Journal article
Transformation and crystallization energetics of synthetic and biogenic amorphous calcium carbonate
Proceedings of the National Academy of Sciences - PNAS, Vol.107(38), pp.16438-16443
09/21/2010
DOI: 10.1073/pnas.1009959107
PMCID: PMC2944757
PMID: 20810918
Abstract
Amorphous calcium carbonate (ACC) is a metastable phase often observed during low temperature inorganic synthesis and biomineralization. ACC transforms with aging or heating into a less hydrated form, and with time crystallizes to calcite or aragonite. The energetics of transformation and crystallization of synthetic and biogenic (extracted from California purple sea urchin larval spicules, Strongylocentrotus purpuratus) ACC were studied using isothermal acid solution calorimetry and differential scanning calorimetry. Transformation and crystallization of ACC can follow an energetically downhill sequence: more metastable hydrated ACC → less metastable hydrated ACC ⇒ anhydrous ACC ∼ biogenic anhydrous ACC ⇒ vaterite → aragonite → calcite. In a given reaction sequence, not all these phases need to occur. The transformations involve a series of ordering, dehydration, and crystallization processes, each lowering the enthalpy (and free energy) of the system, with crystallization of the dehydrated amorphous material lowering the enthalpy the most. ACC is much more metastable with respect to calcite than the crystalline polymorphs vaterite or aragonite. The anhydrous ACC is less metastable than the hydrated, implying that the structural reorganization during dehydration is exothermic and irreversible. Dehydrated synthetic and anhydrous biogenic ACC are similar in enthalpy. The transformation sequence observed in biomineralization could be mainly energetically driven; the first phase deposited is hydrated ACC, which then converts to anhydrous ACC, and finally crystallizes to calcite. The initial formation of ACC may be a first step in the precipitation of calcite under a wide variety of conditions, including geological CO(2) sequestration.
Details
- Title: Subtitle
- Transformation and crystallization energetics of synthetic and biogenic amorphous calcium carbonate
- Creators
- A V Radha - Peter A. Rock Thermochemistry Laboratory and Nanomaterials in the Environment, Agriculture, and Technology Organized Research Unit (NEAT ORU), University of California at Davis, One Shields Avenue, Davis, CA 95616, USATori Z ForbesChristopher E KillianP U P A GilbertAlexandra Navrotsky
- Resource Type
- Journal article
- Publication Details
- Proceedings of the National Academy of Sciences - PNAS, Vol.107(38), pp.16438-16443
- DOI
- 10.1073/pnas.1009959107
- PMID
- 20810918
- PMCID
- PMC2944757
- NLM abbreviation
- Proc Natl Acad Sci U S A
- ISSN
- 0027-8424
- eISSN
- 1091-6490
- Publisher
- United States
- Language
- English
- Date published
- 09/21/2010
- Academic Unit
- Civil and Environmental Engineering; Chemistry
- Record Identifier
- 9983985859302771
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