Page 57 - Curriculum Visions Dynamic Book

(Below) Better saw and grinder blades are coated with diamond, aluminium oxide, tungsten carbide, or silicon carbide. This dramatically increases their life and lets them cut into materials that are harder than the steel of the blade (for example, other ceramics).
the properties needed and the advantage that it is cheap to make. However, it is possible to improve on alumina by using composites. One of them is silicon carbide and a base of silica. The grains in this material are not as liable to come loose as in alumina. That is important because when any grain gets loose, it becomes a piece of “grit” and is an abrasive likely to cause damage in a short time.
Ceramics can be toughened by using fibres of other materials such as glass and carbon.
Ceramics are often used to hold liquids, especially if they are corrosive. In these cases ceramics go into valves and pipes, pump parts, and seals.
Ceramics are also important in making high-temperature dies, such as, for example, to draw wires. Here the dies need to be both tough and heat resistant.
graphite is an example of a ceramic
used as a lubricant. The layered structure of graphite means that it readily flakes. The flakes
themselves are very strong, but the bonds between flakes are weak. As a result, the flakes can prevent wear, and they do not wear themselves. Graphites are especially valuable where oils would cause mess (for example, door locks) or at high temperatures, when oils would break down.
Hard-wearing ceramics are also found in the home. Ceramic taps contain valves where one finely ground ceramic disk moves past another in order to control the flow of water. These valves wear in and work better with time rather than wearing out. Ceramic balls are also found in the end of roller ball pens.
Wear-resistant ceramics are also found in many parts of a car. For example, they are the major component of a catalytic converter, which reduces pollution from exhausts. The converter’s active ingredient is platinum metal. But it is very expensive. To keep down the cost, the platinum is sprayed as a fine layer on a scaffold of ceramic. The ceramic is either
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