Phosphorous free antiwear formulations: Zinc thiosemicarbazones–borate ester mixtures

Abstract

Antiwear properties of zinc(II) complexes of salicylaldehyde N(4)-phenyl- p-substituted thiosemicarbazones and their synergic action with Vanlube 289 additive were evaluated in paraffin oil on four ball tester using steel balls of 12.7 mm diameter and the results were compared with those of zinc dibutyl dithiophosphate. On the basis of mean wear scar diameter, mean wear volume, friction coefficient, running-in and steady-state wear rate under optimum conditions, the following order of efficiency emerged: Zinc(II) thiosemicarbazones + Vanlube 289 > Vanlube 289 > ZDDP > Zinc(II) thiosemicarbazones. Among the zinc(II) complexes alone or their synergic formulations, salicylaldehyde N(4)- p-methoxyphenylthiosemicarbazones [Zn(HSTC- p-OMePh)2] exhibits best antiwear properties followed by salicylaldehyde N(4)- p-chlorophenylthiosemicarbazone [Zn(HSTC- p-ClPh)2], salicylaldehyde N(4)- p-methylphenylthiosemicarbazone [Zn(HSTC- p-MePh)2] and salicylaldehyde N(4)- p-phenyl thiosemicarbazones [Zn(HSTC-Ph)2] derivatives. The topography of the wear scar studied by atomic force microscopy and scanning electron microscopy in absence and presence of the additives indicated reduced roughness of the surface in presence of the additives. The admixtures containing zinc(II) complexes and their synergic formulations with Vanlube 289 showed presence of sulfur, nitrogen, oxygen and zinc in the energy-dispersive X-ray analysis of the wear scar.