Crystallization kinetics of the tungsten-tellurite glasses

The crystallization kinetics of the (1 − x)TeO₂-xWO₃ (where x = 0.10, 0.15, and 0.20, in molar ratio) glass system was studied by non-isothermal methods using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. DSC measurements were performed at different heating rates to study crystallization kinetics of the first crystallization reactions of the glasses. XRD analysis of tungsten-tellurite glasses heat-treated above the first crystallization temperatures revealed that the first crystallization peaks attributed to the α-TeO₂ and γ-TeO₂ crystalline phases for 0.90TeO₂-0.10WO₃ and 0.85TeO₂-0.15WO₃ samples and α-TeO₂ and WO₃ crystalline phases for the 0.80TeO₂-0.20WO₃ sample. Avrami constants, n, calculated from Ozawa equation, were found between 1.14 and 1.44. The activation energies, E_A, for the first crystallization reactions were determined by using the modified Kissinger equation as 379 kJ/mol, 288.1 kJ/mol and 228.8 kJ/mol, for 0.90TeO₂-0.10WO₃, 0.85TeO₂-0.15WO₃ and 0.80TeO₂-0.20WO₃ glasses, respectively.