Chemically modified nanomaterials as lubricant additive: Time stability, friction, and wear

Abstract

This work reviews the results on the temporal stability of nanodispersions containing chemically modified nanoadditives: carbon-based nanomaterials, metals, metal oxides, metal sulfides, nanocomposites, among others. Morphology, size, coating type and concentration of the NPs as well as the viscosity of the base oil are the main characteristics that affect stability. Coated spherical NPs with mean diameter lower than 20 nm are the most common among those which led to nanolubricants with stabilities longer than two months. The tribological results of the nanolubricants with stabilities higher than one month are also reviewed. Regardless the base oil, chemically modified nanoparticles reduced wear more than friction, reaching reductions of friction up to 75% and wear volume up to 99%. As for the tribological mechanisms involving chemically modified nanoparticles, the formation of adsorbed or tribochemical reaction films on worn surfaces were reported more often.