Improvement of tribological properties of conventional lubricant oil by addition of nanoparticles and carbon nanostructures

Nanofluids for lubrication are raising great interest for their potential impact on energy and automotive industries [1]. Increasing the load carrying capability and reducing friction entail energy saving while decreasing wear implies rise of machine reliability. Nanolubricants are characterized by a new range of potential utilization of nanoparticles in the field of tribology [2], assuming that dispersed nanoparticles can act as ball-bearings to minimize friction and wear phenomena in mechanical couplings. Many authors reported that adding nanoparticles to a lubricant oil leads to improvements of tribological properties since they could significantly reduce the coefficient of friction and increase the load-carrying capability of coupled surfaces [3]. Among available nanoparticles, carbon nanostructures showed promising results as additives in lubricant oils. Recently, a new class of nano-structured carbon, the Single Wall Carbon Nano-Horns (SWCNH), was used to prepare nanofluids [4] and appeared interesting, because of their relative easiness in fabrication, lower cost and less impact on environmental issues in respect to other metallic nanoparticles or to carbon nanotubes. The present work illustrates the preparation of stable nano-oils based on SWCNHs, a comparison with nanolubricants containing different kind of nanoparticles and shows their tribological behaviour at different temperatures. The tribological properties of these nanofluids were evaluated by Stribeck tests, in order to compare the effects of additives on friction coefficient in main lubrication regimes. Then wear tests were carried out to confirm data obtained from Stribeck characterization. The new nanolubricants containing SWCNHs revealed to be promising candidates to develop a new class of composite lubricants, suitable and effective in different operating environments.