EFFECT OF HYDROTHERMAL TEMPERATURE ON SYNTHESIS OF HYDROXYAPATITE FROM LIMESTONE VIA HYDROTHERMAL METHOD

Objective: In this study, the effect of hydrothermal temperature on the synthesis of hydroxyapatite (HAp) from limestone was investigated.Methods: Precursors of limestone (CaCO3) and diammonium hydrogen phosphate ((NH4)2HPO4) with Ca/P ratio of 1.67 was mixed at pH 10 in order to synthesize hydroxyapatite by hydrothermal method. The solution was hydrothermally treated in an autoclave at various temperatures of 120, 160 and 200 °C for 24 h. Nano powder formed was then characterized.Results: The hydroxyapatite obtained by hydrothermal method at various temperatures was characterized. The analysis of Fourier Transform Infrared (FTIR) revealed that HAp had phosphate (PO43-) and hydroxyl (O-H) groups although carbonate (CO32-) group remained. X-Ray Diffraction (XRD) revealed that the size of nanosize crystals was formed and then provided a large surface area. Scanning Electron Microscopy (SEM) results showed that HAp had a spherical shape. There was more agglomeration at 200 °C than at 160 °C. The ratio of the results of Energy Dispersive X-ray (EDX) analysis in 160 °C was 1.95 and at 200 °C was 1.71Conclusion: The hydroxyapatite prepared at a temperature of 200 °C had smaller crystal size than the hydroxyapatite prepared at the temperatures of 120 and 160 °C. SEM pictures showed that the nanoparticle hydroxyapatite had a spherical shape.