Tribochemical Reaction of Stearic Acid on Copper Surface Studied by Surface Enhanced Raman Spectroscopy

Micro-Raman spectroscopy was used to study the tribochemical reaction of a copper surface and stearic acid in pin-on-disc wear tests. The characteristic Raman bands of cupric stearate at 1547, 623, 288, and 243 wavenumbers were observed in the spectra of the worn copper surfaces. This confirms the formation of cupric stearate. The tribochemical reaction was initiated by the formation of a chemisorbed stearic acid on the native oxide film of the copper surface. This chemisorbed stearic acid exists as a monomer and is bonded to the copper surface in a nearly perpendicular configuration. The presence of this native oxide film is necessary for this chemisorption to occur. The chemisorbed stearic acid is converted into cupric stearate by tribochemical interactions.