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Within this group, silver has the greatest importance for switching devices in the higher energy technology. Other precious metals such as gold and platinum are only used in applications for the information technology in the form of thin surface layers. As a nonprecious metal, tungsten is used for some special applications such as, for example, automotive horn contacts. In some rarer cases, pure copper is used, but mainly paired to a silver-based contact material.
Besides these few pure metals, a larger number of alloy materials made by melt technology are available for the use as contacts. An alloy is characterized by the fact, that its components are completely or partially soluble in each other in the solid state. Phase diagrams for multiple metal compositions show the number and type of the crystal structure as a function of the temperature and composition of the alloying components.
Alloying allows to improve the properties of one material at the cost of changing them for the second material. As an example, the hardness of a base metal may be increased while at the same time the electrical conductivity decreases with even small additions of the second alloying component.
Composite materials are a material group whose properties are of great importance for electrical contacts that are used in switching devices for higher
Those used in electrical contacts are heterogeneous materials, composed of two or more uniformly dispersed components, in which the largest volume portion consists of a metal.
The properties of composite materials are determined mainly independent from each other by the properties of their individual components. Therefore it is, for example, possible to combine the high melting point and arc erosion resistance of tungsten with the low melting and good electrical conductivity of copper or the high conductivity of silver with the weld resistant metalloid graphite. (<xr id="fig:Powder metallurgical manufacturing of composite materials (schematic)"/>) shows the schematic manufacturing processes from powder blending to contact material. Three basic process variations are typically applied:
*Sintering without liquid phase (Press-Sinter-Repress, PSR)
Main Article: [[Tungsten and Molybdenum Based Materials| Tungsten and Molybdenum Based Materials]]
==Special Contact Materials (VAKURIT) for Vacuum Switches==
The trade name VAKURIT is assigned to a family of low gas content contact materials, are developed for the use in vacuum switching devices [[Special_Contact_Materials_(VAKURIT)_for_Vacuum_Switches|Table 1]] .
Main Article: [[Special Contact Materials (VAKURIT) for Vacuum Switches| Special Contact Materials (VAKURIT) for Vacuum Switches]]
==References==
