Structural Changes upon Dehydration of Amorphous Calcium Carbonate

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• 作者：Millicent P. Schmidt ; Andrew J. Ilott ; Brian L. Phillips ; Richard J. Reeder
• 刊名：Crystal Growth & Design
• 出版年：2014
• 出版时间：March 5, 2014
• 年：2014
• 卷：14
• 期：3
• 页码：938-951
• 全文大小：668K
• 年卷期：v.14,no.3(March 5, 2014)
• ISSN：1528-7505

文摘

Amorphous calcium carbonate (ACC) is a common transient precursor to biogenic crystalline calcium carbonate, but factors controlling the amorphous to crystalline transformation remain unclear. We present a structural analysis and comparison of hydrated and partially dehydrated, synthetic ACC samples. Thermogravimetric analysis showed total H₂O losses of 46% with heating to 115 掳C and 75% for heating to 150 掳C. The ¹H NMR spectra of hydrous ACC, obtained both directly and indirectly, via ¹³C-detection, contain signals from four principal hydrogen environments: translationally rigid structural H₂O, a restrictedly mobile H₂O environment, fluidlike mobile H₂O that is decoupled from rigid H and C, and hydroxyl. The retention of some restrictedly mobile H₂O and lack of change in X-ray total scattering and absorption spectroscopy data for dehydrated ACC suggest that thermal dehydration does not significantly disrupt the calcium-rich ACC framework. NMR results and thermal analyses of samples dehydrated isothermally for extended periods indicate that the H₂O loss mechanism is kinetically hindered and occurs in three stages: simultaneous loss of fluidlike mobile, restrictedly mobile, and rigid H₂O 鈫?loss of restrictedly mobile and rigid H₂O 鈫?loss of hydroxyl and trapped rigid and mobile components that cannot be removed without transformation to crystalline calcium carbonate.