Thermal and microstructural characterization and crystallization kinetic studies in the TeO2−B2O3 system

Thermal, phase and microstructural characterization of the (1−x)TeO2−xB2O3 system, where 0.05 ≤ x ≤ 0.40 in molar ratio, was realized by applying differential thermal analysis, differential scanning calorimetry, X-ray diffraction and scanning electron microscopy/energy dispersive X-ray spectrometer techniques to investigate the glass forming region, phase equilibria, microstructural characterization of the TeO2−B2O3 system and to study the crystallization kinetics of the boro-tellurite glasses. Samples were prepared using a conventional melt quenching technique at 750 °C. Glass forming range of the system was determined as 5–25 mol% B2O3 and thermal behavior of the glasses were examined by running thermal analysis. In order to obtain the thermal equilibrium, as-cast samples were heat-treated above all crystallization reaction temperatures at 520 °C and the phase equilibria investigations were realized with the heat-treated samples. Monotectic reaction of the binary system: liquid1 → liquid2 + TeO2, was detected at 666 ± 2 °C. A stable phase separation region where the samples show two different phases, white colored opaque and light yellow transparent, was investigated in terms of the phase equilibria and the morphology. Non-isothermal investigation of crystallization kinetics of the boro-tellurite glasses were realized in terms of the crystallization mechanism and the activation energy by using the Ozawa and the modified Kissinger techniques, respectively. The activation energy of the crystallization reaction was calculated as around 300 kJ mol−1.