硫酸鈣的裂縫癒合與強度恢復機理探討

Abstract

裂縫在陶瓷材料的機械性表現中一直扮演很重要的角色，裂縫出現會顯著地影響陶瓷材料之壽命及機械行為。當裂縫生成後會成長並穿透整個材料，最終導致材料之破壞。已經有許多研究提出不同的方法來解決裂縫衍生之問題，在這些方法之中，裂縫癒合是其中最能夠有效使材料強度恢復的方法之一。 硫酸鈣做為臨床上使用的醫療材料已有長遠之歷史，其擁有極佳之生物相容性及生物降解性，並能被人體完全吸收。硫酸鈣在被人體完全降解之前會轉變為磷酸鈣鹽類，而這種磷酸鈣鹽類通常伴隨著緻密的片狀結構，這種能產生緻密結構的相轉變創造了可以實施癒合裂縫的機會。在這份研究中，硫酸鈣被作為原始材料並析出磷酸鈣鹽類來達到裂縫癒合之效果。 實驗結果顯示，只要有磷酸根離子參與反應，緻密的析出物就會產生。隨著添加不同濃度的磷酸根溶液，硫酸鈣試樣之強度也隨之上升。當額外的鈣離子及磷酸根離子被添加時，試樣之機械強度也隨之恢復，並可達到本來強度的百分之六十。試樣的表面形貌及微結構及裂縫之長度均使用電子顯微鏡進行觀測，結果顯示裂縫之長度隨著實驗的製程進行逐漸降低，緻密析出物也確實幫助縮短裂縫長度。析出物的相鑑定是由X光繞射分析儀進行，結果顯示析出物應為磷酸氫鈣以及氫氧基磷灰石之混和物，而隨著磷酸根之濃度上升，氫氧基磷灰石也更傾向產生。在比較了撓曲強度以及裂縫長度之關係後，結果顯示兩者為負相關，而且裂縫癒合之機制能夠同時使用微觀及巨觀之角度解釋。

Crack has played an important role on the performance of ceramics. The presence of crack would significantly affect the mechanical behavior and life duration of ceramics. After its initiation, crack would propagate through the whole material. It may lead to failure in the end. Many studies proposed various treatments to solve the problems associated with crack. Among these treatments, crack healing is one of the most efficient methods to recover the strength. Calcium sulfate (CaSO4, CS) has been used for clinical application for a long time. It exhibits high biocompatibility and degradability. Calcium sulfate can be resorbed within human body, it would transform into calcium phosphate in human body before complete degradation. The calcium phosphate products are usually in the form of dense structure. The formation of calcium phosphate precipitates may induce chance to fulfill crack healing. In the present study, the precipitation of calcium phosphate is used to heal the cracks within calcium sulfate. The result showed that dense structure would be formed as long as the phosphate ions are involved. By adding solution with various phosphate ion concentration into calcium sulfate specimens, the extent of strength recovery is evaluated. It showed that the strength of specimen is recovered partly with the addition of phosphate and calcium ions. The strength recovery can reach 60% of the original value. The microstructure observations are conducted by SEM. Both morphology and crack length are observed. It showed that crack length was decreased with the treatment; furthermore, the precipitation did shorten the crack length. XRD phase identification was also conducted. The phase analysis indicates that the product of precipitation may be a mixture of different calcium phosphate. It also showed that hydroxyapatite tends to form with the increase of phosphate ion concentration. After comparing the results of flexural strength and crack length, the crack length vs strength chart was proposed. The result showed that crack length and strength are negatively relative to each other. And the mechanism of strength recovery can be explained in terms of both microscale and macroscale.