On “how to start a fire”, or transverse forced-convection, hyperbaric laser chemical vapor deposition of fibers and textiles

Abstract

This work explores the transverse forced flow of precursor gases during hyperbaric pressure laser chemical vapor deposition (HP-LCVD). Axial and mass growth rates of carbon fibers are measured experimentally, and a numerical model is developed that provides fiber growth rates in both the mass-transport-limited (MTL) and kinetically limited (KL) regimes. It is found that the fiber’s transport-limited rate increases as the square root of the flow velocity, while simultaneously, the temperature drops with the inverse square root of the flow velocity. Growth is enhanced by forced flow so long as the reaction zone remains within the MTL regime; upon reaching a critical temperature and flow rate, however, fibers enter the KL regime, and the growth rate declines with rising flow rate. Molecular properties of the precursors employed and gas concentrations ultimately determine the range of the MTL and the locations of the critical temperature and flow rate. The growth rates of fibers can indeed be enhanced by transverse forced convection—to at least three times the zero-flow steady-state rate, provided an MTL regime exists. Complex three-dimensional structures may be grown from these fibers in a freeform manner, and the more rapidly such microstructures can be fabricated, the more practical HP-LCVD becomes for industrial use, including the fabrication of novel textiles.