Base medium effect on the tribological behavior of oil-water double soluble bismuth dithiophosphate

Purpose - The purpose of this paper is to understand the effect of base media on the tribological performance and tribochemistry of bismuth thiophosphate additive. Design/methodology/approach - The oil-water double soluble additive bismuth dithiophosphate was prepared and identified. The contributions of the two base media on the additive tribological behavior and the tribofilm components were comparatively studied. Findings - The extreme pressure (EP) and friction-reducing properties are remarkably improved with water substituted for paraffin as the base medium. The EP performance of the lubricating media containing this additive mainly results from the tribochemical reaction film on the rubbing surface, not from the viscosity of the base media. In water or paraffin medium, the adsorption process of this additive from the lubricant bulk onto the rubbing surface and the components and the properties of the tribochemical reaction films formed are different, which have important effect on the tribological performance. Research limitations/implications - The paper mainly focuses on how the water medium with polarity and the liquid paraffin base medium with non-polarity affect on the tribological performance of the bismuth thiophosphate additive. Practical implications - The research has found a water-oil double soluble lubrication additive with outstanding EP and friction-reducing performance. Originality/value - The designed experiment provides a new approach to further learn the action mechanism of thiophosphate additive.