In Situ Analysis of the Tribochemical Reaction of CNx by FTIR

Carbon Nitride (CNx) coating was reported to show a superlow friction coefficient when it slid against a Si3N4 ball in nitrogen gas at atmospheric pressure. This superlow friction phenomenon occurred after a number of sliding cycles, in the so-called running-in period, due to the nitrogen atom desorption from the topmost CNx coating surface; its the surface became a graphite-like layer, and a transfer layer was formed on the counter material surface. However, a friction test and surface analysis should be conducted simultaneously, when detailed frictional phenomena including functional groups are observed on the topmost CNx surface. It was supposed that several functional groups were adsorbed on the topmost surface of the carbon system coating when the specimen was withdrawn from the synthesis chamber. In this study, we constructed a friction test apparatus in a FTIR analytic chamber to conduct friction tests and surface analysis without taking the friction test chamber out of the analytical chamber. The analysis results of 1500 cycles each indicated that the -OH or -NH functional group gradually increased with the number of sliding cycles. However, the group decreased suddenly as the friction coefficient decreased. Finally, these kinds of functional groups were not detected when the CNx coating showed superlow friction phenomena