Synergistic effect of 1,3-diketone fluid and carbon-based nanoparticles as hybrid eco-friendly additives in polyalphaolefin oil

Considering the growing demand for eco-friendly lubricating additives, this work investigated 1,3-diketone fluid (EPND) as a novel surface-active additive, together with nanodiamonds (D), cellulose nanocrystals (C) and graphene (G) as the nanoadditives in polyalphaolefin (PAO) base oil. In the ball-on-disk friction tests, EPND and nanoparticles synergistically co-worked through the running-in process of two stages. During the initial running-in stage, the tribochemical reaction between EPND and steel surface decreased the solid asperities and reduced the contact pressure. Afterward, nanoparticles gradually entered the frictional interface during the secondary running-in stage and further enhanced the lubrication through the polishing effect by D, the mending effect by C or interlaminar shearing by G, respectively. Among the tested hybrid additives, EPND/G induced the lowest friction because the tribochemical reaction of EPND could proceed more thoroughly than in the cases of EPND/D and EPND/C. Moreover, as the tribochemical wear induced by EPND was self-limited with the continuous decrease of asperity contacts, EPND/G also led to the smallest wear in the long-term operation. The result of this study provides a comprehensive understanding of the interactions between the surface-active and nanoparticle additives at different operation stages, which is helpful for the design of novel hybrid eco-friendly additives.