Comparing Boron and Aluminum Nanoparticle Combustion in Teflon Using Ultrafast Emission Spectroscopy

Boron and aluminum nanoparticle combustion in Teflon AF was studied using time-resolved emission spectroscopy after laser flash-heating. When a threshold energy density was reached by the nanoparticles, a picosecond emission burst was observed. This was attributed to a dense metal plasma with an emission profile that fit well to a graybody model. Thermodynamics showed that this plasma only represented a small fraction of the nanoparticle mass. Depassivation of the boron particles occurred when the oxide shell boiled off and the metal core was melted. Depassivation of aluminum occurred when the oxide shell melted and the metal core was almost vaporized. The lifetimes for exothermic chemistries could be determined from their effects on the plasma lifetime. The rate of energy release from vapor Al + Teflon reactions has a ∼100 ps lifetime, while energy release from liquid B + Teflon was observed to occur with a ∼200 ps lifetime.