Synergistic lubricating behaviors of graphene and MoS2 dispersed in esterified bio-oil for steel/steel contact

Graphene and MoS2 were dispersed in esterified bio-oil (EBO) and evaluated as lubricants for steel/steel contact. The tribological behaviors of steel/steel pairs were investigated under lubrication of graphene/ MoS2 blends.with different mass ratios, loads and rotating speeds. The micro-morphologies of the worn surfaces were observed by optical and Scanning Electron Microscopy (SEM). The components of the additives and chemical valences of the elements on the rubbed surfaces were analyzed using Raman and X-ray Photoelectron Spectroscopy (XPS). A synergistic lubricating effect for both graphene and MoS2 with contents of 0.5 wt% as additives dispersed in EBO was observed that reduced the friction coefficient and wear of the steel specimens under boundary lubrication regime conditions. This was ascribed to the formation of a thicker adsorbed tribo film containing graphene, MoS2 and organics from the EBO. Graphene was shown to improve the retention of MoS2 on the frictional surfaces and prevent oxidation during rubbing. MoS2, on the other hand, prevented the graphene from being ground into small and defective platelets. (C) 2015 Elsevier B.V. All rights reserved.