Study on thermal decomposition and combustion of insensitive explosive 3,3′-diamino-4,4′-azofurazan (DAAzF)

Thermal decomposition of an explosive with low sensitivity, 3,3′-diamino-4,4′-azofurazan (DAAzF), has been investigated under isothermal conditions at 200-320 °C using the thin-walled glass manometer of the compensation type. Changing the ratio of the sample weight to the vessel volume allowed us to measure the kinetic parameters of DAAzF decomposition predominantly in the solid state (k = 5.0 × 1011 exp(−21,320/T), s−1) and the gas phase (k = 3.3 × 1012 exp(−21,020/T), s−1). The kinetics of decomposition in solution (k = 3.5 × 106 exp(−14,070/T), s−1) have also been measured. Based on the burning rate and thermocouple measurement data, rate constants of DAAzF decomposition in the molten layer at 600-800 °C have been derived from a condensed-phase combustion model (k = 4.6 × 108 exp(−16,680/T), s−1), which is in a good agreement with kinetic data obtained in the solution at 235-260 °C. The mechanism of DAAzF thermolysis and combustion includes initial rupture of C-N bond between the azo-group and furazan ring with subsequent nitrogen evolution and decomposition of the heterocyclic ring. In the combustion wave, the heat release from decomposition of the stable furazan ring follows the heat release from azo-group decomposition, resulting in a distinct two-stage flame structure.