title: Effect of K(+) on the Stoichiometry of Carbonated Hydroxyapatite Obtained by the Hydrolysis of Monetite.
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.
authors.affiliation: Laboratory for Analytical Chemistry, University of Ghent, Krijgslaan 281-S12, B-9000 Ghent, Belgium.
authors.forename: Erna A. P.
authors.initials: EA
authors.lastname: De Maeyer
authors.forename: Ronald M. H.
authors.initials: RM
authors.lastname: Verbeeck
authors.forename: Ilse Y.
authors.initials: IY
authors.lastname: Pieters