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A study of ion and molecule interactions with calcium carbonate polymorphs using Mn2+ ions as a paramagnetic probe

The aim of this work is to study interactions of ions and molecules with calcium carbonate polymorphs during their spontaneous precipitation and their epitaxial growth on the suspended mineral particles by using electron paramagnetic resonance (EPR) spectroscopy of Mn2+ ions, along with other analytical methods and technics. The study of naturally occuring composite materials, shells for instance, are also anticipated. Mn2+ ions substitute for Ca2+ in calcite, aragonite or vaterite crystal lattice and thus provide details of the structure of these centres and their immediate environment. So far, the incorporation of divalent ions (Mg2+, Mn2+, Cu2+, Sr2+, Cd2+, Ba2+, Pb2+) in vaterite and calcite has been studied [1-4], and the mode and sites of incorporation for some of these ions were determined. Besides, the precipitation of calcium carbonates influenced by the addition of suspended mineral particles (montmorillonite, kaolinite, quartz) was investigated [5]. Ca-montmorillonite was found to be a suitable substrate for the overgrowth of calcite, i.e. the lattice parameters of the substrate and the overgrowing solid phase were similar. This means that the lattice mismatch s between calcite and montmorillonite, s = (a-b)/a (where a and b are the stress free lattice parameters of the substratew and the overgrowing phase, respectively), was less than 0.02. It was also found that nucleation of calcium carbonate polymorphs occurs on the particular crystal planes of montmorillonites, i.e. the planes perpendicular on the basal plane. The dimensions of these planes were varied by intercalation of different cations in the montmorillonite interlayers. The forthcoming investigations will be focused on the interactions of small and macromolecules with calcium carbonates, which is a base for the understanding of biocomposite formation and also for the creation of new composite materials. [1] R. A. Serway, (1971) Phys. Rev. B, 608. [2] J. Lech and A. Slezak, (1989) Chem. Phys. Lett. 157, 175. [3] Lj. Brečević, V. Noethig-Laslo, D. Kralj and S. Popović (1996) J. Chem. Phys. Faraday Trans. 92, 1017. [4] V. Noethig-Laslo and Lj. Brečević, Phys. Chem. Chem. Phys. (2000) 2, 5328. [5] D. Kralj and N. Vdović (2000) Wat. Res. 34, 179.

Calcium carbonate; Mn2+; EPR spectroscopy

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