Studies on Lanthanum Complexes of 1-Aryl-2,5-Dithiohydrazodicarbonamides in Paraffin Oil as Extreme Pressure Lubrication Additives

Testing of lanthanum complexes of 1-aryl-2,5-dithiohydrazodicarbonamides of the formula LaL₃ [LH=1-phenyl-2,5-dithiohydrazodicarbonamide(PhTHC), 1-methylphenyl-2,5-dithiohydrazodicarbon-amide(p-MePhTHC), 1-methoxyphenyl-2,5-dithiohydrazodicarbonamide(p-MeOPhTHC), 1-phenyl-2,5-dithiohydrazodicarbonamide(p-ClPhTHC)] for their application as extreme pressure lubrication (EPL) additives was performed on four ball tester using steel balls of 12.7 mm diameter and MoS₂ as reference additive. The efficiency of the complexes has been evaluated using the tribological parameters, wear scar diameter, friction coefficient, initial seizure load, 2.5 s seizure delay load, weld load, mean Hertz load, flash temperature parameter and pressure wear index. The tested complexes behave as good extreme pressure additives; however, the best performance is shown by the p-methoxyphenyl derivative. The surface morphology of the wear scar on steel ball has been studied by atomic force microscopy and scanning electron microscopy. In presence of this complex, roughness of the worn surface is significantly reduced. The composition of wear scar has been analyzed by energy dispersive X-ray spectroscopy. The presence of lanthanum and sulfur in energy dispersive X-ray spectrum emphasizes role of additive in the tribofilm formed on the surface.