Preparation And Friction Properties Of Nano-MoS₂ Based Lubricant Additives

Lubrication is considered to be energy saving in the process of industrialization and one of the most effective way to improve mechanical efficiency,however,with the development of modern social science and technology,the traditional lubricant additives have not reached a high precision performance index in today’s manufacturing,automotive and other fields,at the same time containing P,S,Cl lubricant is not accord with the requirement of green environmental protection.In recent years,with the emergence of nano-tribology,MoS₂has been applied in many lubrication fields as a lubricant additive.The"sandwich"lamellar structure of MoS₂is connected by Vanderwaals force,and the atoms of Mo and S are connected by covalent bond.Under the action of shear force,the atoms of Mo and S are prone to slip.Compared with the commercial lamellar bulk MoS₂,nano-MoS₂has excellent frictional properties.Therefore,it is an urgent task to prepare nano-MoS₂based additives with high anti-friction and anti-wear properties.In this paper,MoS₂based additive was prepared by regulating the morphology of MoS₂with surfactant.XRD,SEM,FT-IR,TG,BET and other characterization methods were used to evaluate the microstructure,preparation mechanism,dispersion and friction properties of a series of MoS₂based additives prepared.Specific research is as follows:1.Using Na₂MoO₄·2H₂O and CS（NH₂）₂as raw materials,using the hydrothermal method,by adding surfactants TEBAC,TBAB and CTAB to adjust the morphology of MoS₂,the dual core-shell MoS₂（DS-MoS₂）,single core-shell MoS₂（SS-MoS₂）and flower sphere MoS₂（FB-MoS₂）were successfully prepared.The influence of the morphology of MoS₂on the friction properties and lubrication mechanism was analyzed and explored through the four-ball friction experiment.The results show that the different microstructure has a great influence on the friction properties.The FB-MoS₂can keep the natural deposition stable for 8 hours in SN 5W-30,and the absorbance is 0.639 under the centrifugal simulated external force condition.The average friction coefficient（AFC）is 0.0668,which is 64%of SN 5W-30 engine oil,and the average spot diameter（AWSD）is 0.575 mm,which is 77%of SN 5W-30engine oil,indicating that FB-MoS₂has excellent anti-wear and anti-friction properties.Combined with XRD and SEM analysis,FB-MoS₂has a relatively large（002）lattice spacing,which is beneficial to its"roll-deformation"and"peel-adsorption"lubrication mechanism process,so it is of great help to its friction reduction and wear resistance.The molecular models of C₁₂and C₁₂-MoS₂were constructed by using the Materials Studio kinetic simulation program to verify the enhanced adsorption capacity of MoS₂and Fe（110）surface.2.Fe₃O₄/MoS₂,TiO₂/MoS₂and SiO₂/MoS₂were prepared by the hydrothermal method to make up for the shortcomings of the"roll-deformation"lubrication mechanism of FB-MoS₂.The effects of spherical nano-oxides on the friction properties and mechanism of FB-MoS₂were investigated by dispersion evaluation and four-ball friction experiments.The results show that SiO₂/MoS₂in SN 5W-30 can keep the natural precipitation stable for 18 hours,and the absorbance is 0.780 under the centrifugal simulated external force condition.The AFC of SiO₂/MoS₂is 0.0637,which is 58.98%of SN 5W-30 engine oil.The AWSD is 0.511 mm,which is 68.68%of that of SN 5W-30 engine oil,indicating that SiO₂/MoS₂has excellent anti-friction and anti-wear properties.Through the mechanism analysis,it is found that the electromagnetic field will cause the Fe₃O₄/MoS₂to agglomerate in the friction process.Due to the relatively large hardness of Fe₃O₄,the ball pits between the friction surfaces can’t be filled well.The hardness of TiO₂is relatively low.With the increase of friction time,TiO₂will gradually deform and be ground to form a very thin adsorption film on the surface of the steel ball.With appropriate hardness,SiO₂can expand the oil film thickness at the protruding position of the friction surface and fill the pit at the depressed position when subjected to external force,realizing the synergistic lubrication of SiO₂and MoS₂,showing excellent lubrication performance.3.Furthermore,SiO₂/MoS₂was taken as the research object.In order to make up for the defect that the adsorption film formed by MoS₂on the friction surface would be destroyed by SiO₂with the extension of friction time,SiO₂/MoS₂/GO and SiO₂/MoS₂/g-C₃N₄were prepared by hydrothermal method,and the dispersion evaluation and four-ball friction experiment were conducted.The effects of 2D layered nanomaterials GO and g-C₃N₄on the friction properties and lubrication mechanism of SiO₂/MoS₂were investigated.The results show that the AFC of SiO₂/MoS₂/GO is 0.0614,which is 58.33%of SN 5W-30 engine oil.AWSD is0.394mm,52.96%of SN 5W-30 engine oil,indicating that SiO₂/MoS₂/GO has excellent anti-friction and anti-wear properties.Both GO and g-C₃N₄are 2D nanomaterials with a layered structure,which are connected by Vanderwaal’s force.Therefore,sliding and lamellar structure stripping is prone to occur when subjected to shear force,filling pits or defects between steel ball contact surfaces and playing a self-repairing role.The experimental results show that compared with g-C₃N₄,GO has better synergistic lubrication ability with SiO₂/MoS₂.4.In order to improve the dispersion performance of SiO₂/MoS₂/GO in SN5W-30,OA-SiO₂/MoS₂/GO was prepared,and the dispersion was evaluated and analyzed under gravity natural settlement conditions and centrifugal simulated external force conditions.The results show that OA-SiO₂/MoS₂/GO in SN 5W-30 can keep the natural deposition stable for more than 20 days,and the absorbance is 0.982under the centrifugal simulated external force condition,and the dispersion stability is good.Four-ball experiment results show that the AFC of OA-SiO₂/MoS₂/GO is0.0593,which is 54.91%of SN 5W-30 engine oil.AWSD is 0.349 mm,which is 47%of SN 5W-30 engine oil,indicating that OA-SiO₂/MoS₂/GO has excellent anti-friction and anti-wear properties.It is further proved that the improvement of dispersion stability contributes to the improvement of friction performance.The above studies can improve the lubrication,anti-friction and anti-wear performance of MoS₂based additives in SN 5W-30 from the aspects of enhancing the function of"micro-bearing",enhancing the stability of the adsorption mode on the friction surface and enhancing the dispersion stability in the base oil.