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Tungsten and Molybdenum Based Materials

551 bytes removed, 09:15, 9 December 2022
Silver–Molybdenum (SILMODUR) Materials
The applications of Ag/WC contacts are similar to those for Ag/W (<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 2.38)-->).
=== Silver–Molybdenum (SILMODUR) Materials===Ag/Mo materials with typically 50-70 wt% molybdenum are usually produced by the powder metallurgical infiltration process (<xr id="fig:Micro structure of Ag Mo 35 65"/><!--(Fig. 2.137)--> and <xr id="tab:Physical Properties of-Contact Materials Based"/><!--(Table 2.36)-->). Their contact properties are similar to those of Ag/W materials (<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)-->). Since the molybdenum oxide is thermally less stable than tungsten oxide , the self-cleaning effect of Ag/Mo contact surface during arcing is more pronounced and the contact resistance remains lower than that of Ag/W. The arc erosion resistance of Ag/Mo however is lower than the one for Ag/W materials. The main applications for Ag/Mo contacts are in equipment protecting switching devices (<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 2.38)-->).
<figtable id="tab:Physical Properties of-Contact Materials Based">
[[File:Physical Properties of-Contact Materials Based.jpg|right|thumb|Physical Properties of Contact Materials Based on Silver–Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)]]
</figtable>
<xr id="fig:Micro structure of Ag W 25 75"/><!--Fig. 2.134:--> Micro structure of Ag/W 25/75
 
<xr id="fig:Micro structure of Ag WC 50 50"/><!--Fig. 2.135:--> Micro structure of Ag/WC 50/50
 
<xr id="fig:Micro structure of -Ag WC 27 C3"/><!--Fig. 2.136:--> Micro structure of Ag/WC27/C3
 
<xr id="fig:Micro structure of Ag Mo 35 65"/><!--Fig. 2.137:--> Micro structure of Ag/Mo 35/65
 
<div class="multiple-images">
<figtable id="tab:Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)">
<caption>'''<!--Table 2.37:-->Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)'''</caption>
<table class="twocolortable">
<tr><th><p class="s12">Material/ DODUCO- Designation</p></th><th><p class="s12">Properties</p></th></tr><tr><td><p class="s12">Silver-Tungsten</p><p class="s12">SIWODUR</p><p class="s12">Silver-tungsten carbide SIWODUR C</p></td><td><p class="s12">Tendency to weld at high make currents in symmetrical pairing,</p><p class="s12">Higher contact resistance and higher temperature rise over increased number of operations through tungsten oxide and tungstate formation, especially for Ag/W,</p><p class="s12">High welding tendency of closed contacts during short circuit,</p><p class="s12">Very high arc erosion resistance, poor arc moving properties, High hardness and low formability,</p><p class="s12">Easy to braze and weld through Ag enriched backing layer</p></td></tr><tr><td><p class="s12">Silver-Tungsten Carbide plus Grafit SIWODUR C Plus</p></td><td><p class="s12">Low contact resistance and low temperature rise through graphite addition,</p><p class="s12">Lower tendency to contact welding, Lower arc erosion resistance than Ag/W</p></td></tr><tr><td><p class="s12">Silver-Molybdenum</p><p class="s12">SILMODUR</p></td><td><p class="s12">Better contact resistance stability due to less stable surface layers,</p><p class="s12">Lower arc erosion resistance than Ag/W</p></td></tr></table>
</figtable>
<figtable id="tab:Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)">
<caption>'''<!--Table 2.38:-->Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)'''</caption>
{| class="twocolortable" style="text-align: left; font-size: 12px"
!Form of Supply
|-
|Ag/W<br />SIWODUR
|Circuit breakers (not current limiting)
|rowspan="3" | Contact tips, brazed and welded<br />contact parts
|-
|Ag/W<br />SIWODUR<br />Ag/WC<br />SIWODUR C<br />Ag/WC/C<br />SIWODUR C/C
|(Main) Power switches<br /> paired with Ag/C)<br />
Fault current circuit breakers<br />(paired with Ag/C)
|-
|Ag/Mo<br />SILMODUR
|Device protection switches
|}