Tribological characteristics of bisphenol AF bis(diphenyl phosphate) as an antiwear additive in polyalkylene glycol and polyurea grease for significantly improved lubrication

A new antiwear additive of Bisphenol AF bis(diphenyl phosphate) (BAFDP) was synthesized and characterized. The tribological behaviors of the additive for polyalkylene glycol (PAG) and polyurea grease (PG) application in steel/steel contacts were evaluated on an Optimol SRV-IV oscillating reciprocating friction and wear tester at elevated temperature. The results revealed that BAFDP could drastically reduce friction and wear of sliding pairs in both PAG and also in PG at 100 °C. The tribological properties of BAFDP are superior to the normally used zinc dialkyldithiophosphate-based additive package (ZDDP) in PAG and PG. Moreover, BAFDP as additive for PAG and PG displays relatively significant tribological properties in temperature-ramp tests by performing well at 50–300 °C, indicating the excellent high temperature friction reduction and anti-wear capacity of BAFDP. XPS results showed that boundary lubrication films composed of Fe(OH)O, Fe3O4, FePO4, FeF2, FeF3, compounds containing the PO bonds, nitrogen oxide, and so forth, were formed on the worn surface, which contributed to excellent friction reduction and antiwear performance.