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→Silver–Tungsten Carbide (SIWODUR C) Materials
=== Silver–Tungsten Carbide (SIWODUR C) Materials===
This group of contact materials contains the typically 40-65 wt-% of the very hard and erosion wear resistant tungsten carbide and the high conductivity silver <xr id="fig:Micro structure of Ag WC 50 50"/> <!--(Fig. 2.135)--> <xr id="tab:Physical Properties of-Contact Materials Based"/><!--(Table 2.36)-->. Compared to Ag/W the Ag/WC (SIWODUR C) materials exhibit a higher resistance against contact welding <xr id="tab:Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)"/><!--(Table 2.37)-->. The rise in contact resistance experienced with Ag/W is less pronounced in Ag/WC because during arcing a protective gas layer of CO is formed which limits the reaction of oxygen on the contact surface and therefore the formation of metal oxides.
Higher requirements on low temperature rise can be fulfilled by adding a small amount of graphite which however increases the arc erosion. Silver–tungsten carbide–graphite materials with for example 27 wt% WC and 3 wt% graphite or 16 wt% WC and 2 wt% graphite are manufactured using the single tip press-sinter-repress (PSR) process <xr id="fig:Micro structure of -Ag WC 27 C3"/><!--(Fig. 2.136)-->.