Formation Process of the Crater Structures of Ni and Cu Contacts at Breaking Arcs

For the investigation of the formation process of the crater structure, evaporated Ni and Cu thin films being formed on bulk Ni and Cu electrodes were eroded by a Single break arc in a de resistive circuit. It was concluded through observations of the eroded area by a scanning electron microscope (SEM) that the diameter of a cathode spot of Ni electrodes is proportional to a square root of current. The diameter of a cathode spot could be estimated to be 30-40 #m for Ni contacts at 60-V dc and 1 A and 22-27µm for Cu contacts at 60-V dc and 0.5 A. The cathode spot of Ni and Cu contacts did not move continuously; they moved the length of the radius of a cathode spot. The cathode spot behavior could be discussed based on the temperature distribution on the cathode spot and the decomposition of the oxide layer on the cathode surface. The model of the formation of a crater structure was proposed by combining the model of microcrater formation and the behavioral model of a cathode spot.