Kinetics of Decomposition of 1,1-Diamino-2,2-dinitroethylene (FOX-7). 6. The Induction Period in the Early Stages of a Reaction in the Solid State

The kinetics of the thermal decomposition of the FOX-7 compound at 155°C under semiopen 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 the gravimetric method. It is found that at the largest m/V, an induction period is observed in the early stages of the reaction, during which the rate of mass loss of the sample is lower by a factor of ten 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 it 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 of FOX-7.