二烷基二硫代磷酸锌润滑添加剂的抗磨机理

Anti-wear property of zinc dialkyldithiophosphate

用量子化学方法计算了4种二烷基二硫代磷酸锌(ZDDP)与铁原子簇的化学吸附作用能,并探讨了此种作用能与抗磨性能的关系。用前线电子密度和原子净电荷作为判据分析了4种添加剂分子与铁原子间键合的强弱和反应性的大小。计算表明二烷基二硫代磷酸锌的活性元素为6位和7位硫原子,其与铁发生摩擦化学反应时,最可能的断键位置是6位和7位硫原子的双键。反应生成由多磷酸盐和铁硫化物组成的反应膜,该膜具有较好的抗磨作用,仲烷基ZDDP比伯烷基ZDDP的抗磨性好,而伯烷基ZDDP的抗磨性优于芳香基ZDDP的。在伯烷基上吸电子基团能增强硫原子与铁原子之间的化学吸附作用力。量子化学的计算预测结果与摩擦学实验结果相符。

The chemical adsorption between four kinds of zinc dialkyldithiophosphates and Fe clusters were investigated by chemical quantum method, and the relationship between adsorption energy and anti-were property was discussed by frontier molecular orbital theory. The bond energy of the interaction between zinc dialkyldithiophosphate molecules and Fe atoms were analyzed by frontier electron densities and net atomic charge of them. The results show that the S6 and S7 atoms are the most likely points of attack during the surface reaction. The attack causes the cleavage of P-S double bonds, then the decomposition products reacting with the surface of Fe metal lead to the formation of the anti-wear and anti-friction film largely composed of polyphosphates and sulphides. As anti-wear agents, the shexyl ZDDP is found to be more effective than the n-hexyl ZDDP, and the n-hexyl ZDDP is superior to the phenyl ZDDP. The electron withdrawing group （F） being introduced into the alkyl groups of the n-hexyl ZDDP is able to strengthen chemical adsorption between ZDDP and Fe atoms. The prediction mechanism of the film formation is in good agreement with experimental results.