Oriented growth of a β-quartz solid solution from a MgO-Al2O3-SiO2 glass coated by a sol-gel ZrO2 layer

Glass sheets with the mol% composition 22.5MgO center dot 22.5Al(2)O(3)center dot 55SiO(2) were coated with a thin ZrO2 layer on both sides via sol-gel dip coating. The samples were heated in a two-step process to 850 degrees C for 1 h and to 1000 degrees 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 beta-quartz solid solution (beta-QSS) crystallize at, or near, the glass surface. After a growth selection during the first ca. 500 mu m of growth, only a highly oriented beta-QSS layer aligned with the c-axis perpendicular to the initial surface continues to grow into the bulk. The beta-QSS was not observed if the glass was not coated with ZrO2 before annealing. The influence of ZrO2 on the crystallization in this system is discussed.