Unraveling changes in the decomposition behavior of Composite Solid Propellants using Mechanoactivated and Recrystallized fine Ammonium Perchlorate

The particle size distribution and the shape of the Ammonium perchlorate (AP) particles are often modulated to control the combustion and ballistic characteristics of a composite solid propellant (CSP). The study compares the decomposition kinetics of CSPs containing fine AP particles prepared through mechanical means and the solvent recrystallization technique, resulting in two types of fine AP particles of different morphology. Differential scanning calorimetry (DSC) and Thermogravimetry (TG) study was conducted with formulations of composite solid propellants containing monomodal coarse AP, bimodal recrystallized AP, and bimodal mechanoactivated AP. Some interesting observations were noticed, such as a more prominent low-temperature decomposition reaction was observed in the case of CSP containing mechanoactivated AP, and the mass decomposition rate was higher for the formulations containing mechanoactivated AP in comparison. The enhanced thermal behaviour observed in the CSPs containing fine AP was attributed to the increased defect density induced during their preparation process. FTIR and XRD results exhibited changes in the characteristic peaks of the fine AP, corroborating that the change in morphology was the reason. Friedman's isoconversational method was adapted to obtain the kinetic parameters. The average activation energy obtained for the CSP containing only coarse AP was 185 ± 38 kJ/mol, and CSP containing recrystallized AP and ball-milled AP was found to be 153 ± 30 kJ/mol and 161 ± 28 kJ/mol, respectively. Comparatively high activation energy was observed for the initiation of low-temperature decomposition for #MAPP, indicating a dependence of kinetics on the morphology of crystals. These findings provide insight into how AP microstructure influences the early stages of CSP decomposition and highlight the importance of physically modifying oxidizer particles to tailor the thermal response of composite propellants.