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→Silver–Tungsten (SIWODUR) Materials
=== Silver–Tungsten (SIWODUR) Materials===
Ag/W (SIWODUR) contact materials combine the high electrical and thermal conductivity of silver with the high arc erosion resistance of the high melting tungsten metal <xr id="fig:Physical Properties of-Contact Materials Based"/> (Table 2.36). The manufacturing of materials with typically 50-80 wt% tungsten is performed by the powder metallurgical processes of liquid phase sintering or by infiltration. Particle size and shape of the starting powders are determining the micro structure and the contact specific properties of this material group <xr id="fig:fig2.134"/> (Fig. 2.134 ) and <xr id="fig:fig2.135"/> (Fig. 2.135), <xr id="tab:tab2.37"/> (Table 2.37)''.
During repeated switching under arcing loads tungsten oxides and mixed oxides (silver tungstates – Ag<sub>2</sub> WO<sub>4</sub> ) are formed on the Ag/W surface creating 2 4 poorly conducting layers which increase the contact resistance and by this the temperature rise during current carrying. Because of this fact the Ag/W is paired in many applications with Ag/C contact parts.
