Aqueous Foams as Templates for the Synthesis of Calcite Crystal Assemblies of Spherical Morphology
ABSTRACT The crystallization of calcite in the form of spheroaggregates in aqueous foam stabilized by the surfactant sodium bis-2-ethylhexyl-sulfosuccinate (aerosol OT, AOT) by a method of ion entrapment is described. Reaction of Na2CO3 with Ca2+ ions electrostatically entrapped in the foam results in the formation of flat, platelike calcite crystals, possibly in the plateau border regions of the foam. Hydrodynamic flow patterns in the foam are believed to transport the calcite platelets from the plateau border regions into the larger plateau junctions where they assemble into spherical structures by hydrophobic association. The large interfacial area of the liquid lamellae in the foam provides an attractive and versatile template for the large-scale synthesis of not only minerals but also other nanoscale materials.
Article: Monodisperse Calcium Carbonate Microtablets Forming at 70°C in Prerefrigerated CaCl2–Gelatin–Urea Solutions[show abstract] [hide abstract]
ABSTRACT: Calcium carbonate particles with a unique tablet shape were produced by simply aging the prerefrigerated (at 4°C for 24 h) CaCl2–gelatin–urea solutions at 70°C for 24 h in ordinary glass media bottles. Gelatin is known to be the denatured collagen. The thermal decomposition of dissolved urea was exploited to provide the Ca2+ ion and gelatin-containing solutions with aqueous carbonate ions. Monodisperse CaCO3 microtablets formed in solution had a mean particle size of 4±2.5 μm. CaCO3 microtablets were biphasic in nature and comprised of about 93% vaterite and 7% calcite. Identical solutions used without prerefrigeration yielded only trigonal prismatic calcite crystals upon aging at 70°C for 24 h. Prerefrigeration of CaCl2–gelatin–urea solutions was thus shown to have a remarkable effect on the particle morphology. Samples were characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy, and powder X-ray diffraction.International Journal of Applied Ceramic Technology 07/2008; 6(1):53 - 59. · 1.38 Impact Factor