The past decades have witnessed great advances in nanotechnology since tremendous efforts have been devoted for the design, synthesis, and application of nanoparticles. However, for most mineral materials such as calcium sulfate, it is still a challenge to prepare their nanoparticles, especially with uniform size and high monodispersity. In this work, we report a route to regulate the morphology and structure of α-calcium sulfate hemihydrate (α-HH) and successfully synthesize and stabilize its mesocrystals for the first time. The ellipsoidal mesocrystals in length of 300-500 nm are composed by α-HH nanoparticles arranged in the same crystallographic fashion and interspaced with EDTA. The time-dependent experiments indicate the α-HH aggregates evolve from irregular structure to mesocrystal structure with the subsequent growth of subunits and then partially fuse into single crystals. Disorganizing the mesocrystal structure before the emergence of fusion reaps α-HH nanorods in a length of 30-80 nm and a width of 10-20 nm with high monodispersion. This ingenious concept paves an alternative way for nanoparticle preparation and is readily extended to other inorganic systems.
We report a new class of glycerol−water system to transform FGD gypsum into α-calcium sulfate hemihydrate (α-HH) mediated by trace NaCl and Na 2 EDTA to regulate the phase transformation rate as well as the crystal morphology to achieve crystals with high mechanical strength. NaCl plays a role in accelerating the nucleation and crystal growth process, whereas Na 2 EDTA regulates the morphology of α-HH from columnar to lamellar. The paste made from columnar α-HH with higher aspect ratio deserves higher dry bending/compressive strength of 13.6/37.6 MPa, which is comparable with those prepared in nitrate− water medium, chloride−water medium, or by autoclave method. This study provides an improved alternative of glycerol−water system to transform FGD gypsum into α-HH with controlled morphology, high mechanical strength, and less corrosion to the equipment. We also establish the relationship between the mechanical strength of paste and the aspect ratio of α-HH crystals.
We report a facile and green chemical solution approach to synthesize monodisperse α-calcium sulfate hemihydrate (α-HH) nanoellipsoids with a length of 600 nm and a width of 300 nm by simply mixing Ca(2+) and SO4(2-) glycerol-water precursor solutions in the presence of Na2EDTA. The α-HH nanoellipsoid is formed through a Na2EDTA-mediated self-assembly of small primary building blocks (α-HH domains: ∼14 nm). The study on the morphological evolution of α-HH reveals that the controlled synergy of supersaturation (precursor concentration) and Na2EDTA is crucial for the development of α-HH into nanoellipsoids. Further thermal annealing of the nanoellipsoid could make the α-HH domains transit into calcium sulfate anhydrites and grow up, generating the gaps between them and resulting in a porous structure. This work paves a new way for preparing high-quality α-HH nanoellipsoids with a monodisperse nanosize and a porous structure, promising their future application in many fields such as biomedicine.
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.
The involvement of amorphous calcium sulfate (ACS) as a precursor to calcium sulfate crystallization remains an important but poorly understood phenomenon, especially the mechanism by which ACS evolves to the...
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