The rheological and tribological properties of calcium sulfonate complex greases

Abstract

In this study, we synthesized two types of calcium sulfonate complex greases (barium soap and calcium soap) and investigated their physical, rheological, and tribological properties in detail. The test results showed that the evolution of their linear viscoelasticity functions with frequency were quite similar to those of traditional lubricating greases. Moreover, these two calcium sulfonate complex greases had good friction-reducing and antiwear properties at room temperature and at 150 °C. In addition, by adding an organic molybdenum compound (MoDTC) to the base greases, we obtained a very low friction coefficient (0.065) for one of the greases (calcium soap) at 400 N and 500 N (maximum Hertzian pressures of 3.47 GPa and 3.74 GPa, respectively) at 150 °C. X-ray photoelectron spectroscopy (XPS) analysis showed that the tribofilm was composed of some complex oxide species and CaCO3 that had formed on the worn surface.