MoS2 single sheet lubrication by molybdenum dithiocarbamate

The mechanisms by which Modtc reduces friction in the centirange under boundary lubrication have been investigated using analytical tribometry. First, the SRV friction test was coupled with energy-filtering TEM on wear fragments and spatially-resolved XPS inside the wear scars. Second, we performed UHV friction tests on Modtc tribofilms previously created on a large area. The overall data demonstrate that the mechanisms of friction-reduction by Modtc is attributed to the effect of sliding between single layers of MoS₂ only, and not to intra-sliding in MoS₂ 3-D crystal. Highly-dispersed MoS₂ sheets are present in a carbon matrix in the tribofilm material. The growth of the 2-D MoS₂ single sheets is thought to be formed by degradation of the Modtc molecule by electron transfer mechanisms activated by the friction process. The lubrication of the uncoated, stationary counterface is attributed to successive transfer of individual sheets towards the friction surface. Practically, in these conditions only a few per cent of dispersed MoS₂ is sufficient to lubricate at the same level as pure MoS₂.