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

Abstract

The non-isothermal decomposition of ZnC 2O 4·2H 2O–FeC 2O 4·2H 2O (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–Redfern 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 Mössbauer spectrum of the mixture calcined at 250 °C 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 Fe 2O 3, 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 °C, the obvious increase in the percentage of the six-line indicates a progress of the crystallization process of iron(III) oxide. At 800 °C, an asymmetric central doublet is observed due to the presence of 57 Fe resonant atoms in different structural environments. For sample, at 1000 °C, a symmetric doublet characteristic of ZnFe 2O 4 was obtained.