PHYSICAL AND CHEMICAL-PROPERTIES OF METAL-OXIDE ADDITIONS TO AG-SNO2 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.