Synthesis Of Surface Modified Zinc Oxide Nanoparticles And Eevaluation Of Their Tribological And Antioxidant Properties

The emergence of nano-technology promotes the development of modern tribology.Nanoparticles have excellent tribological properties as lubricating oil additives,especially when zinc oxide nanoparticles as lubricating oil additives,they have the advantages of self-repairing,less dosage,remarkable friction reduction and antiwear properties and anti-oxidation.However,the preparation of zinc oxide nanoparticles usually involves complex nucleation and modification processes.In this paper,aiming at how to develop a single raw material and simple preparation method,we designed and synthesized appropriate modifiers to make them suitable for different lubricating base oils and related the structure-activity relationship between the lubricating and antioxidant properties and structures of nano-zinc oxide with different structures and components in different friction pairs and lubricating base oils.All these become the key problems to promote the application of nano-zinc oxide in the field of lubricating oil additives.The main results of this paper are as follows:?1?One-step preparation of ZnO nanoparticles and their properties as lubricant additives for aluminium-based friction pairsIn order to overcome the problem that commercial lubricant additive zinc dialkyl dithiophosphate?ZDDP?can not form film on aluminum-based friction pairs with low strength and severe wear resistance,oil-soluble and well dispersed zinc oxide?ZODDP?nanoparticles modified by ZDDP were prepared by one-step in-situ surface-modification technique using ZDDP as raw material.Structural analysis showed that the core of zinc oxide nanoparticles was hexagonal ZnO nanocrystals with average particle size ranging from 2.4 to 5.2 nm.The modification agent and nanonuclei were chelated by non-chemical bonds.Compared with raw material ZDDP,the content of sulfur and phosphorus decreased by 77.9%-82.8%and77.3%-80.7%,respectively.The tribological properties of ZODDP as the additives of DIOS in steel/aluminium and steel/aluminium alloy friction pairs were evaluated by using UMT-2 micro-friction and wear tester.The results show that when 0.4 wt%ZODDP was added to DIOS,the wear rates of aluminium and aluminium alloy discs decreased by 74.0%and 44.0%,respectively.The wear surface was analyzed by SEM,EDS and XPS.It was found that the excellent tribological properties of ZODDP are attributed to the weak chemical interaction between ZnO nanoparticles and modifiers,which promotes the tribological reaction between modifiers and aluminium-based friction pair materials.The zinc oxide friction film combined with friction products AlPO₄ and Al₂?SO₄?₃ can well protect the surface of friction pairs from adhesion wear between steel balls and aluminium materials,and overcome the problem that ZDDP can not form effective friction film on the surface of aluminium-based friction pairs with low strength.The results show that ZDDP can overcome the problem that small molecular ZDDP can not form effective friction film on friction pair materials with low strength by preparing nano-zinc oxide.ZODDP is expected to be a cheap and easy-to-obtain lubricant additive and can be used in lubrication of aluminium-based materials.?2?Preparation of perfluorooctanoic acid modified ZnO nanoparticles and their properties as perfluoropolyether lubricant additivessAs the molecular chain of perfluoropolyether?PFPE?is composed of perfluoroether chains,it is hardly compatible with any traditional lubrication additives,so its tribological properties can not be effectively improved.In this chapter,perfluorooctanoic acid?PFOA?modified ZnO nanorods and ZnO nanoparticles were prepared by a simple one-step in situ surface modification technique.Structural analysis showed that the core of zinc oxide nanoparticles was hexagonal wurtzite type.The modifier modified the surface of zinc oxide nanoparticles in the form of chemical bonds,and dispersed it in PFPE with good dispersion.The tribological properties of ZnO nanoparticles as PFPE additives were evaluated by using UMT-2micro-friction and wear tester.The results show that compared with PFPE lubrication,the friction coefficient and wear rate decrease by 2.8%and 49.8%respectively after adding 3.0 wt%ZnO nanoparticles.When adding 2.0 wt%ZnO nanorods,the friction coefficient and wear rate decrease by 5.4%and 57.4%,respectively.SEM,EDS and XPS analysis showed that ZnO nanorods and ZnO nanoparticles formed protective and lubricious film composed of zinc oxide deposited film,Fe₂O₃/FeF₃ dense tribochemical reaction film and adsorbed organic matter during the friction process.The synergistic effect of these lubrication films greatly improved the wear resistance of PFPE.?3?Antioxidation properties of surface-modified ZnO nanoparticles as lubricant additivesThe first two chapters mainly explore the tribological properties of ZnO nanoparticles in lubricating oil,and the high temperature oxidation resistance of lubricating oil is also the guarantee of lubricating oil quality.ZnO nanoparticles not only has anti-wear and friction reducing effect,but also has anti-oxidation performance.It is a lubricant additive with many functions.In this chapter,the antioxidant properties of surface-modified ZnO nanoparticles in lubricating oil were evaluated by high temperature differential thermal scanner?PDSC?.The antioxidant properties of these nanoparticles as lubricating oil additives were evaluated by programmed heating method and constant temperature method.The activation energies of lubricating oil samples were calculated by Kissinger method and Flynn-Wall-Ozawa method,and the apparent activation energies of the samples were compared.Its antioxidant activity was characterized.The results showed that the oxidation resistance of PFOA modified ZnO nanoparticles in PFPE was not obvious because of the excellent antioxidant performance of PFPE,but the di-n-octyl dithiophosphate modified ZnO showed excellent antioxidant performance when used as base oil DIOS additive.According to Kissinger and Flynn-Wall-Ozawa methods,the activation energy of samples was calculated.The results showed that the activation energy of oil samples added with ZODDP was the largest,indicating that the addition of ZODDP could improve the antioxidant ability of DIOS base oil.It is expected to play a guiding role in the study of antioxidant ability of inorganic nanoparticles in lubricating oil in the future.