Aluminum combustion enhancement in AP free nitramine- based solid propellants by PVDF coating

Abstract

Optimizing the ignition and combustion characteristics of Al by fluorine-containing oxidizers have attracted significant interest. However, few of them dedicated to alleviate the incomplete combustion of Al in propellant. Herein, we demonstrated that the combustion of micron-Al in AP free nitramine-based propellants can be greatly enhanced by thin coating layer of PVDF, resulting decreased volume fraction of agglomerates exceeding the initial particle size and active Al content in condensed combustion products (CCPs). After extensive analysis from thermal reactivity, single particle ignition and observation of particles evolution from burning surface to flame zone, we propose that the combustion efficiency is promoted by the fragmentation of chain structured aluminum skeleton by gas recoil near burning surface, oxidation acceleration by diffusion of Al and oxidative gas through the cracks among the particle shell in the dark zone and the subsequent ejection of molten Al triggered by gasification of low boiling point AlF₃ in the flame zone. The findings in this work suggest that core–shell Al@PVDF has a great potential to be further used in the development of future highly energetic solid propellants.