Tribological Performance of Novel Boron Dithiocarbamate Lubricant Additives

Abstract: Different lubricant additives such as dialkyldithiophosphates (DTPs) of different metals have been extensively used as multifunctional additives to control wear and friction in mechanical systems. These additives can produce protective films on steel rubbing surfaces and, therefore, control friction and reduce wear. On the other hand, these additives contain large amounts of metals, phosphorus and sulfur, which can adversely affect the environment by degrading catalytic converters in automobiles. Boron based additives are recognized as friction modifiers, corrosion inhibitors, antioxidants, and effective antiwear additives. These additives are emerging as attractive alternatives for the additives already used in lubricants. The aim of the project is to investigate the tribological performance of some novel alkylborate dithiocarbamates.This project was performed in the following steps:1- Chemical synthesis of three different borated dialkyl dithiocarbamate additives with alkyl chains of different lengths.2- Tribological tests of novel compounds using a four ball tribometer.3- Surface analysis using an optical profiler (Veeco WYkO NT 1100) and Scanning Electron Microscopy coupled with X-ray Energy Dispersive Spectroscopy (SEM/EDS).The effect of the alkyl chain length in both DTC and the borate molecular moities of three B-DTC compounds on the tribological performance was studied. An increase in the alkyl chain length at the borate side improves antiwear properties in steel-steel contact. It was found that cyclo-N,N-alkylenedithiocarbamato-S-alkyl-di-n-alkyl-borate previously synthesized and studied [1], has the best antiwear performance compared with the other compounds synthesized in this work. All the novel additives were able to stabilize friction coefficient over a wide concentration range of the additives in the base oil. B-DTC additives with long alkyl chains show greater reduction in friction compared to the one with short alkyl chains. A possible explanation of this phenomenon is that longer chains have improved deposition process of additives on surfaces leading to a thicker and more stable tribofilm. EDS spectra show the presence of sulfur atoms on the rubbing surfaces lubricated by the base oil with B-DTC additives.