Tribological Study of the SOCNTs@MoS2 Composite as a Lubricant Additive: Synergistic Effect

Different layers of MoS2 were grown on the surface of carbon nanotubes (CNTs) successfully with a facile and effective chemical vapor deposition method. The pristine CNTs (PCNTs) were pretreated with 5 mol L-1 HNO3, 10 mol L-1 HNO3, and mixed acid (sulfuric acid/nitric acid = 3:1) to obtain weakly oxidized CNTs (WOCNTs), moderately oxidized CNTs (MOCNTs), and strongly oxidized CNTs (SOCNTs). According to the results of SEM, EDS, TEM, Raman, XRD, and XPS, more layers of MoS2 were grown on the surface of SOCNTs uniformly due to the abundant defects on its surface. The friction-reducing and antiwear performance of dibutyl phthalate (DBP) containing SOCNTs, MoS2, SOCNTs/MoS2 mixture, and SOCNTs@MoS2 composite were investigated under 392 N and 1200 rpm at room temperature by four-ball tribotester. The DBP containing 0.02 wt % SOCNTs@MoS2 composite exhibited the best tribological performance, and the friction coefficient and wear scar diameter (WSD) were reduced by 57.93% and 19.08%, respectively. The synergistic effect between SOCNTs and MoS2 was further explored by comparing the lubricant mechanism of the different additives. A possible mechanism was proposed, and the SOCNTs@MoS2 composite can be deposited on the rubbing surface due to the microstructure and translated into tribo-film which can protect the friction pair.