Synthesis, structure, and solubility of carbonated barium chlor- and hydroxylapatites
Two series of carbonated barium apatites [BaApZ = Ba 10(PO 4) 6Z 2] were prepared in aqueous solution. Carbonated barium hydroxylapatites (CBaApOH) were prepared by mixing solutions of Ba(NO 3) 2 with (NH 4) 2HPO 4 and (NH 4) 2CO 3 at pH 12. Carbonated barium chlorapatites (CBaApCl) could only be prepared by stirring barium chlorapatite with (NH 4) 2CO 3 at pH 10 for 1 week. Powder X-ray diffraction showed no evidence of the presence of BaCO 3 or other possible impurities such as BaHPO 4 in the carbonated products. Variations in carbonate content of the apatites had little effect on the width of peaks in their XRD patterns. The cell parameters determined by full pattern analysis were also relatively independent of the carbonate content of the apatites, although CBaApCl showed a slight decrease in a-axis length with increasing carbonate content. The slight decrease in the a-axis length, the amount of carbonate incorporated in the apatites, and the specific IR absorbances in the carbonate spectral regions support the mechanism of carbonate substitution for phosphate (B-type). In contrast, the barium:phosphate ratio determined for several apatites of different carbonate concentrations suggests carbonate substitution for the monovalent anion (A-type). Raman spectroscopy of CBaApOH confirmed that carbonate incorporation causes atomic disorder within the structure and that apparently carbonate-saturated CBaApOH still contains appreciable hydroxyl. Activity-based K sp values were determined for both series of carbonated apatites and show that the solubilities of both CBaApCl and CBaApOH remain almost constant at low carbonate concentrations but increase at higher carbonate values (assuming B-type substitution). The K sp values for uncarbonated BaApCl and BaApOH were determined by extrapolation to 0% carbonate (10 -103 and 10 -107 for BaApCl and BaApOH, respectively). © 2012 Published by Elsevier Ltd. All rights reserved.
Yoder, Claude H.; Pasteris, Jill D.; Krol, Katherine A.; Weidner, Victoria L.; and Schaeffer, Richard W., "Synthesis, structure, and solubility of carbonated barium chlor- and hydroxylapatites" (2012). Educator Scholarship. 24.