Abstract
Purpose - The purpose of this paper is to investigate the hydrolytic stability of several S-hydroxyethyl N,N-dialkyl dithiocarbamate-derived borates SNB1, SNB2, and SNB3, to evaluate their tribological performances used as additives in polyalpha olefins (PAO), and to explore the tribochemical action mechanism. Design/methodology/approach - First, the three additives are synthesized and characterized. Second, the hydrolytic stabilities of the three compounds are investigated. As the third step, they are, respectively, added to PAO and a series of samples with different concentrations of the additives in PAO are prepared, respectively. Their tribological properties are evaluated with two types of four-ball machines, and then the wear scars were observed using a JSM-5600LV scanning electron microscope. Finally, the elements on the worn surface are analyzed with a X-ray photoelectron spectroscope (XPS). Findings - The three novel compounds possess relatively good hydrolytic stabilities, excellent anti-wear (AW) performances, friction reduction properties, and load-carrying capacity. There is an optimum concentration of each of the three additives for their AW properties. According to the XPS analytical results, a boundary lubrication protective film has formed during friction consisting of FeSO4 film, Fe2O3 film, and the complicated adsorption film composed of N-containing organic compounds. In the protective films, a large quantity of compounds containing element B is not found. Research limitations/implications - The antioxidation performances and the anticorrosion properties are not estimated. Practical implications - Three novel AW/extreme pressure (EP) additives are synthesized, and may be they have the potential industrial application as AW/EP additives in lubricating oil. Originality/value - The present work provides a research method of N,S-containing organic borates as lubricating oil additives.
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