Analytical and HREM study of the early stages of SiO2-Al2O3-(Mg, Zn)O glass crystallisation

The transformation from the amorphous into the crystalline structure at temperatures close to temperature of glass transition of 750 degreesC was investigated in a 47SiO(2)-22Al(2)O(3)-17MgO-2ZnO-12TiO(2) glasses with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). The investigations indicated that heat treatment of this glass results in the formation of rod-like crystals of high-temperature quartz structure. At the early stages of crystallisation, the formation of (Mg, Al) titanates was observed. TEM of glasses heat-treated at 725 degreesC showed nucleation and growth of small dendrite-like precipitates enriched in Ti and depleted in Si. High-resolution transmission electron microscopy (HRTEM) has indicated that the crystallisation is occurring through a local ordering of the atoms in the amorphous glass structure, within areas up to 5 nm. Above 900 degreesC an enstatite (Mg, Zn)SiO3 phase is formed. (C) 2003 Elsevier Science B.V. All rights reserved.