A facile method to control the structure and morphology of α-calcium sulfate hemihydrate†
We report a facile method to control the structure and morphology of alpha-calcium sulfate hemihydrate (α-HH) crystals precipitated in Na2EDTA-containing ethylene glycol aqueous solutions by simply tuning the volume ratio of ethylene glycol to water (G/W). At a low G/W from 0.4 to 2.5, single crystalline α-HH particles with a hexagonal prism shape precipitate from the solution, the corresponding aspect ratio of the prisms varies from 2.7 to 0.1. While at a high G/W from 5.0 to 50.0, polycrystalline α-HH particles form with spherical and ellipsoidal shapes and the diameter of the polycrystalline spheres reduces from 2 μm to 300 nm. The synergetic effect of supersaturation and Na2EDTA activity resulting from G/W accounts for the evolution of the structure and morphology of α-HH. This method allows α-HH synthesis in micro- and nanoscale size, thus enabling its morphology/structure-dependent applications.