Traditionally ceramics are classed as clay based materials. However, as the field of ceramics has expanded, they can be defined as inorganic, non-metallic materials that are heat treated during processing or use. They tend to be brittle, hard and inert, and have ionic or covalent bonding. Diamond meets all of these criteria.

Diamond is a form of carbon that is crystallised in a cubic structure with each carbon atom linked by a strong, rigid chemical bond to four other atoms.

Until the 1950s, diamond was available in relatively small quantities at fairly high prices, the word creating an image of brilliant gemstones and wealth. The broad range of valuable properties has driven the development of routes to make synthetic diamonds, which has produced new products and applications.
Sources

Diamond can now be found from several sources:

· Naturally occurring diamond; about 20 tonnes of diamond are mined each year. Half are gem quality and half are industrial quality.

· Synthetic single crystal diamond; about 90 tonnes of diamond are made annually by the high-pressure and high temperature (HPHT) method. Most industrial diamond is made from graphite at pressures of 4.5 to 6.0 GPa and temperatures of 1400 to 1600°C with the aid of a molten transition metal catalyst. These diamonds are considerably cheaper than natural diamond.

· Polycrystalline diamonds are formed usually by either cementing diamond grains together using metal as a bonding agent or sintering using Boron Carbide as a sintering aid.

· Vapour phase deposition. Both chemical vapour deposition (CVD) and physical vapour phase deposition (PVD) produce thin diamond films. About 10 tonnes of vapour phase grown diamond films are produce annually. Their cost is more than four times that of naturally occurring diamond. However, their application can be justified economically as they are used in thin film form and make a significant difference to component properties.