(546c) Combustion Studies of Microscale Aluminum Functionalized with Perfluorotetradecanoic Acid

Micron aluminum (Al) particles are highly reactive when combined with a solid oxidizer, but not exceptionally reactive in an ambient air environment unless they are well dispersed. While enthalpy of oxidation for Al is high; many variables influence the viability of harnessing stored chemical energy within a single Al particle whose reaction is diffusion controlled. One way to enhance Al oxidation is to functionalize the particle surface with a condensed phase oxidizing agent. Fluorocarbons such as perfluorocarboxylic acids have been used to enhance Al combustion for nanoscale Al particles with some success. This study extends previous work toward synthesizing microscale Al particles with surface functionalized perfluorotetradecanoic acid (PFTD) (C14HF27O2) and then characterizing reactivity. Samples were prepared with varying PFTD concentrations ranging from 0 to 25 wt. %. Equilibrium analysis including differential scanning calorimetry, DSC, and thermal gravimetric analysis, TG, reveals that 25 wt. % PFTD concentration is the minimum threshold to induce measurable exothermic pre-ignition reaction (PIR) behavior. In each sample, fluorinated species mostly evaporate upon PFTD decomposition but solid phase CF2O2H likely bonds with the Al particle surface. At higher heating rates (e.g., 100 °C/s) two stages of combustion were observed: the first associated with Al reaction with fluorine species from PFTD and a later stage associated with Al reacting with oxygen from the environment. Overall, functionalizing microscale Al particles with a fluorinated polymer facilitates its reaction in an air environment, even for small concentrations of PFTD coating (i.e., 5 wt. %).