Preparation of α‐Calcium Sulfate Hemihydrate from Calcium Sulfate Dihydrate in Methanol–Water Solution under Mild Conditions

Abstract

For the first time, a-calcium sulfate hemihydrate (a-HH) was successfully prepared from calcium sulfate dihydrate (DH) in methanol-water solution under atmospheric pressure. The effect of methanol concentrations (40-73 mol%) on the transition from DH to a-HH were investigated at temperatures (601-751C) within a reaction time of 36 h. The results showed that an increase in methanol concentration could lower the transition temperature. The transition was speeded up by increasing methanol concentration from 47 to 57 mol% at 751C. When the temperature dropped to 701C, the transition rate firstly increased with the methanol concentration until it reached 69 mol% and then exhibited a reverse trend with increasing methanol concentration from 71 to 73 mol%. The accelerating effect, involved during the nucleation of a-HH, attributes to the elevated supersaturation due to the fall in the water activity resulting from the increasing methanol concentration. The retarding effect, involved during the crystal growth of a-HH, was likely derived from the specific adsorption of methanol molecules onto the surfaces of a-HH crystals. Overall, the aqueous solution of methanol could act as a novel category of medium suitable for the a-HH preparation from DH. D. Viehland-contributing editor

Ultrasonic Irradiation during the Calcium Sulfate Hemihydrate to Dihydrate Transformation Process

“…The more sensitive DSC results support the XRD results. The thermograms recorded for the CSD crystals obtained in the pure solution without ultrasonic irradiation include two characteristic endothermic peaks at 135.2 °C and 148.4 °C, which confirmed that all the crystals acquired were composed of CSD .…”

A simple strategy for the synthesis of well-defined bassanite nanorods

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The crystal growth kinetics of alpha calcium sulfate hemihydrate in concentrated CaCl2–HCl solutions

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