Friction-Induced Structure and Composition Change Mechanisms of Bio-Fuel Soot Particles

Friction-induced the formation of lubricating film including the engine soot particles had been researched extensively, but the composition and structure change mechanisms of soot particles on wear zone were limited. An end-face tribo-meter was utilized to investigate the composition and structure change mechanisms of biomass fuel soot(BS) particles in lubrication oils(such as liquid paraffin and fully formation engine lubricating oil) with and without TiF₃ or FeF₃ at rotation speed 1500 r/min and load 294 N for 60 min. The variations of composition and structure of BS particles on the wear zones were characterized by the X-ray photoelectron spectroscopy and Raman spectroscopy, moreover, the corresponding mechanisms were also discussed. Results show that the structure variation of BS particles, i.e. decrease of the amorphous carbon content(R3), increase of the order graphene content(I_D2/I_G') and increase of the surface defect sites of graphene(I_D1/I_G'), were observed on the wear zones. The mechanisms of structure and composition change of BS particles were ascribed to friction-induced the peeling of outer layer of BS particles and friction heat on the wear zones resulting in the formation of the better boundary lubrication film. TiF₃ and FeF₃ promoted the increase of graphene micro-crystal content on the wear zones at some conditions.