Synthesis, Crystal Structure, and Thermal Properties of CaSO4·2H2O Single Crystals

Abstract

Single crystals were grown at room temperature from the precursors CaCO 3 and NH 2 SO 3 H by a gel method using agar-agar gel as the medium of growth. Differential scanning calorimetry, thermogravimetric-differential thermal analysis, and X-ray diffraction measurements were performed on the single crystals. The crystal structure of the grown crystals was confirmed to be very similar to that of calcium sulfate dihydrate (CaSO 4 • 2H 2 O, gypsum). The temperature at which dehydration and evaporation of intercalated water molecules in the single crystal occurred was found to be 375.9 K, which was very close to that in CaSO 4 • 2H 2 O. From all these results, we identified the grown single crystals as CaSO 4 • 2H 2 O. The weight loss owing to the thermal decomposition of anhydrous CaSO 4 formed by the dehydration of the single gypsum crystals was found to occur at ~1530 K. This weight loss was probably caused by the evolution of SO 3 gas by sublimation, and the chalky white substance left in the open vessel after decomposition was calcium oxide (CaO).

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“…DTG eğrilerinden de açıkça görüleceği üzere dehidrasyon süreci birbirini takip eden iki aşamada gerçekleşmektedir. Birinci aşamada kalsiyum sülfat dihidrat, hemihidrata ikinci aşamada ise susuz kalsiyum sülfata dönüşmektedir [8]. Saf kalsiyum sülfat dihidratın termogravimetrik analizi, %11'lik ilk kütle kaybının 99-150C sıcaklık aralığında, ikinci kütle kaybının ise 150-175C sıcaklık aralığında gerçekleştiğini ve %9 olduğunu ortaya koymuştur.…”

Effect of Microwave Heating on Moulding Sand Properties with Gypsum Binder

“…This mineral can be colorless or white. It also occurs in yellowish, pinkish, brownish or grayish color [1][2][3][4].…”