Formation and Transformation of Amorphous Calcium-Magnesium Carbonates in Synthetic Seawater

• Main Author: Singer, Jared
• Other Authors: Bowers, Geoffrey
• Format: Thesis
• Language: English
• Published: New York State College of Ceramics at Alfred University. Kazuo Inamori School of Engineering. 2013
• Subjects: Ocean acidification
• Online Access: http://hdl.handle.net/10829/7350

Advisory committee members: Scott Misture, S.K. Sundaram, Nathan Mellott. Dissertation completed in partial fulfillment of the requirements for the degree of PHD in Material Science and Engineering at the Kazuo Inamori School of Engineering, New York State College of Ceramics at Alfred University The aqueous chemistry, precipitation, and crystallization of metal-carbonates comprises a vast field of research that underlies the urgency of CO2 sequestration, ocean-acidification, and biomineralization. The results of recent experimental and computational studies suggest that amorphous calcium and magnesium carbonates are precipitated from supersaturated aqueous conditions by non-classical aggregation of ion pairs, dimers, dynamically-ordered-liquid-likeoxypolymers (DOLLOPS), and prenucleation clusters (PNCs). We present the first high field (20 T) 43Ca and 25Mg NMR studies of amorphous calcium-magnesium carbonates (ACC, ACMC, AMC) materials. Direct integration of computational techniques with experimental NMR provides a novel step forward toward multi-scale integration of computational and experimental techniques. Supporting information is derived from X-ray diffraction (XRD), thermogravimetric/differential thermal analysis (TGA-DTA), and scanning electron microscopy – energy dispersive spectroscopy (SEM-EDS) and provides important comparison to the bulk structures and composition. High field NMR of amorphous carbonates demonstrates that amorphous carbonates contain various types of local disorder, but does not corroborate the theory of polyamorphism nor nano scale phase separations postulated by other workers. Carbon (13C) NMR of 13Cenriched materials indicates a degree of Ca-Mg solid solution in ACMCs, as ACMC 13C resonances cannot be adequately reconstructed from the pure ACC and AMC 13C resonances. However, with increasing Mg-content (and therefore H2O content) 13C NMR resonances are strongly influenced by water-carbonate hydrogen bonding, shifting to lower resonance frequency and broadening. The 13C-NMR are ...