Non-isothermal decomposition of zinc oxalate-iron(II) oxalate mixture

The non-isothermal decomposition of ZnC2O4.2H(2)O-FeC2O4.2H(2)O (1:2 mole ratio) mixture has been studied in air. The dehydration was found to proceed through a two-stage reaction followed by two-stage reaction attributed to the decomposition of each metal oxalate in the mixture to its metal oxide. Kinetic analysis of the dynamic thermogravimetric curves according to the integral composite method on comparison with the integral methods of Coats-Recifern and Ozawa showed that the oxalate decomposition reactions are best described by the two-phase boundary models. The Arhenius parameters were calculated and discussed. The Mossbauer spectrum of the mixture calcined at 250 degreesC shows two types of components corresponding to the oxidation of iron(II) to iron(III). The first is characterized by a doublet owing to the quadrupole interaction due to the formation of fine particles of paramagnetic Fe2O3, having colloidal dimensions and the other is characterized by a sextet associated with the magnetically oriented iron(III) oxide. On increasing the calcination temperature to 400 degreesC, the obvious increase in the percentage of the six-line indicates a progress of the crystallization process of iron(III) oxide. At 800 degreesC, an asymmetric central doublet is observed due to the presence of 57 Fe resonant atoms in different structural environments. For sample, at 1000 degreesC, a symmetric doublet characteristic of ZnFe2O4 was obtained. (C) 2003 Elsevier Science B.V. All rights reserved.