Crystal structure formation of hemihydrate calcium sulfate whiskers (HH-CSWs) prepared using FGD gypsum

摘要

Hemihydrate calcium sulfate whiskers (HH-CSWs) were hydrothermally synthesized in a sulfuric acid solution using different concentrations of CuCl2 (0, 0.5, 1.0, 1.5, and 2.0 wt%). The morphologies, phase structures, and structural formations of the hydrothermal products were analyzed. It was found that the synthesized HH-CSW samples were mixtures of crystals with different structures. Further, as the CuCl2 concentration was increased, the primary crystal structure of the samples changed from monoclinic to hexagonal and then back to monoclinic. The sample synthesized using 1.0 wt% CuCl2 primarily consisted of crystals with a hexagonal structure. Scanning electron microscopy imaging confirmed that the samples consisted of crystals of different morphologies (i.e., those with hexagonal and monoclinic structures). The effect of the CuCl2 concentration on the crystal structure transition is discussed. (C) 2019 Elsevier Ltd. All rights reserved.