Tribological performance of organic cadmium compound as lubricant additive

The oil-soluble cadmium dipropyldithiophosphate additive was synthesized. A four-ball tester was used to evaluate the tribological performance of the additive in a mineral oil under different loads and lubricant grease synthesized compared with some commercial additives. The results show that it exhibits excellent antiwear and load-carrying capacities and is better than other additives. The surface analytical tools such as scanning electron microscope (SEM) with energy dispersive X-ray (EDX), X-ray photoelectron spectrometer (XPS) were used to investigate the topography, the compositions, and chemical states of some typical elements on the rubbing surface of worn scar.Smooth and light topography of worn scar further confirms that the additive shows good antiwear capacities. The results of EDX and XPS analyses indicate that tribochemical mixed protective films consisting of atomic cadmium, sulphides, sulphates and phosphates are formed on the rubbing surface, which contribute to improving the tribological properties of lubricant and grease. Particularly, the soft cadmium film formed plays an important role in improving antiwear properties of oils. Finally, antiwear mechanism of the additive and formation scheme of atomic cadmium was proposed.