Thermal decomposition of iron(VI) oxides, K2FeO4 and BaFeO4, in an inert atmosphere

The thermal decomposition of solid samples of iron(VI) oxides, K2FeO4·0.088 H2O (1) and BaFeO4·0.25H2O (2) in inert atmosphere has been examined using simultaneous thermogravimetry and differential thermal analysis (TG/DTA), in combination with in situ analysis of the evolved gases by online coupled mass spectrometer (EGA–MS). The final decomposition products were characterized by 57Fe Mössbauer spectroscopy. Water molecules were released first, followed by a distinct decomposition step with endothermic DTA peak of 1 and 2 at 273 and 248 °C, respectively, corresponding to the evolution of molecular oxygen as confirmed by EGA–MS. The released amounts of O2 were determined as 0.42 and 0.52 mol pro formula of 1 and 2, respectively. The decomposition product of K2FeO4 at 250 °C was determined as Fe(III) species in the form of KFeO2. Formation of an amorphous mixture of superoxide, peroxide, and oxide of potassium may be other products of the thermal conversion of iron(VI) oxide 1 to account for less than expected released oxygen. The thermogravimetric and Mössbauer data suggest that barium iron perovskite with the intermediate valence state of iron (between III and IV) was the product of thermal decomposition of iron(VI) oxide 2.

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