Morphology and Polymorph Control of Calcium Carbonate by Additives
Date Issued
2012
Date
2012
Author(s)
Huang, Yu-Chieh
Abstract
Biomineralization refers to a process of forming inorganic minerals such as shell, skeleton, tooth and etc., in biological systems of various organisms. Calcium carbonate, one of the most plentiful biominerals, is the major inorganic composition in mollusk shells, coral, and sea urchin. Organisms such as calcitic coccolithophoridae, the aragonitic pteropoda and ascidians with vaterite spicules are highly selective in the biomineralization of one polymorph or another. How Nature achieves such a precise polymorph selection in organisms is a key issue in the field of biomineralization. To shed light on this process, calcium carbonate is precipitated in the presence of different simple molecules to study how these additives affect the polymorph and morphology of calcium carbonate.
In this study, aragonite polymorph is obtained without any additives under high temperature and pressure using hydrothermal method. However, other polymorphs of calcium carbonate such as calcite and vaterite can be induced by adding various additives in the same system. In the gas diffusion system at ambient temperature and pressure, we obtain the calcite phase without additives while phase transformation from calcite to aragonite is observed in the presence of magnesium ions. The as-synthesized calcium carbonates are characterized by various methods including IR, SEM, ICP-MS, XRD and NMR. Various techniques of solid-state NMR techniques are used to investigate the structure of calcium carbonate as well as the additives at the molecular level. Particularly, 43Ca and 13C nuclei are utilized for the characterization of calcium carbonate environments. Our study reveals that pure polymorphs can be selectively acquired under sophisticated physical/chemical conditions. In addition, a possible mechanism of calcite-to-aragonite transformation is proposed with the emphasis on the role of magnesium ions.
Subjects
Biomineralization
calcium carbonate
polymorphism
solid-state NMR spectroscopy
Ca-43 NMR
Type
thesis
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