Comparative Study on the Tribological Performances of Barium Perrhenate, Molybdenum Disulfide, and Calcium Carbonate as Lubricant Additives in a Wide Temperature Range

ABSTRACT

Barium perrhenate [Ba(ReO₄)₂], a compound used as an oil additive, was synthesized via the aqua-solution method. Its tribological properties were examined using the four-ball test and ball-on-disc tribotester in a wide temperature range and compared with those of oil that contained the additive molybdenum disulfide (MoS₂) and calcium carbonate (CaCO₃) compound. X-ray diffraction analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and differential thermal analysis/thermogravimetry were performed to determine the possible mechanism of the antifriction behavior of the lubricants. Results of the four-ball test showed that all of the additives can improve the extreme pressure property of the base oil and decrease the wear scar diameters of low-carbon steel balls. The results of the ball-on-disc test suggested that the MoS₂ additive exhibited better lubrication property than the Ba(ReO₄)₂ and CaCO₃ additives at below 450°C. The CaCO₃ additive displayed moderate performance in friction reducing in the high-temperature period. The Ba(ReO₄)₂ additive exhibited preferable comprehensive antifriction performance in a wide temperature range because of its intrinsic shear-susceptible property and crystalline change with varied temperatures, which could form a protective layer with some native oxides of the disc sample and thus effectively prevented direct contact between rubbing parts. The detailed friction-reducing mechanism of the three additives is also discussed.

KEYWORDS:

• Barium perrhenate
• molybdenum disulfide
• calcium carbonate
• oil additive
• wide temperature range
• antifriction

Acknowledgements

This work reported here was supported by the National Natural Science Foundation of China (No. 51175489).