Thermal decomposition of ferrous oxalate dihydrate studied by direct current electrical conductivity measurements

Abstract

The feasibility of the use of direct current electrical conductivity,σ, measurements in the study of solid-state reactions involved in the synthesis ofγ-Fe2O3 from ferrous oxalate dihydrate has been reported. The study has been carried out in static air, dynamic air, dry nitrogen and dynamic air + water vapour environments. The conductivity data determined in static air are quite complex; nevertheless, the formation of Fe3O4 andα-Fe2O3 with the probable intermediate formation ofγ-Fe2O3 has been indicated. In dry nitrogen the step corresponding to dehydration is well resolved in the temperature region 145–220° C; the formation of FeO and Fe3O4 is also well characterized. In dry dynamic air the reaction further proceeds to the formation ofα-Fe2O3. In dynamic air containing water vapour there are definite indications of the formation ofγ-Fe2O3 prior to the formation ofα-Fe2O3. Definite experimental conditions have been determined for the formation ofγ-Fe2O3 in dynamic air containing water vapour. The conductivity measurements have been supplemented with infra-red spectroscopy and X-ray diffraction pattern measurements. The electrical conductivity measurements were found to give additional information on the solid-state reaction to that obtained from conventional thermal analytical techniques (such as differential thermal, thermogravimetric and differential thermogravimetric analyses).γFe2O3, obtained from the decomposition of FeC2O4 · 2H2O in dynamic air + water was found to have a coercive force of 3.142 A m−1, a saturation magnetization value of 7.1 T kg−1 and a ratio of remanence to saturation magnetization of 0.64.