Oxidation Properties of W–5% Re and W–26% Re Tungsten–Rhenium Thermocouple Wires

Herein, the oxidation properties, i.e., oxidation processes in air, oxidation-product composition, and oxide-film growth, of tungsten–rhenium thermocouple wires were investigated via differential scanning calorimetry (DSC), thermogravimetry (TG), X-ray diffraction (XRD), and scanning electron microscopy (SEM). A tungsten–rhenium thermocouple was protected against oxidation using solidification technology, and the cross sections of the thermocouple wires were observed via SEM. The results showed that the oxidation-initiation temperatures for the W–26% Re and W–5% Re thermocouple wires were ≤681 and ≤873°C, respectively, in air. Moreover, the major oxidization product at high temperature was WO 3 . The oxide layers were unable to form protective films owing to the generation of stress-induced cracks that grew in radiating lines. The protected tungsten–rhenium thermocouple wires remained intact during oxidation, and oxide layers were not detected.