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→Silver–Tungsten Materials
=== Silver–Tungsten Materials===
Ag/W contact materials combine the high electrical and thermal conductivity of silver with the high arc erosion resistance of the high melting tungsten metal (<xr id="tab:Physical Properties of-Contact Materials Based"/><!--(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 (<xr id="fig:Micro structure of Ag W 25 75"/><!--(Fig. 2.134)-->, <xr id="fig:Micro structure of Ag WC 50 50"/><!--(Fig. 2.135)--> and <xr id="tab:Contact and Switching Physical Properties of Contact Materials Based on Silver – -Tungsten (SIWODUR), Silver–Tungsten Silver-Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)"/><!--(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 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:Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)"/><!--(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.
<figtable id="tab:Physical Properties of Contact Materials Based on Silver-Tungsten, Silver-Tungsten Carbide and Silver Molybdenum">
<caption>'''<!--Table 2.7:-->Physical Properties of Contact Materials Based on Silver-Tungsten, Silver-Tungsten Carbide and Silver Molybdenum'''</caption>
{| class="twocolortable" style="text-align: left; font-size: 12px"
|-
!Material
!Chemical<br/>Composition<br/>[wt.%]
!Density<br/>[g/cm<sup>3</sup>]
!Melting Point<br/>[°C]
!Electrical<br/>Resistivity<br/>[µΩ*cm]
!Electrical<br/>Conductivity<br/>[% IACS]
!Electrical<br/>Conductivity<br/>[MS/m]
!Vickers<br/>Hardness<br/>[HV10]
!Chopping Current<br/>(99%-Value)<br/>[A]
|-
|W/Cu 80/20 - low gas<br/>VAKURIT W/Cu 20
|W: 20±2<br/>Cu: Rest
|15,2 - 15,8
|1083
|4,55 - 6,25
|28 - 35
|16 - 20
|210 - 250
|5
|-
|W/Cu 30Sb1 - low gas<br/>VAKURIT W/Cu30Sb
|W: 70±2<br/>Sb: 0,5 - 1,0<br/>Cu: Rest
|13,8 - 14,5
|630
|5,26 - 7,14
|24 - 33
|14 - 19
|220
|4
|-
|WC/Ag 60/40 - low gas<br/>VAKURIT WC/Ag40
|WC: 60±2<br/>Ag: 40±2
|12,7
|960
|4,34 - 5,88
|30 - 40
|17 - 23
|180 - 250
|1,5
|-
|WC/Ag 50/50 - low gas<br/>VAKURIT WC/Ag50
|WC: 50±2<br/>Ag: 50±2
|12,2
|960
|3,45 - 4,34
|40 - 50
|23 - 29
|140 - 170
|1,8
|-
|Cu/Cr 75/25 - low gas<br/>VAKURIT Cu/Cr25
|Cr: 25±1<br/>Cu: Rest
|7,8 - 8,3
|1083
| ≤3,70
| ≥47
| ≥27
| >60
|4,5
|-
|Cu/Cr 60/40 - low gas<br/>VAKURIT Cu/Cr40
|Cr: 40±1<br/>Cu: Rest
|7,3 - 7,9
|1083
| ≤4,55
| ≥40
| ≥22
| >70
|4,5
|-
|Cu/Cr 50/50 - low gas<br/>VAKURIT Cu/Cr50
|Cr: 50±1<br/>Cu: Rest
|7,0 - 7,5
|1083
| ≤6,25
| ≥28
| ≥16
| >80
|5
|-
|}
</figtable>
=== Silver–Tungsten Carbide Materials===