Abstract
The effect of various matrials added to γ-Fe2O3 on transformation into α-Fe2O3 was investigated by means of D. T. A., high temperature X-ray diffraction technique and others. The promotion of transformation by addition of metallic compounds such as metal oxides and metal salts, which was widely confirmed in many other reactions taking part in solids, was hardly recognized in this study, howevever, the immersion of γ-Fe2O3 into mineral acid solutions such as hydrochloric acid and sulfuric acid solution had the remarkable effect on this transformation.The obtained results are summarized as follows:(1) Such a effect by the immersion of γ-Fe2O3 into hydrochloric acid and sulfuric acid solution disappeared by washing till the sample got free from chloride and sulfate ions absorbed on it. This result allows us to consider that the accelerating action for this transformation does not relate to degraded particle size of γ-Fe2O3.(2) γ-Fe2O3 treated with two mineral acid solutions was locally converted, espevially in its surface, to FeOCl and hydrated FeSO4 respectively by the reaction with the mineral acids at elevated temperature.(3) The beginning temperature of the transformation of the treated γ-Fe2O3 coincided completely with that of thermal decomposition of FeOCI and FeSO4⋅H2O respectively.(4) Both anhydrous FeSO4 and FeCl3 produced by these thermal decompositions have a hygroscopic character as known well.The authors conclude from the results mentioned above that catalytic action due to the immersion of γ-Fe2O3 into mineral acid solutions relates to the accelerating action on dehydration of crystal water contained as crystal stabilizer into γ-Fe2O3.
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