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

Thermal and microstructural characterization of the TeO2-WO3 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-xWO(3) 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 degrees 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 degrees 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 degrees C, the endothermic reaction indicating the phase transformation reaction of WO3 from orthorhombic to tetragonal was determined at 743 +/- 1 degrees C. alpha-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. (C) 2011 Elsevier B.V. All rights reserved.