Study On Tribological Properties Of Nano Lubricant Additives Of Two-dimensional Layered β-Nickel Hydroxide And Hexagonal Boron Nitride

Lubrication is the most common way to effectively improve the tribological properties of mechanical systems,in which the lubricant additives play a vital role.Nanomaterials have been considered as a new type of lubricant additives due to their unique structure and size effect.Among them,two dimensional materials show great potential for lubricating application due to their unique layered structure.In this paper,the preparation,morphology and structure ofβ-nickel hydroxide（β-Ni（OH）₂）and hexagonal boron nitride（h-BN）based nanocomposites were studied,as well as their tribological properties as nano lubricant additives in base oil.The mechanisms of anti-wear and friction-reducing of these nano-materials as lubricant additives and the synergistic lubricating effect of the nanocomposites were also discussed in this work.The specific research contents are as follows:（1）The two-dimensional layeredβ-Ni（OH）₂ and the nanocomposite ofβ-Ni（OH）₂ dotted with nano-particles of nickel were prepared by hydrothermal synthesis.The tribological properties of Ni/β-Ni（OH）₂ nanocomposite in the base oil of poly-alpha-olefin 6（PAO6）were systematically studied with the oleic acid as dispersant.The results showed that Ni nanoparticles were uniformly distributed on the surface ofβ-Ni（OH）₂ and the nanocomposite of Ni/β-Ni（OH）₂ exhibited better dispersibility and tribological properties as compared withβ-Ni（OH）₂.The increased interlayer spaces after in situ reduction of Ni inβ-Ni（OH）₂ resulted in Ni/β-Ni（OH）₂ easier to disperse in the oil with aid of dispersant of oleic acid.The cooperation of the layeredβ-Ni（OH）₂ and the dotted Ni particles in the nanocomposite during rubbing process favored the formation of a reaction protective tribo-film on the friction interfaces,which corresponded to the further improvement of the tribological properties of the friction pairs.（2）The modified hexagonal boron nitride（f-BN）was prepared by hydrothermal modification.The effects of f-BN as lubricant additive on the tribological properties of hard molybdenum nitride coating were systemically studied.The results showed that long alkyl chains were successfully grafted on the surface of hexagonal boron nitride,and the f-BN exhibited better dispersibility in oil and had better tribological behaviors than pristine hexagonal boron nitride（p-BN）.The stable molybdenum oxides（Mo O_x）were more prone to form at the friction interfaces under the lubrication of f-BN dispersed oil.The formed Mo O_xwith friction reduction and anti-wear properties could cooperate with f-BN to achieved better tribological performances.（3）The nanocomposites of hexagonal boron nitride dotted with nano-Cu particles（Cu/h-BN）were prepared by hydrothermal absorption and pyrolysis reduction.The tribological properties of Cu/h-BN as lubricant additive in the base oil of PAO10 were systematically studied.The results showed that Cu nanoparticles were dotted on the surfaces of h-BN.In addition,the nanocomposite of Cu/h-BN presented better tribological properties than the single used nano-material of nano Cu or h-BN.The nanocomposite of Cu/h-BN could fill up the valley pits and polish the protrusions on the friction interfaces to smooth the wear surfaces,in addition,the presence of nano-Cu in the nanocomposite could accelerate its deposition on the wear surfaces during the sliding process,which could form a protective tribo-film and then achieved better performance of friction-reducing and anti-wear.