Chemical gradients at the surface of TiO2-doped cordierite glass-ceramics

After crystallizing monolithic cordierite glass samples nucleated by TiO2, ToF-SIMS, GI-XRD and Raman spectroscopic measurements were performed on their surface. Compositional gradients (Mg and Al depletion, Si and Ti enrichment) and a different crystalline assemblage from the one in the interior were identified. The Al-Si ordering process during the indialite-cordierite phase transition appeared moreover to proceed slower on the surface. These differences were absent in the TiO2 -free reference sample; they were therefore related to the role of TiO2 as a nucleating agent and to the resulting crystallization sequence. In addition, similar effects were observed in powders of the same composition as the monoliths.