Combustion characteristics of cross-linked fluorinated polymer supported aluminum/oxidizer microsphere in HTPB propellant

Combustion behaviors of propellant depend heavily on the architecture of the pocket bounded by coarse AP particles. In order to achieve a better control of the meso-scale architecture of the pocket, overcoming random mixing of the fine particles inside propellant, two kinds of cross-linked fluorinated polymer supported Aluminum/Oxidizer microspheres containing fine Al and oxidizer particles are fabricated by emulsion solvent evaporation and in-situ polymerization method (ESV-ISP), which are used to replace the fine Al and oxidizer particles of the Al/AP/HMX/HTPB propellant. The morphologies of the Al/Oxidizer microspheres and the corresponding propellants are studied, it shows that the fine Al and oxidizer particles are well dispersed and arranged in the microspheres. Besides, the average sizes of the microspheres are ranging from 113.9 ± 4.3 μm to 183.0 ± 5.9 μm, and equivalent to that of the Al-rich clusters located inside the pocket. The energy property and combustion performance of the propellants indicated that the combustion heat of the propellants containing Al/Oxidizer microsphere is increased by about 200 J/g, while the fraction of residual active aluminum is decreased by 77.8%, additionally, the D50 and D(4,3) of the combustion residue are both reduced significantly. Large Al aggregate nearby the burning surface is observed clearly in the blank propellant, while it could not be observed in the propellants containing Al/Oxidizer microsphere. Furthermore, compared to the pressure exponent (n), 0.34, of the B-Propellant, the n of the Al/AP-Propellant and the Al/HMX-Propellant significantly drop to 0.24 and 0.25, respectively, and the burning rate (r) could be adjusted and controlled by the Al/Oxidizer microsphere consisting of different fine oxidizer particles. It demonstrates that using the structurally ordered Al/Oxidizer microsphere could successfully achieve a better control of the meso-scale architecture of the pocket in typical Al/AP/HMX/HTPB propellant.