Preparation Of Nano-TiO₂by Plasma Assisted Ball Milling And Its Tribological Properties

Nano-TiO₂powder is a kind of important functional material. It is widely used as lubricantadditive due to its excellent tribological performance. So how to prepare nano-TiO₂powderswith good dispersion conveniently has been a research emphasis in recent years.In this paper, we select lauric acid sodium salt （LASS） and cetyl trimethyl ammoniumbromide （CTAB） as the ball-milling process control agents, which are the anion and cation typesurface-modifiers. Surface-modified TiO₂powders were prepared by the plasma-assisted ballmilling device via three kinds of routes,1) adding surface-modifiers by plasma-assisted ballmilling method （referred as discharged and modified hereafter）,2) adding surface-modifiers byordinary ball milling method （referred as no discharged but modified hereafter）,3) withoutsurface-modifiers by ordinary ball milling method （referred as no discharged and modifiedhereafter）. TiO₂powders milled for different times via the three routes are used as marinelubricant additives, and the dispersion and tribological properties of these TiO₂powders aretested.Scanning electron microscopy （SEM） is used to observe these different kinds of TiO₂powders by three technologies. The results showed that lamellae nano-TiO₂powders wereprepared by discharged and modified way, with which have primary particle size about30nmand obvious signs of melting. The refinement process is accelerated by the synergistic effect ofthe plasma and surface-modifiers. Hard-agglomerations of TiO₂powders were prepared by nodischarged but modified way which has primary particle size about200nm.Loose-agglomerations of TiO₂powders were prepared by no discharged and modified way whichhas primary particle size about150nm. X-ray diffraction analysis showed that anatise phasetransformed to rutile phase and a new polymorph of the orthorhombic structure appeared duringthe ball milling process via three routes. Infrared spectroscopy （IR） analysis showed that thesurface of nano-TiO₂powders prepared by discharged and modified ball milling is coateduniformly by surface-modifier.The dispersion of different TiO₂powders via three kinds of preparation routes in40CAmarine lubricants are tested by gravity sedimentation method and lipophilic degree’s testing. Theresults show that nano-TiO₂powders prepared by discharged and modified way have the bestdispersion, whose lipophilic degree is up to50.7%. TiO₂powders prepared by no discharged and modified way have the worst dispersion whose lipophilic degree is only21%. The dispersion andlipophilic degree of the TiO₂powders prepared by no discharged but modified way between theformer two. The highest lipophilic degree of discharged and modified TiO₂powders is due to thefaster adsorbtion on the TiO₂powders surface by the plasma activation in plasma assistedball-milling, which change TiO₂powders surface from polar to non-polar.The tribological performances of different TiO₂powders prepared via three routes are testedby adding into40CA marine lubricant. When discharged and modified nano-TiO₂powders addedinto the lubricant, the frictional coefficient is the least and the abrasion loss of friction pairs is theleast at the same time. The surface roughness of friction pairs is reduced too. With the wear timeextending,“negative wear” phenomenon appeared on the friction pairs. The results of SEM andenergy dispersive microanalysis （EDS） on the worn surfaces show that plenty of nano-TiO₂powders deposited in the grinding and furrows of the friction surface. However, the anti-frictionquality is poor when adding no discharged but modified TiO₂powders or adding no dischargedand modified TiO₂powders. There aren’t any TiO₂powders deposits on the worn surfaces whenthe last two powders added. It is shown that the surface modified nano-TiO₂powders preparedby plasma assisted ball-milling not only have excellent anti-friction quality but also havewonderful self-repairing performance.