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Download fileMicroscopic Studies of Calcium Sulfate Crystallization and Transformation at Aqueous–Organic Interfaces
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posted on 2016-08-19, 00:00 authored by Emma R. Ravenhill, Paul M. Kirkman, Patrick R. UnwinThe calcium sulfate crystal system
is of considerable fundamental
and practical interest, consisting of the three hydrates, gypsum (CaSO4·2H2O), bassanite (CaSO4·0.5H2O), and anhydrite (CaSO4). Each has significant
applications; however, synthesis of anhydrite via conventional aqueous
methods requires elevated temperatures and therefore high energy costs.
Herein, we investigate calcium sulfate crystal growth across a nonmiscible
aqueous–organic (hexane or dodecane) interface. This process
is visualized via in situ optical microscopy, which produces high
magnification videos of the crystal growth process. The use of interferometry,
Raman spectroscopy, and X-ray diffraction allows the full range of
calcium sulfate morphologies and hydrates to be analyzed subsequently
in considerable detail. In the case of dodecane, gypsum is the final
product, but the use of hexane in an open (evaporating) system results
in anhydrite crystals, via gypsum, at room temperature. A dissolution–precipitation
mechanism between neighboring microcrystals is responsible for this
transformation. This work opens up a simple new crystal synthesis
route for controlling and directing crystallization and transformation.
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dodecanecalcium sulfate crystal growthRaman spectroscopycalcium sulfate morphologiesanhydrite crystalscrystal synthesis routegypsumtransformationcrystal growth processmagnification videoscalcium sulfate crystal systemCalcium Sulfate Crystallizationhydratehexaneenergy costsMicroscopic StudiesCaSO 4system resultsroom temperatureX-ray diffraction