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Thermochemistry of strontium incorporation in aragonite from atomistic simulations |
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| Authors: | Sergio E Ruiz-Hernandez Ricardo Grau-Crespo A Rabdel Ruiz-Salvador Nora H De Leeuw |
| Institution: | a National Aquarium of Cuba, Ave. 3ra, Esquina 62, Miramar, Havana, Cuba b Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK c Zeolites Engineering Laboratory, Institute of Materials Research and Engineering (IMRE), University of Havana, Havana 10400, Cuba |
| Abstract: | We have investigated the thermodynamics of mixing between aragonite (orthorhombic CaCO3) and strontianite (SrCO3). In agreement with experiment, our simulations predict that there is a miscibility gap between the two solids at ambient conditions. All SrxCa1−xCO3 solids with compositions 0.12 < x < 0.87 are metastable with respect to separation into a Ca-rich and a Sr-rich phase. The concentration of Sr in coral aragonites (x ∼ 0.01) lies in the miscibility region of the phase diagram, and therefore formation of separated Sr-rich phases in coral aragonites is not thermodynamically favorable. The miscibility gap disappears at around 380 K. The enthalpy of mixing, which is positive and nearly symmetric with respect to x = 0.5, is the dominant contribution to the excess free energy, while the vibrational and configurational entropic contributions are small and of opposite sign. We provide a detailed comparison of our simulation results with available experimental data. |
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