Application of molybdenum complexes of 1-aryl-2,5-dithiohydrazodicarbonamides as extreme pressure lubricant additives

Some molybdenum complexes of 1-aryl-2,5-dithiohydrazodicarbonamides have been synthesized and evaluated for their extreme pressure (EP) additive properties using a four-ball machine. The test specimens used were steel balls of 12.7 mm diameter. Compatibility of the synthesized additives has been discussed on the basis of various parameters like wear scar diameter, friction coefficient, initial seizure load (ISL), 2.5 s seizure delay load (SDL), weld load (WL), mean specific pressure at contact points, mean Hertz load (MHL), pressure wear index (PWI) and flash temperature parameter (FTP). All the tested molybdenum complexes have been found to show significant E.P. efficiency under the experimental conditions of four ball test, however, the best performance was exhibited by p-methoxyphenyl and p-chlorophenyl derivatives. The topography of wear scar surface of ball at different loads and tribochemistry at just before WL in presence of p-methoxyphenyl derivative has been studied by scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) respectively. Presence of molybdenum, sulfur, nitrogen and oxygen on the ball surface detected by AES provides an evidence in favor of decomposition of the additive leading to formation of tribologically active substances which bear the load up to WL.