Phase Transitions and Deoxidizing Effect in the Thermal Decomposition of Hydrous Ferrous Oxalate

Powder of hydrous ferrous oxalate is annealed in non-oxidizing atmosphere of Ar, and the solid decomposition products obtained at various temperatures are studied by Mössbauer effect (ME) and X-ray diffraction (XRD). The results indicate that in Ar the initial product which is wüstite changes into magnetite and α-Fe with increasing annealing temperature, at the same time a small amount of Fe4C appears. Annealing the oxalate at higher temperature, the magnetite in the solid products begins to transform into non-stoichiometric FeO (Fe1–xO or FeOx), and so an obvious deoxidizing effect of magnetite is indicated. At about 600°C, the transition from magnetite to Fe1–xO is already completed. Further results show that the deoxidizing effect does not result from the action of Ar and suggest that the deoxidizing effect of oxide is a general phenomenon.