Synthesis of hydroxyapatite via phase transformation of calcium hydrogen phosphate dihydrate: Effects of temperature variation on phase and morphology

Abstract In this study, hydroxyapatite (HA) was synthesized via dissolution-precipitation reaction of calcium hydrogen phosphate dihydrate (CaHPO4·2H2O; DCPD) and calcium hydroxide (Ca(OH)2) by hydrothermal process in distilled water. The hydrothermal treatment temperatures were varied (100, 150 and 200 °C) and the effects of this variation on the formation of HA phase and its morphology were investigated. The transformation rate for DCPD to HA was evaluated using X-ray diffraction (XRD) analysis. The morphology of the synthesized HA was observed using field emission electron microscope (FESEM) and transmission electron microscope (TEM). The elemental compositions were analysed by energy dispersive X-ray spectroscopy (EDS). Observation show that different morphologies of HA were obtained with different hydrothermal treatment temperatures. HA nanorods were obtained at lower temperatures (100 and 150 °C) while hexagonal and nanospherical shapes were formed at a higher temperature (200 °C). The crystallinity of HA obtained at the different temperatures were in the range of 50–57% which is similar to the crystallinity of bone minerals (51–57%). It was observed that lower hydrothermal treatment temperatures (150 and 100 °C) yielded nanorod shaped HA with crystallite size of 40–60 nm length and 20 nm diameter which is suitable for clinical applications.