Thermal Stability of Ammonium Nitrate: A Critical Narrative Review

Abstract

Ammonium nitrate is a simple inorganic salt with a complex safety profile. It is essential to fertiliser production and has important uses as an oxidising component in explosives and propellant systems, yet its decomposition behaviour has contributed to some of the most damaging industrial accidents of the past century. This review examines the thermal stability of ammonium nitrate across crystal polymorphism, decomposition chemistry, heat and mass transfer, additives, contamination, engineered stabilisation, energetic formulation and process-safety practice. The central argument is that thermal stability is not a fixed property that can be represented by one onset temperature or one activation-energy value. It is an observed behaviour that depends on composition, moisture, acidity, impurity profile, physical form, heating rate, atmosphere, gas exchange, confinement, scale and storage history. Recent thermal-analysis studies have clarified how chlorides, acids, pyrite, rust, transition-metal species and some organic contaminants can reduce the stability margin, while selected phosphates, carbonates, magnesium compounds, sulphates, urea and mineral additives may inhibit decomposition under defined conditions. Newer materials-design approaches, including phase-stabilised ammonium nitrate, metal-organic frameworks, zeolitic imidazolate frameworks, ferrites, coordination complexes and energetic co-crystals, show that crystal chemistry and catalytic architecture can be used to reshape phase transitions and decomposition pathways. These advances, however, must be interpreted carefully: a formulation that performs well in a propellant is not necessarily safer for bulk storage. The review concludes that safe use of ammonium nitrate depends on compatible formulation, strict contamination control, ventilation, inventory management, fire prevention and cautious translation of laboratory data to real storage and emergency scenarios.