Improvement Of Graphene, Graphite Nanosheet And Molybdenum Disulfide 2D Nano Additives On Lubrication Performance Of Lithium-Based And Polyurea Greases

In this paper,the lubricating properties of lithium-based and polyurea lubricating grease were studied.Firstly,the lubrication properties of graphene-enhanced lithium grease were studied.Secondly,2D graphite nanosheets were prepared from expanded graphite and the lubricating properties of lithium grease were studied.Thirdly,the flocculent 2D nano molybdenum disulphide was synthesized and the lubricating properties of polyurea grease were studied.It is found that 2D nano-materials can effectively improve the lubricating properties of lithium grease and polyurea grease.The specific conclusion is as follows.The enhancement effect of a commercial graphene material as a lithium grease additive was studied.Characterization revealed that the commercial graphene was 1-7layers,indicating almost no defects.The friction coefficient of the lithium grease containing 2 wt%graphene was only 0.104,which was 15%lower than that of the lithium grease.The wear resistance of the lithium grease with graphene increased with the increase of the amount of graphene added.Compared with the lithium grease,the working load of the graphene-containing lithium grease increased by 60%.2D graphite nanosheets were prepared from expanded graphite by sanding in water,anhydrous ethanol,propylene triol and 1,4-butanediol.Anhydroethanol has lower viscosity,higher polarity and smaller molecular size,and has better intercalation and stripping,which is conducive to the preparation of thin 2D graphite nanosheets.In anhydrous ethanol solution,graphite nanosheets with average thickness of 25 nm were prepared by grinding for 8 h at room temperature.Compared with the lithium grease,when the content of nano-graphite sheet in the lithium grease is 2wt%,the average friction coefficient decreases by 27%,the wear mark diameter decreases from 0.883mm to 0.641 mm,and the sintering load and comprehensive wear index are 1.6 times and 1.4 times of the comparison samples of the lithium grease,respectively.The nano-graphite can effectively improve the lubrication,wear resistance and extreme pressure properties of lithium grease.Two dimensional flocculent MoS₂ nanosheets were prepared by hydrothermal/calcining method using ammonium molybdate and thiourea as raw materials.A large flocculent 2D MoS₂ nanosheets was synthesized without organic modifier.Using cetyl trimethylammonium bromide?CTAB?and sodium dodecyl benzyl sulfonate as organic modifiers,flocculent 2D MoS₂ nanosheets were synthesized.Long carbon chain polyethylene glycol organic modifier induces the formation of rod-shaped nanometer MoS₂.Floccus 2D MoS₂ nanosheet synthesized by CTAB was selected as the additive of polyurea grease.When the content of MoS₂ nanometer sheet in polyurea grease increased from 0 to 2%,the average friction coefficient decreased by 19%,the wear mark diameter decreased from 0.815mm to 0.524mm,the maximum no-bite load increased by 60%,the sintering load and the wear index increased by 60%and 70%,respectively.Two dimensional graphene,graphite nanosheets,molybdenum disulfide nanosheets effectively improve the lubrication performance,anti-wear performance,and extreme pressure performance of lithium-based greases and polyurea greases.This is because the two-dimensional nano-additive in the grease acts as a nano-bearing between the friction pairs,thereby enhancing the friction characteristics of the grease.Two-dimensional graphene,graphite nanosheets,and 2D molybdenum disulfide nanosheets can be used as additives with good performance in industrial greases.