Carbon Nanotube−MoS₂ Composites as Solid Lubricants

Solid lubricants (SLs) characterized by low coefficients of friction (μ) and wear rates (w) drastically improve the life span of instruments that undergo extreme frictional wear. However, the performance of SLs such as sputtered or nanoparticulate molybdenum disulfide (MoS₂), tungsten disulfide (WS₂), 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 MoS₂ produced by electrodeposition of MoS₂ on vertically aligned CNT films have low μ (∼0.03) and w (∼10⁻¹³ mm³/N·mm) even at 300 °C, which are about 2 orders of magnitude better than those of nanoparticulate MoS₂-based coatings. The high load-bearing capacity of CNTs provides a strong enduring support to MoS₂ nanoclusters and is responsible for their ultralow w. 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.