Attributing to the toughness of the W-Mo metal and non-wttability of ZrO2 in molten steel, the W-Mo and ZrO2 composite has solved the two key problems of thermal shock resistance and corrosion resistance for metallurgical applications. Compared with the traditional refractories (such as Al2O3eC, MgOeC and Al2O3eZrO2eC) , it has much higher strength and lower porosity. As a result, it can be used for a fast molten steel temperature sensor . Concretely, a thin-walled sensor (thickness: about 3 mm) can be fabricated for a fast temperature response, as the traditional Al2O3eC sensor has an obvious response lag due to its thick-walled structure (thickness: 20–30 mm).
Generally, the sensor is dipped into molten steel directly for measuring the temperature of tundish. Recently, more and more steel companies want the sensor to have an additional functionality for measuring the baking temperature of tundish. The baking is heated up to around 1100–1200 °C for removing water and reducing the temperature difference between the tundish and molten steel. However, the baking would cause an oxidation problem of the WeMo and ZrO2 composite sensor, leading to that the baking temperature has to be measured by another special temperature sensor at present. Table 1 shows a typical baking schedule. It means that the sensor will be oxidized in a wide temperature range (room temperature ~ 1200 °C) for a long time (2.5 h ~ 4 h).
Due to easy oxidization characteristics of the Mo and W, the oxidation of the sensor is a serious problem. Oxidation of the Mo starts at around 400 °C. Especially at temperatures above 790 °C, its oxidation product MoO3 volatilizes and accelerates the oxidation. Meanwhile, the W also is oxidized easily, and its oxidation product (WO3) is readily to be evaporated at above 1300 °C. As a result, a pest oxidation of the WeMo and ZrO2 composite occurs. Generally, anti-oxidation additives and coatings can be applied to protect the materials against oxidation . However, the anti-oxidation additives may make the properties (such as high temperature strength and corrosion resistance) of the WeMo and ZrO2 composite deteriorate. Thus, an anti-oxidation coating that can work under the above mentioned oxidation conditions has to be developed.
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