Study On Preparation And Tribological Properties Of Graphene As Lubricating Material Based On The Methods Of Environmentally Friendly Exfoliating

High performance lubricant additive is the core component of lubricant.In spite of small lubricant additive consumption in the lubricant,it plays a key role in giving new characteristics to the lubricant and remedying the performance defects of the lubricant.A small amount of graphene as lubricant additive can not only reduce the friction coefficient as nano bearings,but also can significantly improve the wear resistance of lubricant by forming a lubricating protective film to reduce direct contact between friction surfaces Although graphene shows good tribological properties as a lubricant additive,it still has many key scientific and technological bottlenecks in practical application.On the basis of the improved preparation conditions,green and efficient exfoliating process was studied,its feasibility was analyzed,and the tribological properties of the prepared graphene as a lubricant additive were investigated in this paper.In addition,the study on the structural evolution of 2D materials in the friction interface has laid a foundation for the research on their structure-activity relationshipThis paper includes the following specific research work(1)Few-layer graphene nanosheets were prepared from graphite oxide by high temperature expansion under decomposition and reduction of oxalic acid.The results show that the graphene has the thickness of 3.5 nm(about 10 layers)and the transverse dimension of about 0.5 ?m.The expansion reduction mechanism of oxalic acid as green intercalator between graphite oxide layers was proposed.It is found from the test of tribological properties of the graphene nanosheets that the lubricant containing 0.04wt.%grapheme has the 35.8%smaller average friction coefficient and 32.8%smaller average wear scar diameter of grease than pure lubricant;the grapheme-containing lubricant shows better load-carrying capacity than pure lubricant,has the Pb value of 595 N,i.e.about 24.0%higher Pb value than pure lubricant,and thus exhibits excellent tribological properties(2)In order to solve the problems of high cost,complicated process and environmental pollution in the existing methods,the Li+/Na+hydrothermal exfoliating method and ultrasonic exfoliating method for preparation of few-layer graphene nanosheets from graphite were developed.The few-layer graphene with the thickness of 2.65 nm(7-8 layers)was prepared from Li+/Na+and-OH under hydrothermal conditions,with the yield of 64%It is found that the castor oil containing 0.06wt.%graphene prepared by this method has 36.84%smaller friction coefficient and 48.57%smaller wear scar diameter than pure castor oil.In addition,the graphene nanosheets prepared by the ultrasonic-assisted process are about 2.38-2.56 nm thick(7-8 layers).The lubricant containing 0.06wt.%graphene prepared by this method has 21.35%smaller average friction coefficient and 30.32%wear loss than pure lubricant(3)In order to study the relationship between the structure change and the friction coefficient of 2D material in the contact surface,the in-situ friction experiments of the bulky materials,including graphite,boron nitride,WS2,MoS2,etc.,were carried out by four-ball friction and wear testing machine.The experiments prove that the nanostructure changes from multi-layer to few-layer during slide,which is conducive to the formation of a friction protective film and plays a key role in the lubrication process(4)In order to explore the industrialization potential of the preparation process,the scale-up experiments(10 multiples)and cost analysis of the three exfoliating processes within the maximum allowable operating range of laboratory equipment were carried out according to the industrial production and market conditions.The hydrothermal exfoliating process has the smallest difference in yield and friction performance from the lab experiments.In addition,the hydrothermal exfoliating process has some advantages,such as a simple process,low cost,etc.However,some problems in the scale-up experiment,including low yield,small product size,small specific surface area,etc.,are the main obstacles to industrial production.