Due to the increasingly stringent environmental regulations, in order to reduce emissions, catalytic converters are widely used in engines. Since phosphorus can poison the catalyst therein, it is required to limit the phosphorus content in the engine oil formulation. At present, oil-soluble organic molybdenum is widely used in internal combustion engine oil to reduce the amount of zinc dialkyldithiophosphate (ZnDDP) used, and at the same time, the friction reducing performance of the engine friction pair is improved, and the efficiency is improved. In order to improve the transmission efficiency of the friction pair and reduce the friction coefficient, organic molybdenum has been widely used as a friction modifier.
Adding a small amount of ZnDDP to the base oil can not effectively improve the antiwear and antifriction performance of the oil. However, in the base oil, ZnDDP has synergistic effect with organic molybdenum (MoDTC, MoDTP). When lubricating with lubricating medium with organic molybdenum, firstly It is the physical adsorption of organic molybdenum. With the increase of temperature, under the action of thermochemistry and tribochemistry, organic molybdenum decomposes, and the decomposition products and the surface of the friction pair undergo complex chemical reactions to form a stable anti-wear anti-friction protection layer. Therefore, it plays a role in reducing friction and wear. The addition of ZnDDP acts as a synergistic effect, promoting the decomposition of organic molybdenum and making it have a better lubricating effect.
When lubricated with oil (synthetic oil +0.7% MoDTC + 0.3% ZnDDP), XPS analysis of the surface of the wear spot under 392 N conditions can be inferred that MoS2, Mo2O3 and FeS are formed on the surface of the friction pair. The formation mechanism of organic molybdenum on the rubbing surface can be considered as some polar atoms such as S, P, N, etc. contained in the molecule, or polar groups such as -OH, NH2, -SO3 and the like. These more active components are strongly adsorbed on the metal surface by the surface energy of the metal. When the mechanical movement is carried out, the friction metal surface load is increased, the adsorption oil film can not meet the requirements, and the polar molecules will rapidly undergo a series of complicated chemical reactions under the special high temperature, high pressure and ZnDDp catalysis in the friction environment. A lubricating film comprising MoS2, Mo2O3, FePO4, FeS, FeO, etc. is formed. When the surface protective film is mainly MoS2, it has a small friction coefficient.