The Effect of Additive Concentration on Material Erosion in Matrix-Strengthened Silver-Cadmium Oxide

A matrix-strengthening agent, GeO2, has been added to AgdO contact material. This agent acts to enhance the wetting of molten lver on the contact surface, thus reducing its susceptibility to arc erosion. he erosion characteristics of matrix-strengthened materials, over the concentration range from 0.15 to 2.0 wt% GeO2, have been evaluated and compared to those of standard additive-free Ag-CdO. The material loss rate for matrix-strengthened samples has been found to be relatively inderodent of GeO2concentration up to about 0.5 wt% but increases at higher additive levels. The matrix-strengthened materials do have a somewhat higher steady-state material loss rate than does additive-free Ag-CdO. However metallographic sections reveal a distinct reduction in the degree i thermal stress cracking and a pronounced blunting of incipient crack tips by inflow of molten silver. This decreases the probability of macroscopic chunk material loss, thus extending operational life. The improved crack resistance shows no clear concentration dependence and was observed at all levels tested. The matrix-strengthening additive affects other Ag-CdO contact properties. Measurements of the concentration dependence of both the interfacial resistance and the asymmetry of material loss between the members of a contact pair suggest that GeO2preferentially gregates at the contact surface after a number of arc events. Evidence of such segregation has been obtained from Spectroscopic examinations of the electric arcs supported by matrix-strengthened Ag-CdO electrodes, as well from various analytical measurements on the eroded specimens. Such segregation enables maximization of the matrix-strengthening effect with a minimum of additive content.