EFFECT OF GAMMA-IRRADIATION ON THE THERMAL-DECOMPOSITION OF PURE AND DOPED (BA2+) CESIUM BROMATE

Effect of gamma-irradiation on the isothermal decomposition of pure and doped (Ba2+, 0.50 mol%) caesium bromate has been studied in the temperature range 633-673 K. It is indicated that though the pure and pure irradiated crystals are immune to decomposition, doped and doped irradiated crystals undergo decomposition rapidly. There is initial rapid gas evolution representing 1-2% reaction, which is completely eliminated in doped irradiated crystals. The other stages exhibited by the crystals are, (1) acceleratory and (2) decay stages. Presence of two decay stages (one short and one long) is indicated in the doped substance, and the short decay diminishes with increase in temperature and virtually remains absent at 673 K. The acceleratory as well as decay periods of doped and doped irradiated crystals are analysed according to Prout-Tompkins. Avrami-Erofeev and Contracting square models. The rate constants in all the stages increase with increase in temperature. The energy of activation for the acceleratory periods of both the substances are almost same (+/- 10 kJ/mol) irrespective of the kinetic equation employed. Similar is the case with decay stages. But the energy of activation of the decay stages are higher than those of the acceleratory stages. Microscopic observation reveals that the reaction begins essentially on surfaces by the rapid formation of an interface and is followed by the penetration of the interface into the crystallite. The melting of a eutectic formed between the product CsBr and the parent material causes a marked increase in the rate.