Modeling of Laser Vaporization and Plume Chemistry in a Boron Nitride Nanotube Production Rig

Abstract

Flow in a pressurized, vapor condensation (PVC) boron nitride nanotube (BNNT) production rig is modeled. A laser provides a thermal energy source to the tip of a boron fiber bundle in a high pressure nitrogen chamber causing a plume of boronrich gas to rise. The buoyancy driven flow is modeled as a mixture of thermally perfect gases (B, B 2 , N, N 2 , BN) in either thermochemical equilibrium or chemical nonequilibrium assuming steady-state melt and vaporization from a 1 mm radius spot at the axis of an axisymmetric chamber. The simulation is intended to define the macroscopic thermochemical environment from which boron-rich species, including nanotubes, condense out of the plume. Simulations indicate a high temperature environment (T > 4400K) for elevated pressures within 1 mm of the surface sufficient to dissociate molecular nitrogen and form BN at the base of the plume. Modifications to Program LAURA, a finite-volume based solver for hypersonic flows including coupled radiation and ablation, are described to enable this simulation. Simulations indicate that high pressure synthesis conditions enable formation of BN vapor in the plume that may serve to enhance formation of exceptionally long nanotubes in the PVC process.