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[[File:Physical and Mechanical Properties.jpg|right|thumb|Physical and Mechanical Properties as well as Manufacturing Processes and Forms of Supply of Extruded Silver Cadmium Oxide (DODURIT CdO) Contact Materials]]

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 an oxygen rich atmosphere in of 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 getting 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 an Ag backing suitable for easy attachment by brazing (sometimes called "Conventional Ag/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 an easily brazable AgCd alloy backing <xr id="fig:Micro structure of AgCdO9010ZH"/><!--(Fig. 2.85)-->. These materials 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 into a die close to the final desired shape, the "green" tips are sintered, and in most cases , the repress process forms the exact 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.

Over the past years, many Ag/CdO contact materials have been replaced by Ag/SnO₂ based materials with 2-14 wt% SnO₂ because of the toxicity of Cadmium. This changeover was further favored by the fact that Ag/SnO₂ 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:Contact and Switching Properties of Silver–Metal Oxide Materials"/><!--(Table 2.30)-->. Ag/SnO₂ 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:tab2.28"/><!--(Tab. 2.28)--> und <xr id="tab:tab2.29"/><!--(Table 2.29)-->.

Manufacturing of Ag/SnO₂ 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. Adding a brazable fine silver layer to such materials results in a semifinished material , suitable for the manufacture as smaller weld profiles <xr id="fig:Micro structure of Ag SnO2 92 8 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:Application Examples of Silver–Metal Oxide Materials"/><!--(Table 2.31)-->.

In the manufacture for the initial powder mixes , different processes are applied which provide specific advantages of the resulting materials in respect to their contact properties <!--[[#figures|(Figs. 43 – 75)]]-->. Some of them are described here as follows::'''a) Powder blending from single component powders''' <br> In this common process all components , including additives that are part of the powder mix , are blended as single powders. The blending is usually performed in the dry stage in blenders of different design.

:'''b) Powder blending on the basis of doped powders''' <br> For incorporation of additive oxides in the SnO₂ powder , the reactive spray process has shown advantages. This process starts with a waterbased solution of the tin and other metal compounds. This solution is nebulized under high pressure and temperature in a reactor chamber. Through the rapid evaporation of the water , each small droplet is converted into a salt crystal and from there gets transformed by oxidation into a tin oxide particle in which the additive metals are distributed evenly as oxides. The so created doped AgSnO₂ powder is then mechanically mixed with silver powder.

:'''c) Powder blending based on coated oxide powders''' <br> In this process , tin oxide powder is blended with lower meting additive oxides such as for example Ag₂ MoO₄ and then heat treated. The SnO₂ particles are coated in this step with a thin layer of the additive oxide.

:'''e) Powder blending based on chemically precipitated compound powders''' <br> A silver salt solution is added to a suspension of for example SnO₂ 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 SnO₂.

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 using the press-sinter-repress (PSR) process <xr id="tab:Physical Properties of Powder Metallurgical Silver-Metal Oxide Materials with Fine Silver Backing Produced by the Press-Sinter-Repress Process"/><!--(Table 2.27)-->.

Silver zinc oxide contact materials with mostly 6 - 10 wt% oxide content , including other small metal oxides , are produced exclusively by powder metallurgy [[#figures1|(Figs. 76 – 81)]],<!--(Table 2.28)-->. Adding WO₃ or Ag₂WO₄ in the process - as described in the preceding chapter on Ag/SnO₂ - 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:Contact and Switching Properties of Silver–Metal Oxide Materials"/><!--(Tab. 2.30)--> and <xr id="tab:Application Examples of Silver–Metal Oxide Materials"/><!--(Tab. 2.31)-->.

|High resistance against welding during current -on -switching for currents up to<br />5kA especially for powder metallurgical materials,<br />

Use of Ag/CdO in automotive components is prohibited because of Cd toxicity,<br />Prohibition of use in consumer products and appliances in the EU.

Very high resistance against welding during current -on -switching,<br />Weld resistance increases with higher oxide contents,<br />

High resistance against welding during current -on -switching<br />(capacitor contactors),<br />

Ag/C contact materials exhibit on the one hand an extremely high resistance to contact welding but on the other have a low arc erosion resistance. This is caused by the reaction of graphite with the oxygen in the surrounding atmosphere at the high temperatures created by the arcing. The weld resistance is especially high for materials with the graphite particle orientation parallel to the arcing contact surface. Since the contact surface after arcing consists of pure silver , the contact resistance stays consistently consistantly low during the electrical life of the contact parts.

A disadvantage of the Ag/C materials is their rather high erosion rate. In materials with parallel graphite orientation this can be improved , if a part of the graphite is incorporated into the material in the form of fibers (GRAPHOR DF), <xr id="fig:Micro structure of Ag C DF"/><!--(Fig. 2.133)-->. The weld resistance is determined by the total content of graphite particles.

welding Welding the actual process depends on the material's graphite orientation. For Ag/C tips with vertical graphite orientation the contacts are assembled with single tips. For parallel orientation a more economical attachment starting with contact material in strip or profile tape form is used in integrated stamping and welding operations with the tape fed into the weld station, cut off to tip form and then welded to the carrier material before forming the final contact assembly part. For special low energy welding , the Ag/C profile tapes can be pre-coated with a thin layer of high temperature brazing alloys such as CuAgP.

The main applications for Ag/C materials are protective switching devices such as miniature molded case circuit breakers, motor-protective circuit breakers, and fault current circuit breakers, where during short circuit failures , highest resistance against welding is required <xr id="tab:tab2.34"/><!--(Table 2.34)-->. For higher currents the low arc erosion resistance of Ag/C is compensated by asymmetrical pairing with more erosion resistant materials such as Ag/Ni, Ag/W and Ag/WC.

!Material/<br />DODUCO-<br />Designation