Oriented crystallization of a β-Quartz Solid Solution from a MgO/Al2O3/SiO2 glass in contact with tetragonal ZrO2 ceramics
Model experiments concerning the nucleation of MgO/Al2O3/SiO2 glass are reported. A glass with the composition 22.5MgO·22.5Al2O3·55SiO2 (in mol%) is brought into contact with ceramic samples of tetragonal ZrO2 at a temperature of 1500 °C. This leads to a heavy corrosion of the ceramics and the diffusion of zirconia into the glass. Subsequent thermal treatments at 820/850 °C and 1050 °C provoke the formation of different phases at the glass/ceramic interface: monoclinic and tetragonal ZrO2, β-quartz solid solution (β-QSS), and spinel. At some distance from the ceramics, the only detected crystalline phase is the highly oriented β-QSS. Only mullite is observed at the air/glass interface where it also grows into the bulk. A sample directly crystallized at 1050 °C shows a very different behavior and only mullite is formed at both the air/glass as well as the glass/ceramic interface. The thermal treatment at the nucleation temperatures of 820/850 °C is thus essential for the precipitation of zirconia and β-QSS in the glass. X-ray diffraction, high resolution (scanning) transmission electron microscopy, and scanning electron microscopy including electron backscatter diffraction are performed to elucidate the underlying mechanisms.