Enhanced tribology properties of ZnO/Al₂O₃ composite nanoparticles as liquid lubricating additives

Monodispersed and hydrophobic ZnO/Al₂O₃ composite nanoparticles are prepared by a nonhydrolytic sol–gel method. ZnCl₂ and AlCl₃ are dissolved in acetone and used as precursors. Oleic acid is adopted as an oxygen donor. The tribology properties of the prepared ZnO/Al₂O₃ composite nanoparticles are studied by the four-ball friction and thrust ring friction test. It is demonstrated that the average friction coefficient and the wear scar diameter are reduced by 37.5 and 26.2%, respectively, in comparison with pure lubricating oil. Moreover, the ZnO/Al₂O₃ composite nanoparticles bear the merits of ZnO and Al₂O₃ when used as lubricant additives, exhibiting both excellent antifriction and antiwear behaviors simultaneously. The ZnO/Al₂O₃ composite nanoparticles improve the lubrication effect not only by turning the sliding friction into rolling friction, but also forming a hard Al₂O₃ protective film onto the thrust-ring surface containing ZnO/Al₂O₃ nanoparticles, which have much potentiality in industrial applications.