Investigation of tribological performance of the ultra-dispersive TBC-CNTs as additives for aqueous lubrication

Carbon nanotubes (CNTs), as water-based additives, are potential candidates for reducing friction and wear whereas the weak dispersion stability impedes their application in aqueous lubrication. Therefore, CNTs were functionally modified by 4-tert-butylcatechol (TBC) nucleophilic for synthesizing the ultra-dispersive TBC-CNTs. The particle sizes and dispersibility of TBC-CNTs in water were investigated. It was found that particle sizes of the most of CNTs were reduced after modification and 0.035 wt% TBC-CNTs remained uniformly dispersed in water for 2 months. The lubrication behavior of TBC-CNTs as water-based additives for ceramic/steel tribo-pairs was investigated by using a ball-on-disc apparatus. Notably, the optimum concentration of TBC-CNTs was determined 0.2 wt% that contributed to 30.6 % of friction reduction and 28.3 % of wear resistance, respectively, at 0.6 m/s and 8 N. The tiny structure of TBC-CNTs contributed to their entrance into the contact interface and playing lubricating roles. Furtherly, the increase of water film thickness within contacts and formation of lubrication film on rubbing surfaces caused by TBC-CNTs addition resulted in the friction and wear reduction.