Abstract
Semi-solid lubricants, such as grease and gels, are mixtures of oil, thickeners, and gel agents. In this study, the concentration of the urea thickener and gel agent at the point of elastohydrodynamic lubrication (EHL) contact was investigated by in situ observation with a micro-Fourier transform infrared spectrometer (micro-FTIR). Micro-FTIR was used in conjunction with a ball-on-disk lubrication tester. The lubricant film was analyzed by micro-FTIR under dynamic conditions. Characteristic peaks correlating to the C-H stretching mode at 2850-3000 cm-1 and the N-H stretching mode at 3000-3500 cm-1 were found to originate from the oil and the urea thickener and gel agent, respectively. The concentration of the thickener and gel agent were estimated from these characteristic IR peaks. The results showed that the concentration of urea thickener and gel agent was increased drastically at the Hertzian contact region. Meanwhile, infrared spectra under hydrostatic pressure were obtained using a diamond-anvil cell. It was confirmed that the hydrogen bonding of the urea thickener and gel agent was stabilized under high-pressure conditions.
