Search

Moving mechanical interfaces are commonly lubricated and separated by a combination of fluid films and solid 'tribofilms', which together ensure easy slippage and long wear life (1). The efficacy of the fluid film is governed by the viscosity of the base oil in the lubricant; the efficacy of the solid tribofilm, which is produced as a result of sliding contact between moving parts, relies upon the effectiveness of the lubricant's anti-wear additive (typically zinc dialkyldithiophosphate) (2). Minimizing friction and wear continues to be a challenge, and recent efforts have focused on enhancing the anti-friction and anti-wear properties of lubricants by incorporating inorganic nanoparticles and ionic liquids (3,4). Here, we describe the in operando formation of carbon-based tribofilms via dissociative extraction from base-oil molecules on catalytically active, sliding nanometre-scale crystalline surfaces, enabling base oils to provide not only the fluid but also the solid tribofilm. We study nanocrystalline catalytic coatings composed of nitrides of either molybdenum or vanadium, containing either copper or nickel catalysts, respectively. Structurally, the resulting tribofilms are similar to diamond-like carbon (5). Ball-on-disk tests at contact pressures of 1.3 gigapascals reveal that these tribofilms nearly eliminate wear, and provide lower friction than tribofilms formed with zinc dialkyldithiophosphate. Reactive and ab initio molecular-dynamics simulations show that the catalytic action of the coatings facilitates dehydrogenation of linear olefins in the lubricating oil and random scission of their carbon-carbon backbones; the products recombine to nucleate and grow a compact, amorphous lubricating tribofilm., Transportation vehicles account for about 19% of the world's energy consumption and some 23% of total greenhouse-gas emissions every year (6). With ever-increasing mobility, these numbers will undoubtedly surge and [...]

A high-pressure chamber is used to study lubricant compressibility when refrigeration oil is diluted by refrigerant. The tested lubricant in this work is a POE (polyol ester) oil, POE diluted with nonchlorinated (HFC) refrigerant R-134a, a naphthenic mineral oil, and the mineral oil diluted with the chlorinated (HCFC) refrigerant R-22. The high-pressure chamber experiments show that by adding 20 wt% of R-134a to the polyol ester oil, the stiffness of the lubricant increases by approximately 38 wt% at 1 GPa and is much higher than for R-22 and mineral oil. [DOI: 10.1115/1.2125967]