, Because of opacity, micron-size crystals may also be present on region B. They are not observed on TEM analysis by virtue of the high magnification applied. In an attempt to observe such crystals, the GC sample nucleated at 1073 K for 2880 min (2 days) and with growth treatment at 1243 K for 6h, Fig. 5.53 a), after a 5s-chemical etching with HF 5.3vol% was observed in an optical microscope, Comparing TEM images from regions A and B of the GC sample presented on fig. 5.53 b)

, the scientific standpoint, the system under study was unable to yield a colorless transparent glass-ceramic. The role of TiO2 is fundamental in the bulk crystallization of glass-ceramics of this MAS system

, TiO2 (formulation 75-25/25Ti) was necessary to trigger internal nucleation in the glass. Even so

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