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→Silver-Metal Oxide Materials Ag/CdO, Ag/SnO2, Ag/ZnO
The manufacturing of strips and wires by internal oxidation starts with a molten alloy of silver and cadmium. During a heat treatment below it's melting point in a oxygen rich atmosphere in such a homogeneous alloy the oxygen diffuses from the surface into the bulk of the material and oxidizes the Cd to CdO in a more or less fine particle precipitation inside the Ag matrix. The CdO particles are rather fine in the surface area and are becoming larger further away towards the center of the material <xr id="fig:Micro structure of AgCdO9010"/> (Fig. 2.83).
During the manufacturing of Ag/CdO contact material by internal oxidation the processes vary depending on the type of semi-finished material. For Ag/CdO wires a complete oxidation of the AgCd wire is performed, followed by wire-drawing to the required diameter <xr id="fig:Strain hardening of internally oxidized AgCdO9010"/> (Figs. 2.77) and <xr id="fig:Softening of internally oxidized AgCdO9010"/> (Fig. 2.78). The resulting material is used for example in the production of contact rivets. For Ag/CdO strip materials two processes are commonly used: Cladding of an AgCd alloy strip with fine silver followed by complete oxidation results in a strip material with a small depletion area in the center of it's thickness and a Ag backing suitable for easy attachment by brazing (sometimes called “Conventional "Conventional Ag/CdO”CdO"). Using a technology that allows the partial oxidation of a dual-strip AgCd alloy material in a higher pressure pure oxygen atmosphere yields a composite Ag/CdO strip material that has besides a relatively fine CdO precipitation also a easily brazable AgCd alloy backing <xr id="fig:Micro structure of AgCdO9010ZH"/> (Fig. 2.85). These materials (DODURIT CdO ZH) are mainly used as the basis for contact profiles and contact tips.
During powder metallurgical production the powder mixed made by different processes are typically converted by pressing, sintering and extrusion to wires and strips. The high degree of deformation during hot extrusion produces a uniform and fine dispersion of CdO particles in the Ag matrix while at the same time achieving a high density which is advantageous for good contact properties <xr id="fig:Micro structure of AgCdO9010P"/> (Fig. 2.84). To obtain a backing suitable for brazing, a fine silver layer is applied by either com-pound extrusion or hot cladding prior to or right after the extrusion <xr id="fig:Micro structure of AgCdO8812WP"/> (Fig. 2.86).
For larger contact tips, and especially those with a rounded shape, the single tip Press-Sinter-Repress process (PSR) offers economical advantages. The powder mix is pressed in a die close to the final desired shape, the “green” "green" tips are sintered, and in most cases the repress process forms the final exact shape while at the same time increasing the contact density and hardness.
Using different silver powders and minor additives for the basic Ag and CdO starting materials can help influence certain contact properties for specialized applications.
:'''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:tab2.27Physical Properties of Powder Metallurgical Silver-Metal Oxide Materials with Fine Silver Backing Produced by the Press-Sinter-Repress Process"/> (Table 2.27).
<div id="figures">
<xr id="fig:Strain hardening of AgSNO2 92 8 PE"/> Fig. 2.87: Strain hardening of Ag/SnO<sub>2</sub> 92/8 PE by cold working
<figtable id="tab:tab2.27Physical Properties of Powder Metallurgical Silver-Metal Oxide Materials with Fine Silver Backing Produced by the Press-Sinter-Repress Process"><caption>'''Table 2.27: Physical Properties of Powder Metallurgical Silver-Metal Oxide Materials with Fine Silver Backing Produced by the Press-Sinter-Repress Process'''</caption>
<table class="twocolortable">
<tr><th rowspan="2"><p class="s11">Material/</p><p class="s11">DODUCO- Designation</p></th><th rowspan="2"><p class="s11">Additives</p></th><th rowspan="2"><p class="s11">Density</p><p class="s11">[ g/cm<sup>3</sup>]</p></th><th rowspan="2"><p class="s11">Electrical</p><p class="s11">Resistivity</p><p class="s11">[µ<span class="s14">S ·</span>cm]</p></th><th colspan="2"><p class="s11">Electrical</p><p class="s11">Conductivity</p></th><th rowspan="2"><p class="s11">Vickers</p><p class="s11">Hardness</p><p class="s11">HV 10.</p></th></tr>
<figtable id="tab:tab2.28">
<caption>'''Table 2.28: Physical and Mechanical Properties as well as Manufacturing Processes and Forms of Supply of Extruded Silver-Zinc Oxide (DODURIT ZnO) Contact'''</caption>
{| class="twocolortable" style="text-align: left; font-size: 12px"
<div id="figures1">
<xr id="fig:fig2.120Strain hardening of Ag ZnO 92 8 PW25"/> Fig. 2.120: Strain hardening of Ag/ZnO 92/8 PW25 by cold working
<xr id="fig:fig2.121Softening of Ag ZnO 92 8 PW25"/> Fig. 2.121: Softening of Ag/ZnO 92/8 PW25 after annealing for 1 hr after 30% cold working
<xr id="fig:fig2.122Strain hardening of Ag ZnO 92 8 WPW25"/> Fig. 2.122: Strain hardening of Ag/ZnO 92/8 WPW25 by cold working
<xr id="fig:fig2.123Softening of Ag ZnO 92 8 WPW25"/> Fig. 2.123: Softening of Ag/ZnO 92/8 WPW25 after annealing for 1hr after different degrees of cold working
<xr id="fig:fig2.124Micro structure of Ag ZnO 92 8 Pw25"/> Fig. 2.124: Micro structure of Ag/ZnO 92/8 Pw25: a) perpendicular to extrusion direction
b) parallel to extrusion direction
<xr id="fig:fig2.125Micro structure of Ag ZnO 92 8 WPW25"/> Fig. 2.125: 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
</div>
<div class="multiple-images">
<figure id="fig:fig2.120Strain hardening of Ag ZnO 92 8 PW25">
[[File:Strain hardening of Ag ZnO 92 8 PW25.jpg|left|thumb|<caption>Strain hardening of Ag/ZnO 92/8 PW25 by cold working</caption>]]
</figure>
<figure id="fig:fig2.121Softening of Ag ZnO 92 8 PW25">
[[File:Softening of Ag ZnO 92 8 PW25.jpg|left|thumb|<caption>Softening of Ag/ZnO 92/8 PW25 after annealing for 1 hr after 30% cold working</caption>]]
</figure>
<figure id="fig:fig2.122Strain hardening of Ag ZnO 92 8 WPW25">
[[File:Strain hardening of Ag ZnO 92 8 WPW25.jpg|left|thumb|<caption>Strain hardening of Ag/ZnO 92/8 WPW25 by cold working</caption>]]
</figure>
<figure id="fig:fig2.123Softening of Ag ZnO 92 8 WPW25">
[[File:Softening of Ag ZnO 92 8 WPW25.jpg|left|thumb|<caption>Softening of Ag/ZnO 92/8 WPW25 after annealing for 1hr after different degrees of cold working</caption>]]
</figure>
<figure id="fig:fig2.124Micro structure of Ag ZnO 92 8 Pw25">
[[File:Micro structure of Ag ZnO 92 8 Pw25.jpg|left|thumb|<caption>Micro structure of Ag/ZnO 92/8 Pw25: a) perpendicular to extrusion direction b) parallel to extrusion direction</caption>]]
</figure>
<figure id="fig:fig2.125Micro structure of Ag ZnO 92 8 WPW25">
[[File:Micro structure of Ag ZnO 92 8 WPW25.jpg|right|thumb|<caption>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</caption>]]
</figure>
<figtable id="tab:tab2.29">
<caption>'''Table 2.29: Optimizing of Silver–Tin Oxide Materials Regarding their Switching Properties and Forming Behavior'''</caption>
<table class="twocolortable">
<tr><th><p class="s12">Material/</p><p class="s12">Material Group</p></th><th><p class="s12">Special Properties<th colspan="2"></p></th></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 id="tab:tab2.30">
<caption>'''Table 2.30: Contact and Switching Properties of Silver–Metal Oxide Materials'''</caption>
{| class="twocolortable" style="text-align: left; font-size: 12px"
<figtable id="tab:tab2.31">
<caption>'''Table 2.31: Application Examples of Silver–Metal Oxide Materials'''</caption>
<table class="twocolortable">
<tr><th><p class="s12">Material</p></th><th><p class="s12">Application Examples</p></th></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>
