Volume 4, Issue 8 (September 2007)
Synergistic Tribological Performances of Borate Additive in Lubricants
A four-ball tester was used to evaluate the tribological behaviors of nitrogen-containing borate (BNO) combined with zinc dialkyldithiophosphate (ZDDP) and tin dialkyldithiocarbamates (SnDDC) in liquid paraffin or mineral oil, even respectively. The surface analytical tools such as X-ray photoelectron spectrometer (XPS), X-ray diffractometer (XRD), and energy dispersive X-ray (EDX) were used to investigate the chemical states of some typical elements and composition on the rubbing surface of the wear scar. The tribological results show that BNO exhibits better antiwear properties in base oils, and can exhibit good antiwear synergism when it was combined with additives ZDDP and SnDDC, respectively, while the antiwear properties of oil-containing additive packages are optimal under certain concentration ranges. The results of XPS and XRD analyses indicated that BNO can form tribochemical mixed protective films consisting of BN or B2O3 compounds on the rubbing surface, and the combination of BNO with SnDDC may form tin, oxides, sulfide, and N-containing compounds on the rubbing surfaces, which contribute to improving the tribological properties of lubricants. A considerable amount of ZDDP can be partially replaced by BNO in synergistic mixtures, or replaced completely by the combination of BNO with SnDDC, which is especially important for ZDDP used in ecologically sensitive applications.