The effects of fluoropolymers with optimized contents on reactivity and combustion behavior of Al/M_xO_y nanocomposites

Recently fluoropolymers are of great interest as an oxidative binder and modifier in Al-based metastable intermixed composites (MICs) due to the high heat of reaction between Al-F and gas production characteristics. In this paper, Polytetrafluoroethylene (PTFE) and Polyvinylidene Fluoride (PVDF) have been incorporated into three typical Al-based MICs independently using CuO, Fe₂O₃, and Bi₂O₃ as oxidizers, where the contents of Al to metal oxide are maintained optimum stoichiometric ratios. Heats of reaction have been measured by a bomb calorimeter for mechanically mixed MICs samples, from which the optimum fluoropolymer content has been determined using the maximum calorific values as the criteria. After that, the optimized formulations have been prepared by a spray drying method. The thermal behavior, combustion characteristics and pressurization features of the studied Al-based MICs were evaluated and compared with those without fluoropolymers. The experimental results showed that with a minor inclusion of fluoropolymers, the combustion heat was improved by 3.8% to 8.6% depending on the type of oxidizers, and the onset temperature of the exothermic reaction was observed to be decreased by 250 °C for Al/CuO, 200 °C for Al/Fe₂O₃ and 16 °C for Al/Bi₂O₃ with a higher reaction heat release, showing a higher reactivity. Besides, the maximum pressure and pressurization rate were both increased for the fluorine-containing MICs, whereas the burn rates under confinement were found to drop significantly by 72% to 91%. The AlF₃, Cu-Al alloy, and Fe-Al alloy are found in the condensed combustion products (CCPs), and it tends to have smaller and more uniform particles. It probably results from the large difference in the energy and mass transfer process on the combustion surface when the gaseous phase products are generated.