Effect of heating temperature and time of hydrothermal reaction on the synthesis of hydroxyapatite from hen's eggshell

The hydroxyapatite (HA) powder is successfully synthesized from calcined eggshell by the hydrothermal reaction method. The colloidal solution made of calcined eggshell powder, tricalcium phosphate powder, and demineralized water is kept in a closed ceramic vessel to perform hydrothermal reactions. For this purpose, different temperatures (700 - 1000 °C) for various time durations (1, 2, and 3 h) are applied to the solution. X-ray diffraction (XRD) analysis, field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDS) are employed to characterize the prepared powders. The synthesized powders are further assessed in terms of crystalline phase, microstructure, crystallite size, particle size, Ca/P ratio, and crystallinity. In all the reaction products, majorly the HA powders are obtained. The spherical HA grains are found to have a tendency to agglomerate at higher reaction temperatures and times. The applied temperature and heating duration are found to be the crucial parameters that control the properties of the synthesized HA. The HA with the largest crystallite size is obtained from 1000 oC of heating temperature applied for 3 h. However, the HA with high crystallinity is obtained from 800 oC temperature applied for 1 h of time. Non-stoichiometric HAs are obtained from all different reaction temperatures and time durations. Mostly Ca-rich (Ca/P > 1.67) HAs are formed in all powders except the one prepared at 900 ° C, where the formation of Ca-deficient (Ca/P < 1.67) HA is noticed. The near-stoichiometric HA can be produced from 900 oC of reaction temperature applied for 1 h. The study illustrates that HA can be synthesized successfully from chicken eggshell by hydrothermal reaction method in less time by applying high heating temperature.