Pii: S0142-9612(99)00076-9

In this paper, the decomposition and reconstruction behavior of hydroxyapatite (HAP) during heating and cooling in air atmosphere were studied. The commercial HAP were chosen and gradually heated to 15003C and cooled to room temperature by a program controlled SiC heated furnace. X-ray di!raction (XRD) and Fourier-transformed infrared (FTIR) analysis were used to investigate the change of crystalline phases and functional groups of HAP at di!erent temperatures. Weight change of samples was recorded by thermogravimetric analysis (TGA) during heating and cooling. The results revealed that HAP gradually releases its OH~ ions and transforms into OHAP in the temperature of 1000}13603C. Above 13603C, the OHAP would decompose into TTCP and aTCP phase. The OH~ stretching bands of HAP could be traced by FTIR even at the temperature of 13503C which indicates HAP decomposition. HAP does not dehydrate completely before decomposition. We speculated that some oxyapatite (OAP) might be formed during dehydration with a great amount of OHAP still left in the system even up to the temperature of decomposition. In the temperature range of 1400}15003C, there was no signi"cant di!erence in XRD patterns, only TTCP and aTCP crystalline phases were observed. When the HAP gradually cools from 15003C, a part of TTCP and aTCP would directly reconstruct into OAP around 13503C. OAP existed in the temperature range of 1350}13003C during cooling. When the temperature decreased to 12903C, a part of TTCP and aTCP reconstructed into OHAP by rehydration reaction and OAP were rehydrated into OHAP as well. At 11003C, the rest of TTCP and aTCP reconstitutes into HAP. As the temperature decreases, the OHAP is gradually rehydrated and reconstituted into HAP. ( 1999 Elsevier Science Ltd. All rights reserved.