以化學共沉澱法製備碳酸根磷灰石之結構及特性研究

The Study on the Preparation and the Characteristics of Carbonated Apatite from Chemical Co-precipitation Method process

楊勝智(Sheng-Zhi Yang)

指導教授 ： 李源弘

共同指導教授 ： 張火成

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.10048

摘要

在本研究中利用尿素(urea, (NH2)2CO)水溶液在加熱後，尿素會受溫度的影響，而分解成氨氣(NH3)及二氧化碳(CO2)，所產生的氨氣溶於水中，會產生銨根離子(NH4+)和氫氧根離子(OH-)，而二氧化碳溶在水溶液中，會產生碳酸根(CO32-)，氫氧根離子可提供作氫氧基磷灰石的氫氧根來源，並以硝酸鈣(Ca(NO3)2•4H2O)及磷酸氫二銨((NH4)2HPO4)為鈣離子(Ca2+)及磷酸根(PO43-)來源，利用化學共沉澱法所析出之粉末，碳酸根離子可能會取代氫氧基磷灰石結構中的磷酸根離子或氫氧根離子，而製備出碳酸根含量較高之碳酸根磷灰石(carbonated apatite, CAp)。
起始pH值為8所製備的粉末，起始析出物為磷酸八鈣(OCP)，而後逐漸轉變為缺鈣磷灰石(CDA)，未經熟化的粉末在經900度C煅燒處理後，完全轉變為β相磷酸三鈣(β-TCP)。而當熟化時間增長可提高粉末磷灰石相之熱穩性，熟化12小時的粉末經900度C煅燒處理後，粉末之磷灰石相比例提高，但仍有部分轉變為β-TCP，而無法完全呈磷灰石之穩定相。在起始pH值為12所製備的粉末，一開始的析出物為碳酸根含量較少，結晶性較好之氫氧基磷灰石，而在尿素溶液的環境中，因分解產生的碳酸根取代，使氫氧基磷灰石溶解，而碳酸根磷灰石重新成核，使粉末之結晶性下降，而後碳酸根磷灰石之晶核成長，並逐漸提高粉末中的碳酸根含量。在SEM的照片中，在起始條件為pH8時，所製備的粉末，其晶粒形狀為鬚狀或針狀；在起始條件為pH12，其晶粒則為片狀之結構。
而以Rietveld Method 對粉末進行精算，並計算粉末之結晶指標，對結晶化的程度進行量化，可清楚了解粉末之間結晶程度的差別，以未經熟化的粉末之結晶指標最高，而熟化6小時的粉末結晶指標最弱，熟化12小時的粉末則介於兩者之間，當煅燒至600度C時，粉末之結晶指標會因少部分碳酸根被去除而稍稍下降，但在煅燒至900度C時，粉末的結構會由碳酸根取代磷灰石轉變為氫氧基磷灰石，而使結晶指標明顯提高。
在研究的結果中，在起始pH值為12，所製備的粉末，其碳酸根含量為6.03 ~ 8.20 wt.%，且在600度C煅燒後，仍可維持只有少量之碳酸根的損失，結構中之碳酸根較安定，而在起始pH為8下，所製備粉末的碳酸根含量在2.21~4.42 wt.%之間，且在600度C煅燒後，結構中的碳酸根較不穩定，損失超過一半，所以在研究中顯示，在pH 12的條件下可得到較穩定之碳酸根磷灰石。

關鍵字

碳酸根磷灰石 ； 尿素 ； Rietveld Method ； 結晶指標

並列摘要

In this research of carbonated apatite synthesis, urea solution was heated and decomposed into NH3 and CO2 due to the heat. NH3 dissolved in the water produces NH4+ and OH- while CO2 dissolved in the water produce CO32-. After the designated time (NH4)2HPO4 and Ca(NO3)2•4H2O were added to the urea solution in order to provide PO43- and Ca2+.
The research shows that CO32- might be able to replace the PO43- and OH- within the carbonated apatite (CAp, Ca10-x(PO4)6-x(CO3)x+y(OH)2-x-2y) utilizing the chemical co-precipitation method in order to produce CAp with higher percentage of CO32-.
The first precipitates at initial pH8 were octacalcium phosphate(OCP). OCP would gradually transform to calcium-deficient apatite(CDA). After a heat treatment at 900°C, the powder turned into β-TCP. To prolong the aging time can increase the stability of apatite phase. After heat treatment at 900°C, the percentage of apatite phase in the powder has rised with the increasing of aging time. However, some still transformed into β-TCP which shows that the apatite phase can’t be fully stabilized. The educt of the precipitates at initial pH 12, hydroxyapatite (HAp), has less CO32- but better crystallinity. In the urea solution, HAp would gradually dissolved and regenerate into CAp. The crystal of CAp would continue to grow and gradually increase the content of CO32-. In the SEM micrographs, the morphology of the powders prepared at initial pH8 were whisker or needle-like and the powders prepared at pH 12 were plate-like.
Refine the XRD patterns of the powders with Rietveld Method and find out the Crystallinity Index (CI) so as to understand the different crystallinity between the powders. The non-aging powders at initial pH 12 ranked the highest on CI and 6hr-aging powder the lowest. When heated at 600°C, the crystallinity of the powders would slightly decrease due to the removal of some CO32-. Yet when heated at 900°C, CAp would turn into HAp, significantly increasing the crystallinity.
In this study, the powders prepared at initial pH 12 contain more carbonate ions than at initial pH 8. Moreover, the carbonate in the powders prepared at initial pH 12 is more stable than the powders prepared at initial pH 8.

並列關鍵字

carbonated apatite (CAp) ； urea ； Rietveld Method ； Crystallinity Index (CI)

參考文獻

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