The enhancement of hydroxyapatite thermal stability by Al doping

Al-substituted hydroxyapatite (Al-HA) powders with apatite structure and particle size of 30-70 nm were obtained via precipitation method. The effect of Al content on specific surface area and morphology of powders was studied, and a formation of highly anisotropic phase due to Al doping was observed. The influence of heat treatment in 300-1400 degrees C range on the phase composition, lattice parameters, Fourier-transform infrared spectroscopy (FTIR) spectra and mass loss of powders was investigated. Introduction of Al in the hydroxyapatite (HA) lattice in the range 0.5-1.0 mol.% resulted in the improvement in thermal stability, which had not been reported previously. Incorporation of 5-10 mol.% of Al resulted in the formation of biphasic materials based on HA and whitlockite-like structure at 900 degrees C and apatite and alpha-tricalcium phosphate (alpha-TCP) phases at 1200-1400 degrees C. Introduction of 20 mol.% of Al resulted in the formation of isomorphic Al-substituted whitlockite phase Ca9Al(PO4)(7). We have estimated the onset of Ca9Al(PO4)(7) transformation into alpha-TCP phase at 1400 degrees C. (C) 2019 Published by Elsevier B.V.