Carbon nanoparticles as new lubricant additives

A present challenge in engine lubrication is to find new environment-friendly additives. We focused our interest on nested carbon nanoparticles (nanotubes and onions) as lubricant additives since they present two main advantages. Their nanometric size enables them to enter easily the contact and their nested structure confers them a great chemical inertia. Carbon nanotubes can be assimilated to rolling-up of graphite planes. Single-wall nanotubes containing nickel and yttrium show very interesting tribological properties. Results obtained let suppose a role of the catalyst in the lubrication mechanism. Multi-wall nanotubes without catalyst particles present also interesting properties. We developed a dedicated tribometer which uses a transparent flat. Thus, structural modifications of carbon nanotubes were followed during friction test by in-situ Raman analyses. Carbon onions can be described as several hollow spheres with different diameters (fullerenes) fit together. One way to synthesise them is by annealing of diamond nanoparticles. Depending on the temperature of annealing, they are: perfectly graphitized and spherical, or faceted, or contained a residual diamond core. We observed a deleterious effect of the presence of a diamond core. A comparison of the properties of spherical onions and faceted ones is currently under consideration. The studied nanoparticles appeared to be good substitutes to the chemical molecules used at present. One of their main advantages is their efficiency at ambient temperature. This point is very useful during the cold start of engines.