Resumo:
A glass matrix with nominal composition 50Li2O·45B2O3·5Al2O3 (mol%) was synthesized, and its physical properties were investigated by differential thermal analysis (DTA), X-ray diffraction (XRD), and atomic force microscopy (AFM). The glass transition temperature T g, the crystallization-onset temperature T x,, the crystallization peak temperatures T c1 and T c2, and the fusion peak temperatures T m1 and T m2 were determined from at least two glass matrix phases to be approximately 382, 457, 486, 574, 761, and 787 °C, respectively, at 5 °C/min heating rate. Heat treatments at 450 °C for an increasing sequence of time intervals allowed control over the amount of crystallization. Additional information on the crystallization kinetics for the LBA glass matrix was gathered from AFM images, DTA thermograms, and XRD diffractograms. The latter technique showed that LiBO2 (ICDD-16568) and Li3AlB2O6 (ICDD-51754) phases are formed in the glass–ceramic system. Debye–Scherrer analysis of the XRD peaks revealed a competition between the evolutions of crystal phases during heat treatment. Activation energies for crystallization, obtained from theoretical models applied to the DTA data showed that the crystallization is heterogeneous. The AFM images demonstrated that this heterogeneous crystallization starts at the surface of the LBA glass matrix and identified crystal sizes in agreement with the results of the Debye–Scherrer analysis. Our study shows that thermal and structural characterization techniques can be combined with theoretical results drawn from well-tested models to offer a unified view of crystallization in a glass–ceramics system.
