Main Articel: [[Tungsten and Molybdenum Based Materials| Tungsten and Molybdenum Based 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 ''(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. 2.134 and 2.135) (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.
Silver–tungsten contact tips are used in a variety of shapes and are produced for
the ease of attachment with a fine silver backing layer and quite often an
additional thin layer of a brazing alloy. The attachment to contact carriers is
usually done by brazing, but also by direct resistance welding for smaller tips.
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 ''(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===
