Analysis of Water Vapor Oxidation of Fe and Fe–Cr Alloys by Measuring the Partial Pressures of Hydrogen and Oxygen

The oxidation behaviors of the Fe, Fe–15mass%Cr and Fe–30mass%Cr alloys were investigated at 1173 K in Ar–H2O and Ar–O2–H2O atmospheres using an oxygen sensor and a hydrogen sensor installed at the outlet of an experimental reactor. In Ar–H2O, the changes in the hydrogen partial pressure were continuously measured using the hydrogen sensor, and the amounts of generated hydrogen and resultant consumed oxygen were calculated. The calculated gross mass gain was in close agreement with that gravimetrically obtained after the experiment. In Ar–O2–H2O, the amount of oxygen consumed from the ambient oxygen gas in the atmosphere was calculated from the change in the oxygen partial pressure measured using the oxygen sensor. In this case, the gross mass gain was analyzed as the sum of the amount of oxygen consumed from the ambient oxygen and that supplied from the steam dissolution. The oxidation patterns were classified into three types: (1) water vapor oxidation (in Ar–H2O), (2) water vapor oxidation and oxygen oxidation (in Ar–500 ppmO2–H2O except for Fe–30Cr), and (3) oxygen oxidation (in Ar–1%O2–H2O). It was demonstrated that a gas monitoring method using a combination of hydrogen and oxygen sensors is useful for investigating the water vapor oxidation in an atmosphere containing water vapor and oxygen.