Clay is the most important raw material for traditional ceramics such as bricks, tiles, sanitary ceramics and tableware. The word ‘earthenware’ for ceramic pots and jugs is an indication that their raw materials are literally obtained from the ground. Clay is a natural product whose composition varies. Clay particles are flat hexagonal plates with a size of less than 2 μm, which consist mainly of aluminium silicates with a layered crystal structure. When there is water in between, it is difficult for these plates to detach from each other, allowing for clay to form a solid mass.
In order to make a brick, mix clay with water to make a mass that can be pressed well into the shape of a brick. Then dry this brick shape to remove excess water, and bake the brick in an oven at a temperature of more than 1000 °C to obtain a strong product. In fact, the natural product clay is converted directly into the useful product brick.
Porcelain originates from several raw materials. Mix the natural compounds kaolin – a white type of clay – with quartz and feldspar, shape the desired product from this mass, bake it in the oven and apply a glass-like coating (glaze). Et voila, you have made a vase or plate – or an electrical insulator to be used at high voltages.
Since the 1980’s, a new type of ceramics has skyrocketed: advanced ceramics, also known as technical ceramics. Hardly any raw materials from nature are used here; instead, pure and high quality powders form the basis. These powders – with small (sub-micron) grains and narrow grain size distribution – from a synthetic production route are processed in various steps into products with special, also high-quality physical and mechanical properties.
From a chemical point of view, advanced ceramics – just as traditional ceramics – are compounds that consist of metallic and non-metallic elements: oxides such as alumina and zirconia, nitrides such as silicon nitride and titanium nitride, and carbides such as silicon carbide. Advanced ceramics are strong and hard due to the strong ionic or covalent bonds between the elements.
Due to their hardness, their exceptional wear resistance and their resistance to aggressive chemicals and high temperatures, advanced ceramics can still be used when other materials – like most polymers and metals – reach their limits. In addition, they are usually excellent electrical and thermal insulators, but the extensive advanced-ceramic family also has members with exactly the opposite properties. No wonder that you encounter these materials everywhere – in satellites, microelectronics, cars and within the chemical industry, to name just a few applications.