No 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

Calcium carbonate crystallisation on surfaces has been studied extensively due to its prominence in biomineralisation, but the role of surface charge in nucleation and growth is not well understood. We have employed potential-controlled Highly Oriented Pyrolytic Graphite (HOPG) surfaces to demonstrate the significant impact of surface charge on calcium carbonate crystallisation: at negatively charged HOPG surfaces, calcite, aragonite and vaterite all nucleate from high energy positively-charged crystal faces, contrasting with the stable (104) calcite planes nucleated at positively charged surfaces. These observations are explained and rationalised.

Correction for 'Calcium carbonate crystallisation at charged graphite surfaces' by E. R. Ravenhill et al., Chem. Commun., 2017, DOI: .