The intial step of tribochemical reactions of perfluoropolyether on amorphous carbon

Abstract

The initial step of tribochemical reactions of perfluoropolyether (PFPE) on amorphous carbon of a magnetic disk was investigated with attenuated total reflectance (ATR) spectroscopy. Wear tests on lubricated disks were carried out using an Al 2O 3TiC sliding tip in the form of a flat strip sliding perpendicular to the strip axis. This sliding tip provided a wide sliding area to allow easy detection of a trace amount of reaction product. An ATR analysis showed that a small amount of carbonyl group was formed in teh lubricant layer after the wear test. X-ray photoelectron spectra indicated that metal fluoride, which has been reported as a typical product in catalytic degradation of PFPE on the sliding materials, was not formed on the surface of the sliding tip after the wear test. Meanwhile a little carbonyl group was also observed in the ATR spectrum of eluted PFPE lubricant from a disk after UV irradiation. Molecular orbital simulations were performed to explain these initial steps of triboreaction and photoelectron-induced reaction. The similarity between the results of the wear test and the photoelectron-induced reaction suggested that a neural radical, which was formed from an anion radical after an electron attachment to PFPE, reacted with another PFPE molecule and led to the formation of a carbonyl group.