Changes

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:fig2.1Powder metallurgical manufacturing of composite materials (schematic)"/> shows the schematic manufacturing processes from powder blending to contact material. Three basic process variations are typically

<figure id="fig:fig2.1Powder metallurgical manufacturing of composite materials (schematic)">

The platinum group metals include the elements Pt, Pd, Rh, Ru, Ir, and Os [[Platinum_Metal_Based_Materials|Table 2.61]] <!--(Table 2.6)-->. For electrical contacts platinum and palladium have practical significance as base alloy materials and ruthenium and iridium are used as alloying components. Pt and Pd have similar corrosion resistance as gold but because of their catalytical properties they tend to polymerize adsorbed organic vapors on contact surfaces. During frictional movement between contact surfaces the polymerized compounds known as “brown powder” are formed which can lead to significantly increase in contact resistance. Therefore Pt and Pd are typically used as alloys and not in their pure form for electrical contact applications.

The trade name VAKURIT is assigned to a family of low gas content contact materials developed for the use in vacuum switching devices [[Special_Contact_Materials_(VAKURIT)_for_Vacuum_Switches|Table 2.421]] (Table 2.42).