Change of phase composition and morphology of sonochemically synthesised hydroxyapatite nanoparticles with glycosaminoglycans during thermal treatment

Based on the preparation of glycosaminoglycans (GAGs) stabilised hydroxyapatite (HAP) nanoparticle suspension via sonochemical synthesis, the change of phase composition and morphology of freeze dried HAP nanoparticles with GAGs was investigated from 500 to 1200°C by TEM, X-ray diffraction, Fourier transform infrared spectroscopy and SEM. Results show that thermal treatment brought the phase transformation and the morphology change of HAP nanoparticles. In the low temperature stage (∼650°C), the samples were mainly composed of HAP as main crystalline phase and β-NaCaPO₄ as minor crystalline phase. This phase transformation was mainly attributed to the residues containing sodium derived from combustion of GAGs. The particles were near spherical, and the nanocrystalline nature was retained. In the high temperature stage (650–1200°C), the samples were glass ceramic powders composed of HAP, β-tricalcium phosphate, Na₃Ca₆(PO₄)₅, β-NaCaPO₄ and Na–Ca–P–O glass phase. The grains rapidly grew into larger particles with morphology transformation from rodlike shape to irregular shape and the size increase from (0·1–0·15) × (0·3–0·5) μm to 1·5–10 μm.