| Methods derived from surface science were used to investigate the surface chemistry of adsorbed lubricants under ultrahigh vacuum condition. Studies were performed to probe the thermal decomposition mechanisms of the vapor phase lubricants on metal and ceramic surfaces with the goal of understanding lubricious film formation mechanisms.; The surface chemistry of alkylphosphate and arylphosphate on a polycrystalline Fe surface was investigated to illustrate some of the initial steps in the reaction mechanisms of alkyl and arylphosphate vapor phase lubricants. The alkylphosphates decompose via alkyl intermediates that readily undergo beta-hydride elimination and desorb into the gas phase as olefins, thus removing carbon from the surface. In contrast, the arylphosphates generate aryloxy intermediates by P-O bond scission and aryl intermediates by further C-O bond scission. Neither of these intermediates can undergo beta-hydride elimination and, thus, they decompose to deposit carbon onto the Fe surface. The higher efficiency for carbon deposition by the arylphosphates may be the primary reason for the superior performance of the arylphosphates over alkylphosphates as vapor phase lubricants.; The possible differences in decomposition mechanisms of ortho-, meta-, and para-tricresylphosphate (TCP) vapor phase lubricants on Fe were examined. It is shown that the TCP isomers decompose by the same reaction mechanisms and with roughly the same kinetics on Fe.; The thermal chemistry of m-TCP on the clean and phosphorous covered Ni(100) surfaces was studied in order to understand the differences between its reactivity on Fe and Ni. This research was motivated by the previous observation that TCP lubricates Fe but not Ni. Upon heating to 800 K m-TCP decomposes on the clean Ni(100) surface to deposit carbon and phosphorous with the evolution of H2, CO, benzene, and toluene into the gas phase. The adsorption and heating of m-TCP on the phosphorus modified Ni surface does not result in significant decomposition. The clean Ni substrate is able to activate TCP decomposition in much the same way that clean Fe surfaces induce TCP decomposition. The differences in the chemistry of TCP on the clean metal surfaces cannot explain the fact that TCP vapor forms thick lubricating films on Fe but not on Ni.; The feasibility is demonstrated of a new approach to the vapor phase lubrication of ceramics using vapor delivery of metals. (Abstract shortened by UMI.)... |
