification at lower temperatures.

Calcined alumina is produced by thermal treatment of aluminium hydroxide and is used primarily in sintered ceramic bodies. Fused alumina is produced by electric arc melting and is used primarily as an abrasive and refractory aggregate. Calcined alumina has higher chemical purity and more controlled sintering reactivity for technical ceramic applications.