Dehydration of Calcium Sulfite Tetrahydrate
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概要
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The dehydration process of calcium sulfite tetrahydrate (CaSO<SUB>3</SUB>.4H<SUB>2</SUB>O) which was unstable at room temperature, the formation of intermediate phase, the crystal shape and size of the dehydrated calcium sulfite hemihydrate (CaSO<SUB>3</SUB>. 1/2H<SUB>2</SUB>O) were studied under various conditions of heating and aqueous solutions.<BR>TG-DTA curves of the tetrahydrate single crystal showed three endotherms weight losses of three steps at 1.25°C/min and TG curves under isothermal heating reached an equilibrium state corresponding to elimination of about 2 mol or 1 mol of crystal water. These phenomena indicated that the 3. 5 mol of crystal waters of the tetrahydrate had unequal bond strengths. Also this fact was suggested by infrared spectra. Therefore it was suggested that the formation of intermediate phases as CaSO<SUB>3</SUB>·2H<SUB>2</SUB>O and CaSO<SUB>3</SUB>.H<SUB>2</SUB>O existed. But the existence of new phases were not confirmed from X-ray diffraction patterns in the dehydration process.<BR>The crystal of α-hemihydrate formed from dehydration of the tetrahydrate powders was mainly aggregation of plate crystals with about 1-3 μm size in the skelton structure of tetrahydrate. Also the unknown phase formed in instantaneous reactions of the CaCl<SUB>2</SUB>-Na2SO<SUB>3</SUB> and the Ca (NO<SUB>3</SUB>) <SUB>2</SUB>-Na2SO<SUB>3</SUB> system at 3-5°C. It was suggested that the unknown phase was CaSO<SUB>3</SUB>·H<SUB>2</SUB>O from TG-DTA curves.
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