Highly efficient sulfur and phosphorous-free antiwear additives for paraffin oil

Abstract

Antiwear behavior of lanthanum Schiff bases of the formula LaLNO3 (where LH2 = Salicylidene-1,2-phenylenediamine(H2Saloph), Salicylidene-1,4-phenylenediamine(H2Salpph), Salicylidene diaminodiphenylenemethane(H2Saldphm)) has been studied on Four-Ball tester in paraffin oil. The results have been compared with zinc dibutyldithiophosphate (ZDDP) and organoborate (Vanlube 289). The additive concentration was optimized by conducting tests for different concentrations 0.5, 1.0, 1.5, and 2% w/v of the additives at 392 N applied load for 30-min duration. All the antiwear tests have been performed at optimized additives concentration (1% w/v) by varying loads from 294, 392, 490, 588, to 686 N for 30-min test duration and by varying test duration from 15, 30, 60, and 90 min at 392 N load. The determined tribological parameters show that all complexes act as good antiwear additives. Their activity is even better than ZDDP/borate ester. When mixtures of complexes with Vanlube 289 are tested, tremendous synergistic interaction is observed. Out of the three tested complexes, [La(Saldphm)NO3] shows excellent antiwear properties and possesses very high load-bearing capacity. Surface morphology of worn scar has been studied by scanning electron microscopy and atomic force microscopy. These micrographs of wear scar in the presence of [La(Saldphm)NO3] at 392 N applied load for 90-min duration show drastic increase in surface smoothness. Energy dispersive X-ray analysis of worn surface under similar experimental conditions in presence of the above complex exhibits presence of lanthanum on steel surface indicating adsorption of additive on rubbing surface, which leads to the formation of strong tribofilm. Further, X-ray Photoelectron Spectoscropy (XPS) of the tribofilm shows presence of adsorbed nitrogen and mixture of oxides B2O3, La2O3, Fe2O3/Fe3O4.