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URN etd-0831106-125156 Statistics This thesis had been viewed 3597 times. Download 2633 times. Author Yi-Chun Chen Author's Email Address No Public. Department Materials Engineering Year 2005 Semester 2 Degree Master Type of Document Master's Thesis Language zh-TW.Big5 Chinese Page Count 90 Title Negative Thermal Expansion Lithium Aluminosilicate Glass-Ceramics Keyword hysteresis the negative thermal expansion β-eucryptite glass-ceramics glass-ceramics β-eucryptite the negative thermal expansion hysteresis Abstract 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.
Advisor Committee Prof. Jiin-Jyh Shyu - advisor
Yuan-Chei Ding - co-chair
Yung-Jen Lin - co-chair
Files Date of Defense 2006-07-17 Date of Submission 2006-08-31