Wear debris analysis in rotating Ag-Cu electrical contacts

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A copper slip ring was rotated in contact with two current-carrying silver wire brushes in an ultrahigh vacuum system. The copper ring was initially sputter cleaned and the experiments were performed in humidified CO 2 at atmospheric pressure. The wear particles produced at the two contacts were collected for subsequent investigations by scanning electron microscopy and electron probe microanalysis. Currents ranging from 0 to 40 A were used and the slip ring was rotated at 150 rev min −1. In one zerocurrent experiment a speed of 15 rev min −1 was used for comparison. The wear particles consisted of pure silver, pure copper and mixed particles with the relative amounts depending on the current through the contact. Some of the characteristic features of the most frequently occurring wear particles are explained and the mechanisms for the generation of the particles are discussed.