Preparation Of Organic Borate Ester Lubricating Additives

Organic borate ester possesses good anti-wear, friction-reducing properties, nontoxic and degradation easily, so it is a kind of promising green lubricating oil additives in the future. At present, organic borate ester as a new type of green lubricating oil additive has caused wide public concern. However, the hydrolytic stability of borate ester is greatly limits the borate ester as lubricating oil additives used in industrial gears, automotive engine and hydraulic system. Therefore, in the view of improving the tribological performance of borate ester and improving the hydrolytic stability of borate ester has important significance for the development of green lubricating oil additives.In this work, from the perspective of molecular design, three kinds of organic borate esters which contain the structure of dialkyl dithiocarbamate, SNB, SNB1C and SNB2C, were synthesized through esterification reaction using n-butyl amine, carbon disulfide, boric acid and cyclohexanol as raw material. The structures of these three synthesized borate esters were characterized using Fourier infrared spectrometer (IR) and element analyzer. Results show that the synthesized of three kinds of borate esters consistent with the target molecules.The oil-soluble property, hydrolytic stability and copper corrosion level of synthesized of three kinds of organic borate esters contaiong nitrogen and sulfur, SNB, SNB1C and SNB2C, were determined respectively. Results show that the synthesized of three organic borate esters as additives in poly alpha olefin (PAO) have good solubility; all these three kinds of organic borate esters havel high hydrolysis stability and copper corrosion property.The maximum non-seizure load (PB), friction coefficient and wear scar diameter (WSD) of the base oil lubricated by the synthesized borate esters, SNB, SNB1C and SNB2C, were characterisized by the MRS-10 type four-ball tester respectively. The results showed that the carrying capacity, antiwear additives anti-friction performance decreases with the increase of alkyl structure, and molecules of sulfur content in most of the SNB showed the best tribological performance. Compared with the base oil, the PB value lubricated by 2.5% SNB was increased by 137, and the WSD value and friction coefficient were readuced by 46% and 43% respectively.A novel kind of vulcanized butyl oleate (denoted SBO) was synthesized and used as lubricating additive mixed with synthetic SNB. The tribological properties of the mixed additives in PAO under different mass fraction was evaluated. The results showed that adding 1.0% SBO and 1.5% SNB, the WSD value and the friction coefficient of the oil sample reached the minimum value,0.053 mm and 0.084, respectively. Compared with the base oil containing with 2.5% SBO, the WSD value (0.055 mm) and the friction coefficient (0.096) were readuced by 4% and 14.3%, respectively.The worn surfaces of the steel balls were analyzed by scanning electron microscope (SEM/EDS) and X-ray photoelectron spectroscopy (XPS) respectively. Results show that the surfaces of the steel balls lubricated by these three synthesized borate esters are smoother than the steel balls lubricated by base oil. At the same time, during the course of friction, the synthesized borate esters were reacted with the steel surface and formed a complex low shear strength chemical reaction film containing FeSx and FeSO4 on the surface of the steel balls.