Glass samples of stoichiometric cordierite composition, increasingly doped with TiO2 as nucleating agent, were ceramized up to 1300°C and analysed to highlight differences in their crystalline evolution. Employed analytical methods included (HT)-XRD, DSC, Raman spectroscopy and SEM. The specimens displayed a gradual transition to effective bulk crystallization with increasing TiO2-doping, manifested by earlier and sharper formation of HQss. 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 Miyashiro's index[1] and Raman splitting at various temperatures: remarkable differences in ordering were spotted between surface and bulk of the samples, again hypothesized to be connected to the stability of Ti-bearing phases.

References:

[1] A. Miyashiro, Cordierite-indialite relations, J. Am. Sci. 255 (1954) 43-62