Type
Text
Type
Dissertation
Advisor
Reeder, Richard J. | Phillips, Brian | Parise, John | Rasbury, E. | Michel, Frederick.
Date
2014-12-01
Keywords
Geochemistry | amorphous, calcium, carbonate, kinetics, structure, transformation
Department
Department of Geosciences.
Language
en_US
Source
This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree.
Identifier
http://hdl.handle.net/11401/77662
Publisher
The Graduate School, Stony Brook University: Stony Brook, NY.
Format
application/pdf
Abstract
Amorphous calcium carbonate (ACC) is a common transient precursor in the formation of more stable crystalline calcium carbonate minerals, most notably calcite, vaterite, and aragonite. Formation of ACC from calcium carbonate rich aqueous solution rather than direct crystallization of crystalline polymorphs by organisms provides several advantages: control of morphology, grain size, orientation, hardness, and other bulk properties as well as reduction of energy costs during growth cycles. Despite decades of study, stabilization and transformation mechanisms of synthetic and biogenic ACC remain unclear. In particular, the roles of H2O and inorganic phosphate in ACC structure and transformation, and the variables affecting transformation kinetics and polymorph selection are understudied. In this research, we addressed structure and kinetic behavior of ACC through four complementary investigations: two studies focus on synthetic ACC stabilization and two focus on synthetic and biogenic ACC transformation behavior in solution at ambient temperatures. We explored ACC stabilization via compositional and thermal analyses, X-ray scattering, X-ray absorption spectroscopy, and nuclear magnetic resonance spectroscopy. Transformation experiments used a novel method of in situ structural analysis that provided quantitative kinetic and structural data and allowed us to visualize the ACC transformation pathway. Results revealed the complexity of H2O structure in ACC samples synthesized from three methods, indicating that the distinct hydrous populations produced define ACC behavior. Transformation kinetics and polymorph selection were strongly affected by the hydration state and type of synthetic ACC reacted. In situ transformation experiments also showed differences in kinetic behavior due to reaction medium. The structural role of hydrous components was again evident in in situ transformation experiments for ACC from a biogenic lobster gastrolith (LG) reacted with water. LG exhibited distinctly different behavior than synthetic ACC samples; LG transformation rates were significantly slower and a larger ACC fraction remained at comparable time points. Inorganic phosphate stabilizes ACC, increasing its resistance to crystallization. This research is underpinned by the relationship between microscopic structural features and macroscopic properties and behavior. Manipulation of molecular-scale variables for controlling macroscopic properties allows important applications in materials science and engineering, and a greater understanding of biominerals may guide our design of functional materials. | 142 pages
Recommended Citation
Schmidt, Millicent Promise, "Stabilization and transformation of amorphous calcium carbonate: structural and kinetic studies" (2014). Stony Brook Theses and Dissertations Collection, 2006-2020 (closed to submissions). 3454.
https://commons.library.stonybrook.edu/stony-brook-theses-and-dissertations-collection/3454