| Friction and wear are ubiquitous in nature,which brings great loss to our life and production.Lubricating oil is the most common lubricating material to reduce friction,reduce wear and prolong life of machine.In order to improve the lubricating performance of lubricating oil,it is usually necessary to add a variety of antifriction and antiwear additives in the base oil.Graphene oxide(GO),a unique two-dimensional layer structure,with a very low friction coefficient and high hardness,and strong corrosion resistance and excellent oxidation resistance,has become one of hot issues in tribological field in recent years.However,if GO is to be used as a lubricant and anti-wear additive,it is necessary to solve the problem of stability and transparency in oil.This paper mainly discussed(1)The structure-activity relationship between size and tribological properties of GO.(2)Surface modification technology development of GO and its dispersibility and tribological properties.(3)Preparation and tribological properties of borate/GO nanocomposites.The size of GO was successfully controlled by controlling the oxidation temperature of Hummer' method.Three as-prepared GO nanosheets were named as GO-20,GO-27 and GO-35.The average size of them was 25 ?m,22 ?m and 18 ?m,respectively.XRD,SEM,FT-IR,EDS and AFM were used to characterize three kinds of GO nanosheets.The results showed that with increasing the oxidation temperature,the size of GO nanosheets decreased gradually,and the C/O ratio also decreased.The tribological testing results showed that the friction coefficient of GO35-based oil was reduced by 18.5%and 8.5%,respectively,compared with that of GO20-based oil and GO27-based oil,and the wear scar diameter was decreased by 11.3%and 5.2%,respectively.It was proved that the smaller the size of GO nanosheets was,the lower the C/O ratio was and the better the antifriction and antiwear properties were.The reason was that the lower C/O ratio of GO nanosheets had more active groups,which were beneficial to the dispersion in oil.In order to improve the dispersibility of GO in oil,oleic diethanolamide borate(ODAB),which was of excellent biodegradability,was used to modify GO nanosheets.FT-IR,XRD,UV-vis,Raman,TEM and XPS were used to reveal the structure of the modified GO(MGO).It was proved that ODAB was successfully attached to the surface of GO nanosheets by means of dehydration condensation.The dispersibility,stability and transparency of MGO in base oil were studied.The results showed that MGO nanosheets showed excellent dispersibility and transparency in oil.The wear scar diameter and the average friction coefficient of MGO-based oil were decreased by about 42%and 38.4%compared to the base oil,which exhibited the excellent tribological performance of MGO.In order to further improve the tribological properties of GO,we composited calcium borate(CB),lanthanum borate(LB)and zinc borate(ZB)nanoparticles on GO surfaces by a liquid phase ultrasonic stripping technique.Moreover,we used physical grinding,oleic acid(OA)and oleic diethanolamide(OD)modification to improve the dispersibility of as-prepared nanocomposites in oil,respectively.XRD,SEM,FT-IR,Raman,UV-vis,TEM,TGA and EDS were used to reveal the structure and morphology of the nanocomposites.The results showed that the average friction coefficient and wear scar diameter of the CB/GO-based oil,the OA-LB/GO-based oil and the OD-ZB/GO-based oil were decreased by 46.6%and 37.5%,30.8%and 44.3%,48.2%and 37.6%,respectively.It was proved that the nanocomposites were of excellent tribological properties. |
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