Study of the tribological behaviors of [S-(2H-thiophen-2-yl)]-methyl-alkyl xanthates as additives in rapeseed oil

The xanthate derivatives of thiophen including [S-(2H-thiophen-2-yl)]-methyl-ethyl xanthate (coded as TMEX), [S-(2H-thiophen-2-yl)]-methyl-butyl xanthate (coded as TMBX) and [S-(2H-thiophen-2-yl)]-methyl-octyl xanthate (coded as TMOX) were synthesized. The tribological behavior of the synthesized compounds as additives in rapeseed oil (RO) was investigated with four-ball friction and wear testers. The worn surfaces of the lubricated GCr15 steel were analyzed by means of X-ray photoelectron spectroscopy and scanning electron microscopy. The lubricating mechanisms were discussed on the basis of X-ray photoelectron spectroscopic and scanning electron microscopic analyses of the worn steel surfaces. It was found that the xanthate derivatives of thiophen as additives in RO improve the antiwear, friction-reducing properties and remarkably increase the load-carrying capacity of the base stock. X-ray photoelectron spectrometer (XPS) analytical results of the worn surfaces indicate that tribochemical reactions were involved for steel–steel pair lubricated with thiophen-rapeseed oil and the RO containing [S-(2H-thiophen-2-yl)]-methyl-alkyl xanthates (coded as TMAX).