A tribochemical investigation of the reaction products on Pd plated contacts

Fretting experiments on Pd-plated pairs were carried out in an organic/air atmosphere including benzene, cyclohexane, and n-hexane, to understand the relationships between the tribological properties, the chemical form of reaction products, and the electric conductivity to form organic reaction products at the contact. During the initial stage of fretting experiments in these atmospheres, the contact resistance was rather low and stable, compared with that in ambient air. Quantitative analysis of C and O on the contact surface by electron probe X-ray microanalyzer showed that a small amount of reaction product existed in and around the contact area, and the atomic composition of C and O of the product was mostly stoichiometric. Analytical results using Fourier transformed infrared absorption spectroscopy showed that the products include carbonyl, hydroxide, and minor amount of the initial organic compounds in dried atmosphere. Experimental results suggested that Pd surface fretted with no electric current across it induced catalytic reactions to oxidize the organic molecules to form carbonyl or carboxyl group in ambient atmosphere. The reaction product which was generated in dried atmosphere with organic vapor effectively maintained the contact resistance at a low and stable value. The wear rate of the contact surface, film thickness of the reaction product, and different effects of oxidation rate in dried and ambient air are discussed.