Thermal analysis of La-Ba oxalate and role of gamma-irradiation there on

Lanthanum-barium oxalate was prepared and characterised by chemical and the rmal analysis, X-ray diffraction and plasma emission spectroscopy. X-ray an alysis showed the presence of a uniphase system. The kinetics of decomposit ion of oxalates of La and Ba as well as coprecipitated La-Ba oxalate have b een investigated in air using dynamic thermogravimetry. The decomposition o f mixed oxalate occurred with two over-lapping exotherms, corresponding to the decomposition of lanthanum oxalate followed by that of barium. The kinetics of decomposition of the irradiated salt was studied over the s ame temperature range as that of the unirradiated one in air and activation energies obtained from the slopes of Coat-Redfern's plot. Kinetic analyses following various theoretical models of solid state reactions showed that the best fit was obtained for a third order reaction and geometrical models . It was evident that though there was increase in the activation energy as well as frequency factor with increasing radiation dose, reverse phenomeno n takes place in the case of reaction rate. The effect of gamma -irradiatio n on the process and the mechanism involved therein has been discussed. (C) 2001 Elsevier Science B.V. All rights reserved.