The study employed a two-step synthesis method to prepare Al@PFHP@fluoropolymer energetic composites with a core–shell structure. PFHP and HF acid are used for surface etching and modification of raw Al powder. PFHP bonds to the surface of Al powder, with redundant C-F providing hydrogen bonding sites, driving dissolved PVDF and P(VDF-HFP) polymer chains in the liquid phase to migrate, nucleate, and grow on the surface of the Al powder, and consequently the formation of a continuous shell layer through hydrogen-bonding self-assembly. The Al powder coated with fluoropolymer exhibited strong hydrophobic and corrosion-resistant properties, ensuring long-term storage and environmental adaptability. Compared to mechanically mixed Al@PFHP/fluoropolymer, the Al@PFHP@fluoropolymer composites show significant improvements in thermal reactivity, ignition, and combustion performance. The close integration of fluoropolymer and Al shortens the mass and heat transfer distances during the reaction process. Additionally, the low-boiling-point AlF 3 does not hinder diffusion process in the combustion zone, which is conducive to the alleviation of the reaction sintering phenomenon and the rapid and concentrated release of energy. Therefore, through the dual strategy of using fluorine-containing oxidizers and structure optimization, efficient reaction of Al@PFHP@fluoropolymer is achieved, also promoting efficient combustion of Al powder. The synthesis process of this energetic composite is simple yet yields exceptionally high performance, enabling large-scale production and application potential in military ammunition and rocket propulsion systems.
Wen Ao,Zhan Wen,Lu Liu,Yang Wang,Yu Zhang,Peijin Liu,Zhao Qin,Larry K.B. Li
In this experimental study, we explore how the combustion and agglomeration characteristics of solid propellants can be modified by replacing aluminum with ternary Al/CuO/PVDF(Polyvinylidene Fluoride) metastable intermolecular composites (MICs). Using thermogravimetric−differential scanning calorimetry, a laser ignition setup, and a high-pressure propellant combustion system , we examine the thermal reactivity, ignition behavior, burning rate, agglomeration, and condensed combustion products of various MICs-inclusion propellants. We find that the use of ternary Al/CuO/PVDF MICs can decrease the onset temperature and increase the oxidation efficiency of Al, as compared with common binary MICs. The ratio of CuO/PVDF is found to have a strong effect on the combustion intensity of the metallic powders , but only a weak effect on their ignition delay . Higher proportion of PVDF is found to have a negative effect on the combustion rate. Specifically, the combustion intensity is found to decrease first and then increase as the PVDF content increases. The exothermic Al/CuO reaction is found to alter the heat transfer of the condensed layer on the propellant surface, while PVDF plays a critical role in the thermal feedback of the gaseous reaction. When combined, these two factors lead to a ± 30% variation in the propellant burning rate. Furthermore, ternary MICs are found to reduce agglomeration during propellant combustion. The two optimal formulations are 2.5 wt.% CuO/2.5 wt.% PVDF and 3.5 wt.% CuO/1.5 wt.% PVDF. The use of these formulations is found to decrease the mean particle size of the condensed combustion products to only 11 μm, as compared with 76 μm for the original Al-inclusion propellant. High-speed microscope images reveal the existence of crack phenomena in the pockets surrounding the AP particles on the burning surface due to the Al/CuO reaction, as well as the floccule breakup mechanism of Al aggregates in the presence of PVDF, both of which reduce agglomeration. Overall, this study shows that replacing Al with ternary Al/CuO/PVDF MICs has significant effects on the agglomeration, combustion and ignition features of aluminized propellants. The findings of this study can be used to aid the development of highly adjustable functional catalysts for solid propellants.
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