A facile method to control the structure and morphology of α-calcium sulfate hemihydrate

Abstract

We report a facile method to control the structure and morphology of alpha-calcium sulfate hemihydrate (α-HH) crystals precipitated in Na 2 EDTA-contained 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 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 shape and the diameter of the polycrystalline spheres reduces from 2 µm to 300 nm. The synergetic effect of supersaturation and Na 2 EDTA activity resulted from G/W accounts for the evolution of structure and morphology of α-HH. This method allows α-HH synthesis in micro and nanoscale size, thus enabling its morphology/structure-dependent applications.

Simultaneous control of particle size and morphology of α‐CaSO4·1/2H2O with organic additives

“…In the presence of 65% weight fraction glycerol and without succinic acid, the C 1s spectra of α‐HH can be fitted with three components. In addition to the major component at 284.8 eV, the component located at 286.5 eV should be associated with C–O in glycerol, indicating the adsorption of trace amount of glycerol on the crystal surfaces . Additionally, the high binding energy component of the C 1s at 289.4 should come from the carbonate species (CO 3 2− ) of the limestone in the FGD gypsum, which agreed with the XRD pattern of the FGD gypsum as shown in Figure .…”

“…Traditional crystal growth theories (such as von Weimarn's rule) believe that the crystal size is determined by the crystal nucleation rate and growth rate . The increase in glycerol content greatly increased the maximal relative supersaturation ( S max ) of α‐HH (Table ), which inevitably increased the α‐HH nucleation rate, thereby boosting a large number of nuclei and resulting in the formation of massive small α‐HH particles . Although the increase in S max also increased the crystal growth rate, the increase in the viscosity and density of the mixture (Table ) with increased glycerol content brought in an opposite effect (Equation and ) .…”

Shape‐Tunable Selective Synthesis of Bismuth Fluoride Nanostructures for Versatile Applications

“…Typically, a low supersaturation gives weak driving force for nucleation and results in a slow nucleation and growth. In contrast, a high supersaturation leads to rapid nucleation and production of a large number of nuclei, thus creating polycrystals . Evidently, the supersaturation at the F/Bi ratio of 0.75 is inadequate to form spherical particles by generating enough nuclei at once.…”

Effects of Cationic Polyacrylamide on Hydrothermal Formation of Ultralong α‐CaSO4·0.5H2O Whiskers

“…obtained α‐CaSO 4 ·0.5H 2 O whiskers with tunable aspect ratio by using succinic acid as the morphology modifier. The effective use of other organic additives such as sodium dicarboxylates, cetyltrimethyl ammonium bromide (CTAB), malic acid, and ethylene glycol has also been reported . The morphology modification effects of these organic species were generally attributed to their selective adsorption onto different facet of the α‐CaSO 4 ·0.5H 2 O crystals.…”

“…The effective use of other organic additives such as sodium dicarboxylates, cetyltrimethyl ammonium bromide (CTAB), malic acid, and ethylene glycol has also been reported. [17,[22][23][24][25][26][27] The morphology modification effects of these organic species were generally attributed to their selective adsorption onto different facet of the α-CaSO 4 ·0.5H 2 O crystals. However, up to now, the influence of polymer molecules on the hydrothermal formation of CaSO 4 ·0.5H 2 O whiskers has not been reported yet.…”