Physical and chemical properties of metal oxide additions to Ag-SnO 2 contact materials and predictions of electrical performance

The new contact material AgSnO₂, which is replacing AgCdO in many applications, requires the addition of doping agents to improve electrical contact performance. These additions effect thermodynamic stability, the wettability of the SnO₂ surface by liquid silver, as well as the microstructure of the area melted by the electric arc. This work considers the frequently used dopants WO₃, MoO₃, Bi₂O₃, CuO and RuO₂, as well as others: ZnO, Ta₂O₅, HgO, RuO₂, Sb₂O₃, TeO₂ and TaC. DTA and TGA analyses are performed on mixtures of these metal oxides with SnO₂, Ag, and AgSnO₂. Reactions products, if present, are characterized by x-ray diffraction. The wetting angles of molten silver on surfaces of these mixtures are established. The results are used to interpret the microstructures found in the molten regions of AgSnO₂ materials doped with these substances. These structures are interpreted and related to performance in arcing contact applications