Study on tribological properties and action mechanism of organic cadmium compound in lubricants

An oil-soluble cadmium dipropyldithiophosphate additive was synthesized. The tribological behavior of the additive in mineral base oil and greases was evaluated using four-ball tester, and compared with some same typical additives. The results show that it exhibits better antiwear and load-carrying properties than base oils and these additives. The topography, compositions contents and chemical states of typical elements on the worn scar were analyzed by Scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) and X-ray photoelectron spectrometer (XPS). Smooth and light topography of worn scar further confirms that the additive showed good tribological properties. The results of energy dispersive X-ray and X-ray photoelectron spectrometer analyses indicated that tribochemically boundary films formed on the rubbing surface consists of atomic cadmium, sulphides, sulphates and phosphates, which contribute to improve the lubrication and wear properties of lubricants and greases, the deposited soft cadmium layer especially plays an important role in improving antiwear and load carrying properties of oils. Finally, formation scheme of atomic cadmium and action mechanism of the additive were proposed.