Synergistic studies of Schiff base with organoborate as efficient antiwear lubricant additive

Abstract

Schiff base derived from condensation of 4-aminotriazole with indole-3-carboxylaldehyde has been characterized by Fourier-transform infrared and 1H NMR spectroscopic techniques. The tribological properties of synthesized Schiff base have been evaluated using four-ball tester at optimized concentration (1% w/v) and compared with its individual components. The tribological testing has been performed by varying load for 30 min duration and varying test durations at 392 N load. The synergistic action of Schiff base with commercial borate ester effectively enhances the antiwear properties of base oil and its load-carrying capacity. Pronounced reduction in the values of mean wear scar diameter, friction coefficient (µ), mean wear volume (MWV), and wear rates confirm the synergistic interaction between Schiff base and borate ester. The best tribological properties are shown by synergistic mixture, followed by Schiff base, then indole-3-carbaldehyde, and finally 4-aminotriazole. The surface topography of worn surfaces has been studied by scanning electron microscopy and contact mode atomic force microscopy which show the drastic decrease in surface roughness in the presence of synergistic mixture. The energy-dispersive X-ray analysis of worn surface lubricated with synergistic formulation exhibits nitrogen, carbon, boron, and oxygen indicating the adsorption of additive on the metal surface to form in situ protective tribofilms, which prevent direct metal–metal contact thus reducing friction and wear. The quantum chemical calculations studies show that there is significant interaction of Schiff base additive with the metal surface than those of its individual components and the data correlate very well with the obtained tribological results.