Effect of Oxygen on Water Vapor Oxidation of Fe by Oxygen Partial Pressure Control Using Gas Sensor

An oxygen pump sensor was installed in front of an oxidation furnace to supply and discharge oxygen to the Ar–H2O atmosphere and accurately control the oxygen partial pressure in the atmosphere. Furthermore, the oxidation rate was set after the oxidation furnace. It was measured by an oxygen sensor and a hydrogen sensor. Pure iron was used as the sample. The purpose of this study was to clarify the oxidation behavior of water vapor and oxygen. As a result, it was clarified that the amount of hydrogen generated by the oxidation of water vapor and Fe decreases when oxygen is supplied. In addition, when the oxygen supply amount increased, oxidation by the water vapor did not occur. On the other hand, it was clarified that when oxygen in the atmosphere is discharged, oxidation by oxygen is suppressed and only oxidation by the water vapor occurs. In the cross-sectional microstructure after oxidation, Fe3O4 was formed in the outer layer in the environment where the oxygen was discharged, but by supplying oxygen, the oxide layer became thicker and Fe2O3 was formed in the outer layer. The mass gain increased as the oxygen was supplied. Considering the ratio of oxidation by water vapor and oxidation by oxygen, it was clarified by this method that the mass gain is greater when the oxidation by oxygen is dominant.