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

The new contact material AgSnO/sub 2/, 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 SnO/sub 2/ surface by liquid silver, as well as the microstructure of the area melted by the electric arc. This work considers the frequently used dopants WO/sub 3/, MoO/sub 3/, Bi/sub 2/O/sub 3/, CuO and RuO/sub 2/, as well as others: ZnO, Ta/sub 2/O/sub 5/, HgO, RuO/sub 2/, Sb/sub 2/O/sub 3/, TeO/sub 2/ and TaC. DTA and TGA analyses are performed on mixtures of these metal oxides with SnO/sub 2/, Ag, and AgSnO/sub 2/. 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 AgSnO/sub 2/ materials doped with these substances. These structures are interpreted and related to performance in arcing contact applications. >