Preparation, Characterization And Tribological Properties Of Oil-Dispersible Nanosized Borate

The different borate nanoparticles（calcium borate，zinc borate and copper borate） were successfullysynthesized via extraction method, where oleic acid was used for surface-capping of target product. Themicrostructure as well as chemical feature and chemical state of resultant surface-capped boratenanoparticles was analyzed, and the lubricating behavior of as-prepared oil-dispersible borate nanoparticleswas evaluated. It has been found that surface modification of nanoparticles with oleic acid can not onlycontrol the particle size and hence effectively prevent their agglomeration, but also the uncoordinated polarhydrophobic groups of the modifying agents can endow borate nanoparticles with good dispersibility inordinary orangic solvents and good long-term physical-chemical stability. This provides a feasible approachto oil-dispersible borate nanoparticles as lubricating additives. The main contents and research results ofthis thesis are as follows:(1)The surface-capped borate nanoparticles can be uniformly dispersed and stable existing in ordinaryorangic solvents (chloroform, petroleum ether, toluene) without irreversible agglomeration anddecomposition. And it can also be isolated as powders by oven drying. The morphology, structure andchemical composition of the nanoparticles have been analyzed by means of transmission electronmicroscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectrometry (FT-IR),thermogravimetric analysis and differential thermogravimetric analysis (TGA/DTG) and a contact anglemeter. The result indicates that oleic acid is bonded to the O-H groups at the surface of calcium borate viachemical bond.It confirms that intermolecular forces has been formed between carboxylic ion and thesurface of borate,which shows that oleic acid has formed a long-chain hydrophobic layer on the surface ofborate nanoparticles.Then the surface-modified borate nanoparticles can disperse in ordinary orangicsolvents. Although the existing of surface-modified layer can prevent the formation of lager bridginghydroxyl,there are still few hydroxyl.It is why the post-drying powder has slight agglomeration. Thesurface-modified borate nanoparticles appear as irregular hollow flake with a size of about50-100nm,which was amorphous. The surface-modified zinc borate nanoparticles appear as irregular flake with asize of about40-60nm,which was amorphous. The surface-modified cooper borate nanoparticles appear asirregular rectangle flake with a size of about50nm,which was amorphous.The results showed that the chemical formula of unmodified calcium borate is CaO·B2O5·1.5H2O; the chemical formula of unmodifiedzinc borate is2ZnO·3B2O3·3H2O,and the chemical formula of unmodified copper borate is Cu(BO2)2·2H2O.However, the surface-capped borate powder has poor re-dispersion capacity in ordinary orangic solvents.(2) The tribological behavior of oil-soluble borate nanoparticles as a lubricant was evaluated with afour-ball friction and wear tester and an Optimol SRV-1reciprocal oscillating friction and wear tester. Ithas been found that the tribological properties are related to the addition quantity of borate nanoparticlesunder the same load and the amount of addition has an optimum value.And the tribological properties arerelated to load at the same addition rate. The optimum value of calcium borate is0.6%; the optimum valueof zinc borate is0.5%,and the optimum value of copper borate is0.7%.The test results are basicallyidentical between a four-ball tester and an Optimol SRV-1reciprocal oscillating tester.When the load is300N, The wear scar diameter of oil-soluble borate is0.323mm,0.328mm and0.333mm respectively.Thediameterof worn spot reduded by49.3%,48.5%and47,7%respectively. Resultant modified boratenanoparticles, as compared with pure liquid paraffin and pure borate nanoparticles, can reduce the frictionand wear of steel-steel sliding pairs effectively. The worn surface of steel ball present ploughing. Thepossible reason is that post-drying powder has slight agglomeration.The grain-abrasion occurred duringfriction process because of esisting of large particles in liquid paraffin.On the other hand, compact reactionfilm has not formed in the surface of wear scar.In the meantime, the oil-soluble borate nanoparticlespossesses good extreme pressure properties, with maximum non-seizure load (PB value) and weld load (PDvalue) being as high as804N (copper borate:431N)and1676N at a proper concentration.Furthermore, it islikely that the poor re-dispersion capacity and stability in ordinary orangic solvents of the surface-cappedborate powder accounts for the poor lubrication performance.(3)This is the innovation point in this paper.A new approach is developed to prepare fine performanceborate nanoparticles.This method need neither harsh reaction condition,nor complex experimentinstrument.And the experiment process is easy.It is beneficial to large scal production.