Preparation of magnesium-substituted hydroxyapatite powders by the mechanochemical-hydrothermal method

Magnesium-substituted hydroxyapatite (Mg-HAp) powders with different crystallinity levels were prepared at room temperature via a heterogeneous reaction between Mg(OH)(2)/Ca(OH)(2) powders and an (NH4)(2)HPO4 solution using the mechanochemical-hydrothermal route. The as-prepared products contained unreacted Mg(OH)(2) and therefore had to undergo purification in ammonium citrate aqueous solutions at room temperature. X-ray diffraction, infrared spectroscopy, thermogravimetric and chemical analyses were performed and it was determined that the purified powders were phase-pure Mg-HAp containing 0.24-28.4 wt% of Mg. The concentration of Mg was slightly lower near the surface than in the bulk of the HAp crystals as indicated by Xray photoelectron spectroscopy. Dynamic light scattering revealed that the median particle size of the room temperature Mg-HAp powders was in the range of 102 nm-1.2 mum with a specific surface area between 91 and 269 m(2)/g. Scanning electron microscopy confirmed that the Mg-HAp powders consisted of submicron agglomerates of nanosized crystals, less than approximate to20 nm. (C) 2003 Elsevier Ltd. All rights reserved.