study on the hydroxyapatite thermal decomposition reaction and reaction kinetics by dilatometer

• Main Authors: Chia-Hao Kuo, 郭迦豪
• Other Authors: Mao-Hua Teng
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/45598619037636210805

碩士 === 國立臺灣大學 === 地質科學研究所 === 103 === Hydroxyapatite (HA) is a natural mineral apatite comprising hydroxyl functional groups in its structure, and is widely used as a bone replacement material because of its substantial bioactivity and biocompatibility. A well-controlled thermal processing procedure is essential to manufacture high-strength HA bioceramics. However, the procedure of the processing involves not only sintering but also thermal decomposition which could lead to the degradation of bioceramics properties. In the process of HA decomposition, as the temperature increasing, there are two reactions: dehydroxylation and phase transformation. It is crucial to examine the temperature range of HA decomposition, since it will further influence the strength and the solubility of the bioceramics. However, previous researched discussing about the HA thermal decomposition temperature range were inconsistent. In the present study, we aimed to use the dilatometer, which can detect the length difference when temperature increases in-situ and continuously, to identify the range of temperature during dehydroxylation to address the contradictory findings in literature. The detected data were then analyzed by numerical simulation method and were fitted by Master Kinetics Curve (MKC), which was developed by our group and has been proved can fit sintering, phase transformation and thermal decomposition. In addition, we used three different methods to cool the heated HA powder, analyzed the powder by XRD and FTIR, and then compared the dilatometer results. We found that the adequate cooling method for studying the thermal decomposition of HA is quenching with liquid nitrogen because it’s rapid cooling and water-free characteristics. The dilatometer results clearly showed that a shrinkage reaction of samples, caused by dehydroxylation, occurred prior to the phase transformation at ca. 900oC to 1100oC. The XRD results showed that the phase transformation of HA began at 1300oC, and fully phase transformed when 1500oC; all of the HA phase in powder transform to tetracalcium phosphate and alpha-tricalcium phosphate. The present study found that the numerical simulation method can successfully distinguish the overlapping reactions and be modeled by the MKC. The MKC fitting results of each reaction implicates that the method could be applied to data fitting for more complex reaction mechanism.