Control of crystallization kinetics and study of the thermal, structural and morphological properties of an Li₂O-B₂O₃-Al₂O₃ vitreous system

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 Li₃AIB₂O₆ (ICDD- 51754) phases are formed in the glass-ceramic system. Debye-Schemer 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-Schemer 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. (author)