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Growth process and crystallographic properties of ammonia-induced vaterite
Published online by Cambridge University Press: 01 February 2011
Abstract
Metastable vaterite crystals were produced by increasing the pH of Ca2+- and CO3 2--containing solutions through diffusing ammonia gas. The SEM and TEM studies indicate that this ammonia-induced vaterite is polycrystalline with a 6-fold symmetry of the crystal aggregate. The morphology and crystallographic properties of this assemblage change druing crystallization. One hour after nucleation starts, vaterite grains display a spherical structure composed of nano-particles (5-10 nm) with random crystallographic orientations. After that, horizontal layers begin to develop at the edge of the sphere and gradually tilt toward the center as they grow vertically, which results in a three-dimensional morphology with a dent in the center. The vaterite grains mature fully 16 hours after nucleation. TEM analysis indicates the grown vaterite grain (50-60 μm) consists of numerous hexagonal pieces of single crystals (1-2 μm) of similar crystallographic orientations. High-resolution TEM demonstrates that these single crystals grow along (001) with {110} hexagonal boundaries.
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- Copyright © Materials Research Society 2010
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