Modelling the increase in anisotropic reaction rates in metal nanoparticle oxidation usingcarbon nanotubes as thermal conduits

Abstract

Nanostructured energetic materials are attracting attention for their faster reactionrates compared to materials with micron-scale particles. We numerically solvethe coupled energy balances for a carbon nanotube with an annular coating ofreactive metal, such that coupling to thermal transport in the nanotube acceleratesreaction in the annulus. For the case of Zr metal, the nanotube increases thevelocity of the reaction front in the direction of the nanotube length from 530 to5100 mm s−1. This offers a proof-of-concept for one-dimensional anisotropic energetic materials,which could find new applications in inorganic synthesis and novel propellants.Nanotube conductivity as well as the relative sizes of the Zr annulus and thenanotube limit enhancement of the reaction velocity to a maximum of a factor of∼10. Interestingly, the interfacial heat conductance is not the most significant factor affectingthe coupling, due to the large temperature differences (more than 1000 K) between thenanotube and the annulus at the reaction front and directional heat conduction in thenanotube. Although the enhancement is insufficient to change a Zr/nanotube compositefrom a deflagrating to a detonating material, using faster-reacting materials may enablenanotubes to effect this transition.