Microscopic Studies of Calcium Sulfate Crystallization and Transformation at Aqueous–Organic Interfaces

Abstract

The 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 have 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 non-miscible 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.3

Adverse Effects of Inherent CaO in Coconut Shell-Derived Activated Carbon on Its Performance during Flue Gas Desulfurization

“…The surface energy of the (010) faces is 2.02 J/m 2 , having a face energy higher than that of (001) faces (0.40 J/m 2 ) and (100) faces (0.59 J/m 2 ), suggesting that (010) faces is the most active crystal growth surface for CSD whiskers. It is easier for the crystal nucleus to grow along the (010) faces to achieve stability. ,, Therefore, CSD whiskers grow along the c shapes as needles and flakes.…”

“…It is easier for the crystal nucleus to grow along the (010) faces to achieve stability. 42,45,46 Therefore, CSD whiskers grow along the c shapes as needles and flakes.…”

In Situ Kinetic Observations on Crystal Nucleation and Growth

“…417,418 Recently, Unwin and co-workers investigated the crystal growth of calcium sulfate from immiscible aqueous−organic interfaces via in situ optical microscopy in combination with Raman spectroscopy and X-ray diffraction and highlighted the organic solvent regulated crystalline mechanisms, which resulted in different final products. 419 Specifically, gypsum was synthesized with the presence of dodecane, while the anhydrite crystal was generated from the aqueous-hexane interface via a gypsum intermediate phase and a dissolution-precipitation mechanism.…”

Continuous, Large-Scale, and High Proportion of Bioinspired Phosphogypsum Composites via Reactive Extrusion

“…However, these high-cost treatment methods limit the application of building gypsum on an industrial scale. Much effort has been proposed for controlling the crystallization and morphology of calcium sulfate, such as inorganic additives [ 5 , 6 , 7 , 8 ], organic acids [ 9 ], surfactants [ 10 , 11 ], and aqueous-organic systems [ 12 ], but the as-prepared samples only presented rods, plates, and whiskers. A more interesting microstructure has not yet been reported.…”