Comparison of the Inherent Arc Erosion Behaviors of Silver-Cadmium Oxide and Silver-Tin Oxide Contact Materials

Powder metallurgically produced silver-cadmium oxide and silver-tin oxide materials with equal volume percentages of oxide were electrically tested to evaluate and compare the effects of the different oxides on the arc erosion behaviors. The silver-tin oxide material had less steady-state erosion, better weld resistance, and higher contact resitance compared to silver-cadmium oxide. The eroded surface structures were examined and used to explain these quantitative results. The arc-affected erosion surfaces of the silver-tin oxide material consisted of silver, tin oxide, and porosity distributed across the contact surface, yielding Iow weld strengths but high contact resistance. The silver-cadmium oxide eroded surfaces had large elevated oxide-depleted areas which yielded Iow contact resistance but higher weld strengths. Theories of how these 'eroded surface structures developed under the given conditions are presented for the silver-cadmium oxide and the silver-tin oxide materials.