2023 Volume 68 Issue 7 Pages 483-489
Dilute concentration as 0.1 mass% of oleic acid in PAO as a base oil was detected successfully by micro-SEIRAS (surface enhanced infra-red absorption spectroscopy) which is newly developed with a micro-Fourier transform infrared spectroscopy (FTIR) and a hemispherical silicon prism coated with a thin layer of Au for SEIRAS. In situ observation of lubricant film by micro-SEIRAS was carried out under lubricating conditions. When lubricant oil between the prism and the steel ball was sheared by rotating ball, the absorbance of carboxyl group increased gradually and the absorbance was maintained even after the termination of shearing. The result suggests that oleic acid was concentrated in a thin layer on the prism from lubricant oil by shearing. According to the observation, it was found that the concentrated layer of oleic acid was formed by shearing of lubricant oil and the layer was stable under a static condition. Since monomer of carboxyl group as well dimer was observed under shearing,even adsorbed oleic acid on the prism surface can be detected by SEIRAS.
