Hydroquinone bis(diphenyl phosphate) as an Antiwear/Extreme Pressure Additive in Polyalkylene Glycol for Steel/Steel Contacts at Elevated Temperature

The tribological behaviors of hydroquinone bis(diphenyl phosphate) (HDP) and tricresyl phosphate (TCP) for polyalkylene glycol (PAG) were evaluated at 200 °C. Results showed that HDP could effectively reduce the friction coefficient and prevent wear of sliding pairs during the test. The best tribological properties of HDP achieves at the concentration of 4 wt %. At this level, the wear volume of the lower disk can be reduced by a factor of 2.4 and the load-carrying capacity can increase from 500 N to 930 N, with respect to pure PAG. Furthermore, HDP exhibited better antiwear (AW) and extreme pressure (EP) properties than TCP, despite the fact that their friction-reducing performances were similar. Boundary lubrication films composed of FeOOH, Fe 2 O 3, FePO 4, and polyether compounds were formed on the worn surface, which resulted in excellent friction reduction and AW performance.