Synthesis, characterization and tribological performance of two novel borate esters containing nitrogen as a multifunctional additive in synthetic ester base oil

Abstract

For the development of national industry green environmental protection, the use of zinc dialkyl dithiophosphate (ZDDP) should be reduced in the process of mechanical lubrication, two novel borate esters, SS-(5-disulfanyl-1,3,4-thiadiazol-2-yl) O-(6-stearoyl-1,3,6,2-dioxazaborocan-2-yl) carbono(dithioperoxoate) (BNSD) and 6-stearoyl-1,3,6,2-dioxazaborocan-2-yl stearate (BNCD), were synthesized and characterized by FT-IR and TGA. Tribological performance of ZDDP, BNSD and BNCD as a multifunctional additive in synthetic ester base oil were investigated under different loads using a MR-S10 four-ball and MFT-3000 friction and wear test machine. A scanning electron microscope and laser scanning confocal microscope were used to observe worn scar surface morphology of the balls. The chemical compositions of worn surface were analyzed by X-ray photoelectron spectroscopy and the tribofilm of the worn surface was observed by transmission electron microscope. The TGA curves showed that BNSD and BNCD had a better thermal stability than ZDDP. BNSD exhibits excellent anti-wear and friction-reducing properties, the P B value is increase to 784 N when the optimized concentration is 0.3% the minimum WSD of BNSD-based lubricant is approximately 0.52 mm and decreased by 35% compared with the base oil. A protective tribofilm of the ball steel was analyzed by XPS and TEM, which revealed that B2O3 and Fe2B constitute the triboilm and about 5 nm. Therefore, BNSD could be a candidate as anti-wear and friction-reducing agent in lubricants instead of ZDDP.