Preparation and Characterization of Barium–Strontium Hydroxyapatites

Abstract

Barium–strontium hydroxyapatite solid solutions with different molar ratio Ba/(Ba + Sr) were synthesized by a wet method and characterized by various means. The solid solution particles could be prepared at molar ratios ranging from 0 to 1; however, Ba2+ions were more difficult to be incorporated into hydroxyapatite crystals compared to Sr2+ions. With increasing Ba2+content, the particles grew and finally turned into pure rod-shaped barium hydroxyapatite particles with a size of ca. 0.2 × 2 μm. The resulting particles were agglomerates consisted of primary fine particles except for strontium hydroxyapatite. The molar ratios (Ba + Sr)/P of all the particles were larger than the stoichiometric ratio of 1.67, suggesting that CO32−ions, OH−ions, and/or H2O molecules substitute for PO43−ions in the crystal lattices. The amount of CO2adsorbed irreversibly on the particles increased with increasing (Ba + Sr)/P except for strontium hydroxyapatite and fitted a curve with a minimum at a cation/P ratio of ca. 1.56 as well as other HAPs.