International Journal of Energetic Materials and Chemical Propulsion, 16(1):81–101 (2017) FUEL-RICH ALUMINUM–METAL FLUORIDE THERMITES Siva Kumar Valluri, 1 Ian Monk, 1 Mirko Schoenitz, 1 & Edward Dreizin 1,2,* 1 New Jersey Institute of Technology, Newark, New Jersey 07102, USA 2 Tomsk State University, Tomsk, 634050, Russia *Address all correspondence to: Edward Dreizin, New Jersey Institute of Technology, Newark, New Jersey 07102, USA; Tel.: 973-596-5751, E-mail: dreizin@njit.edu Nanocomposite thermite powders using aluminum as fuel with cobalt and bismuth fluorides as ox- idizers were prepared by arrested reactive milling. Each material contained 50 wt% of aluminum and 50 wt% of a fluoride, resulting in fuel-rich compositions. The reactions in the prepared powders were characterized by thermo-analytical measurements; powders were ignited as coatings on an elec- trically heated filament and by electrostatic discharge. It was observed that the exothermic reactions begin in aluminum–metal fluoride thermites at lower temperatures than in any previously prepared reactive nanocomposites based on aluminum. Redox reactions in Al·CoF 2 and Al·BiF 3 nanocom- posite started around 200 and 250°C, respectively. The results suggest that the initial reactions are rate-limited by the decomposition of fluorides. In the oxygenated environments, metals generated by reducing the starting fluorides oxidize readily. The newly formed oxides are rapidly reduced by excess aluminum, accelerating aluminum oxidation at low temperatures. The low-temperature ther- mally activated reactions lead to low ignition temperatures for the powders heated on the filament. Despite the low ignition temperatures, both prepared materials were relatively insensitive to ignition by an electric spark, making them attractive components of advanced energetic formulations. KEY WORDS: reactive materials, energetics, nanocomposites, metal combustion, me- chanical milling 1. INTRODUCTION The use of species that are more electronegative than oxygen, i.e., fluorine, as oxidizers may lead to different ignition mechanisms and generate gaseous combustion products, expected to broaden the range of applications for metal-based reactive materials. The benefits of fluorinated oxidizers were recognized in early research by Professor Kuo and his colleagues (Chen et al., 1991; Risha et al., 2003; Ulas et al., 2001; Yeh et al., 1997). In their pioneering work (Risha et al., 2003), the benefits of fluorinated binders were explored for nano-sized metal particles in solid propellants. In another classic study from Professor Kuo’s group (Ulas et al., 2001), combustion of boron in fluorine-containing gas was shown to occur in one stage, unlike the two-stage combustion observed in oxygenated oxidizing gases. A fluorinated oxidizing environment was also shown to accelerate removal of the natural boron oxide and thus shorten boron ignition delays. For condensed reactive materials (RMs), combining metal fuels with fluorine-containing polymers such as polytetrafluoroethylene (PTFE) was reported to be of interest (Beckert and 2150–766X/17/$35.00 © 2017 by Begell House, Inc. www.begellhouse.com 81