Effects of phosphate additives on the thermal decomposition properties of ammonium nitrate: Integrated kinetic, thermal analysis and safety assessment methods

• Phosphate additives increase decomposition activation energy of AN. • Phosphates delay thermal decomposition onset and reduce total heat release of AN. • Phosphates inhibit the decomposition of AN through multiple complex mechanisms. Ammonium nitrate (AN) has been widely used in industry, but it is subject to thermal decomposition and explosion risks during storage and transportation. How to enhance the safety of AN while ensuring its performance as a chemical raw material, particularly in the field of agricultural fertilizers? This study investigates the effects of diammonium (DAP) and monoammonium (MAP) phosphates on AN thermal decomposition properties through kinetic, calorimetric, and gas analytical methods. Results indicate that DAP and MAP elevate the average activation energy for the thermal decomposition of AN by approximately 34 % and 39 %, respectively. Furthermore, both additives delay the initial reaction temperature and reduce the total heat release without altering the kinetic reaction mechanisms. The measured decomposition energies of 1286 J·g −1 for AN with DAP and 1319 J·g −1 with MAP indicate that enthalpy suppression occurs via chemical interactions, rather than simple thermal dilution. Under adiabatic conditions, additive-modified systems exhibit prolonged induction periods and suppressed pressure rise rates, with DAP outperforming MAP due to its higher ammonium content promoting ammonia-mediated inhibition. Mechanistic studies reveal synergistic stabilization pathways: complex salt formation disrupting AN crystalline redox activity, endothermic decomposition of phosphate additives absorbing reaction heat, and ammonia-driven reverse reaction equilibrium modulation. Gas analysis confirms DAP/MAP significantly reduce hazardous nitrogen oxide emissions while accelerating initial decomposition via weakly acidic proton release. Thermal hazard assessments demonstrate 5 wt% additive incorporation elevates self-accelerating decomposition temperatures, substantially enhancing storage stability. These findings offer design principles for phosphate-based stabilizers to improve ammonium nitrate safety in industrial and agricultural applications.