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Soma, Yasutaka; Kato, Chiaki; Yamamoto, Masahiro
no journal, ,
Surface oxide layers were formed within crevices of type 316L stainless steels in pure water at 561 K and 8 MPa. Cross-sectional structures of the surface oxides were analyzed using transmission electron microscopy. Under the condition of a dissolved oxygen concentration of 2 ppm, the properties of the surface oxide layer changed with the crevice position and dual or triplex layered oxides were formed, which had not been observed on a boldly exposed surface. The thickness of the inner oxide layer showed a local maximum at a certain distance from the crevice mouth. These oxide characteristics suggest the presence of locally varying electrochemical conditions. Potential-pH diagrams of the multilayered oxides suggest that the potential decreased at the early stage of exposure and then re-increased, accompanied by weak acidification.
Igarashi, Takahiro; Komatsu, Atsushi; Motooka, Takafumi; Ueno, Fumiyoshi; Yamamoto, Masahiro
no journal, ,
We simulated intergranular corrosion considering various fluctuations of corrosion rates (CR) for grain boundaries (GB): exponential, normal and uniform distributions. The relationship among the roughness of corroded surface, maximum intergranular corrosion depth, and fluctuations of CRs of GBs was evaluated. The cross-sectional images by simulation with the case of exponential distribution was relatively resemble to cross-sectional images obtained by corrosion tests in terms of roughness of corrosion surface. The simulation using normal and uniform distributions of CR of GB indicated that maximum corrosion depth became deeper with increasing deviation range of fluctuations. These results suggested that the roughness of corroded surface was controlled by fluctuation of CRs of GBs.
Sato, Tomonori; Motooka, Takafumi; Hata, Kuniki; Yamamoto, Masahiro; Tsukada, Takashi
no journal, ,
In the water containing hydrazine and dissolved nitrogen under irradiation condition, water radiolysis considering the hydrazine and nitrogen co-existence is important. So, the water radiolysis calculation was performed for the water containing hydrazine and nitrogen gas under 
ray irradiation. The calculated results successfully reproduced the measured results. The effects of hydrazine and nitrogen co-existence on the water radiolysis was evaluated. The hydrazine hardly affected the generation of nitrate ion. On the other hand, the hydrazine increased the concentrations of nitrite ion and ammonia.