POWDER METALLURGICAL SILVER-METAL OXIDE ELECTRICAL CONTACTS BY AN ELECTROLESS COATING PROCESS

Electrical contacts grade Ag-CdO and Ag-ZnO composite powders have bee n produced by two different processing routes, i.e. the conventional p owder metallurgy (PM) route involving mixing/blending of silver and ox ide phase particles and the electroless coating route. The conventiona l PM route often exhibits grossly inhomogeneous distribution of the ox ide phase in the silver matrix leading to inferior electrical contact properties. The electroless coating process has been developed as an a lternative to overcome this problem. The powders so produced were char acterized by X-ray diffraction, scanning electron microscopy and elect ron spectroscopy for chemical analysis. They were subjected to pressin g, sintering, repressing and hot pressing operations to obtain high de nsity cylindrical compacts. Compacts were then evaluated for density, hardness, microstructure and electrical properties. The effects of the powder processing route on the characteristics of powder as well as t he properties of the final compacts for both the Ag-CdO and Ag-ZnO sys tems have been studied.