The non-isochemical crystallization of glasses leads to glass-ceramics in which the chemical composition of the amorphous matrix differs from that of the parent glass. It is challenging to solely analyse the properties of these residual glassy phases because they frequently contain finely dispersed crystals. In this study, the composition of the residual glass matrix after the crystallization of a glass with the mol% composition 50.6 SiO2 · 20.7 MgO · 20.7 Al2O3 · 5.6 ZrO2 · 2.4 Y2O3 is analysed by scanning transmission electron microscopy (STEM) including energy dispersive X-ray analysis (EDXS). A batch of the residual glass with the determined composition is subsequently melted and selected properties are analysed. Furthermore, the crystallization behaviour of this residual glass is studied by X-ray diffraction, scanning electron microscopy including electron backscatter diffraction and STEM-EDXS analyses. The residual glass shows sole surface crystallization of indialite and multiple yttrium silicates while bulk nucleation does not occur. This is in contrast to the crystallization behaviour of the parent glass, in which a predominant bulk nucleation of spinel and ZrO2 is observed. The crystallization of the residual glass probably leads to different crystalline phases when it is in contact to air, rather than when it is enclosed within the microstructure of the parent glass-ceramics.

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Glasses with the mol% composition of 51.9 SiO 2 / 21.2 Al 2 O 3 / 21.2 MgO/ 5.7 ZrO 2 without and with the addition of 2.5 mol% Y 2 O 3 were melted and subsequently transformed into glass-ceramics via annealing. Both glass-ceramics show strong differences in the microstructure and in the phase composition after crystallization at 950 °C for 5 h and subsequently at 1060 °C for different annealing times. In the glass without Y 2 O 3 , the main crystal phase is a quartz solid solution accompanied by the precipitation of ZrO 2 and spinel. By contrast, glass-ceramics without the presence of a quartz solid solution were observed after the crystallization of the Y 2 O 3 -containing glass, using the same heat treatment. This is confirmed by analytical scanning transmission electron microscopy analysis and Xray absorption near-edge structure spectroscopy data gathered at the Zr L 2 -, Y L 2,3 -, Si K-and Al Ledges. Furthermore, using X-ray absorption spectroscopy the coordination of the respective elements is analysed, and changes of the coordination during crystallization are monitored.

Glass sheets with the mol% composition 22.5MgO•22.5Al 2 O 3 •55SiO 2 were coated with a thin ZrO 2 layer on both sides via sol-gel dip coating. The samples were heated in a two-step process to 850 °C for 1 h and to 1000 °C for another 3 or 20 h. X-ray diffraction (XRD), optical microscopy and scanning electron microscopy (SEM), including electron backscatter diffraction (EBSD), were performed to investigate the crystallization of this surface modified glass. Two types of indialite and a β-quartz solid solution (β-QSS) crystallize at, or near, the glass surface. After a growth selection during the first ca. 500 μm of growth, only a highly oriented β-QSS layer aligned with the c-axis perpendicular to the initial surface continues to grow into the bulk. The β-QSS was not observed if the glass was not coated with ZrO 2 before annealing. The influence of ZrO 2 on the crystallization in this system is discussed.