有机二硫化物润滑添加剂抗磨极压性能的密度泛函理论研究

用量子化学的密度泛函理论计算了12种有机二硫化物和铁原子簇的分子轨道指数及其与铁原子簇的化学吸附作用能, 探讨了这种作用能与抗磨性能的关系; 运用轨道能量近似原则讨论了有机二硫化物与铁原子的作用方式; 以前线电子密度、超离域性指数和原子净电荷作为判据分析了12种有机二硫化物与铁原子间键合的强弱、反应性的大小等表征有机二硫化物与金属作用强弱的参数。结果表明: 有机二硫化物与铁接触时, 在较缓和条件下, SS键优先断裂与金属发生化学吸附形成配位键, 起到抗磨作用; 在高负荷下, 与金属发生常规条件下不能发生的化学反应, 即CS键断裂生成无机膜, 起到极压作用; 且随着碳链的增长, 有机二硫化物的抗磨性能愈来愈好, 但极压性能愈来愈差; 运用量子化学计算得到的预测结果与摩擦学试验结果具有良好的一致性, 可为同类极压添加剂化合物的分子设计提供较为可靠的参考依据和理论方法。

Density Functional Theory Study on the Anti-wear and Extreme Pressure Properties for Disulfide Compounds as Lubricant Additive

The organic disulfide compounds are known as versatile chemistry-engineering products, which can improve the lubricating effectiveness of mineral oils, especially their load-carrying properties. These properties are entirely different depending on the disulfides structure. The ability of disulfides to prevent wear and damage of sliding surfaces is associated with their tendency to form layers on rubbing surfaces by adsorption and chemical reaction. The molecular orbital parameters and chemical adsorption of twelve organic disulfide compounds and iron atom cluster have been calculated by use of a quantum chemistry method. The interaction pattern between the organic disulfide compounds and iron atom was discussed based on the approximate rule of orbital energy. Some parameters characterizing the action strength between the organic disulfide compounds and iron atom, such as the bonding strength, reactive strength and static action strength, were analyzed by using frontier electron density, super de-localizability and net atomic charge as criteria. The results indicate that anti-wear properties of organic disulfide compounds are related to the different abilities to form chemical adsorption layers on frictional surfaces by the scission of SS chemical bond, and extreme pressure properties are correlated more with the chemical reactivity between the organic disulfide compounds and iron atom because the CS chemical bonds of disulfide compounds are broken and the formed radicals produce an inorganic film contacted with the metal. Furthermore, the friction-resisting ability is strengthened while the extreme pressure ability is weakened with the increase of carbon chain, and the prediction results based on quantum chemistry calculations are in good accordance with the friction and wear test results, which may provide reliable reference and theoretical methods in the molecular design for new and more extreme pressure (EP) additives.