The concealed role of reactive metal passive oxide layer: novel activated aluminum particles, combustion, kinetics, and ballistic performance

Abstract Passive oxide layer on the surface of aluminum particles could impede combustion efficiency and burning rate. Passive aluminum (P-Al) and active aluminum without passive oxide layer (A-Al) of 5 µm were adopted for this study. Whereas P-Al demonstrated surface oxygen content of 7.23 mass%, A-Al demonstrated surface oxygen content of 0.23 mass%. Aluminum particles were integrated into ammonium perchlorate (AP) matrix. Whereas P-Al demonstrated an increase in AP decomposition enthalpy by 60%, A-Al boosted AP decomposition enthalpy by 123%. The surface passive oxide layer could render full exploitation of aluminum energy content. A-Al particles demonstrated decrease in AP activation energy by 43% using Kissinger's model. Solid propellant formulations based on 16 mass% aluminum particles were developed by mechanical mixing and vacuum casting; ballistic performance was evaluated using small-scale ballistic evaluation rocket motor. A-Al particles offered an increase in burning rate, specific impulse, and total thrust impulse by 80%, 5%, and 6.7%, respectively. These outcomes mean enhanced performance with extended range. Burning rate–pressure relation was determined using photo-acoustic wave. A-Al particles demonstrated pressure exponent of 0.28 compared with 0.19 for P-Al particles. It can be concluded that A-Al particles secured enhanced performance, with stable combustion process.