Tungsten is characterized by its advantageous properties of high melting and boiling points, sufficient electrical and thermal conductivity and high hardness and density (<xr id="tab:tab2.35Mechanical_Properties_of_Tungsten_and_Molybdenum"/> <!--(Table 2.35)-->). It is mainly used in the form of brazed contact tips for switching duties , that require a rapid switching sequence , such as horn contacts for cars and trucks.

<figtable id="tab:tab2.35Mechanical_Properties_of_Tungsten_and_Molybdenum"><caption>'''<!--Table 2.35: -->Mechanical Properties of Tungsten and Molybdenum'''</caption><table borderclass="1" cellspacing="0" style="border-collapse:collapsetwocolortable"><tr><tdth><p class="s12">Material</p></tdth><tdth><p class="s12">Micro Structure Condition</p></tdth><tdth><p class="s12">Vickers</p><p class="s12">Hardness HV 10</p></tdth><tdth><p class="s12">Tensile Strength</p><p class="s12">[MPa]</p></tdth></tr><tr><td><p class="s12">WolframTungsten</p></td><td><p class="s12">Lightly worked structure</p><p class="s12">(wire and strip &gt; 1.0 mm thick)</p><p class="s12">Strongly worked structure</p><p class="s12">(wire and strip &lt; 1.0 mm thick)</p><p class="s12">Re-crystallized structure</p></td><td><p class="s12">300 - 500</p><p class="s12">500 - 750</p><p class="s12">360</p></td><td><p class="s12">1000 - 1800</p><p class="s12">1500 - 5000</p><p class="s12">1000 - 1200</p></td></tr><tr><td><p class="s12">MolybdänMolybdenum</p></td><td><p class="s12">Lightly worked structure</p><p class="s12">(wire and strip &gt; 1.0 mm thick)</p><p class="s12">Strongly worked structure</p><p class="s12">(wire and strip &lt; 1.0 mm thick)</p><p class="s12">Re-crystallized structure</p></td><td><p class="s12">140 - 320</p><p class="s12">260 - 550</p><p class="s12">140 - 160</p></td><td><p class="s12">600 - 1100</p><p class="s12">800 - 2500</p><p class="s12">600 - 900</p></td></tr></table>

=== 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 meltingtungsten metal ''(<xr id="tab:Physical Properties of Contact Materials Based on Silver-Tungsten, Silver-Tungsten Carbide and Silver Molybdenum"/><!--(Table 2.36)''-->). The manufacturing of materials with typically 50-80 wt% tungsten is performed by the powder metallurgical processes ofliquid 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:fig2.134Micro structure of Ag W 25 75"/> <!--(Fig. 2.134 and )-->, <xr id="fig:fig2.135Micro structure of Ag WC 50 50"/> <!--(Fig. 2.135, )--> and <xr id="tab:tab2.37Physical Properties of Contact Materials Based on Silver-Tungsten, Silver-Tungsten Carbide and Silver Molybdenum"/> (Table 2.37)''.

During repeated switching under arcing loads , tungsten oxides and mixed oxides (silver tungstates – Ag₂ WO₄ ) 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 or Ag/WC/C contact parts.

switches and industrial circuit breakers (<xr id="tab:tab2.38Contact 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=== Silver–Tungsten Carbide (SIWODUR C) "tab:Physical Properties of Contact Materials===This group of contact materials contains the typically 40Based on Silver-65 wtTungsten, Silver-% of the very hard Tungsten Carbide and erosion wear resistant tungsten carbide and the high conductivity silver Silver Molybdenum"><caption>'''(Fig. 2.135) (<!--Table 2.36)'7:-->Physical Properties of Contact Materials Based on Silver-Tungsten, Silver-Tungsten Carbide and Silver Molybdenum'. Compared to Ag/W the Ag/WC (SIWODUR C) materials exhibit a higher resistance against contact welding ''(Table 2.37)''. The rise in contact resistance experienced with Ag</W is less pronounced in Ag/WC because during arcing a protective gas layer of CO is formed which limits the reaction of oxygen on the contact surface and therefore the formation of metal oxides.caption>

Higher requirements on low temperature rise can be fulfilled by adding a small amount of graphite which however increases the arc erosion. Silver–tungsten{| class="twocolortable" style="text-align: left; font-size: 12px"|-!Materialcarbide–graphite materials with for example 27 !Silver<br/>Content<br/>[wt.% WC and ]!Density<br/>[g/cm^{3 wt% graphite or 16 wt% WC and 2 wt% graphite are manufactured using the single tip press}]!Electrical<br/>Conductivity<br/>[MS/m]!Vickers<br/>Hardness<br/>[HV5]|-|Ag/W 50/50 [[#text-reference|¹]]<br/>|47 - 53|12,9 - 13,9|29 -sinter38|110 -repress (PSR) process ''(Fig. 2.136)''.175|-The applications of |Ag/WC contacts are similar to those for W 40/60 [[#text-reference|¹]]|37 - 43|13,9 - 14,5|21 - 32|150 - 240|-|Ag/W ''(Table 2.35/65 [[#text-reference|¹]]|32 - 38)''.|14,1 - 15,1|21 - 31=== Silver–Molybdenum (SILMODUR) Materials===|160 - 260|-|Ag/Mo materials with typically 50W 32/68 [[#text-70 wt% molybdenum are usually produced by the powder metallurgical infiltration process reference|<sup>1<xr id="fig:fig2.137"/sup> (Fig. ]]|29 - 35|14,3 - 15,2.137) (Table |21 - 30|180 - 265|-|Ag/WC 60/40 [[#text-reference|¹]]|57 - 63|11,6 - 12,2.36)''. Their contact properties are similar to those of |21 - 29|140 - 200|-|Ag/W materials WC 40/60 [[#text-reference|<sup>1<xr id="tab:tab2./sup>]]|37"- 43|12,5 - 13,3|18 - 25|230 - 340|-|Ag/WC 80/16C2 [[#text-reference|² (Table ]]|80 - 84|9,2.37). Since the molybdenum oxide is thermally less stable than tungsten oxide the self-cleaning effect of 9,9|30 - 38|35 - 55|-|Ag/Mo contact surface during arcing is more pronounced and the contact resistance remains lower than that of WC 80/17C3 [[#text-reference|²]]|78 - 82|9,1 - 9,8|23 - 33|35 - 55|-|Ag/W. The arc erosion resistance of WC 80/19C1 [[#text-reference|²]]|78 - 82|9,5 - 10,5|28 - 43|40 - 60|-|Ag/Mo however is lower than the one for AgWC 70/28C2 [[#text-reference|<sup>2</W materials. The main applications for sup>]]|68 - 72|9,6 - 10,3|24 - 32|35 - 55|-|Ag/Mo contacts are in equipment protecting switching devices 65/35 [[#text-reference|¹]]|62 - 68|9,9 - 10,9|16 - 28|140 - 130|-|}<xr div id="tab:tab2.38text-reference">₁manufactured by infiltration</div><div id="text-reference">_{(Table 2.38).} manufactured by press sinter-repress</div></figtable>

Fig. 2.134: Micro structure of Ag/W 25/75=== Silver–Tungsten Carbide Materials===[[File:Micro structure This group of Ag W 25 75.jpg|right|thumb|Micro structure contact materials contains typically 40-65 wt-% of Ag/W 25/75]]Fig. 2.135the very hard and erosion wear resistant tungsten carbide and the high conductivity silver (<xr id="fig: Micro structure of Ag/WC 50/50[[File:Micro structure of Ag WC 50 50.jpg|right|thumb|Micro structure of Ag"/WC 50/50]]><!--(Fig. 2.136135)--> and <xr id="tab: Micro structure Physical Properties of Contact Materials Based on Silver-Tungsten, Silver-Tungsten Carbide and Silver Molybdenum"/><!--(Table 2.36)-->). Compared to Ag/WC27W the Ag/C3[[FileWC materials exhibit a higher resistance against contact welding (<xr id="tab:Micro structure Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)"/><!--(Table 2.37)--Ag WC 27 C3>).jpg|right|thumb|Micro structure of The rise in contact resistance experienced with Ag/WC27W is less pronounced in Ag/C3]]Fig. 2.137: Micro structure WC because during arcing, a protective gas layer of CO is formed, which limits the reaction of Ag/Mo 35/65[[File:Micro structure oxygen on the contact surface and therefore the formation of Ag Mo 35 65metal oxides.jpg|right|thumb|Micro structure of Ag/Mo 35/65]]

'''Table 2.36The applications of Ag/WC contacts are similar to those for Ag/W (<xr id="tab: Physical Contact and Switching Properties of Contact Materials Based on Silver–Tungsten Silver – Tungsten (SIWODUR),Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)'''"/><!--(Table 2.38)-->).

=== Silver–Molybdenum 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 on Silver-Tungsten, Silver-Tungsten Carbide and Silver Molybdenum"/><!--(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)--teile>).

<figtable figure id="tabfig:tab2Micro structure of Ag W 25 75"> [[File:Micro structure of Ag W 25 75.37jpg|left|thumb|<caption>Micro structure of Ag/W 25/75</caption>]]</figure><figure id="fig:Micro structure of Ag WC 50 50"> '''Table 2[[File:Micro structure of Ag WC 50 50.37jpg|left|thumb|<caption>Micro structure of Ag/WC 50/50</caption>]]</figure><figure id="fig: Contact and Switching Properties Micro structure of Contact Materials Based on Silver – Tungsten-Ag WC 27 C3"> (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)'''[[File:Micro structure of -Ag WC 27 C3.jpg|left|thumb|<caption>Micro structure of Ag/WC27/C3</caption>]]</figure><figure id="fig:Micro structure of Ag Mo 35 65"> [[File:Micro structure of Ag Mo 35 65.jpg|left|thumb|<caption>Micro structure of Ag/Mo 35/65</caption>]]</figure></div><div class="clear"></div>

<table borderfigtable id="1tab:Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)" cellspacing="0" style><caption>'''<!--Table 2.37:-->Contact and Switching Properties of Contact Materials Based on Silver – Tungsten, Silver–Tungsten Carbide and Silver Molybdenum'''</caption><table class="border-collapse:collapsetwocolortable"><tr><tdth><p class="s12">Material/ DODUCO- Designation</p></tdth><tdth><p class="s12">Properties</p></tdth></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 PlusGraphite</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/WWC</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 id="tab:tab2.38Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)"><caption>'''<!--Table 2.38: Application Examples -->Contact and Forms Switching Properties of Supply for Contact Materials Basedon Silver–Tungsten (SIWODUR)Silver – Tungsten, Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)'''</caption>

|Ag/W<br />SIWODUR

|Ag/W<br />SIWODUR<br />Ag/WC<br />SIWODUR C<br />Ag/WC/C<br />SIWODUR C/C

|Ag/Mo<br />SILMODUR

=== 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 – 6)]] <!--(Figs. 2.138 – 2.141) --> and (<xr id="tab:Physical properties of copper-tungsten 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 <figtable id="tab:Physical properties of copper-tungsten materials exhibit a very high arc erosion resistance "><caption>'''Physical properties of copper-tungsten materials'(Table 2.40)''. Compared to silver–tungsten materials they are however less suitable to carrypermanent current.</caption>

With a solid tungsten skeleton as it is the case for {| class="twocolortable" style="text-align: left; font-size: 12px"|-!Material!Tungsten<br/>Content<br/>[wt.%]!Density<br/>[g/cm³]!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]|-|W/C infiltrated materials with Cu 60/40 <br/>|57 - 63|12,9 - 13,3|1083|3,85 - 4,55|38 - 45|22 - 26|150 - 200|-|W/Cu 65/35|63 - 67|13,6 - 14,0|1083|4,17 - 5,0|34 - 41|20 - 24|160 - 210|-|W/Cu 70/30 |68 -72|13,9 - 14,4|1083|3,85 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.- 5,56|31 - 38|18 - 22|160 - 230|-|W/Cu 75/25 |73 - 77|14,6 - 15,2|1083|4,76 - 5,88|29 - 36|17 - 21|180 - 210|-|W/Cu 80/20|78 - 82|15,3 - 15,9|1083|5,0 - 6,25|28 - 34|16 - 20|180 - 280|-|}</figtable>

During very high thermal stress on the W/Cu contacts, for example during short circuit currents > 40 kA the tungsten skeleton requires special materials exhibit a very high mechanical strengtharc erosion resistance. For such applications a high temperature sintering of tungsten from selected particle size powder is applied before the usual infiltration with copper (example: CUWODUR H)Compared to silver–tungsten materials, they are however less suitable to carry permanent current.

For high voltage load switches the most advantageous contact system consists of With a contact tulip and a contact rod. Both contact assemblies are made usually from solid tungsten skeleton, as it is the mechanically strong and high conductive CuCrZr material and case for W/Cu as C infiltrated materials with 70-85 wt% tungsten, the arcing tips. The thermally lower melting component copper melts and mechanically highly stressed attachment between vaporizes in the two components is often achieved by utilizing electron beam welding or capacitor discharge percussion weldingintense electrical arc. Other attachment methods include brazing and cast-on At the boiling point of copper followed by cold forming steps to increase hardness (2567°C), the still solid tungsten is efficiently “cooled” and strengthremains pretty much unchanged.

The main application areas During very high thermal stress on the W/Cu contacts, for CUWODUR materials are as arcing contacts in load and example during short circuit currents > 40 kA, the tungsten skeleton requires special high power switching in medium and mechanical strength. For such applications, a high voltage switchgear as wellas electrodes for spark gaps and over voltage arresters ''(Table 2.41)''temperature sintering of tungsten from selected particle size powder is applied before the usual infiltration with copper.

'''Table 2For high voltage load switches, the most advantageous contact system consists of a contact tulip and a contact rod. Both contact assemblies are usually made from the mechanically strong and high conductive CuCrZr material and W/Cu as the arcing tips. The thermally and mechanically highly stressed attachment between the two components is often achieved by utilizing electron beam welding or capacitor discharge percussion welding.39: Physical Properties Other attachment methods include brazing and cast-on of Copper–Tungsten (CUWODUR) Contact Materials'''copper, followed by cold forming steps to increase hardness and strength.

[[File:Physical Properties of Copper Tungsten CUWODUR Contact MaterialsThe main application areas for W/Cu materials are as arcing contacts in load and high power switching, in medium and high voltage switchgear as well as electrodes for spark gaps and over voltage arresters.jpg|right|thumb|Physical Properties of Copper Tungsten (CUWODUR) Contact Materials]]2-teilig

Fig. 2.139<div class="multiple-images"><figure id="fig: Micro structure of W/Cu 70/30 G"> [[File:Micro structure of W Cu 70 30 G.jpg|rightleft|thumb|<caption>Micro structure of W/Cu 70/30 G]]Fig. 2.140: Micro structure of W/Cu 70/30 H[[File:Micro structure of W Cu 70 30 H.jpg|right|thumb|Micro structure of W/Cu 70(coarse)</30 Hcaption>]]Fig. 2.138: Micro structure of W</Cu 70/30 F [[File:Micro structure of W Cu 70 30 F.jpg|right|thumb|Micro structure of W/Cu 70/30 F]]Fig. 2.141: Micro structure of W/Cu 80/20 H[[File:Micro structure of W Cu 80 20 H.jpg|right|thumb|Micro structure of W/Cu 80/20 H]]figure>

'''Table 2.40: Contact and Switching Properties of Copper–Tungsten (CUWODUR) Contact Materials'''<table border="1" cellspacing="0" stylefigure id="border-collapsefig:collapse"><tr><td><p class="s12">Material/ DODUCO- Designation</p></td><td><p class="s12">Properties</p></td></tr><tr><td><p class="s12">Micro structure of W/Cu 70 30 F</p><p class="s12">CUWODUR F</p></td><td><p class="s12">Very high arc erosion resistance,</p><p class="s12">Uniform erosion pattern after high operation frequency, Very high mechanical strength,</p><p class="s12">Highly resistant against thermal and mechanical shock</p></td></tr><tr><td><p class="s12">[[File:Micro structure of W/Cu G</p><p class="s12">CUWODUR G</p></td><td><p class="s12">Very high arc erosion resistance, Very high mechanical strength,</p><p class="s12">Highly resistant against thermal and mechanical shock70 30 F.jpg|left|thumb|</p></td></tr><tr><td><p class="s12"caption>Micro structure of W/Cu H<70/p><p class="s12">CUWODUR H30 (fine)</p></td><td><p class="s12">Very high arc erosion resistance, very high mechanical strength, Especially high resistance against thermal and mechanical shock.</p></td></trcaption>]]</tablefigure>

'''Table 2.41: Application Examples and Forms of Supply for Tungsten– Copper (CUWODUR) Contact Materials'''<table border="1" cellspacing="0" style="border-collapse:collapse"><tr><td><p class="s12">Material</p></td><tddiv><p div class="s12clear">Application Examples</p></td><td><p class="s12">Form of Supply</p></td></tr><tr><td><p class="s12">W/Cu F</p></td><td><p class="s12">Transformer tap changers,</p><p class="s12">Medium voltage circuit breakers</p></td><td><p class="s12">Contact tips, formed parts, brazed</p><p class="s12">and welded contact parts</p></td></tr><tr><td><p class="s12">W/Cu G</p></td><td><p class="s12">Overvoltage arresters with spark gap,</p><p class="s12">Medium voltage circuit breakers, Medium voltage power switches, High voltage power switches and circuit breakers</p></td><td><p class="s12">Contact tips, formed parts, brazed</p><p class="s12">and welded contact parts; Contact tulips, rods and tubes</p></td></tr><tr><td><p class="s12">W/Cu H</p></td><td><p class="s12">High voltage power switches and circuit</p><p class="s12">breakers for very high short circuit currents</p></td><td><p class="s12">Welded contact parts; Contact tulips,</p><p class="s12">rods</p></td></tr></tablediv>