Tribological behavior of the synthetic chlorine- and fluorine-containing silicon oil as aerospace lubricant

Purpose- The purpose of this paper is to examine the tribological behavior of the synthetic chlorine- and fluorine-containing silicon oil as an aerospace lubricant.Design/methodology/approach- The chlorinated-phenyl and methyl terminated silicone oil (CPSO), chlorinated-phenyl and trifluorinated-propyl with methyl terminated silicone oil (FCPSO) were prepared. Their physical properties such as saturated vapor pressure and the evaporation weight loss were evaluated. The tribological properties of the silicon oils under moderate load were investigated with an Optimol SRV oscillating friction and wear tester, as well as Four-ball friction and wear tester according to the standard method of ASTM D 4172 under higher load. The elemental composition generated on steel ball surface were analyzed on a scanning electron microscope with a Kevex energy dispersive X-ray analyzer attachment (SEM/EDS), and the chemical nature of elements on worn surface lubricated with FCPSO were studied by X-ray photoelectron spectrometer (XPS).Findings- It is found that the CPSO and FCPSO show good tribological behavior for steel/CuSn alloy tribological pairs and are superior to hosphazene (X-1P) and perfluoropolyether in terms of friction-reduction ability and anti-wear performance. The anti-wear performance of FCPSO as lubricants for steel-steel contacts is superior to CPSO. The EDS results showed existence of F and Si on the worn surface with lubrication of FCPSO, while XPS results indicated the occurrence of tribochemical reaction of FCPSO with friction pair during sliding process with the formation of FeCl₂, FeF₂ and the absorption silicon oil films on the lubricated metal surface.Originality/value- The results substantiate that chemical reactive elemental such as chlorine or fluorine, which is substituted into silicon oil, helps to improve the anti-wear and load-carrying capacity of the liquid lubricant. So the excellent thermal stability, low-temperature fluidity, very low-saturated vapor pressure and excellent lubricity for steel/CuSn alloy of the silicon oil of FCPSO and CPSO make it an attractive alternative to conventional liquid lubricant for space mechanism.