Pyrolysis of ammonium perfluorooctanoate (APFO) and its interaction with nano-aluminum

Abstract

Application of ammonium perfluorooctanoate (APFO) in nano-aluminum (nAl) based energetic nanocomposites is proposed in this work. By fixating fluorine in AlF3, combustion as oxidizer introduces both an efficient defluorination strategy and a high performance power source for APFO. The laser ignition temperature build-up of nAl/APFO is about 2300 °C/s, and the combustion temperature approaches 1240 °C with an energy density of 12.6 kJ/g. The combustion residue of nAl/APFO contains AlF3 as primary condensed product with graphite, tar and Al2O3. And the gaseous fluorinated product is CF4 with low abundance. With the higher heat release obtained from oxygen bomb comparing to the stoichiometric value, results exhibit a high defluorination efficiency. The pyrolysis mechanism of APFO and its interaction with nAl were investigated by DSC-TG-PyMS-FTIR, T-jump-PyGC-MS coupling analysis and in-situ XRD. It shows that APFO undergoes multi-stage pyrolysis including proton transfer, skeletal chain breakage succeeded by a distinct polymerization before C-F bond cleavage. Al2O3 on the surface of nAl adsorbs the evolved fluorides after the initial pyrolysis of APFO in nAl/APFO, which also decreases the apparent activation energies of the last two stages of pyrolysis. The passivation layer on the surface of Al corroded by HF and perfluorocarboxylic acid before the violent fluorination of active Al core.