利用熱膨脹儀探討氫氧基磷灰石之熱分解反應與反應動力學

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

郭迦豪(Chia-Hao Kuo)

指導教授 ： 鄧茂華

國立臺灣大學/理學院/地質科學研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.01043

摘要

氫氧基磷灰石(Hydroxyapatite，簡稱HA)為人體骨骼和牙齒的主要成分，因極具生物相容性，故常用於生醫材料領域；係主要為製成骨填補材或與骨組織結合之支架的應用範疇。以高溫製備生醫陶瓷時，氫氧基磷灰石會在升溫的過程中熱分解脫去氫氧基，產生相變化；而相變會使得材料機械強度降低不利於應用。為避免製備過程中有熱分解情形發生，前人便針對脫氫氧基反應及相變反應的溫度範圍研究，但由於氫氧基磷灰石的熱分解產物在常壓下極易受降溫過程中水氣的作用而改變定性分析結果，致使眾人對於熱分解溫度之範圍無一致的答案。為解決前人研究中熱分解溫度不一致之問題，本研究利用熱膨脹儀此種以直接觀察氫氧基磷灰石升溫過程中體積變化之分析手段，配合不同的粉末冷卻方式來進行材料特性之研究和探討，藉以針對氫氧基磷灰石熱分解溫度範圍不一致之情形提出說明與解釋。研究過程輔以XRD與FTIR進行分析，並進一步利用數值模擬與主導動力學曲線(Master Kinetics Curve, MKC)了解氫氧基磷灰石在升溫燒結的過程中脫氫氧基反應及相變反應的溫度範圍與反應動力學。
實驗結果顯示，利用液態氮冷卻的方法可快速降溫且能保留粉末於高溫時的礦物晶相，降溫過程亦不會受水氣作用而改變產物性質；故對於研究氫氧基磷灰石熱分解之材料特性，以液態氮冷卻高溫粉末至室溫再進行後續分析最為適當。XRD結果顯示，1300oC時氫氧基磷灰石開始相變，到1500oC時完全相變化為四鈣磷酸鹽(C4P)以及α-三鈣磷酸鹽(αC3P )。FTIR結果顯示，脫氫氧基反應與相變反應皆不會改變粉末中OH-鍵的存在與否，所以無法藉由FTIR結果界定脫氫氧基反應發生的溫度範圍。
本研究藉熱膨脹儀成功在常壓下界定氫氧基磷灰石之脫氫氧基反應發生的溫度範圍為900oC至1100oC。綜合XRD與熱膨脹儀的結果可知，氫氧基磷灰石的最佳燒結溫度在1300oC以前；如此可得最緻密且無相變發生的樣品。此外，熱膨脹儀1100oC至1500oC的結果顯示，燒結反應與相變反應的溫度範圍有部分重疊，故本研究利用數值模擬方法分離溫度重疊的反應並以主導動力學曲線擬合。主導動力學曲線擬合的結果顯示，數值模擬所得各反應的曲線皆可由MKC擬合，各資料點皆符合擬合曲線，表示利用數值模擬方法分離不同機制的反應是一套有效的分析法。此結果也表示，主導動力學曲線配合數值模擬的分析法可應用於複雜反應機制之擬合。

關鍵字

氫氧基磷灰石；熱膨脹儀；熱分解；主導動力學曲線

並列摘要

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.

並列關鍵字

hydroxyapatite ； dilatometer ； thermal decomposition ； Master Kinetics Curve

參考文獻

[33] 張育維 (2007) “奈米二氧化鈦之視燒結活化能與相變研究”，國立台灣大學碩士論文。

[30] 林書弘 (2007) “蒸發岩礦物熱分解反應動力學之研究方法與應用探討”，國立台灣大學碩士論文。

[29] 王紹宇 (2011) “主導動力學曲線與三種不同動力學模型之比較研究”，國立台灣大學碩士論文。

[2] Y. Fujishiro, L. L. Hench, and H. Oonishi, (1997) “Quantitative rates of in-vivo bone generation for bioglass and hydroxyapatite particles as bone graft substitute” J. Mater. Sci. Mater. Med., 8, 649-651.

[3] K. Soballe, E. S. Hansen, H. B. Rasmussen, C. M. Pedersen, and C. Bunger, (1990) “Hydroxyapatite coating enhances fixation of porous coated implants” Acta Orthop. Scand, 61(4), 299-306.