Comparative study on energy release of aluminum particles promoted by ferric fluoride and polytetrafluoroethylene

Fluoride has shown great potential for improving the burning rate and combustion efficiency of aluminum (Al) particles. Herein, the effects of metal fluoride (ferric fluoride, FeF 3 ) and organic fluoride (polytetrafluoroethylene, PTFE) on the combustion of Al particles were comparatively investigated using various characterization methods. The results showed that both FeF 3 and PTFE could improve the thermal reaction properties of Al particles, including thermal oxidation rate, heat release, mass gain, and thermal oxidation efficiency, and the improvement of FeF 3 was better. Thermal reaction curves and tube furnace tests together demonstrated that fluoride and Al particles undergo pre-ignition reaction at low heating rates. Combustion diagnostic results and condensed combustion products (CCPs) analysis of the samples revealed that both fluorides reduced the ignition delay time and increased the combustion intensity, burning rate, combustion efficiency and maximum combustion temperature. When ammonium perchlorate (AP) was not added, PTFE improved the combustion performance of Al particles better due to its high gas production characteristics. PTFE is not as good as FeF 3 after adding AP. Furthermore, varying the FeF 3 content in the binary mixture (Al/FeF 3 ) between 5 % and 20 % did not significantly affect the combustion characteristics of the samples. Interestingly, the high-speed camera captured the jetting phenomenon of Al droplets during combustion, which is attributed to the erosive effect of F on the alumina cap. The jet phenomenon is the direct evidence of the reaction between Al particles and F during combustion, which provides new insights into the complex reaction mechanism between the two. Statistics on a large number of particles indicated that FeF 3 can increase the frequency of the particle jet phenomenon. Finally, the phenomenological mechanism of fluoride promoting Al particle combustion is proposed. Considering the catalytic effect of metals and their corresponding oxides on AP, the addition of metal fluorides to AP-based energetic materials may be a more preferable option.