Use of refractory-metal diffusion inhibitors to slow Ostwald ripening of catalytic metal particles: A route to ultra-long Carbon Nanotubes (CNT)

Growth of Carbon Nanotubes (CNTs) to lengths useful in many materials applications is currently limited by a number of factors, the most important of these being Ostwald ripening and subsequent deactivation of the metal catalyst particles from which the CNTs nucleate and grow. Here is proposed and demonstrated a novel method for overcoming this limitation. It is shown that inclusion of refractory, high-melting-point metals in the metallic catalyst used for CNT growth can substantially enhance the lifetimes of the particles of catalytic metals, enabling growth of CNTs to much greater lengths than possible using the pure catalytic metals. This lifetime enhancement occurs because the refractory metal inhibits the surface diffusion of the catalyst metals, slowing the Ostwald ripening of the catalytic particles and allowing them to grow CNTs for greater times, resulting in longer CNTs. The system investigated employs Rhenium as the diffusion inhibitor and Molybdenum as the CNT growth catalyst.