Fundamental Analysis of Cu Brush-Ag Slip Ring Sliding Electrical Contacts

Electrical contacts involving current-carrying copper-wire brushes sliding on a sputter-cleaned silver slip ring and rotating in an ambient of 1 atm of wet CO2were characterized by Auger electron spectroscopy (AES), scanning electron microscopy (SEM), X-ray energy spectroscopy (XES), reflection high-energy electron diffraction (RHEED), and in situ measurements of contact resistance. AES analysis of the slip rings showed 1) carbon formation at the contact zone and 2) increasing amounts of Cu transfer from the brushes to the slip ring with increasing contact current. SEM and XES analyses of the brushes, slip ring, and wear particles showed that the copper content of the wear particles and the copper concentration of the slip ring surface increased with increasing contact current. RHEED studies of the wear particles showed that higher currents resulted in larger grain sizes. Initially, high values of the contact resistance decreased to fractions of a milliohm, and then after approximately 2000 cycles, gradually became more erratic as the contact deteriorated. This deterioration was caused by the accumulation of Ag debris on the Cu brush ends.