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Enhanced MoS2antiwear performance by the presence of ZnSO4against ZDDP

Zinc dithiophosphate is the most commonly used antiwear additive in lubricating oil. However, zinc dithiophosphate has a poisoning effect on engine catalysis via phosphorus and zinc content that reduces the efficiency causing hazardous emission increase, therefore, it needs to be replaced with an alternative additive. In this study, the antiwear performance of molybdenum disulfide (MoS2) is enhanced by zinc sulfate (ZnSO4) addition and subjected to tribometer tests at different contact pressures to explore the MoS2 + ZnSO4friction and antiwear performance against MoS2and zinc dithiophosphate. Wear rates and surface morphology changes were carried out by an optical microscope, optical profilometer, and atomic force microscope analysis. Furthermore, tribochemical and surface energies of tribofilms were evaluated via scanning electron microscope/energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscope adhesion force mapping analysis. Results showed that ZnSO4addition to MoS2 + base oil improves the antiwear performance of the lubricating oil significantly and it presents similar friction characteristics to zinc dithiophosphate.