Kinetics of decomposition of 1,1-diamino-2,2-dinitroethylene (FOX-7). 6. The induction period at the early stages of the reaction in the solid state

The kinetics of thermal decomposition of FOX-7 compound at 155 °C under semi-open conditions in vessels with a volume of V = 0.8–0.9 cm3 in an air atmosphere and the degree of filling of the vessel with substances m/V = 0.03–0.72 g/cm3 has been studied by gravimetric method. It was found that at the largest m/V, an induction period is observed at the early stages of the reaction, during which the rate of mass loss of the sample is ten times less than the rate of decomposition of FOX-7 in the solid phase. With a decrease in m/V, the induction period is shortened and at m/ V = 0.04 g/cm3 disappears altogether. The appearance of the induction period is due to the fact that nitronic acid, which is the only product of the first stage of decomposition of FOX-7, is well adsorbed on the surface of FOX-7 crystals. At the same time, it almost completely loses its reactivity. As a result, until the end of the adsorption process, the decomposition of FOX-7 proceeds without the formation of gaseous products, and the reaction rate is not fixed by the gravimetric method suitable for studying the kinetics of the reaction at the early stages of decomposition FOX-7.