Investigation of tribological properties of MoS2 and CaF2 particles as oil additives and their effects on surface contact

Nowadays, researches on the use of alkali metal salts as friction-reducing and anti-wear oil additives are continuing. In this study, the tribological effects of heavy metal containing MoS₂ and alkali metal salt CaF₂ additives on pure engine oil (20W50) were investigated using block-on-ring tester configured as surface contact geometry. The tests were performed at various contact loads, revolutions, and additive ratios. The crystal structure of the additives and their effects on surface quality and surface roughness analysed by x-ray crystallography, scanning electron microscope and profilometry. Moreover, Energy dispersive spectrometry was used for element detection on worn surfaces. Results indicated that additives of MoS₂ and CaF₂ can reduce the friction, increase the capacity of load-carrying and the wear resistance of surfaces. The additives improved the operation of the base oil in boundary lubrication zone by increasing the tribofilm forming effect. It was observed that the CaF₂ additive exhibited more stable friction behaviour, while the MoS₂ additive has better protective effects against scratches on the block surface.