Alumina (Aluminium Oxide) - The Different Types of Commercially Available Grades

Alumina (Aluminium Oxide) - The Different Types of Commercially Available Grades

Very large tonnages are also used in the manufacture of monolithic and brick refractories. It is also mixed with other materials such as flake graphite for other, more difficult applications are envisaged, such as pouring spouts and sliding gate valves.

Key Properties

Aluminium Oxides key properties are shown below.

• High compression strength

• High hardness

• Resistant to abrasion

• Resistant to chemical attack by a wide range of chemicals even at elevated temperatures

• High thermal conductivity

• Resistant to thermal shock

Fused

White Fused Alumina is made in electric arc furnaces by passing a current between vertical carbon electrodes. The heat generated melts the alumina. The furnace consists of a water cooled steel shell and 3-20 tonne batches of material are fused at any one time. The fused alumina has a high density, low porosity, low permeability and high refractoriness. As a result of these characteristics, it is used in the manufacture of abrasives and refractories.

The only compound of silicon and carbon is Silicon Carbide (SiC), or carborundum. SiC does occur naturally as the mineral moissanite, but this is extremely rare. However, it has been mass produced in powder form for use as an abrasive since 1893. As an abrasive, it has been used for over one hundred years in grinding wheels and many other abrasive applications.

With today’s technology, high-quality technical grade ceramics have been developed with SiC which exhibit very advantageous mechanical properties such as:

• Exceptional hardness

• High strength

• Low density

• High elastic modulus

• High thermal shock resistance

• Superior chemical inertness

• High thermal conductivity

• Low thermal expansion

These high strength and very durable ceramics are widely used in applications such as automotive brakes and clutches along with ceramic plates embedded in bulletproof vests. Silicon carbide is also used in semiconductor electronic devices operating at high temperatures and/or high voltages such as flame igniters, resistance heating, and harsh environment electronic components.