Evaluation of kinetic parameters for the thermal decomposition of gamma-irradiated anhydrous lanthanum nitrate

Abstract

The thermal decomposition of gamma-irradiated anhydrous lanthanum nitrate was studied by dynamic thermogravimetry. The decomposition proceeds via three consecutive stages characterized by different activation energies. The reaction order, activation energy, frequency factor and entropy of activation were calculated using the Coats-Redfern, Freeman-Carroll and Horowitz-Metzger methods and were compared with those of the unirradiated salt. Irradiation enhances the decomposition and the effect increases with the irradiation dose. The activation energies of all the three stages decrease on irradiation. The mechanism of the decomposition of unirradiated and irradiated anhydrous lanthanum nitrate follows the Mampel model equation, − ln(1 − α) for g(α), and the rate-controlling process is random nucleation with the formation of a nucleus on every particle.

Kinetic analysis for non-isothermal decomposition of un-irradiated and gamma-irradiated anhydrous cadmium nitrate

“…It is evident from the Table 3 that the activation energy decreases on irradiation. The similar observations were reported [43,44] for the thermal decomposition of -irradiated potassium bromate and lanthanum nitrate.…”

“…But the relative contribution of the crystal defects and chemical damage fragment has, however not been ascertained. Generally, the effect of irradiation is to decrease the induction period, if any and decrease the energy of activation of the decomposition [35,44]. In the present case, the decomposition of cadmium nitrate sets in before melting and proceeds to completion in the melt phase.…”

“…In systems containing molecular ions, irradiation produces chemical damage, displacements and extended lattice defects [44][45][46]. The influence of irradiation on solid decompositions has been ascribed to these effects which One produce as well as facilitate formation and growth of nucleation centres [47].…”