XANES analysis of tribochemical and thermal films generating from some organic polysulfides

X-ray absorption near edge structure (XANES) spectroscopy has been firstly used to characterize the chemical nature of tribochemical and thermal films generated from alkyl, benzyl and acyl-containing organic polysulfides. It has been found that the thermal films generated from these polysulfides are mainly composed of FeSO4, and alkyl disulfides also exist in the subsurface and bulk of thermal films generated from acyl-containing polysulfides. Under tribochemical conditions, the composition of film is dependent on the molecular structure of the additives. Namely, the tribochemical film generated from alkyl polysulfide is composed of alkyl disulfide in the out surface, a mixture of FeSO4, FeS2 and sulfoxide in the subsurface, and FeSO4 in the bulk; the composition of the tribochemical film for benzyl polysulfide consists of FeSO4 in the out surface, while the composition in subsurface and bulk is the same as the alkyl polysulfide. For acyl-containing polysulfides, the tribochemical films consist of alkyl disulfide in the out surface, and FeS2 in the subsurface and bulk.