Tribological properties of fluorine-containing additives of silicone oil

An oil soluble fluorine-containing octadecylamine salt of decapentylfluorooctanoic acid was synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), 1H-nuclear magnetic resonance (1H NMR) and 19F NMR. The thermal stability of octadecylamine salt of decapentylfluorooctanoic acid was measured by a thermogravimetric (TG) analysis. The anti-wear and friction-reducing properties of the amine salt as a silicone-based lubricating oil additive were evaluated using a four-ball tribotester. The results indicated that both the wear resistance and the load-carrying capacity of a silicone-based lubricating oil 4609 shock absorption liquid were improved and the friction coefficient was decreased by the additive. The wear scar, after being cleaned using an ultrasonic bath in petroleum ether, was characterized with scanning electron microscopy (SEM) and X-ray photoelectron spectrometry (XPS). It was found that the boundary film on the worn surface was composed of fluorine-containing organic film and iron fluoride such as FeF2, which provided the oil with improved anti-wear and friction-reducing properties.