barium hydroxyapatite

Description

Barium Hydroxyapatite is prepared by the aqueous reaction of a soluble barium salt with trisodium phosphate:
10BaCl2 (aq) + 6Na3PO4 (aq) ?Ba10(OH)2(PO4)6 (s) + 18NaCl (aq) + 2HCl
Alternately, it can be prepared by the aqueous reaction of the monobasic salt and the hydroxide at about 60–80°C with addition of NaOH to control pH to a minimum of 10–11.
3Ba(H2PO4)2 (aq) + 2Ba(OH)2 (solid) ?Ba5OH(PO4)3 (solid) + 8H2O
Its molecular weight is 1728.3662 g/mol and the CAS number of 12356-34-2. Barium readily forms mixed hydroxyapatties with both calcium and strontium hydroxyapatites. These hydroxyapatites can be OH deficient, with the charge balance maintained by Ba²⁺, Sr²⁺ or Ca²⁺ vacancies. It has been found that Ba²⁺ ions are more difficult to be incorporated into hydroxyapatite crystals compared to Sr2²⁺ions. In a mixture with increasing Ba²⁺content, the particles grew and finally turned into pure rod-shaped barium hydroxyapatite particles with a size of ca. 0.2μ.

Preparation

When barium hydroxyapatite, (Ba10(PO4)6(OH)2, (abbreviated-BaHAp) was synthesized by a wet method using Ba(OH)2·8H2O and (NH4)2HPO4 as starting materials, the Ba-HAp obtained had a Ba/P atomic ratio of 1.76 and contained CO3 groups. Thus, any solution method to prepare this compound must be protected fromthe ambient atmosphere in order to obtain a pure salt.
Carbonated barium hydroxyapatite Ba10(PO4)6 (OH)2-2x(CO3)x, where X= 0.30–0.57, produced BaHAP particles with different Ba/P molar ratios. These were prepared by a wet method and CO32^- ions were incorporated into OH^- sites of a BaHAP lattice during the preparation at high pH solution. The obtained BaHAP particles were well crystallized and showed a high thermostability. On elevating the mixing temperature of the H3PO4 and Ba(OH)2 solutions, the mean particle size of BaHAP particles decreased and their specific surface area increased. The amount of CO2 adsorbed irreversibly on BaHAP particles increased as their Ba/P molar ratio increased.
In another study, carbonate-containing barium hydroxyapatite was prepared by solid-state reactions in air at 950°C. Obtained samples were investigated by X-ray powder diffraction and IR spectroscopy.