Tribological Properties of Nanofluid Prepared by Composite of Multi-walled Carbon Nanotube and Oleic Acid

Multi-walled carbon nanotubes (MWCNTs) were filled with oleic acid (OA) to prepare the composite additives for use in the nanofluid. The influence of additive concentration, acid treatment time of MWCNTs, the test conditions on the tribological properties of the nanofluid were investigated, and the lubrication mechanism of the composite was also studied. The results showed that the OA was successfully filled into the MWCNTs with a filling rate of about 20%. In the process of friction, the friction coefficient of nanofluid prepared by the composite tended to decrease gradually, and its final friction reduction effect was even better than that of the oleic acid emulsion under different loads. The nanofluid could achieve better tribological properties as the concentration of the composite was about 0.1%. The tribological properties of the nanofluid would be improved with the increase of the acidification time. It was supposed that the composite could release the OA to form a lubrication layer during the friction process, which enabling the MWCNTs to play a role of "micro-bearing" on the formed lubrication film, thus the better tribological properties of the composite were achieved.