負熱膨脹性鋰鋁矽酸鹽玻璃陶瓷

Negative Thermal Expansion Lithium Aluminosilicate Glass-Ceramics

陳奕君(Yi-Chun Chen)

指導教授 ： 徐錦志

大同大學/工程學院/材料工程學系所/碩士(2006年)

摘要

自然界中材料幾乎為熱脹冷縮的特性。目前越高科技化的精密元件，越希冀其不受溫度的影響而改變尺寸，造成自身性質變化。在鋰鋁矽酸鹽(lithium aluminosilicate，Li2O-Al2O3-SiO2，簡稱LAS)系統中的固溶體β–eucryptite相具有負熱膨脹係數，其與正膨脹性的精密元件複合，可藉由應力補償，控制該元件的尺寸變化，以防性質變異。
　　本研究是以在LAS系統中，可形成具負熱膨脹性玻璃陶瓷的成分為基礎，探討SiO2比例、成核劑種類與過量Li2O對熱膨脹性之影響。研究中發現Li2O:Al2O3:SiO2莫耳比為1:1:2可獲得較明顯的負膨脹性，而成核劑(TiO2 /及ZrO2)若添加超過3-4mole %則將使整體膨脹係數往正值發展；在有無添加微過量Li2O方面，在相同熱處理條件下，隨著Li2O增加，可獲得較小之晶粒徑，但若超過一定量則可能會有正熱膨脹結晶相出現。
　　因鋰鋁矽酸鹽負熱膨脹係數玻璃陶瓷中之玻璃母相與β–eucryptite相之熱失配效應過大，導致基材於升降溫過程結構改變，所引發的熱遲滯現象十分顯著，其間接影響熱補償元件應用壽命，故本實驗另一研究為觀察此基材中遲滯現象的變化。

關鍵字

玻璃陶瓷 ； β-鋰霞石 ； 負熱膨脹 ； 磁滯現象

並列摘要

Most materials have positive thermal expansion (PCTE) .β-eucryptite (Li2O．Al2O3．2SiO2) solid solutions have negative coefficients of thermal expansion (NCTE) ,which can be coupled with PCTE components to reduce the variation of temperature coefficients of the components.The main objective of this thesis is to investigate the formation and properties of negative thermal expansion glass-ceramics containing β-eucryptite. The effects of composition modification (SiO2 content, the kinds and amount of nucleation agents, excess Li2O) on CTE were also examined. According to the experimental results, the glass-ceramics with molar compositions of Li2O．Al2O3．nSiO2 (n=2~3) have more negative CTEs when n~2. When the glass-ceramics containing more than 3-4 mole % TiO2 and/or ZrO2 , the CTE values turned to be positive . When excess Li2O was added to the glass-ceramics of n~2 , crystal size can be reduced. Further increase the Li2O content (to about 4 mole %) could result in the precipitation of positive thermal expansion crystalline phase.
Because of strong thermal expansion mismatch between the glass matrix and β-eucryptite phase in NEGC, the micro structure of the glass - ceramics changed (e.g. formation of microcracks) with the variation of temperature environmental,resulting in thermal hysteresis.

並列關鍵字

glass-ceramics ； β-eucryptite ； the negative thermal expansion ； hysteresis

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