Synergistic catalysis-activation mechanism of NiF2 modifier for boosting the combustion performance and energy release of aluminized HTPB propellants

The dense oxide layer on the surface of aluminum (Al) particles is recognized as a major limitation to their combustion efficiency in solid propellants. Metal fluorides have emerged as promising combustion modifiers capable of enhancing Al reactivity through a catalytic-activation synergy. However, the systematic influence of NiF 2 content on this process remains poorly understood. In this work, the effect of NiF 2 content on the combustion performance of Al/AP composite fuels and hydroxyl-terminated polybutadiene (HTPB)-based propellants was systematically investigated. A series of composites and propellants with varying NiF 2 loadings were prepared and evaluated using an oxygen bomb calorimeter, thermal analysis, high-speed photography, and product characterization. The optimal NiF 2 content was determined to be 6 wt%, at which the composite fuel achieved a maximum reaction heat of 9357.62 J/g, corresponding to a 12.3% increase relative to the unmodified sample. Thermal analysis revealed that an appropriate amount of NiF 2 leads to the merging of the low- and high-temperature decomposition peaks of AP and the concentration of the exothermic event, indicative of a synergistic catalytic effect; excessive addition, in contrast, was found to suppress heat release. In propellant combustion, the SP-2 sample containing 2 wt% NiF 2 exhibited the most pronounced pressure-dependent burning-rate increase, with a maximum increase of 26.9% over the pressure range of 1.5–2.5 MPa. Product analysis further demonstrated that the condensed combustion products (CCPs) of SP-2 contain a higher proportion of Al 2 O 3 , exhibit a significantly reduced and multimodal particle size distribution with abundant submicron particles, and feature detectable AlN, confirming that NiF 2 effectively inhibits molten Al agglomeration and promotes combustion completeness. Therefore, the optimal working window of NiF 2 in the Al/AP system is identified, and its synergistic oxide-layer erosion and catalytic decomposition mechanism is elucidated, providing a key basis for the development of high-performance Al-based propellants.