Nickel/Multi-walled Carbon Nanotube Nanocomposite Synthesized in Supercritical Fluid as Efficient Lubricant Additive for Mineral Oil

The nanocomposite of multi-walled carbon nanotube (MWCNT) decorated by nickel nanoparticles (Ni-NPs) was synthesized through a facile chemical reduction in supercritical carbon dioxide (SCCO2) fluid. The spherical nickel nanoparticles were highly dispersed on external wall surfaces of MWCNT with a narrow particle size distribution and had a face-centered cubic crystal structure and an average diameter about 5nm. Tribological performances of the as-prepared nanocomposite as oil additive were investigated by using a ball-on-disk tribometer. It was found that when the nanocomposite was dispersed into pure mineral oil with an optimum mass concentration of about 0.20wt%, the friction coefficient and wear rate were reduced by 44.2% and 56.4%, respectively. The mineral oil with the nanocomposite showed better tribological performances than the mineral oil with MWCNT or Ni-NPs alone, which confirmed the synergistic friction-reducing and anti-wear effect of the nanocomposite. Morphologies and chemical compositions of wear surfaces were examined by scanning electron microscopy (SEM), Taylor profilometer and X-ray photoelectron spectroscopy (XPS). Good friction and wear performances of the nanocomposite can be explained by physical deposition films formed on the wear surface and the synergistic effect between the anchored Ni-NPs and MWCNT of the nanocomposite.