| Organic borate ester is a kind of green lubricating oil additive with no environmental pollution and good tribological performances. However, since boron is an electron-deficient element and has a great affinity with oxygen, borate esters are susceptible to hydrolysis which limit the wide use of borate esters as additives in lubricants. Therefore, it is very important to improve the hydrolytic stability of organic borate esters for the development of new borate ester lubricating additives. Dialkyldithiocarbamates and N-containing heterocyclic compounds have been proven to possess excellent tribological properties, and have been widely used in the field of antifriction, antiwear and extreme pressure. Based on rational molecular design, boron, dialkyldithiocarbamates or N-containing heterocyclic structure could be introduced to one molecular structure, in order to produce four kinds of novel borate esters containing N, S element. The hydrolytic stability and tribological properties of the synthestic borate ester were also studied using rapeseed oil as base oil.The following innovative progresses were achieved in this work:(1) A hydroxyl derivative containing N, S named as NSO was synthesized and a borate ester named as NSOB1 was synthesized by esterification using NSO as raw material. Another borate ester named as NSOB2 was synthesized by transesterification using NSOB1 and N, N-dimethylethanolamine as raw materials. The structures of these synthesized additives were characterized using Fourier infrared spectrometer(FTIR) and element analyzer. The thermal stabilities, oil-soluble properties, hydrolytic stabilities and tribological properties of these synthesized additives were determined respectively.. Results showed that the synthetic additives had good thermal stabilities whose decomposition temperature were above 240°C and they all had good solubilities in rapeseed oil. NSOB1 and NSOB2 had highly hydrolysis stabilities. NSOB1 was not hydrolyzed over 7 days, and NSOB2 was not hydrolyzed over 10 days. The oil sample containing 2.0%(wt%) of NSO, NSOB1 and NSOB2 showed the most excellent loading abilities, their PB values were improved by 42.04%, 44.89%, 45.85% respectively, compared to that of base oil.. The oil samples containing 1.0% of NSO, 2% of NSOB1 and 1.5% of NSOB2 had the best antiwear properties, whose WSD were readuced by 29.85%, 23.54% and 28.09%, respectively, compared to that of base oil. The oil samples containing 1.5% of the additives had the best friction-reducing, the friction coefficients of them were lower than that of the base oil. The surfaces of the steel balls lubricated by the synthetic additives were smoother than the steel balls lubricated by base oil, especially the NSOB1 and NSOB2’s.(2) The synthetic borate ester NSOB1 and NSOB2 were mixed with T202 respectively, and the tribological properties of them were also tested. The results showed that the PB value reached the maximum of 1570 N when the ratio of NSOB1 and T202 was 3 : 7. The WSD value reached the minimum value of 0.437 mm when the ratio of NSOB1 and T202 was 1 : 9, and the friction coefficient of the oil sample reached the minimum value of 0.0466 when the ratio of NSOB1 and T202 was 7 : 3. When the ratio of NSOB2 and T202 was 7 : 3, the PB value was 1720 N, the friction coefficient reached the minimum value of 0.0413. When the ratio of T202 and NSOB2 was 5 : 5, the WSD value reached the minimum value of 0.414 mm. Using the SEM, the surface of the steel balls lubricated by the best oil samples combined with T202 were much smoother than the surface of the steel balls lubricated by the single agent.(3) A hydroxyl derivative of N, S-containing heterocyclic structure named as BTE was synthesized and a borate ester named as SNHB was synthesized by esterification using BTE as raw material. Anthor borate ester named as NSNHB was synthesized by transesterification using SNHB and N, N-dimethylethanolamine as raw materials. The structure of these synthesized additives were characterized using FTIR and element analyzer. The thermal stabilities, oil-soluble properties, hydrolytic stabilities and tribological properties of these synthesized additives were tested respectively. The results showed that the synthetic additives had good thermal stabilities whose decomposition temperature were above 250 °C and they all had good solubilities in rapeseed oil. SNHB and NSNHB had highly hydrolysis stabilities. SNHB was not hydrolyzed over 7 days,and NSNHB was not hydrolyzed over 15 days. The oil sample containing 2.0%(wt%) of BTE, SNHB and NSNHB showed the most excellent loading abilities, their PB values were improved by 26.12%, 50.42% and 52.53%, respectively, compared to that of base oil. The oil samples containing 1.5% of BTE, SNHB and NSNHB exhibited the best antiwear properties, whose WSD were readuced by 27.92%, 29.67% and 28.97%, respectively, compared to that of base oil. The oil samples containing 1.5% of these additives esibited the best friction-reducing, the friction coefficients of them were lower than that of the base oil. The surfaces of the steel balls lubricated by the synthetic additives were smoother than the steel balls lubricated by base oil, especially the SNHB and NSNHB’s.(4) The synthetic borate ester SNHB and NSNHB were mixed with T202 respectively, and the tribological properties of them were also tested. The PB value reached its maximum of 1560 N when the ratio of SNHB and T202 was 5 : 5. The WSD value and the friction coefficient of the oil sample reached the minimum value of 0.453 mm and 0.0456, respectively when the ratio of SNHB and T202 was 7 : 3. The WSD value and the friction coefficient of the oil sample reached the minimum value, which were 0.0412 mm and 0.0390, respectively, and the PB value was 1700 N when the ratio of NSNHB and T202 was 7 : 3. Using the SEM, the surface of the steel balls lubricated by the best oil samples combined with T202 were much smoother than the surface of the steel balls lubricated by the single agent. At the same time, there were no obvious scratches and bruises. |
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