Kinetics of the thermal decomposition of CuC2O4-ZnC2O4 mixture in air

The thermal decomposition processes taking place in the solid state oxalate mixture of CuC2O4-ZnC2O4-2H(2)O (1:1 mole ratios) have been studied in air using DTA-TG, XRD and SEM techniques. DTA-TG curves showed that, the decomposition proceeds through three well-defined steps with DTA peaks closely correspond to the weight loss obtained. The decomposition behaviour of the oxalate mixture is in good agreement with that of the individual oxalates. XRD showed an increase in the intensity of the diffraction lines on rising the calcinations temperature from 400 to 800degreesC attributed to the grain growth of the decomposition products. SEM experiments confirmed this result as the very small crystallites obtained at 400 degreesC are re-textured and coalesced into aggregates of large crystals with sharp edges and angles when calcined at 800degreesC. Kinetic analysis of the oxalate decomposition steps was performed under non-isothermal conditions using different integral methods of analysis. The dynamic TG curves obeyed the Avrami-Erofeev equation characteristic of solid-state nucleation-growth mechanism and consistent with the textural changes accompanying the decomposition revealed by SEM experiments. The activation parameters were calculated and discussed in view of the electronegativity of the metal ions. (C) 2003 Elsevier Science B.V. All rights reserved.