Synergistic effects of phase stabilization and CuO nano-catalyst on the thermokinetic decomposition and ballistic performance of ammonium nitrate-based green propellants

The development of high-performance, low-smoke solid propellants is a critical imperative for advanced propulsion, seeking to eliminate the corrosive hydrogen chloride emissions associated with conventional ammonium perchlorate (AP) oxidizers. While ammonium nitrate (AN) is a sustainable green alternative, its deployment is fundamentally restricted by sluggish combustion kinetics and deleterious volumetric expansions during room-temperature phase transitions. This study reports a dual-functional engineering strategy to overcome these bottlenecks by hybridizing AN with 20 μm potassium nitrate (KNO 3 ) and 20 nm copper oxide (CuO) nanoparticles. X-ray diffraction (XRD) confirmed the synthesis of a stable co-crystalline KNO 3 /AN matrix, effectively suppressing the cationic rotational mobility responsible for the IV to III phase transition at 52.99 °C. Differential Scanning Calorimetry (DSC) and thermogravimetric analysis (TGA) demonstrated that the CuO nanoparticles exert a synergistic catalytic effect, facilitating a high exothermic heat release of 415 J/g and a substantial reduction in activation energy (E a ) by up to 74.31 kJ/mol as corroborated by Kissinger, OFW, and Friedman isoconversional models. Ballistic evaluation of HTPB-based propellant strands across a 1–10 MPa regime revealed that the KNO 3 /CuO/AN nanocomposite achieved a transformative 179% increase in the burning rate coefficient (a = 4.05). Most notably, the nano-catalytic intervention successfully mitigated the pressure sensitivity of the AN system, reducing the pressure exponent (n) from a hazardous 0.65 to a stable 0.48. This shift suggests a mechanistic transition where the rate-controlling step is dominated by catalyzed condensed-phase reactions rather than gas-phase pressure. These results demonstrate that the engineered quaternary nanocomposite provides the requisite thermal stability, structural integrity, and ballistic predictability to serve as a viable, high-performance replacement for AP in modern tactical propulsion applications.