Tribopolymer film formation on sliding electrical contacts exposed to siloxanes

Investigations of mechanical shear driven organic film formation, or tribofilms, on catalytic metal surfaces in sliding electrical contacts date back to Hermance and Egan's seminal work on mated palladium contacts. In this report we describe investigations of tribofilm formation from outgassing epoxy vapors, consisting of multiple siloxane species, and from isolated constituent species including octamethyltrisiloxane (OMTS). Experiments performed in varying vapor concentrations of OMTS resulted in the formation of tribopolymer films with similar morphology and impact on electrical contact resistance (ECR) as previously published results of sliding electrical contacts in similar conditions submerged in higher molecular weight polymethyldisiloxane (PDMS) fluid. Infrared (IR) spectroscopy was used to confirm the characteristic signatures of siloxanes and silanes in tribopolymer deposits found in wear scars formed in OMTS. Comparisons to prior studies also showed that the films formed from outgassing epoxy vapor constituents (including OMTS and a multitude of other species) have similar characteristics to the silicon-carbon-oxygen (Si-C-O) films previously found to form in high molecular weight PDMS fluid-filled devices. Tribopolymer formation was demonstrated for a range of electrical contact alloy mated pairs (Paliney-7, Neyoro-G, NiPtRe). Experiments in increasing concentrations of OMTS vapor showed that a persistent tribofilm is rapidly formed under cyclic sliding contact shear that can interrupt electrical current, with a formation rate that increases with increasing concentration. Overall, this work demonstrates the ease with which trace organics can promote the formation of insulating tribopolymer films in electrical contacts and factors that can influence their growth.