Powder metallurgical silver-metal oxide electrical contacts by an electroless coating process

Electrical contacts grade Ag-CdO and Ag-ZnO composite powders have been produced by two different processing routes, i.e. the conventional powder metallurgy (PM) route involving mixing/blending of silver and oxide phase particles and the electroless coating route. The conventional PM route often exhibits grossly inhomogeneous distribution of the oxide phase in the silver matrix leading to inferior electrical contact properties. The electroless coating process has been developed as an alternative to overcome this problem. The powders so produced were characterized by X-ray diffraction, scanning electron microscopy and electron spectroscopy for chemical analysis. They were subjected to pressing, sintering, repressing and hot pressing operations to obtain high density 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 the properties of the final compacts for both the Ag-CdO and Ag-ZnO systems have been studied

Effect of lithium addition on density and oxide-phase morphology of Ag-ZnO electrical contact materials

The effect of trace additions of lithium as lithium nitrate, to spray-coprecipitated silver-zinc oxide powder, on density and oxide-phase morphology of Ag-ZnO contact materials has been investigated. The Li-treated powders are characterized by particle size analyser and ESCA. The pressed-sintered-hot pressed compacts with and without Li are evaluated for density, microhardness, electrical conductivity and microstructure. The morphological evaluation of ZnO phase is done using quantitative image analysis technique. The mechanism of activation due to Li and the resultant changes in oxide-phase morphology for Ag-ZnO composite system are analysed. (C) 199