Safe preparation, energetic performance and reaction mechanism of corrosion-resistant Al/PVDF nanocomposite films

In this study, to improve the safety in the preparation process of energetic materials, vacuum freeze-drying technology is applied to develop nanoenergetic thin films in which Al nanoparticles (Al NPs) are used as the fuel and polyvinylidene fluoride (PVDF) powders act as the oxidant. The whole process effectively avoids high temperature and thus ensures operational safety. The morphology and composition characterizations confirm that Al NPs are dispersed uniformly in the hydrophobic energetic binder, endowing the films with increased water-proof, anti-aging and anti-corrosion characteristics. The results of thermal analysis show that a pre-ignition reaction (PIR) destroys the Al2O3 shell and a sharp exothermic peak from the reaction between the exposed Al core and PVDF is found before the melting point of Al. Combustion tests reveal that the film with the highest content of Al NPs possesses the fastest flame propagation speed. The preliminary reaction mechanism obtained by probing the reaction products and intermediates suggests that a two-step reaction exists when the film is slowly heated in N2, while a competitive reaction between oxidation and fluorination of Al NPs is observed when the film burns in air. These results indicate the promising potential of vacuum freeze-drying technology in manufacturing nanoenergetic materials.