Effects of parameters of sol–gel process on the phase evolution of sol–gel-derived hydroxyapatite

It has been established that hydroxyapatite powders can be produced using an alkoxide-based sol–gel technique. Nanocrystalline powders of hydroxyapatite (HA) were prepared from Ca(NO3)2·4H2O and PO(OC2H5)3 as calcium and phosphorus precursors, respectively, using a sol–gel route. For a number of samples, sol of phosphorus was first hydrolyzed for 24 h with distilled water. The sol temperature, aging time and heat treatment temperature on apatite formation were systematically studied. Increasing the aging time affected the reducing of CaO. Also, increasing the mixed sol solution temperature up to 80 °C had a positive effect on the disappearance of impurity phases. With the increase of the calcination temperature >600 °C, calcium phosphate impurity phases disappeared. Structural evolution during the synthesis of hydroxyapatite is investigated by using infrared (IR) analysis, X-ray diffraction (XRD), thermal behavior (DTA), and elemental analysis of electron microscopy examination (SEM). X-ray diffraction with the aid of Scherrer and Williamson–Hall equations has been used to characterize the distributions of crystallite size and micro-strain of HA powders .The results indicated that mean crystallite size increased and micro-strain decreased significantly with the rise in firing temperature.