2,808
edits
Changes
→Silver-Metal Oxide Materials Ag/CdO, Ag/SnO2, Ag/ZnO
*Silver–tin oxide(SISTADOX)materials
Over the past years, many Ag/CdO contact materials have been replaced by Ag/SnO<sub>2</sub> based materials with 2-14 wt% SnO<sub>2</sub> because of the toxicity of Cadmium. This changeover was further favored by the fact that Ag/SnO<sub>2</sub> contacts quite often show improved contact and switching properties such as lower arc erosion, higher weld resistance, and a significant lower tendency towards material transfer in DC switching circuits ''<xr id="tab:tab2.30"/> (Table 2.30)''. Ag/SnO<sub>2</sub> materials have been optimized for a broad range of applications by other metal oxide additives and modification in the manufacturing processes that result in different metallurgical, physical and electrical properties ''<xr id="tab:tab2.29"/> (Table 2.29)''.
Manufacturing of Ag/SnO<sub>2</sub> by ''internal oxidation'' is possible in principle, but during heat treatment of alloys containing > 5 wt% of tin in oxygen, dense oxide layers formed on the surface of the material prohibit the further diffusion of oxygen into the bulk of the material. By adding Indium or Bismuth to the alloy the internal oxidation is possible and results in materials that typically are rather hard and brittle and may show somewhat elevated contact resistance and is limited to applications in relays. To make a ductile material with fine oxide dispersion (SISTADOX TOS F) ''(Fig. 2.114)'' it is necessary to use special process variations in oxidation and extrusion which lead to materials with improved properties in relays. Adding a brazable fine silver layer to such materials results in a semifinished material suitable for the manufacture as smaller weld profiles
(SISTADOX WTOS F) ''(Fig. 2.116)''. Because of their resistance to material transfer and low arc erosion these materials find for example a broader
application in automotive relays ''<xr id="tab:tab2.31"/> (Table 2.31)''.
''Powder metallurgy'' plays a significant role in the manufacturing of Ag/SnO<sub>2</sub> contact materials. Besides SnO<sub>2</sub> a smaller amount (<1 wt%) of one or more other metal oxides such as WO<sub>3</sub>, MoO<sub>3</sub>, CuO and/or Bi<sub>2</sub>O<sub>3</sub> are added. These
:'''e) Powder blending based on chemically precipitated compound powders''' <br> A silver salt solution is added to a suspension of for example SnO<sub>2</sub> together with a precipitation agent. In a chemical reaction silver and silver oxide respectively are precipitated around the additive metal oxide particles who act as crystallization sites. Further chemical treatment then reduces the silver oxide with the resulting precipitated powder being a mix of Ag and SnO<sub>2</sub>.
Further processing of these differently produced powders follows the conventional processes of pressing, sintering and hot extrusion to wires and strips. From these contact parts such as contact rivets and tips are manufactured. To obtain a brazable backing the same processes as used for Ag/CdO are applied. As for Ag/CdO, larger contact tips can also be manufactured more economically using the press-sinter-repress (PSR) process ''<xr id="tab:tab2.27"/> (Table 2.27).''
Fig. 2.87: Strain hardening of Ag/SnO<sub>2</sub> 92/8 PE by cold working
<figtable id="tab:tab2.27">
'''Table 2.27: Physical Properties of Powder Metallurgical Silver-Metal Oxide Materials
with Fine Silver Backing Produced by the Press-Sinter-Repress Process'''
<table border="1" cellspacing="0" style="border-collapse:collapse"><tr><td><p class="s11">Material/</p><p class="s11">DODUCO- Designation</p></td><td><p class="s11">Additives</p></td><td><p class="s11">Density</p><p class="s11">[ g/cm<span class="s13">3</span>]</p></td><td><p class="s11">Electrical</p><p class="s11">Resistivity</p><p class="s11">[µ<span class="s14">S ·</span>cm]</p></td><td><p class="s11">Electrical</p><p class="s11">Conductivity</p></td><td><p class="s11">Vickers</p><p class="s11">Hardness</p><p class="s11">HV 10.</p></td></tr><tr><td><p class="s11">Material/</p><p class="s11">DODUCO- Designation</p></td><td><p class="s11">Additives</p></td><td><p class="s11">Density</p><p class="s11">[ g/cm<span class="s13">3</span>]</p></td><td><p class="s11">Electrical</p><p class="s11">Resistivity</p><p class="s11">[µ<span class="s14">S ·</span>cm]</p></td><td><p class="s11">[% IACS]</p></td><td><p class="s11">[MS/m]</p></td><td><p class="s11">Vickers</p><p class="s11">Hardness</p><p class="s11">HV 10.</p></td></tr><tr><td><p class="s11">AgCdO 90/10EP</p><p class="s11">DODURIT CdO 10EP</p></td><td/><td><p class="s11">10.1</p></td><td><p class="s11">2.08</p></td><td><p class="s12">83</p></td><td><p class="s12">48</p></td><td><p class="s11">60</p></td></tr><tr><td><p class="s11">AgCdO 85/15 EP DODURIT CdO 15EP</p></td><td/><td><p class="s11">9.9</p></td><td><p class="s11">2.27</p></td><td><p class="s12">76</p></td><td><p class="s12">44</p></td><td><p class="s11">65</p></td></tr><tr><td><p class="s11">AgSnO² 90/10 EPX SISTADOX 10EPX</p></td><td><p class="s11">CuO and</p><p class="s11">Bi² O³</p></td><td><p class="s11">9.8</p></td><td><p class="s11">2.22</p></td><td><p class="s12">78</p></td><td><p class="s12">45</p></td><td><p class="s11">55</p></td></tr><tr><td><p class="s11">AgSnO² 88/12EPX SISTADOX 12EPX</p></td><td><p class="s11">CuO and</p><p class="s11">Bi² O³</p></td><td><p class="s11">9.6</p></td><td><p class="s11">2.63</p></td><td><p class="s12">66</p></td><td><p class="s12">38</p></td><td><p class="s11">60</p></td></tr></table>
Form of Support: formed parts, stamped parts, contact tips
</figtable>
*'''Silver–zinc oxide (DODURIT ZnO) materials'''
Silver zinc oxide (DODURIT ZnO) contact materials with mostly 6 - 10 wt% oxide content including other small metal oxides are produced exclusively by powder metallurgy ''(Figs. 2.120 – 2.125)'' ''(Table 2.28)''. Adding Ag<sub>2</sub>WO<sub>4</sub> in the process b) as described in the preceding chapter on Ag/SnO<sub>2</sub> has proven most effective for applications in AC relays, wiring devices, and appliance controls. Just like with the other Ag metal oxide materials, semi-finished materials in strip and wire form are used to manufacture contact tips and rivets. Because of their high resistance against welding and arc erosion Ag/ZnO materials present an economic alternative to Cd free Ag-tin oxide contact materials ''<xr id="tab:tab2.30"/> (Tables Tab. 2.30 ) and <xr id="tab:tab2.31"/> (Tab. 2.31)''.
[[File:Micro structure of Ag ZnO 92 8 WPW25.jpg|right|thumb|Micro structure of Ag/ZnO 92/8 WPW25:a) perpendicular to extrusion direction b) parallel to extrusion direction, 1) Ag/ZnO contact layer, 2) Ag backing layer]]
<figtable id="tab:tab2.29">
'''Table 2.29: Optimizing of Silver–Tin Oxide Materials Regarding their Switching Properties and Forming Behavior'''
<table border="1" cellspacing="0" style="border-collapse:collapse"><tr><td><p class="s12">Material/</p><p class="s12">Material Group</p></td><td><p class="s12">Special Properties</p></td></tr><tr><td><p class="s12">Ag/SnO<span class="s48">2 </span>PE</p></td><td><p class="s12">Especially suitable for automotive relays</p><p class="s12">(lamp loads)</p></td><td><p class="s12">Good formability (contact rivets)</p></td></tr><tr><td><p class="s12">Ag/SnO<span class="s48">2 </span>98/2 PX/PC</p></td><td><p class="s12">Especially good heat resistance</p></td><td><p class="s12">Easily riveted, can be directly welded</p></td></tr><tr><td><p class="s12">Ag/SnO<span class="s48">2 </span>TOS F</p></td><td><p class="s12">Especially suited for high inductive</p><p class="s12">DC loads</p></td><td><p class="s12">Very good formability (contact rivets)</p></td></tr><tr><td><p class="s12">Ag/SnO<span class="s48">2 </span>WPC</p></td><td><p class="s12">For AC-3 and AC-4 applications in motor</p><p class="s12">switches (contactors)</p></td><td/></tr><tr><td><p class="s12">Ag/SnO<span class="s48">2 </span>WPD</p></td><td><p class="s12">Especially suited for severe loads (AC-4)</p><p class="s12">and high switching currents</p></td><td/></tr><tr><td><p class="s12">Ag/SnO<span class="s48">2 </span>WPX</p></td><td><p class="s12">For standard motor loads (AC-3) and</p><p class="s12">Resistive loads (AC-1), DC loads (DC-5)</p></td><td/></tr><tr><td><p class="s12">Ag/SnO<span class="s48">2 </span>WTOSF</p></td><td><p class="s12">Especially suitable for high inductive DC</p><p class="s12">loads</p></td><td/></tr></table>
</figtable>
<figtable id="tab:tab2.30">
'''Table 2.30: Contact and Switching Properties of Silver–Metal Oxide Materials'''
With Ag<sub>2</sub>WO<sub>4</sub> additive especially suitable for AC relays
|}
</figtable>
<figtable id="tab:tab2.31">
'''Table 2.31: Application Examples of Silver–Metal Oxide Materials'''
<table border="1" cellspacing="0" style="border-collapse:collapse"><tr><td><p class="s12">Material</p></td><td><p class="s12">Application Examples</p></td></tr><tr><td><p class="s12">Ag/CdO</p></td><td><p class="s12">Micro switches, Network relays, Wiring devices, Appliance switches, Main switches, contactors, Small (main) power switches</p></td></tr><tr><td><p class="s12">Ag/SnO<span class="s48">2</span></p></td><td><p class="s12">Micro switches, Network relays, Automotive relays, Appliance switches,</p><p class="s12">Main switches, contactors, Fault current protection relays (paired against</p><p class="s12">Ag/C), (Main) Power switches</p></td></tr><tr><td><p class="s12">Ag/ZnO</p></td><td><p class="s12">Wiring devices, AC relays, Appliance switches, Motor-protective circuit</p><p class="s12">breakers (paired with Ag/Ni or Ag/C), Fault current circuit breakers paired againct Ag/C, (Main) Power switches</p></td></tr></table>
</figtable>
====Silver–Graphite (GRAPHOR)-Materials====
