Studies on the formation of γ-Fe 2O 3 by thermal decomposition of ferrous malonate dihydrate

Abstract

The thermal decomposition process of ferrous malonate dihydrate (FeC 3H 2O 4·2H 2O) was studied in atmospheres of static air, dynamic dry nitrogen, dynamic dry air, and dynamic air containing water vapour by means of thermal analysis (simultaneous TGA, DTG and DTA), direct current electrical conductivity measurements, infrared spectroscopy, elemental analysis, gas-liquid chromatography and X-ray powder diffraction analysis. The conductivity data in static air and dynamic air are quite complex: nevertheless, the formation of Fe 3O 4 and α-Fe 2O 3 with the probable intermediate formation of γ-Fe 2O 3 has been indicated. In dry nitrogen the step corresponding to dehydration is well resolved in the temperature region 190–260 °C and the formation of FeO and Fe 3O 4 is also well characterised. A definite indication from the conductivity measurements for the formation of γ-Fe 2O 3 prior to α-Fe 2O 3 was found in an atmosphere of dynamic air containing water vapour. Experimental conditions were determined for the formation of γ-Fe 2O 3 in dynamic air containing water vapour. This compound (γ-Fe 2O 3) was characterised by X-ray diffraction, magnetic hysteresis, scanning electron microscopy and Mössbauer spectroscopy.