Thermal decomposition mechanism of ammonium nitrate and copper (II) oxide mixtures

The purpose of this study is to develop an improved understanding of the thermal decomposition mechanism of ammonium nitrate (AN) and copper(II) oxide (CuO) mixtures. Analysis using differential scanning calorimetry (DSC) and evolved gas analysis based on thermogravimetry-differential thermal analysis-mass spectrometry (TG-DTA-MS) were carried out and decomposition behavior was observed using a hot stage with a CCD camera. DSC results showed that AN/CuO mixture had a higher exothermic onset temperature than pure AN and that CuO does not promote the decomposition of AN. From TG-DTA-MS results, the endothermic reaction of AN/CuO mixture has its onset after the AN melting point of 442 K and results in the evolution of H2O. At approximately 500 K or above, AN/CuO mixture generates significant quantities of N-2 and 1120 and an exothermic reaction begins to offset the endothermic processes. Above 510 K, AN/CuO mixture began to evolve NO2. Observations with a CCD camera have found that AN/CuO mixture transforms from a mixture of colorless liquid AN and black CuO powder into a blue-green liquid which is presumably a solution of copper (II) nitrate. Around 493 K, this liquid changes to a deep blue color due to the presence of a copper (II) amine complex. Finally, above 510 K, the deep blue liquid briefly turns blue-green, then changes into a black powder with the evolution of gas. Based on these results, a decomposition mechanism for AN/CuO mixture is proposed, in which the mixture reacts to form copper (II) nitrate and a copper (II) amine complex following melting and these species then undergo exothermic decomposition to generate N2, 1120, NO2 and CuO.