2,808
edits
Changes
→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 ''(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 ''(Figs<xr id="fig:fig2.134"/> Fig. 2.134 and <xr id="fig:fig2.135"/> 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.
Ag/W materials are mostly used as the arcing contacts in disconnect switches for higher loads and as the main contacts in small and medium duty power
switches and industrial circuit breakers ''<xr id="tab:tab2.38"/> (Table 2.38)''. In north and south america they are also used in large volumes in miniature circuit breakers of small to medium current ratings in domestic wiring as well as for commercial power distribution.
=== Silver–Tungsten Carbide (SIWODUR C) Materials===