Carbon Nanotube−MoS<sub>2</sub> Composites as Solid Lubricants

Solid lubricants (SLs) characterized by low coefficients of friction (μ) and wear rates (<i>w</i>) drastically improve the life span of instruments that undergo extreme frictional wear. However, the performance of SLs such as sputtered or nanoparticulate molybdenum disulfide (MoS<sub>2</sub>), tungsten disulfide (WS<sub>2</sub>), or graphite deteriorates heavily under extreme operational conditions such as elevated temperatures and high humidity. Here, we present our preliminary results, which demonstrate that composites of carbon nanotubes (CNTs) and MoS<sub>2</sub> produced by electrodeposition of MoS<sub>2</sub> on vertically aligned CNT films have low μ (∼0.03) and <i>w</i> (∼10<sup>−13</sup> mm<sup>3</sup>/N·mm) even at 300 °C, which are about 2 orders of magnitude better than those of nanoparticulate MoS<sub>2</sub>-based coatings. The high load-bearing capacity of CNTs provides a strong enduring support to MoS<sub>2</sub> nanoclusters and is responsible for their ultralow <i>w</i>. The incorporation of these composites in liquid lubricants reduces the friction coefficient of the liquid lubricants by ∼15%. The technique described here to produce SL coatings with extremely appealing frictional properties will provide valuable solutions for a variety of tribological applications where the coatings encounter high temperature, reduced pressure, and/or low- and high-humidity conditions.