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Rapid Mix Preparation of Bioinspired Nanoscale Hydroxyapatite for Biomedical Applications
Published on: February 23, 2017
Solubility and Surface Properties of Finely Divided Hydroxyapatite
Y Avnimelech1, E C Moreno1, W E Brown1
1Institute for Materials Research, National Bureau of Standards, Washington, D.C. 20234.
Abstract:
Synthetic hydroxyapatite (OHAp), Ca5(PO4)3OH, was prepared by slow addition of phosphoric acid to a boiling Ca(OH)2 suspension. The solid, precipitated at a pH of about 12, was stabilized by prolonged boiling. The Ca/P ratio of the product was 1.69 ± 0.04 and it had a specific surface area of 26 m2/g. Samples of OHAp were equilibrated with phosphoric acid solutions. Within the pH range studied, 5 to 7, the solubility product, (Ca)5(PO4)3(OH), was found to be 6.3 ± 2.1 × 10-59 at 25 °C. Substantial deviations of the overall dissolution reaction from OHAp stoichiometry were observed and are attributed to nonstoichiometric reactions occurring at the surface. A linear dependence of excessive phosphorus on the surface with decrease in pH was found. Estimates on the extent of deviation from stoichiometry caused by the surface reaction are given.
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