Relation of lattice ion solution composition to octacalcium phosphate dissolution kinetics |
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Authors: | Eileen M Burke George H Nancollas |
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Institution: | Department of Chemistry, Natural Sciences Complex, University of Buffalo, Buffalo, NY 14260-3000, USA |
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Abstract: | The kinetics of dissolution of octacalcium phosphate (OCP) has been investigated under conditions of constant relative undersaturation with respect to OCP, σOCP=−0.57, at pH 4.500, and ionic strength (I), 0.15 mol l−1. The molar calcium/phosphate ratio (R) in the solutions was varied from 0.1 to 10. The dissolution rate decreased by 160% as R increased from 0.1 to 10. The ζ-potential of the OCP surfaces was measured in solutions equilibrated with respect to OCP at pH values ranging from 5.0 to 11. Under stoichiometric conditions (R=1.33), OCP was positively charged at pH values from 5.0 to 10. As the solution calcium concentration was increased, ζ became more positive over the entire pH range studied. At R=0.1, two isoelectric points were apparent at pH values of about 6.3 and pH 9.5. This behavior may be related to the solubility product (Ksp) of OCP. The relationship between surface characteristics and dissolution rate are discussed in terms of kink density and the kinetic ionic ratio model developed previously (J. Zhang, G.H. Nancollas, J. Colloid Interf. Sci., 200 (1998) 131. |
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Keywords: | Dissolution kinetics Octacalcium phosphate ζ-potential Calcium/phosphate ratio |
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