Temporal Evolution of Crystallization in MgO鈥揂l2O3鈥揝iO2鈥揨rO2 Glass Ceramics

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• 作者：Christian Patzig ; Thomas H枚che ; Marc Dittmer ; Christian R眉ssel
• 刊名：Crystal Growth & Design
• 出版年：2012
• 出版时间：April 4, 2012
• 年：2012
• 卷：12
• 期：4
• 页码：2059-2067
• 全文大小：498K
• 年卷期：v.12,no.4(April 4, 2012)
• ISSN：1528-7505

文摘

From glasses with the composition 51.9 SiO₂路21.2 MgO路21.2 Al₂O₃路5.7 ZrO₂ (in mol %), high and low-quartz solid solution glass ceramics were formed upon heat treatment at 950 掳C for different dwell times. A combination of X-ray diffractometry, transmission electron microscopy, and scanning transmission electron microscopy with annular dark field imaging and energy-dispersive X-ray analysis revealed the temporal evolution of the volume crystallization. It is found that the crystallization of high-quartz solid solution is nucleated either directly at star-shaped ZrO₂ crystallites or within a zone of Zr-depleted glass surrounding the latter and proceeds isotropically into the sample volume, thereby expelling secondary, circular ZrO₂ precipitates. With advancing annealing time, the quartz solid solution is depleted in Mg and Al since indialite (Mg₂Al₄Si₅O₁₈) and spinel (MgAl₂O₄) are formed as well, thus enabling a change from high-quartz solid solution to the low-quartz modification while sample cooling. Upon analyses of samples heat treated for different soaking times, different states of crystallization were observed. Using electron diffraction and nanoanalytical techniques, a growth model with special emphasis on the early stages of volume crystallization was developed.