Arc-Erosion Studies of Matrix-Strengthened Silver-Cadmium Oxide

A matrix-strengthening agent has been added to Ag-CdO material in order to reduce it´s susceptibility to arc erosion. The matrix-strengthening agent, added to Ag-CdO as an additional oxide component, was chosen to enhance the wetting of liquid silver on the Ag-CdO surface. The erosion characteristics of Ag-CdO containing various matrix-strengthening additives have been investigated under static-gap conditions and in switching devices. The statlc-gap erosion measurements showed a lower material loss rate for Ag-CdO materials that euntained a matrix-strengthening additive compared to conventional Ag-CdO. The lowest erosion rate was obtained with a material containing the additive exhibiting the lowest interfacial energy against silver. Electron microscopy of the eroded surface of matrixstrengthened Ag-CdO revealed a smooth surface morphology indicative of good wetting between molten silver droplets and the contact surface. The erosion characteristics of materials containing the two most promising additives GeO2and Ta205were evaluated in switching devices. Even though the material loss rate of the matrix-strengthened Ag-CdO was higher than that of conventional Ag-CdO under some test conditions, the surfaces of the matrix-strengthened materials consistently showed a uniform distribution of damage over the contact surface in contrast to the more severe localized damage observed on the conventional Ag-CdO contacts. Metallographic sections of the tested contacts revealed a significant reduction in thermal stress cracking for materials containing the additive. The reduced cracking tendency and more uniform erosion pattern are shown to result in extended cycle life under heavy arcing conditions for matrix-strengthened Ag-CdO compared to conventional Ag-CdO.