2018 Volume 67 Issue 9 Pages 375-380
This research aimed to confirm the formation of Fe3O4 film on Fe immersed in aqueous 45 mass％ NaOH solution containing some oxidants at the boiling temperature, to recognize the optimum immersion time for the formation of thick and protective film, and to reveal the absorption behavior of D2O in the Fe3O4 film at room temperature. The results were obtained as follows. It was confirmed that Fe3O4 film was formed on Fe immersed in the NaOH solution for a time more than 0.6 ks, and the film thickness increased parabolically with an increase in the immersion time. D2O absorption test was carried out to the films formed in the NaOH solution for immersion times of 1.2 and 3.6 ks. An amount of D2O absorbed into the film increased with an increase in an absorption time up to 1000 ks, and an absorption time more than 1000 ks made an amount of D2O constant. The constant amount of D2O was larger for the film formed on Fe immersed in the NaOH solution for 3.6 ks than that for 1.2 ks. The transient of the amount of D2O absorbed into the film was analyzed on the basis of Fick’s law for diffusion, and diffusion coefficients of D2O were obtained to be 5.1×10－15 and 9.9×10－15 cm2･s－1 for the films formed for 1.2 and 3.6 ks, respectively. Therefore it was estimated that the diffusion coefficient of the Fe3O4 film was in the region from 5.1×10－15 to 9.9×10－15 cm2･s－1.
