Modification of Crystal Habit of Gypsum by Ferric Ion

概要

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By many researches on the crystalization of the plate form gypsum crystal, were found many crystal habit modifying agent which are effective in the media other than acidic one1) 2) 3) . We have researched the habit modifyer which modify the crystal to plate form in the acidic medium, and found that ferric ion is effective to this. In the present paper this effect was measured by experiments changing the concentrations of Fe3+ ion and sulfuric acid, the crystal size and the crystal form were analysed by statistcal method, and recognized that the Fe3+ ion over 0.05% conc. modify the crystal to plate form in acidic medium over 1 % sulfuric acid. This habit modifying mechanism can be infered as follows. The pH of the saturated solution of CaSO4 is high as 6.38 (13°C). In the acidic medium the pH of the solution on the end face of the major crystal axis become more favourable to precipitate the Fe (OH) 3 than the end face of minor axis, and this precipitated layer lower the growth rate of this face, this bring the crystalization of plate form gypsum crystals.
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