(612b) Tunable Aluminum and Liquid Fluorocarbon Pyrotechnics

The ability to tune energetic material combustion rate through modification of the condensed phase requires enhanced energy feedback to the condensed phase by either thermal energy generation from condensed phase reactions or from an external source. Enhancement of surface emissivity and enhancement of condensed phase thermal conductivity are two particularly attractive techniques. In this effort, we investigate the enhancement of energy deposition from a pyrotechnic flame through carbon nanotube doping of the liquid phase of an aluminum/liquid fluorocarbon (LFC) pyrotechnic. We report an experimentally observed burning rate of Al/LFC compositions of 1.1 cm/s at 6.89 MPa (1000 psi) with a power law burning rate pressure dependence of 0.66. below 13.8 MPa (2000 psi). Doping of compositions with up to 3 wt.% of a variety of radiometric and thermally enhancing susceptors, including single/multiwall nanotubes and graphene nanoplatelets can result in a sixteen-fold increase in burning rate (16.6 cm/s) at 6.89 MPa with no change to pressure exponent. To explore the mechanism responsible for enhancement, we further quantify the improvements to condensed phase spectral absorptivity and thermal conductivity, estimate flame temperature using two-color high speed video pyrometry and discuss techniques with which thermal conductivity and burning rate enhancement of such formulations can be switched â??on commandâ?? to tune energetic output in situ. Resulting equilibrium calculations and demonstrated burning rate enhancements suggest that in addition to its use as a pyrotechnic, such compositions may be attractive for use as on-command tunable combustion rate microscale propellants.