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→Copper–Tungsten (CUWODUR) Materials
=== Copper–Tungsten (CUWODUR) Materials===
Copper–tungsten (CUWODUR) materials with typically 50-85 wt% tungsten are produced by the infiltration process with the tungsten particle size selectedaccording to the end application [[#figures4|(Figs. 5 – 8)]] (Figs. 2.138 – 2.141) <xr id="fig:Physical Properties of Copper Tungsten CUWODUR Contact Materials"/> (Table 2.39)''. To increase the wettability of the tungsten skeleton by copper a small amount of nickel < 1 wt% is added to the starting powder mix.
W/Cu materials exhibit a very high arc erosion resistance <xr id="tab:tab2.40Contact and Switching Properties of Copper–Tungsten (CUWODUR) Contact Materials"/> (Table 2.40). Compared to silver–tungsten materials they are however less suitable to carry permanent current.
With a solid tungsten skeleton as it is the case for W/C infiltrated materials with 70-85 wt% tungsten the lower melting component copper melts and vaporizes in the intense electrical arc. At the boiling point of copper (2567°C) the still solid tungsten is efficiently “cooled” and remains pretty much unchanged.
as electrodes for spark gaps and over voltage arresters <xr id="tab:tab2.41"/> (Table 2.41).
[[File:Physical Properties of Copper Tungsten CUWODUR Contact Materials.jpg|right|thumb|Physical Properties of Copper Tungsten (CUWODUR) Contact Materials]]
<div id="figures4">
<xr id="fig:fig2.139"/> Fig. 2.139: Micro structure of W/Cu 70/30 G
<figtable id="tab:tab2.40Contact and Switching Properties of Copper–Tungsten (CUWODUR) Contact Materials">
'''Table 2.40: Contact and Switching Properties of Copper–Tungsten (CUWODUR) Contact Materials'''
<table class="twocolortable">