The carbon deposition mechanism in vapor phase lubrication

The study of various alkoxy species on metal surfaces has provided insight into the mechanism by which carbon is deposited into the lubricating films of polyphosphate glass generated by arylphosphate vapor phase lubricants. P revious work using trimethylphosphite has suggested that one of the initial steps in the decomposition of organophosphorus compounds on metal surfaces is cleavage of P-O bonds to produce adsorbed alkoxy species. In the case o f alkyl alkoxy groups (poor ligands for vapor phase lubrication) there are reaction mechanisms such as beta-hydride elimination which efficiently remo ve hydrocarbons from the surface. In the case of the aryl alkoxy groups (go od ligands for vapor phase lubricants) such mechanisms cannot be active due to the lack of beta-hydrogen atoms. Experiments using various alkoxy speci es demonstrate these differences and reveal that phenoxy groups deposit car bon onto the surface quite efficiently while cyclohexanoxy and t-butanoxy g roups do not.