Microwave accelerated synthesis of nanosized calcium deficient hydroxyapatite

Abstract

Rapid synthesis of calcium deficient hydroxyapatite (CDHA, Ca_10−x(HPO₄) _x (PO₄)_6−x(OH)_2−x) with Ca/P ratio 1.5 was done by precipitation using calcium nitrate tetra-hydrate and phosphoric acid and subsequently subjecting to microwave irradiation in a domestic microwave oven for 15 min. Transmission electron microscopy analysis shows needle like morphology of CDHA having length 16–39 nm and width 7–16 nm. The synthesized CDHA has the characteristic HPO²⁻₄ vibration band at 875 cm⁻¹ in Fourier transform infrared (FT-IR) spectra. The X-ray powder diffraction (XRD) analysis shows a pattern corresponding to stoichiometric hydroxyapatite (HA) with broad peaks suggesting that CDHA particles were nanosized. Fourier transform Raman spectroscopy (FT-Raman) do not indicate any fluorescence band that is characteristic of non-stoichiometric HA. The thermal decomposition of CDHA to beta tricalcium phosphate (β-TCP) was also studied for the additional confirmation. The nanosized CDHA was found to be stable up to 600°C.