Kinetics and mechanism of thermal decomposition of ammonium nitrate powder under the action of carbon black

It is shown that in the presence of carbon black, the decomposition rate of solid ammonium nitrate increases strongly (by more than seven orders of magnitude). The kinetic regularities of the decomposition in the temperature range 70–150$^\circ$C are established. At relatively low temperatures, the process proceeds by a two-stage mechanism with corresponding acceleration at each stage. At elevated temperatures, the first stage is absent. The decomposition rate is proportional to the amount of carbon black in the mixture. The activation energy for the decomposition ($\approx$30 kcal/mole) does not vary during transformation. Water decelerates the process. For a water content of $\approx$(4–5)%, an intermediate maximum of the deceleration is observed. The main gaseous decomposition product is N$_2$. The concurrent oxidation of carbon black is terminated by evolution of CO$_2$. The mechanism of the chemical transformations is discussed using the results obtained and information available on the kinetics of individual reactions.