利用熱膨脹儀與兩階段燒結法探討氫氧基磷灰石相變溫度範圍及反應動力學

Study on the temperature range and reaction kinetics of phase transformation of hydroxyapatite using a dilatometer and two-step sintering technique

劉羽珊(Yu-Shan Liu)

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(2018年)

https://doi.org/10.6342/NTU201804023

摘要

氫氧基磷灰石(Hydroxyapatite, Ca10(PO4)6(OH)2, HA)是人體骨骼、牙齒琺瑯質和象牙質中的主要無機組成，可以用來製備生醫材料，過程中常需要經過加熱處理。氫氧基磷灰石隨著溫度的上升會發生三種反應，分別是熱分解、燒結與相變，而其中的相變往往會使由氫氧基磷灰石粉末製備的生醫陶瓷材料的機械性能降低，所以很多學者針對氫氧基磷灰石的相變反應進行溫度範圍研究，然結果皆不一致。
前人多利用X光粉末繞射、傅立葉轉換紅外光譜、拉曼光譜、熱重與差熱分析研究晶格、分子與晶相的定性和定量分析、質量隨溫度的變化以及特定溫度條件下的能量變化情形。本研究利用熱膨脹儀來進行氫氧基磷灰石坯體在升溫過程中隨時及連續的長度變化，換算成體積變化，發現隨著溫度的上升，有兩個主要的收縮反應(熱分解、燒結)，再配合數值模擬方法分離出一個膨脹反應(相變)，但這三種體積變化反應有相當大的溫度重疊範圍。所以，本研究希望藉由兩階段燒結法使燒結反應提前完成，在較低溫將坯體燒結到緻密，以期之後繼續升溫時能測得單獨的相變反應體積變化。
本研究設計以兩階段燒結歷程嘗試解決數據重疊問題，希望能將燒結反應與相變反應之溫度重合部分加以分離。實驗結果為利用升溫速率30℃/min升溫至1170℃持溫5分鐘，再以50℃/min降溫至1120℃持溫6小時，測得坯體之相對密度達99%，並由XRD結果確定在1200℃以下可得到未相變之緻密樣品，後續再利用此方法進行高溫相變反應的實驗。接續上述實驗步驟獲得緻密坯體後，以每分鐘20℃和30℃升溫至1500℃持溫1小時的過程中，測得此緻密坯體有再收縮反應，推測與殘餘孔隙的移除、氫氧基的再結合或是高升溫速率造成的儀器偵測延遲有關。而1400℃後才發生膨脹反應也許是因為緻密坯體要發生相變需要克服坯體中的應力，導致坯體由外向內發生多期次的小規模膨脹。目前比較升溫至1200℃之傳統燒結與兩階段燒結實驗的主導動力學曲線(Master Kinetics Curve, MKC)擬合結果，其視活化能值分別為870.6 kJ/mol及1615 kJ/mol，具有較高初始壓坯密度的兩階段燒結實驗樣本，除了具有較高的視活化能值，LogΘ值也向較小的方向平移，意味著可以較快地達到緻密化。

關鍵字

氫氧基磷灰石 ； 熱膨脹儀 ； 兩階段燒結法 ； 主導動力學曲線

並列摘要

Hydroxyapatite (Ca10(PO4)6(OH)2, HA) under increasing temperature involves two shrinkage reactions, i.e., dehydroxylation and sintering, and one expansion reaction due to phase transformation. The temperature range of the above three reactions, though obviously overlapping, were found contradictory in literature. In this study, we use a dilatometer, which can detect the length variations of a sample in-situ with increasing temperature continuously, to identify the temperature ranges of the three reactions of HA. Among the three reactions, the volume change of sintering, which occurs between the other two reactions, is particularly difficult to separate out.
Here we use a two-step sintering (TSS) technique and try to solve above problem. In the TSS process, the HA samples were fully dense with relative densities over 99% and with no phase transformation before 1200℃. The obtained samples with phase transformation reactions after 1400℃. Furthermore, the Master Kinetics Curve (MKC) results for thermal decomposition reactions (from 700℃ to 1200℃) using conventional sintering (CS) and two-step sintering (TSS) technique, show the apparent activation energy of 870.6 kJ/mol and 1615 kJ/mol, respectively. In TSS Master Kinetics Curve (MKC) results, the curve is shifted to the left relative to CS, which means less sintering time to complete densification with high green density.
Several expansion reaction maybe the densification of samples are too much over, which cause residual stress had to be variant from outside to inside and the phase change also occur, and the other reason is due to the fast heating rate cause the delay of instrument detection.

並列關鍵字

hydroxyapatite ； dilatometer ； two-step sintering ； Master Kinetics Curve

參考文獻

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