Crystallization and SiAl ordering in cordierite glass-ceramics

Glass samples of cordierite composition Mg2Al4Si5O18, increasingly doped with TiO2 as nucleating agent, were ceramized up to 1300 °C and analyzed to highlight differences in their crystalline evolution. Employed analytical methods included HT-XRD, DSC and Raman spectroscopy. Glass-ceramics displayed a gradual transition to effective bulk crystallization with increasing TiO2-doping, manifested by earlier and sharper formation of MgO-Al2O3-SiO2 solid solutions of high-quartz structure. The further phase transformation into indialite equally appeared to be influenced by TiO2-content and to be closely related to the compositional and structural evolution of the seed formers, Mg-Al-titanate and rutile. Furthermore, the indialite-cordierite ordering process was investigated by computation of the ordering index at various temperatures from XRD and Raman, again revealing marked differences between TiO2-free and TiO2-bearing compositions.