溶膠凝膠法製備的鋰鋁矽玻璃陶瓷之成核及結晶行為

Abstract

溶膠 – 凝膠法製備的鋰鋁矽玻璃陶瓷之成核及結晶行為 研究生:林世銘 指導教授:林健正博士 國立交通大學 材料科學與工程學系 摘要 本研究利用Sol-Gel之化學方法製備Li2O-Al2O3-7SiO2系玻璃陶瓷。為了探討成核劑對其成核 - 結晶過程之影響，分別添加6 wt%之TiO2或ZrO2之成核劑於Li2O-Al2O3-7SiO2 系統內。首先透過Sol-Gel之方法製備高純度、高均質性及超細的非晶相粉末，經由非恆溫熱分析方法（non-isothermal Thermal Analysis），探討晶體成長動力學參數，得知沒有添加成核劑之鋰鋁矽（LAS）系統之凝膠粉末的結晶活化能約為410 kJ/mol，而添加TiO2（LAST）、與ZrO2（LASZ）系統之結晶活化能則分別約為290 kJ/mol以及240 kJ/mol。此外，本研究亦將凝膠粉末經1500℃/16 hr高溫融熔淬火後形成玻璃體，經由玻璃體之熱分析結果得知，添加TiO2（GLAST）系統之玻璃粉體，與添加ZrO2（LASZ）系統之玻璃粉體的結晶活化能分別約為270 kJ/mol、153 kJ/mol.。經由以上分析結果可以得知ZrO2 的添加比TiO2更能夠有效的降低其結晶活化能而促進其結晶。再者，LAS、LAST之凝膠粉體與GLAST玻璃粉體的Avrami常數n約為3，而LASZ凝膠粉體與GLASZ玻璃粉體的Avrami常數n則約為4，當n值介於3~4時，顯示上述系統的成核機制傾向於整體成核（volume nucleation），晶核之分佈量均勻且多。本研究同時亦針對GLAST、與GLASZ兩組玻璃粉末之成核速率進行研究，實驗過程中之理論基礎乃是分別引用Marotta等人以及Ray等人所提出之二組不同的成核理論模型，藉由非恆溫之熱分析法 ( non-isothermal Thermal Analysis ) 以Marotta等人所提出之成核理論模型所求得之最大成核速率分別約為2.15×1011/sec×mol(GLAST試片)及6.7×104/sec×mol(GLASZ試片)，而利用Ray等人所提出之成核理論模型所求得的最大成核速率則約為6.7×1025/sec×m3(GLAST試片)，且其產生最大成核速率之溫度分別約為780℃以及770℃。以XRD鑑定經過不同溫度結晶熱處理之試片，獲知1000℃以下之主要晶相為virgilite，其晶體結構為六方晶系之結構（hexagonal）；1000℃以上之主要晶相則為正方晶系（tetragonal）之β-Spodumene固溶體，此晶相具有極低的熱膨脹係數，其熱膨脹係數可藉由TMA之分析取得。而本研究之GLAST與GLASZ玻璃體的熱膨脹係數範圍，經分析均約為10-7/K之數量級。最後利用二段式之熱處理（成核 - 結晶）方式，以SEM直接觀察玻璃體中晶粒成長之情形。藉由適當熱處理的試片原本非晶質的玻璃態可以轉變成為高結晶度型態的微晶陶瓷，且其晶相亦由低溫的介穩相 Virgilite 逐漸的轉變成為高溫的穩定相β-Spodumene。

THE PREPARATION AND NUCLEATION – CRYSTALLIZATION OF LITHIUM ALUMINOSILICATE GLASS – CERAMIC POWDERS BY SOL – GEL PROCESS Student: Shin Min Lin Advisor: Dr. Chien C Lin Institute of Material Science and Engineering National Chiao Tung University ABSTRACT Glass – ceramic powders with a composition of Li2O – Al2O3 – 7SiO2 (LAS) have been synthesized by sol – gel technique using metal alkoxide as starting materials. The effects of TiO2 and ZrO2 dopants on the crystallization and nucleation in LAS glass – ceramic were studied by non – isothermal DTA. The activation energies of crystallization obtained for LAS gel powders and gel powders doped with TiO2 or ZrO2 are 410 , 290 and 240 KJ/mol , respectively. In addition to, the activation energies of crystallization are 270 and 153 KJ/mol for glasses with 6wt% TiO2 and ZrO2 . By the DTA analysis, show that additives ZrO2 , the activation energy of crystallization shifts to lower than additives TiO2 . The results indicate that the LAS system containing ZrO2 promotes to crystallized more efficiently than doped TiO2 . The Avrami index (n) of the LAS specimen without nucleating agent and the LAS specimen with TiO2 are 3. The Avrami index of the LAS specimen containing ZrO2 is 4. It indicates that the mechanism of volume crystallization is predominant when the Avrami index is between 3 and 4. The variation of nucleation rate with temperature has been investigated by non – isothermal thermal analysis. The maximum nucleation rate occured at 780℃ for the LAS system containing TiO2 is 2.15╳1011 / (Sec╳mol) . The maximum nucleation rate occured at 770℃ for the LAS system containing ZrO2 is 6.7╳104 / (Sec╳mol) . The crystall phase of LAS glass – ceramics was investigated by XRD. Two crystallize phase were found after heat treatment at various temperature. The main phase was Virgilite below 1000℃ and β – Spodumene above 1000℃. The thermal expansion coefficient of the LAS system is very low or near zero (10-7/K). Finally, we can controll nucleation and crystallization of glasses specimen by two step heat treatment process. The grain growth of LAS glasses containing TiO2 or ZrO2 was observed by scanning electron microscope (SEM) of cross – sections produced from bulk samples. The phase transformation is from metastable phase Virgilite to stable phase β– Spodumene.