Effects of X- and Γ-Ray Radiation on the Thermal Decomposition of Solid Orthorhombic Ammonium Perchlorate. II. Kinetics and Discussion

The experimental data obtained by thermally decomposing unirradiated and irradiated orthorhombic ammonium perchlorate in the temperature range 193°–238°C has been carefully analyzed. Most of this data consists of pressure vs time curves of the total evolved gas or that not trapped at −95°C or lower, obtained with powders and millimeter‐size crystals. All of these curves can be described by the Avrami–Erofeyev equation. The increase in the acceleratory period rate, which is induced by, and is proportional to, x‐ or γ‐ray irradiation prior to decomposition, can be attributed to the introduction of additional decomposition sites, an increase in the rate that each nucleus grows, or a combination of these. Independent microscopic examination of partially decomposed crystals also indicates that irradiation has increased the concentration of decomposition nuclei. In addition, the $p\mathrm{vs}t$ curve analysis shows that irradiation has increased the rate that potential decomposition sites are converted to active sites. The same activation energy, 28.4 ± 2.5 kcal mole⁻¹, was obtained for both the acceleratory and decay periods from irradiated and unirradiated crystals. Irradiation also increases the duration of the acceleratory period, shortens the decay period, and reduces the induction period. In fact, the induction period $I$ for irradiated NH₄ClO₄ can be described by the relation ${\mathrm{I\hspace{0.17em}=\hspace{0.17em}C}}_1{\mathrm{\hspace{0.17em}-\hspace{0.17em}C}}_2$ log (dose). Taken together, these observations suggest that the same processes occur in both unirradiated and irradiated ammonium perchlorate, but the rate constants are increased by prior irradiation.