Tribological Properties Of Carbon-based/MoS₂ Nanocomposite Powder In Aqueous Lubricating Oil

Due to the long time sailing on the river and sea,it is inevitable that water will mix into the lubrication system of the device,resulting in emulsification failure of lubricating oil,then endanger the normal sailing of the ship.The properties of lubricating oil can be improved to some extent by adding modified nano-powders with special properties.In this thesis using expanded graphite and MoS₂as raw materials,oleic acid,oleic acid and high base calcium sulfonate as surface modifiers,using plasma assisted ball milling equipment to prepare oleic acid modified carbon-based MoS₂composite powder（hereafter referred to as oil-MoS₂/C）and oleic acid combined with high base calcium sulfonate modified carbon-based/MoS₂composite powder（hereafter referred to as oil-sulfo-MoS₂/C）.The microstructure and surface characteristics of the two composite powders were characterized,and the gravity sedimentation experiment was carried out.The tribological properties of the two modified powders were tested by adding them to base oil and emulsified oil respectively,and the antifriction lubrication mechanism was explored.The main research contents of this thesis include:（1）The formation mechanism of two kinds of carbon-based/MoS₂nanocomposite powders prepared by plasma-assisted ball grinding was studied.Under the synergic action of plasma thermal explosion,the expanded graphite is continuously sheared off,and MoS₂is refined into a flake shape of about 20 nm.The thermal explosion splashes onto the graphite lamellar layer and condenses to form a core-shell structure.In the oil-sulfo-MoS₂/C composite powder,the degree of graphite flake peeling is better and the particle size of MoS₂is smaller,indicating that adding calcium sulfonate in the process of ball milling can better refine the powder.（2）The surface modification mechanism of two carbon-based/MoS₂composite powders and their dispersion properties in base oil were studied.After standing in the base oil for 7 days,the two modified powders did not have obvious settling phenomenon.The oleophilic degree values of the original powder and the composite powder were tested respectively.The test results showed that the oleophilic degree values of the original powder were 2.7%and 8.9%,and the oleophilic degree values of oil-MoS₂/C and oil-sulfon-MoS₂/C reached 36.4%and 39.7%,respectively.The results show that the oleic acid modified powder can show good dispersibility and oil-philicity in oil.（3）The tribological test of the two modified carbon-based/MoS₂compound oils at room temperature showed that the two powders showed better lubrication performance than the original oil.This is because in the process of friction,the coating structure of nanopowder sheet and ball can transform the friction into sliding and rolling friction,and deposit on the gully,so as to realize the repair of friction pairs.In emulsified oil,the oxidation degree of oil-sulfo-MoS₂powder is lower,and the corrosion of friction pair is more slight.The XPS（X-ray photoelectron spectroscopy）results show that oil-sulfo-MoS₂can have frictional chemical reaction on the surface of friction pair,and generate a chemical film containing sulfate/sulfonate,which effectively inhibits the influence of water on the self-repairing properties of MoS₂,so that the emulsified oil can maintain good lubrication performance.（4）The tribological test of two modified carbon-based/MoS₂complex oils under harsh environment shows that both modified MoS₂/C can improve the tribological properties of base oil and emulsified oil at high temperature,among which oil-sulfon-MoS₂has better lubrication performance.Compared with base oil and pure emulsified oil,the increase was 35.7%and33.3%,respectively.Through the four-ball extreme pressure test,it is found that both powders can improve the extreme pressure resistance of emulsified oil,among which oil-sulfo-MoS₂has a better performance,which is about 17.7%higher than that of pure emulsified oil.