Investigation of High Temperature Oxidation in Steam for Fe-Cr Alloy Using the Combination of a Hydrogen Sensor and an Oxygen Pump-Sensor

The water vapor oxidation behaviors of Fe and Fe-Cr alloys under isothermal and heat-cyclic conditions in an Ar-12 vol% H2O atmosphere were investigated by measuring both the hydrogen partial pressure using a hydrogen sensor and the oxidizing current of hydrogen using an oxygen pump-sensor, which were installed at the back section of the reactor. First, the performance of the oxygen pump-sensor was evaluated using Ar-1000 ppmH2 gas. As a result, it was found that the hydrogen concentration in the gas can be accurately measured by the oxidizing current of hydrogen. The isothermal oxidation test at 1173 K showed that the mass gain of the Fe-20 mass% Cr alloy was the highest, while the mass gain of the Fe-30 mass% Cr alloy was the lowest. For the Fe-20 mass% Cr alloy showing the highest mass gain, a rapid increase in the oxidation rate was observed during the oxidation test. The cyclic oxidation test indicated that the Fe and Fe-30 mass% Cr alloy had a lower oxidation rate in the second cycle than in the first cycle. On the contrary, for the Fe-20 mass% Cr alloy, the oxidation rate was higher in the second cycle than in the first cycle. For the Fe-30 mass% Cr alloy, the oxidation rate and mass gain during the cyclic oxidation test were low. The oxidation rates measured by the hydrogen sensor and the oxygen pump-sensor were showed the same behavior during the isothermal oxidation test. Since the oxidation rate is measured in situ using the hydrogen sensor and oxygen pump-sensor methods, it was clarified that both methods are effective for studying the water vapor oxidation behavior.