Degradation mechanism and thermal stability of urea nitrate below the melting point

Aging and degradation of urea nitrate below the melting point, at 100 °C, was studied by using thermal analysis and spectroscopic methods including IR, Raman, 1H and 13C NMR techniques. It was found that urea nitrate was completely degraded after 72 h at 100 °C into a mixture of solids (69%) and released gaseous species (31%). The degradation mechanism below the melting point was clearly identified. The remaining solid mixture was composed of ammonium nitrate, urea and biuret while unreacted residual nitric and isocyanic acids as well as traces of ammonia were released as gaseous species at 100 °C. The thermal stability of urea nitrate, under extreme storage conditions (50 °C), was also examined by isothermal nano-calorimetry.