Load-carrying capacity and tribomechanism of DDA/MADE modified MoO3 nanoparticle as an additive for alkylated naphthalene base oil

Abstract

Metal oxide nanoparticles as lubricant additives have attracted much attention, thanks to their excellent anti-wear ability and load-carrying capacity. Unfortunately, organic molybdenum, a small molecule auxiliary of zinc dialkyldithiophosphate (ZDDP) with high reactivity, exhibits poor load-bearing capacity. Therefore, molybdenum oxide nanoparticle (denoted as MONP) was surface-capped by dodecylamine (DDA) and maleic anhydride dodecyl ester (MADE) to obtain DDA/MADE-MONP, an organic-inorganic nanohybrid as a potential replacement of sulfur- and phosphorus-free commercial organic molybdenum additive (Organic-Mo). The as-prepared DDA/MADE-MONP nanohybrid was characterized by X-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy; and its effect on the load-bearing capacity of an alkylated naphthalene base oil (AN30), as used alone and combined with ZDDP, was investigated. Results show that, whether used alone or combined with ZDDP, the as-prepared DDA/MADE-MONP has better load-bearing capacity than the commercial organic molybdenum additive. The reason lies in that DDA/MADE-MONP can release MoO3 nanocores during the friction process to fill up the pits on the worn steel surface and form a dense protective tribofilm.