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PurposeTo study some tribochemical properties of tetrazole derivatives, n‐hexadecanyl (1H‐tetrazol‐1‐yl) acetate (HTA) and 1‐phenyl‐5‐(octylthio)‐tetrazole (PCT) as lubricating oil additives in hydrogenised oil, and estimate the action mechanism.Design/methodology/approach – The two tetrazole compounds were synthesized, and added them in hydrogenised oil with different concentrations. Their anti‐wear properties were evaluated with a four‐ball machine, the wear scar was analyzed with a X‐ray photoelectron spectroscopy (XPS).Findings – The novel compounds possess good anti‐wear, friction reduction properties and good load‐carrying capacity. According to the XPS results, the novel compounds were migrated onto the surface of the steel balls and adsorbed on the surface. The two additive compounds, themselves, and their decomposers contributed to the corresponding tribological performances. With S element contained in the compound PCT, the influence on the load‐carrying capacity of the base oil was enhanced. It may be due to the formation of S2− and SO42− compounds on the worn surface which could form a protective film.Research limitations/implications – Their antioxidant, anticorrosion, anti‐wear properties are not estimated.Practical implications – Two useful EP and AW lubricating oil additives were synthesized, and maybe it is the potential industrial applied lubricating oil additives.Originality/value – This paper provided a study way of some N‐containing heterocyclic compounds as lubricating oil additives.

Key wordsphosphate ester, additive, rape seed oil, four-ball tester, XPS