Preparation of anhydrous FeF2 by solvothermal method and its application in composite energetic materials

In recent years, metal fluorides are increasingly being investigated as promising oxidants in aluminum-based (Al-based) composite energetic materials to improve the ignition and combustion performance, mainly because of their reaction with the otherwise inert alumina shell. However, the hygroscopicity and relatively high cost of many metal fluorides limit their wide applications. In this work, an effective and mild solvothermal method employing inexpensive raw materials is used to synthesize the otherwise costly anhydrous FeF2. A novel Al/FeF2 energetic composite is then prepared using ultrasound-assisted physical mixing and compared with other more common formulations (Al/PTFE, Al/FeF3, Al/Fe2O3, and Al/FeO) in terms of energetic characteristics. Electric ignition and constant-volume combustion tests show that Al/FeF2 has a shorter ignition delay time than that of Al/PTFE, as well as a much faster reaction rate and a much greater pressure output capacity than each of Al/FeF3, Al/Fe2O3, and Al/FeO. High-speed photography demonstrates the large flame area and short flame duration of Al/FeF2. Moreover, thermal analysis reveals the superior exothermic enthalpy of Al/FeF2.Overall, anhydrous FeF2 prepared in this study shows excellent application potential in Al-based composite energetic materials.