Study On Lubricating Effect Of Ultrasonic Dispersion On Graphene/Graphene Oxide Lubricants

In recent years,nano-materials have been widely used as lubricating oil additives.Graphene and graphene oxide have become the research hotspots of many tribologists due to their unique anti-wear and anti-friction properties.However,as a lubricating oil additive,in order to exert good lubricating properties,its dispersion stability in lubricating oil is very important.As an effective way to disperse graphene lubricating oil,ultrasonic dispersion method has important significance for the lubrication effect of graphene lubricating oil.Based on Large-scale Atomic/Molecular Massively Parallel Simulator(LAMMPS)molecular dynamics simulation of molecular motion trajectories of graphene and graphene oxide lubricants in ultrasonic environment,the diffusion coefficients of graphene and graphene oxide are calculated by the root mean square displacement equation,and the ultrasonic dispersion mechanism is revealed from the microscopic point of view.At the same time,the dispersion effect of the two phenomena under different ultrasonic conditions was compared.The simulation results show that the changes of ultrasonic power and ambient temperature will affect the motion state of graphene molecules and graphene oxide molecules in n-hexadecane molecules.When the ultrasonic power is 500 W and the ambient temperature is 323 K,the root mean square displacement curve of the graphene molecule has the highest slope.When the ultrasonic power and ultrasonic time continue to increase,the slope of the curve decreases and the diffusion behavior decreases.When the ultrasonic power is 600 W and the ambient temperature is 333 K,the slope of the root mean square displacement curve of the graphene oxide molecule is the highest.When the ultrasonic power and ultrasound time continues to rise,the slope of the curve decreases and the diffusion behavior decreases.Ultrasonic dispersion of graphene and graphene oxide lubricants with different ultrasonic powers and different ultrasonic times was carried out by ZOLLO-1000 Y ultrasonic cell pulverizer.The graphene and graphene oxide lubricating oil after ultrasonic testing were measured by zeta potential,and the dispersion stability of graphene and graphene oxide lubricating oil under different ultrasonic conditions was characterized by potential intensity.The frictional wear tester spherical contact rotary module was used to investigate the effects of graphene and graphene oxide lubricating oil on the lubrication and cooling performance of GCr15/Si3N4 friction pair under different ultrasonic conditions.The surface of the wear surface of the specimen after the friction and wear test was characterized by scanning electron microscopy.When graphene is used as a lubricant additive,the results of ultrasonic dispersion test,zeta potential measurement test,friction wear test and scanning electron microscope test show that the dispersion stability of graphene lubricating oil has a positive correlation curve with ultrasonic power and ultrasonic time to some extent.The optimal ultrasound conditions were:ultrasonic time of 90 min and ultrasonic power of 500 W.And when the ultrasonic time exceeds 90 min and the ultrasonic power exceeds 500 W,the dispersion stability of the graphene lubricating oil decreases.This property also positively affects the lubrication of graphene lubricants.When graphene oxide is used as a lubricant additive,all test results show that the dispersion stability and lubricating effect of the dispersion system of graphene oxide lubricants obtained under different ultrasonic conditions are different.The optimal ultrasound conditions were: ultrasonic time of 105 min and ultrasonic dispersion power of 600 W.At this time,the dispersion system has the best dispersion effect and the lubrication effect is also optimal.The research shows that the ultrasonic dispersion method can improve the dispersion stability of graphene and graphene oxide lubricating oil,and the ultrasonic dispersion under different ultrasonic conditions can affect the dispersion effect of the dispersion system to varying degrees.The main reason is that graphene and graphene oxide have large specific surface area and are easy to agglomerate and precipitate.A certain degree of ultrasonic dispersion can weaken the surface energy of graphene and graphene oxide molecules,thereby allowing them to diffuse.However,long-term and high-power ultrasonic dispersion will destroy the surface morphology of graphene and graphene oxide,causing them to bend and fold,which will lead to re-agglomeration and precipitation of graphene and graphene oxide molecules.