Synergistic effect of nanodiamonds on the adsorption of tricresyl phosphate on iron oxide surfaces

Nanodiamonds (NDs) have potential uses in many applications, including as additives for liquid lubricants where they may be combined with more traditional chemicals, such as tricresyl phosphate (TCP), to form protective films on sliding surfaces. It has been shown that NDs can function synergistically with TCP to facilitate film formation on air baked iron. Here, reactive molecular dynamics simulations of TCP and NDs on an amorphous iron oxide surface reproduce experimental observations of the temperature at which film formation begins with NDs present and the effect of NDs on film composition. Analysis of chemical bonding in the simulations shows that the film formed in the presence of NDs comprises NDs and TCP that are both directly and indirectly bonded to the surface. Notably, the amount of phosphorus in the film, which is important for surface protection, is increased by TCP molecules that are indirectly bonded to the surface via NDs, which suggests that indirect bonding is one mechanism by which NDs facilitate film growth. The synergy of NDs and TCP has important implications for the development of NDs as emerging lubricant additives which must function with existing additives such as TCP in many applications. Published under license by AIP Publishing.