The Effect of Additives from Groups IA and IIA on the Morphology and Properties of Silver-Cadmium Oxide Contacts

This paper presents a detailed description of the effect of single additive elements selected from Group IA and Group IIA of the Periodic Table on the microstructure and other physical and electrical properties of Ag-10 CdO contact materials produced by internal oxidation of silvercadmium alloys. The additive elements studied in this investigation were lithium, beryllium, magnesium, calcium, strontium, and barium, in amounts from 0.01 w/o to 1.0 w/o. Hardness and electrical conductivity were measured, along with 20,000 cycle make and break contact testing. It was observed that very small amounts of certain additives In these groups can influence the morphology and properties of silver-cadmium oxide contact materials, generally resulting in a refinement of the size of the dispersed particles. The generally accepted assumption that reduction in dispersed particle size always results in lower erosion rates during contact use was shown not always to be true. In concentrations to . 1 w/o, the additives were shown to minimize or eliminate grain boundary precipitation or form divorced grain boundaries. Additive concentrations greater than 0.50 w/o in certain cases can produce heavy grain boundary precipitation and may prevent the normal propagation of the oxidation front. Precipitation of the oxide can occur in a periodic manner, apparently of the Leisegang type, when additions of up to 0.3 w/o magnesium or less than 0.15 w/o beryllium is used. The influence of each additive on the hardness and conductivity of the basic composite is also reported along with the microstructural features and electrical contact performance.