Design And Synthesis Of Graphene Additive For Lubricating Oil

Friction and wear widely exist in daily life and nature.The energy consumption and mechanical loss caused by them are becoming increasingly prominent.Using lubricating oil can effectively reduce friction and wear.Appropriate additives for reducing and wear has become an important part to improve lubricating performance of lubricating oil.Therefore,exploring and developing new environmentally friendly additives of lubricating oil has gradually become an important research directions for researchers in the field of friction.So far,graphene is the thinnest man-made material.It consists of carbon atoms with a thickness of only 0.335 nm.As a kind of graphene derivatives,the graphene oxide(GO)can greatly reduce friction and wear by virtue of its excellent mechanical property,thermal property,ultra-thin layered structure and huge surface area.However,a large number of oxygen-containing functional groups on GO surface make it difficult to disperse stably into lubricating oil because of its hydrophilicity.Therefore,reasonable structural design or composition modification of GO to promote its stable dispersion in lubricating oil is the key to the study of graphene-based lubricating oil additives.Two new long-chain alkyl functionalized ultrafine graphene lubricant additives with high dispersibility and excellent tribological properties,namely,octadecanol grafted GO(RGO-g-OA)and octadecanobromide grafted GO(RGO-g-BO),were prepared by green,simple and efficient preparation steps using the way of particle size miniaturization,surface grafting and chemical reduction in this paper.The structure and morphology of the two products were characterized by X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),transmission electron microscopy(TEM),thermogravimetric analyzer(TGA)and other modern characterization.Structural and morphological studies show that oleophilic long-chain alkyl groups are successfully grafted onto GO surface through the reaction process.The prepared RGO-g-OA and RGO-g-BO additives did not precipitate in lubricating oil after standing for more than two weeks,which indicated that the additives had excellent dispersion stability in lubricating oil.Finally,the tribological properties of the two products as lubricating oil additives were investigated by Optimol SRV oscillating reciprocating friction and wear tester and three-dimensional profiler.The morphology of the wear spots and the elements and components on the surface of the wear spots were analyzed by scanning electron microscopy(SEM),energy dispersive spectrometer(EDS),Raman spectroscopy(Raman),and the tribological mechanism of the additives was studied.The study of friction performance shows that the optimum proportion of additives is 0.005 wt%.Compared with the lubricant without additives,the friction coefficient of RGO-g-OA as lubricating oil additive decreases from 0.072 to 0.065 and the wear volume of lubricating oil decreases from 18354?m~3 to 10316?m~3.At the same time,the friction coefficient of RGO-g-BO as lubricating oil additive decreases from 0.173 to 0.141,the wear volume of lubricating oil decreases from 52151?m~3 to 24391?m~3.Tribological mechanism study shows that there is a lubricating oil film formed during friction on the surface of friction pair after adding lubricating oil with graphene additives,there are graphene components in the oil film,and there are little and shallow grooves on the surface of friction pair.This may be due to that graphene additive can form chemical deposition film on the surface of friction pair,which prevents the friction pair from contacting directly and it relies on its small size effect to fill holes formed in the friction process,thus reducing friction and wear.