A study on the phase transformation of the nanosized hydroxyapatite synthesized by hydrolysis using in situ high temperature X-ray diffraction

The biodegradable hydroxyapatite (HA) was synthesized by hydrolysis and characterized using high temperature X-ray diffraction (HT-XRD), differential thermal analysis and thermogravimetry (DTA/TG), and scanning electron microscopy (SEM). The in situ phase transformation of the HA synthesized from CaHPO4 center dot 2H(2)O (DCPD) and CaCO3 with a Ca/P= 1.5 in 2.5 M NaOH(aq) at 75 degrees C for 1 h was investigated by HT-XRD between 25 and 1500 degrees C. The HA was crystallized at 600 degrees C and maintained as the major phase until 1400 degrees C. The HA steadily transformed to the alpha-tricalcium phosphate (alpha-TCP) which became the major phosphate phase at 1500 degrees C. At 700 degrees C, the minor CaO phase appeared and vanished at 1300 degrees C. The Na+ impurity from the hydrolysis process was responsible for the formation of the NaCaPO4 phase, which appeared above 800 degrees C and disappeared at 1200 degrees C. (c) 2005 Elsevier B.V. All rights reserved.