Investigation on thermal and microstructural characterization of the TeO₂-WO₃ system

Thermal and microstructural characterization of the TeO₂-WO ₃ binary system was accomplished by applying differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Different compositions of the (1 - x)TeO₂-xWO₃ system, where x varies between 0.02 and 0.80 in molar ratio were studied. The samples were prepared by melting high purity powder mixtures of TeO₂ and WO₃ in a platinum crucible with a closed lid at 750 °C for 30 min and quenching in water bath. The glass forming range of the binary system was detected as 0.04 ≤ x ≤ 0.35 in molar ratio. As-cast samples were heat-treated above the crystallization peak temperatures at 550 °C for 24 h to obtain thermal stability and the phase stability of the binary system was investigated by performing systematical thermal, phase and microstructural characterizations with the heat-treated samples. The eutectic reaction of the binary system was detected at 617 ± 3 °C, the endothermic reaction indicating the phase transformation reaction of WO₃ from orthorhombic to tetragonal was determined at 743 ± 1 °C. α-TeO₂ and orthorhombic WO₃ crystalline phases were found to be present in the final structure when the total crystallization was achieved. Microstructural characterization of the TeO₂-WO₃ system was realized for a wide compositional range for the first time in the literature.