Study on Metakaolin-Based Geopolymer and Its Use on Joining Alumina

陶瓷材料的接合長久以來一直是具有挑戰性的研究主題。本研究的主要目的是探討以偏高嶺土基無機聚合物對氧化鋁基板之接合。 無機聚合物具有在接合過程中為液相又能在固化後強硬的特殊條件。本研究中使用氫氧化鈉強鹼溶液活化合成無機聚合物的分解與聚合等化學反應。鈉含量對於無機聚合物整體的性質有極大的影響，因此本研究中設計合成數種不同鈉含量之無機聚合物進行比較。同時，對於接合完成之三層試片進行微結構與機械性質等之量測。 結果顯示過量的鈉會散佈並插入在無機聚合物的結構中，使其不易形成交連架狀結構，進而使聚合度下降。如抗壓強度試驗的結果顯示鈉含量為10.7%的試樣強度明顯減弱。而紅外線光譜的分析結果也顯示聚合度會隨著鈉含量上升而降低。除此之外，由於鈉在高溫下易揮發，因此高鈉含量的試樣在加熱時會有較大的重損甚至產生形變。隨著溫度增加至攝氏700 度以上，原本非晶質的無機聚合物會相變為結晶的霞石。 而針對氧化鋁基板接合的三層試片，透過微結構與成分分析，顯示界面處有氧化鈉的生成，此氧化鈉層做為仲介層提升了氧化鋁與無機聚合物之間的界面強度。此外，四點彎曲試驗的結果也指出界面強度與鈉含量呈現正相關。熱導率的測量結果則顯示填入無機聚合物能夠有效降低氧化鋁基板之間的熱傳導。The joining of ceramic materials is a challenging issue. The primary purpose of the present study explores the use of metakaolin-based geopolymers to bond alumina substrates. The geopolymer mortar is in liquid form before bonding. A strong structure is achieved after curing. In the present study, sodium hydroxide is able to activate the reactions in geopolymer. The sodium content is a critical factor for geopolymers; the sodium content in the geopolymer in the present study is varied. The resulting microstructure and mechanical properties of the Al2O3/geopolymer/Al2O3 joined specimens are measured. The results demonstrate that excess sodium ions locate in the interstices of the structure, making it difficult to form a cross-linked frame, thus reduces the degree of polymerization. Compressive strength test shows a decrease for the specimens with the sodium content of 10.7%. The FTIR analysis indicates that the degree of polymerization is decreased as more sodium is introduced. Moreover, because sodium is relatively volatile, the specimens with high sodium content suffered a severe weight loss and deformation. As the temperature is raised to 700°C, amorphous geopolymer transforms to crystalline nepheline. After examined the microstructure and composition of the trilayer specimens, a sodium oxide layer was found at the interface. This interlayer enhances the adhesion strength between geopolymer and alumina substrate. The steady-state energy release rate measured from the four-point bending test also exhibited a positive correlation with the sodium content. A low thermal conductivity was observed for the trilayer specimens