Add time:08/23/2019         Source:sciencedirect.com

The thermal stability of solid strontium azide is considerably reduced by pre-irradiation with γ-rays (Co60). The isothermal decomposition of the unirradiated salt is followed by measuring the pressure of gas evolved in a constant-volume system. It is characterised by a pronounced induction period which is followed by an acceleratory period which then passes into one of decay. The sigmoid pressure-time plots in the temperature range 120–150°C are described by the power law, p13 = k2t+c2 in the acceleratory period, and by the contracting-sphere formula (1-α)13=k3t+c3 in the decay period. Pre-irradiation of the salt by γ-rays drastically reduces the induction period and increases the velocity constants. The power law is obeyed up to doses of 105 rad. and the exponential law log p = k1t + c1 for γ-ray doses greater than 2·5 × 105 rad. Between these doses neither equation fits. The activation energies for the processes during the induction period, acceleratory and decay periods are approximately the same (average 23·3±1·5 kcal mole−1) and are almost unchanged by preirradiation. It is not possible to detonate the salt in the γ-ray source but by suitable treatment of the irradiated salt with water vapour the former becomes highly explosive. A study of the effects of water vapour at various stages of the decomposition establishes the significant role which strontium metal plays in the decomposition of both the irradiated and unirradiated salt. A theoretical explanation of the decomposition mechanism of the unirradiated and irradiated salts, involving the formation of strontium metal and the interaction of positive holes and excited azide ions, is presented. It is suggested that pre-irradiation by γ-rays produces a high concentration of vacancies in the salt, and that these are responsible for the drastic changes in the subsequent thermal decomposition.

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