Burning characteristics of ammonium nitrate (AN)/ammonium perchlorate (AP) propellants depend on the particle size of AP and fraction of an oxidizer. The burning characteristics of AN/AP propellants were improved using fine AP (FAP) and adding a catalyst. FAP with a mean diameter of 1.7 μm was used, and MnO₂ and Fe₂O₃ were used as catalysts. The burning rate increased as the mass ratio of FAP to the oxidizer content increased. The effect of the catalyst on the increase in the burning rate increased in the order MnO₂<Fe₂O₃ ≤ bicatalyst. The AN/FAP propellants exhibited unstable burning behaviors. The range of the unstable burning behavior was reduced by the addition of the catalyst, and the effect was enhanced in the following order: MnO₂<bicatalyst<Fe₂O₃. The burning characteristics were compared to those of the AN/AP propellant containing another FAP with a mean diameter of 4.1 μm; the difference in the particle size of FAP was only a 2.4 μm. The burning rates of the AN/FAP propellants hardly depend on the particle diameter of FAP. However, the range of the unstable burning behaviors increased with the use of finer AP because of the differences in the burning rates of the FAP-filled region supplemented with Fe₂O₃.

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This study provides insights into the root cause of the 2014 accident that lead to the three-year shutdown of the Waste Isolation Pilot Plant (WIPP) in Carlsbad New Mexico USA. WIPP serves as the only repository in the United States for the disposal of transuranic waste. The accident involved the combination of nitric acid and organic kitty litter within a transuranic waste drum. Our findings suggest that the root cause of the accident was thermal runaway caused by autocatalytic nitric acid chemistry resulting from blockage of the waste drum vent. Accidental confinement resulted in 1) rapid acceleration of the nitric acid chemistry, 2) thermal ignition, and 3) radiation dispersal. In this study, we show the autocatalytic nature of the nitric acid-soaked kitty litter and apply our thermal model to predict the thermal runaway. The financial cost of this incident was more than a half a billion US dollars ($500,000,000). Insights gained from this research are relevant to nuclear waste repositories worldwide and provide specific information on explosion safety.

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5-Amino-1H-tetrazole (ATZ) is a promising fuel material for pyrotechnic compositions with high nitrogen content and energy. However, it forms hydrates when exposed to moisture, which negatively affects the burning performance. In this study, cocrystallization was applied to prevent the hydration of ATZ. As cocrystal-formers, 5-methyl-1H-tetrazole (MTZ), 3,5-diamino-1,2,4-triazole (DATA), and 4-amino-1,2,4-triazole (4ATA) were cocrystallized with ATZ. Cocrystal formation was confirmed using powder X-ray diffraction. The crystal structures of the ATZ/MTZ and ATZ/DATA cocrystals were determined using single-crystal X-ray diffraction. Thermal analyses showed that the onset temperatures of the three cocrystals were higher than that of ATZ. Humidity tests revealed that the ATZ/MTZ and ATZ/DATA cocrystals did not form hydrates and showed low hygroscopicity.

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