Effect of Friction Velocity on Tribological Behavior of Coumarin as Mineral Oil Additive

Abstract

The tribological behavior of lubricants, prepared with a mineral base oil, lauryl alcohol, and different concentrations of coumarin, were examined using a four-ball tester under constant and variable friction velocity conditions. At constant friction velocity, the maximum non-seizure load (PB) increased from 304 N to 392 N at a coumarin concentration of 0.5 wt.%. Lubricants with 0.7 wt.% coumarin exhibited optimum lubricating properties, and the maximum reductions in friction coefficient (FC) and wear scar diameter (WSD) were 20.0% and 11.88%, respectively. Further investigation of the tribological mechanism implied that the ester group in the coumarin molecule established a connection with the surface atom, resulting in the formation of a tribofilm, which further restricted the adhesion wear regime. Additionally, under variable friction velocity conditions, increasing the coumarin concentration had an obvious effect on the mixed lubrication (ML) and elasto-hydrodynamic lubrication (EHL) regions, but not on other lubrication regions. Moreover, a mathematical model was proposed to show the relationship between FC and friction velocity. Importantly, the present work clarifies the effect of friction velocity on the tribological behavior of coumarin, and also supports the use of coumarin as a novel additive in mineral oils.

Coumarin as a green inhibitor of chloride-induced aluminum corrosion: theoretical calculation and experimental exploration

“…Herein, the weak peak at 535.6 eV was ascribed to the satellite peak of C]O structure, which well proved the presence of coumarin on the aluminum surface. 10 The peak at 531.4 eV showed the strongest intensity, which conformed to aluminum oxides/hydroxides, i.e., Al 2 O 3 and Al(OH) 3 . This revealed that the chemical composition of the corroded surface was predominated by Al 2 O 3 and Al(OH) 3 .…”

“…Meanwhile, recent studies have proved that coumarin showed excellent lubrication effects and could be employed successfully in cold-rolling operations. 9,10 Unfortunately, research on corrosion inhibition and surface adsorption mechanism of coumarin, not its derivates, has rarely been reported.…”