The Role of Nickel in Ni-Containing Nanotubes and Onions as Lubricant Additives

We studied tribological properties of Ni-containing single wall carbon nanotubes and carbon nano-onions. Nickel catalyst particles are often necessary to synthesize these carbon nanoparticles. Nanoparticles were used as additives dispersed in a lubricating poly-alpha-olefin base oil. We show superior tribological properties for carbon nanoparticles containing residual nickel cores. Thus, removal of nickel catalyst from carbon particles is not necessary for excellent tribological performances. Mechanisms of friction and wear reduction are discussed in the light of analytical data. Data suggest the tribo-formation of a Ni-doped carbon-like material.