Tribological behaviour of two ash-less and phosphorous-free anti-wear additives and their synergetic effect with zinc dialkyldithiophosphates in mineral oil

Abstract

Two heterocyclic compounds, 1-ethylhexyl-ethyl ester-thiomethyl-2-sulphur-benzo-thiazole (referred to as MBES) and 1-(dibutylamine-sulphur-methyl)-thiomethyl-2-sulphur-benzothiazole (referred to as MBON), as lubricating oil additives, were synthesized to replace or partially replace zincdialkyldithiophosphates (ZDDP). It was found that two heterocyclic compounds added in base oil at a proper concentration showed rather good anti-wear behaviour; there was a pronounced synergism between MBES and 1.0 wt% ZDDP in terms of the anti-wear properties and load-carrying capacities, whereas there was no synergism between MBON and 1.0 wt% ZDDP. X-ray photoelectron spectroscope analytical results showed that the tribofilms generated from the base oil-1.5 wt% MBON mainly contained pyrite, sulphite, and sulphate, whereas the films from the base oil-1.5 wt% MBES only contain sulphate; for the films from the complexes of the additive with 1.0 wt% ZDDP, S-containing compounds in the films are mainly in the form of sulphate and sulphite, and there are some N-containing organic compounds adsorbed on the worn surfaces.