Preparation, characterization, and thermal transformation of poorly crystalline sodium- and carbonate-substituted calcium phosphate

In this paper, we propose a new approach for the preparation of sodium- and carbonate-substituted apatite by a wet precipitation method in aqueous media at 23 °C. The main difference between this method and conventional techniques is that poorly crystalline calcium phosphates are obtained and then heated to form crystalline apatite. The thermal transformations of the samples in the temperature range 80-1000 °C have been determined by temperature-programmed desorption mass spectroscopy and thermogravimetry. The chemical and phase compositions of the sodium- and carbonate-substituted apatite have been studied by inductively coupled plasma (ICP) atomic emission spectroscopy or atomic absorption spectroscopy and X-ray diffraction, respectively. The degree and nature of the carbonate substitution have been determined by CHN analysis and IR spectroscopy, respectively. The samples were subjected to γ irradiation, and the formed radicals were studied by electron paramagnetic resonance (EPR) spectroscopy. SEM has shown nanoparticles (6-12 nm in diameter) with a stability to aggregation under heating to 500-550 °C (increase in size by 30-50 %).