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→Silver-Metal Oxide Materials Ag/CdO, Ag/SnO2, Ag/ZnO
Over the past years, many Ag/CdO contact materials have been replaced by Ag/SnO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) ''<xr id="fig:fig2.114"/> (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) ''<xr id="fig:fig2.116"/> (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).
additives improve the wettability of the oxide particles and increase the viscosity of the Ag melt. They also provide additional benefits to the mechanical and arcing contact properties of materials in this group ''(Table 2.26)''.
'''Table 2.26: Physical and Mechanical Properties as well as Manufacturing Processes and Forms of Supply of Extruded Silver-Tin Oxide (SISTADOX) Contact Materials'''nicht gemacht!
====DEV:LIST====
In the manufacture the initial powder mixes different processes are applied which provide specific advantages of the resulting materials in respect to their contact properties <xrlabel id="fig:figlist" group="fig" />(Figs. 2.87 – 2.119). Some of them are described here as follows:
