Preparation Of Environmental Friendly Oil-Soluble Silicon Dioxide/Copper Composites And Investigation Of Their Tribological Properties As Lubricant Additives

Copper(Cu)nanoparticles as lubricant additives show good tribological properties.But Cu nanoparticles are extremely sensitive to oxygen because Cu nanoparticles show more active chemical properties for its smaller particle size.The oxidation problem has already become one of the main bottlenecks restricting the application and development of Cu nanoparticles.There are many solutions to this problem,but it is uncommon to use the composites of silicon dioxide and copper to prevent the oxidation of Cu nanoparticles.In this paper,two different methods,sol-gel method and reverse microemulsion method,were used to prepare two kinds of particle size of silicon dioxide/copper composite microspheres and rod-shaped composite materials,and its tribological properties as lubricating oil additives were studied.However,using the composites as lubricant additives to test the tribological properties is rarely reported.Besides,the effects of morphology and particle size on the tribological properties of silicon dioxide/copper composites are not clear.Therefore,this paper discussed the correlation among morphology,particle size and tribological properties.Specific research contents and results are as follows:(1)The preparation of oil-soluble rod-shaped silicon dioxide/copper composite materials through solgel method and study of its tribological performanceCopper sulfate as the source of copper,with hydrazine hydrate as reductant,and ammonia hydroxide adjusting pH value,Cu collosol was prepared by chemical reduction method.Then Cu collosol transferred to the alcohol-water system for silicon dioxide coated,and their mixture was stirred at room temperature for 24 h.Rod-shaped silicon dioxide/copper composite materials were synthesized by adjusting the water/alcohol ratio,addition of ammonium hydroxide and tetraethoxysilane.Fourier transform infrared spectroscopy(FTIR),X-ray powder diffraction(XRD)and transmission electron microscopy(TEM)were used to characterize the size,morphology and structure of the composites.Results showed that silicon dioxide is similar to the hollow structure with Cu nanoparticles coated inside the silicon dioxide.The tribological properties of rodshaped silicon dioxide/copper composite materials in diisooctyl sebacate(DIOS)were tested using friction wear testing machine.Results showed that at higher load(100 N),the rod-shaped silicon dioxide/copper composite materials could show good anti-wear properties.Compared with DIOS and silicon dioxide,the wear rate can be reduced by 56.4% and 28.9%.(2)The preparation of oil-soluble silicon dioxide/copper composite microspheres through sol-gel method and study of its tribological performanceThe silicon dioxide/copper composite microspheres were prepared by changing the proportion of ethanol and water,the amount of ammonia hydroxide and tetraethoxysilane using sol-gel method.Then,silicon dioxide/copper composite microspheres were modified by octadecyltrimethoxysilane which can make the composite microspheres well dispersed in lubricating oil.FT-IR,XRD and TEM were used to characterize the size,morphology and structure of the composites.Cu nanoparticles can be uniformly distributed within the silicon dioxide,making Cu nanoparticles were wrapped inside the silicon dioxide which can effectively prevent the oxidation and aggregation of Cu nanoparticles.The tribological properties of silicon dioxide/copper composite microspheres in DIOS were tested using friction wear testing machine.Results showed that silicon dioxide/copper composite microspheres had anti-friction and anti-wear properties to a certain extent.The reason may be a tribo-film formed in the process of friction.It has been found that the tribological performance of spherical composite materials is better by comparing two different morphology of the silicon dioxide/copper composites.(3)The preparation of oil-soluble silicon dioxide/copper composite microspheres through reverse microemulsion method and study of its tribological performanceIn order to study the influence of particle size on tribological performance of silicon dioxide/copper composite microspheres,reverse microemulsion method was used to prepare silicon dioxide/copper composite microspheres with the particle size of 20 nm in this part.Firstly,copper oleate as raw material,Cu nanoparticles modified by oleic acid and oleylamine were prepared by pyrolysis.Then,Cu nanoparticles were putted into the microemulsion system for silicon dioxide coating.FT-IR,XRD and TEM were used to characterize the size,morphology and structure of the composites.The tribological properties of silicon dioxide/copper composite microspheres were tested using friction wear testing machine.Results showed that silicon dioxide/copper composite microspheres had a tiny anti-friction and a good anti-wear properties.It may be because the lubrication film formed by silicon dioxide and copper adsorbed and deposited on the friction pair surface.It has also been found that the tribological performance of composites with smaller size is better by comparing the tribological performances of the silicon dioxide/copper composites with the different size.