Yongfu Wang

Ultralow friction regime from the in situ production of a richer fullerene-like nanostructured carbon in sliding contact

Hitherto, among carbon-based thin films, fullerene-like hydrogenated carbon (FL-C:H) films exhibit unique ultralow friction and wear in open or humid air, but the mechanisms responsible for the friction regime are still not clear. Here, we provide definitive experimental evidences obtained from the wear tracks and debris of FL-C:H films, and show that FL-C:H films’ surface undergoes gradual transformation into a richer and more stable fullerene-like nanostructure, due to the increasing content of pentagonal and heptagonal carbon rings in addition to the six-membered graphene rings, as a result of thermal and strain effects from the repeated friction. The sliding-induced in situ promotion of the FL structures at frictional contact leads to ultralow friction and wear in open air. The results establish an excellent low friction and wear regime for the structural film, and develop the lubrication mechanisms of carbon-based films.

Mild thermal reduction of graphene oxide as a lubrication additive for friction and wear reduction

Recently, studies on graphene-based lubrication additives have been widely researched, but few refer to their preparation by thermal reduction which shows potential in not only significantly lowering the mass-production cost, but also the simple, nonchemical process. In this study, mild thermal reduction of graphene oxide (MRGO) has been achieved by high temperature (700 °C) treatment and the product used as a lubrication additive. It shows a relatively ordered lamellar structure and a certain level of oxygen by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analysis, and exhibits excellent tribological properties as a lubrication additive. The friction coefficient can be reduced by as much as 30% and the rubbing surfaces display few scratches at a lower additive concentration (0.5 wt%) compared with that of base oil (Poly Alpha Olefins Type 6: PAO 6) without MRGO additive under the same friction conditions. Based on the advantages of green, low-cost and simple synthesis operation, the MRGO offers significant potential application as a lubrication additive.

Transforming organic molecular films into carbon films as solid lubricants

To meet the lubrication demands of future MEMS/NEMS, thickness-controllable carbon films have been successfully prepared directly on silicon substrates by carbonizing electrophoresis-deposited trichloroacetic acid (TCA) molecular films. Compared with easily worn-out TCA molecular films, the transformed carbon films exhibit ultra-low friction coefficients and wear rates, along with strong adhesion to silicon substrates. These results prove that the idea of transforming organic molecular films into carbon thin films is a unique and promising approach to fabricate thickness-controllable and wear-resistant carbon-based solid lubricants for MEMS/NEMS.