Tribological evaluation and tribochemistry of some dialkyldithiomalonamides and their Mo-S complexes as EP additives

Abstract

The reported use of molybdenum dithiocarbamates and molybdenum dithiophosphates as antiwear and EP additives has led to attempts by the authors to synthesise certain novel Mo-S complexes, and evaluate their effectiveness. In the present paper, the synthesis of certain 1,5-dialkyl-2,4-dithiomalonamides and their Mo-S complexes, namely, bis(1,5-dialkyl-2,4-dithiomalonamido)-dioxo-molybdenum (VI), and the tribological evaluation of their 0.5% w/v admixtures in paraffin oil by a four-ball test are reported, and the results compared with a dioxo-bis(N,N-diethyldithiocarbamato)-molybdenum(VI) reference additive. The additive, bis(1,5-diethylhexyl-2,4-dithiomalonamido)-dioxo-molybdenum(VI), has been found to reduce significantly both coefficient of friction and wear-scar values, and to give higher load wear index values and flash temperatures, and has been found to be equally effective with alloy steel balls of three different compositions. However, all the Mo-S complexes afforded smaller wear-scar diameters in a one-hour wear test. The wear spots on the used steel ball specimens were subjected to SEM and AES surface analysis for understanding the additive-metal interaction tribochemistry.