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:Mechanical_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:Mechanical_Properties_of_Tungsten_and_Molybdenum"><caption>'''<!--Table 2.35: -->Mechanical Properties of Tungsten and Molybdenum'''</caption><table class="twocolortable"><tr><th><p class="s12">Material</p></th><th><p class="s12">Micro Structure Condition</p></th><th><p class="s12">Vickers</p><p class="s12">Hardness HV 10</p></th><th><p class="s12">Tensile Strength</p><p class="s12">[MPa]</p></th></tr><tr><td><p class="s12">Tungsten</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">Molybdenum</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></figtable>

[[File=== 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:Mechanical 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 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.jpg|right|thumb|Mechanical 2.135)--> and <xr id="tab:Physical Properties of Contact Materials Based on Silver-Tungsten , Silver-Tungsten Carbide and Silver Molybdenum]]"/>).

=== 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 ''(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 ''(Figs. 2.134 and 2.135) (Table 2.37)''. [[File:Contact and Switching Properties of Contact Materials Based on.jpg|right|thumb|Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)]] 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: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=== 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 veryhard and erosion wear resistant tungsten carbide Tungsten Carbide and the high conductivity silverSilver 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)''. Therise in contact resistance experienced with Ag/W is less pronounced in Ag</WCbecause during arcing a protective gas layer of CO is formed which limits thereaction of oxygen on the contact surface and therefore the formation of metaloxides.caption>

Higher requirements on low temperature rise can be fulfilled by adding a small{| class="twocolortable" style="text-align: left; font-size: 12px"|-amount of graphite which however increases the arc erosion. Silver–tungsten!Materialcarbide–graphite materials with for example 27 !Silver<br/>Content<br/>[wt.% ]!Density<br/>[g/cm³]!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 - 38|110 - 175|-|Ag/W 40/60 [[#text-reference|¹]]|37 - 43|13,9 - 14,5|21 - 32|150 - 240|-|Ag/W 35/65 [[#text-reference|¹]]|32 - 38|14,1 - 15,1|21 - 31|160 - 260|-|Ag/W 32/68 [[#text-reference|¹]]|29 - 35|14,3 - 15,2|21 - 30|180 - 265|-|Ag/WC 60/40 [[#text-reference|¹]]|57 - 63|11,6 - 12,2|21 - 29|140 - 200|-|Ag/WC and40/60 [[#text-reference|¹]]|37 - 43|12,5 - 13,3 wt% graphite or 16 wt% |18 - 25|230 - 340|-|Ag/WC 80/16C2 [[#text-reference|²]]|80 - 84|9,2 - 9,9|30 - 38|35 - 55|-|Ag/WC 80/17C3 [[#text-reference|²]]|78 - 82|9,1 - 9,8|23 - 33|35 - 55|-|Ag/WC 80/19C1 [[#text-reference|²]]|78 - 82|9,5 - 10,5|28 - 43|40 - 60|-|Ag/WC and 70/28C2 [[#text-reference|^{2 wt% graphite are}]]|68 - 72|9,6 - 10,3|24 - 32|35 - 55|-|Ag/Mo 65/35 [[#text-reference|¹]]|62 - 68|9,9 - 10,9|16 - 28|140 - 130|-|}<div id="text-reference">₁manufactured using theby infiltration</div>single tip <div id="text-reference">₂ manufactured by press-sinter-repress (PSR) process ''(Fig. 2.136)''.</div></figtable>

The applications === Silver–Tungsten Carbide Materials===This group of contact materials contains typically 40-65 wt-% of the very hard and erosion wear resistant tungsten carbide and the high conductivity silver (<xr id="fig:Micro structure of AgWC 50 50"/><!--(Fig. 2.135)--> and <xr id="tab:Physical Properties of Contact Materials Based on Silver-Tungsten, Silver-Tungsten Carbide and Silver Molybdenum"/WC contacts are similar ><!--(Table 2.36)-->). Compared to those for Ag/W ''the Ag/WC materials exhibit a higher resistance against contact welding (<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 2.3837)-->)''. 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.

=== Silver–Molybdenum (SILMODUR) Materials===Ag/Mo Higher requirements on low temperature rise can be fulfilled by adding a small amount of graphite, which however increases the arc erosion. Silver–tungsten-carbide–graphite materials with typically 50-70 for example 19 wt% WC and 1 wt% graphite or 16 wt% WC and 2 wt% molybdenum graphite are usually produced bymanufactured using the powder metallurgical infiltration process ''single tip press-sinter-repress (Fig. 2.137PSR) process (Table 2.36)''. Theircontact properties are similar to those <xr id="fig:Micro structure of -AgWC 27 C3"/W materials ''><!--(Table Fig. 2.37136)''. Since themolybdenum oxide is thermally less stable than tungsten oxide the self-cleaningeffect of Ag/Mo contact surface during arcing is more pronounced and thecontact resistance remains lower than that of Ag/W. The arc erosion resistanceof Ag/Mo however is lower than the one for Ag/W materials. The mainapplications for Ag/Mo contacts are in equipment protecting switching devices''(Table 2.38->)''.

[[File:Micro structure of.jpg|right|thumb|Micro structure The applications of Ag/W 25/75, Ag/WC 50/50, contacts are similar to those for Ag/WC27/C3W (<xr id="tab:Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR), AgSilver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)"/Mo 35/65]]><!--(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. 2.134137)--> 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: 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)-->). 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 25. The arc erosion resistance of Ag/75Mo 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)-->).

Fig<figure id="fig:Micro structure of Ag W 25 75"> [[File:Micro structure of Ag W 25 75. 2jpg|left|thumb|<caption>Micro structure of Ag/W 25/75</caption>]]</figure><figure id="fig:Micro structure of Ag WC 50 50"> [[File:Micro structure of Ag WC 50 50.137jpg|left|thumb|<caption>Micro structure of Ag/WC 50/50</caption>]]</figure><figure id="fig: Micro structure of -Ag WC 27 C3"> [[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>

[[File{| class="twocolortable" style="text-align: left; font-size:Physical Properties 12px"|-!Material !Application Examples!Form ofSupply|-|Ag/W<br />|Circuit breakers (not current limiting)|rowspan="3" | Contact Materials Based.jpgtips, brazed and welded<br />contact parts|right-|thumbAg/W<br /><br />Ag/WC<br /><br />Ag/WC/C<br /> |Physical Properties of Contact Materials Based on Silver–Tungsten (SIWODURMain), Silver–Tungsten Carbide (SIWODUR Power switches<br /> paired with Ag/C) and Silver Molybdenum <br />Fault current circuit breakers<br />(SILMODURpaired with Ag/C)]]|-|Ag/Mo<br />|Device protection switches|}</figtable>

Table 2.37: Contact and Switching Properties of Contact === Copper–Tungsten Materials Based on Silver – Tungsten===Copper–tungsten materials with typically 50-85 wt% tungsten are produced by the infiltration process with the tungsten particle size selected according to the end application [[#figures4|(SIWODURFigs. 5 – 6), Silver–Tungsten Carbide ]] <!--(SIWODUR CFigs. 2.138 – 2.141)--> and Silver Molybdenum (SILMODUR<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.

Table 2{| 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/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 - 5,56|31 - 38: Application Examples and Forms of Supply for Contact Materials Basedon Silver–Tungsten (SIWODUR)|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, Silver–Tungsten Carbide (SIWODUR C)25|28 - 34|16 - 20|180 - 280|-|}and Silver Molybdenum (SILMODUR)</figtable>

[[File:Application Examples and Forms of Supply for Contact Materials BasedW/Cu materials exhibit a very high arc erosion resistance.jpg|right|thumb|Application Examples and Forms of Supply for Contact Materials Based on Silver–Tungsten (SIWODUR)Compared to silver–tungsten materials, Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)]]they are however less suitable to carry permanent current.

=== Copper–Tungsten (CUWODUR) Materials===Copper–tungsten (CUWODUR) With a solid tungsten skeleton, as it is the case for W/C infiltrated materials with typically 5070-85 wt% tungsten areproduced by , the infiltration process with lower melting component copper melts and vaporizes in the tungsten particle size selectedaccording to intense electrical arc. At the end application ''boiling point of copper (Figs. 2.138 – 2.141) (Table 2.392567°C)''. To increasethe wettability of , the still solid tungsten skeleton by copper a small amount of nickel< 1 wt% is added to the starting powder mixefficiently “cooled” and remains pretty much unchanged.

During very high thermal stress on the W/Cu materials exhibit contacts, for example during short circuit currents > 40 kA, the tungsten skeleton requires special high mechanical strength. For such applications, a very high arc erosion resistance ''(Table 2.40)''.Compared to silver–tungsten materials they are however less suitable to carrypermanent currenttemperature sintering of tungsten from selected particle size powder is applied before the usual infiltration with copper.

With For high voltage load switches, the most advantageous contact system consists of a solid tungsten skeleton as it is contact tulip and a contact rod. Both contact assemblies are usually made from the case for mechanically strong and high conductive CuCrZr material and W/C infiltrated materials with70-85 wt% tungsten Cu as the lower melting component copper melts arcing tips. The thermally and vaporizesin mechanically highly stressed attachment between the intense electrical arctwo components is often achieved by utilizing electron beam welding or capacitor discharge percussion welding. At the boiling point Other attachment methods include brazing and cast-on of copper (2567°C) the still solidtungsten is efficiently “cooled” , followed by cold forming steps to increase hardness and remains pretty much unchangedstrength.

During very high thermal stress on the The main application areas for W/Cu materials are as arcing contactsin load and high power switching, in medium and high voltage switchgear as well as electrodes for example during shortcircuit currents > 40 kA the tungsten skeleton requires special high mechanicalstrength. For such applications a high temperature sintering of tungsten fromselected particle size powder is applied before the usual infiltration with copper(example: CUWODUR H)spark gaps and over voltage arresters.

For high voltage load switches the most advantageous contact system consists<div class="multiple-images"><figure id="fig:Micro structure of a contact tulip and a contact rod. Both contact assemblies are made usuallyW Cu 70 30 G"> from the mechanically strong and high conductive CuCrZr material and [[File:Micro structure of W/Cu asthe arcing tips70 30 G. The thermally and mechanically highly stressed attachmentbetween the two components is often achieved by utilizing electron beamwelding or capacitor discharge percussion welding. Other attachment methodsinclude brazing and cast-on jpg|left|thumb|<caption>Micro structure of copper followed by cold forming steps toW/Cu 70/30 (coarse)</caption>]]increase hardness and strength.</figure>

The main application areas for CUWODUR materials are as arcing contacts in<figure id="fig:Micro structure of W Cu 70 30 F">load and high power switching in medium and high voltage switchgear as wellas electrodes for spark gaps and over voltage arresters ''[[File:Micro structure of W Cu 70 30 F.jpg|left|thumb|<caption>Micro structure of W/Cu 70/30 (Table 2.41fine)''.</caption>]]</figure>

Table 2.39: Physical Properties of Copper–Tungsten (CUWODUR) Contact Materials [[File:Physical Properties of Copper Tungsten CUWODUR Contact Materials.jpg|right|thumb|Physical Properties of Copper Tungsten (CUWODUR) Contact Materials]] Fig. 2.139: Micro structure of W/Cu 70/30 G Fig. 2.140: Micro structure of W/Cu 70</30 Hdiv> Fig. 2.138: Micro structure of W<div class="clear"></Cu 70/30 F Fig. 2.141: Micro structure of W/Cu 80/20 H [[File:Micro structure of2.jpg|right|thumb|Micro structure of W/Cu 70/30 G, W/Cu 70/30 H, W/Cu 70/30 F, W/Cu 80/20 H]] Table 2.40: Contact and Switching Properties of Copper–Tungsten(CUWODUR) Contact Materials[[File:Contact and Switching Properties of Copper Tungsten.jpg|right|thumb|Contact and Switching Properties of Copper-Tungsten (CUWODUR) Contact Materials]] Table 2.41: Application Examples and Forms of Supply for Tungsten–Copper (CUWODUR) Contact Materials[[File:Application Examples and Forms of Supply for Tungsten.jpg|right|thumb|Application Examples and Forms of Supply for Tungsten-Copper (CUWODUR) Contact Materials]]div>