Effect of K(+) on the Stoichiometry of Carbonated Hydroxyapatite Obtained by the Hydrolysis of Monetite |
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Authors: | De Maeyer Erna A P Verbeeck Ronald M H Pieters Ilse Y |
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Institution: | Laboratory for Analytical Chemistry, University of Ghent, Krijgslaan 281-S12, B-9000 Ghent, Belgium. |
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Abstract: | This study investigates the stoichiometry and the thermal stability of K(+)- and CO(3)(2)(-)-containing apatites (KCAp's) obtained by the hydrolysis of monetite. The analysis results of the samples after drying reveal that the KCAp's start to lose carbonate at temperatures = 400 degrees C. The predominant substitution mechanisms for the K(+)- and CO(3)(2)(-) incorporation in calcium hydroxyapatite are Ca(2+) + PO(4)(3)(-) + OH(-) <--> V(Ca) + CO(3)(2)(-) + V(OH)] and Ca(2+) + PO(4)(3)(-) <--> K(+) + CO(3)(2)(-)], where V(X) stands for a vacancy in the X-sublattice. Moreover, a small part of the CO(3)(2)(-) ions are presumably incorporated according to Ca(2+) + 2PO(4)(3)(-) <--> V(Ca) + 2CO(3)(2)(-)]. A comparison of the contributions of these fundamental mechanisms with the results for precipitated Na(+)- and CO(3)(2)(-)-containing apatites shows that no intrinsic coupling whatsoever exists between these mechanisms. |
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