Analytical methods for hydrogen states in materials are reviewed. Principles and characteristics of visualization techniques, such as tritium radioautography, hydrogen microprint technique and scanning secondary ion mass spectroscopy, and thermal desorption analysis are briefly described. Examples of applications to practical cases are presented putting emphasis on the limitations and uncertainties involved in experiments and theories.
The oxide films composed of Cr, Fe, and Ni elements were formed on the surface of Type 304 stainless steel by Metalorganic Chemical Vapor Deposition (MOCVD) for the purpose of radiation buildup control and corrosion resistance improvement of the steel in high temperature water. The results of corrosion tests under simulated BWR and PWR primary water conditions showed that MOCVD films had good stability in high temperature water. The amount of radiation buildup on specimens covered with a Cr2O3 film decreased with increasing film formation temperature. From the XRD spectrum of specimens, it is presumed that the increase in the crystallinity of the film improved the corrosion resistance and reduced the radiation buildup. On the other hand, NiO-Fe2O3 films with spinel structure, such as NiFe2O4, could not reduce the radiation buildup on specimens. The incorporation of 60Co, which was used as radioisotope, into the films was observed, although the corrosion of specimens was reduced. It is concluded that the Cr2O3 film with high crystallinity improves the radiation buildup and the corrosion resistance of the steel under simulated BWR and PWR primary water conditions.
Surface analysis through Auger Electron Spectroscopy was conducted on Type 316 L stainless steel (SS) and two kinds of N-alloyed austenitic SS. One was 16Cr-14Ni-2Mo-0.17N SS, which contained 16%Cr, 14%Ni, 2%Mo and 0.17%N. The other was 18Cr-2Mo-1N SS, which contained 18%Cr, 2%Mo and 1%N. Cr on the surface of 16Cr-14Ni-2Mo-0.17N SS and 18Cr-2Mo-1N SS was concentrated after active dissolution treatments in 0.5 mol · dm-3 H2SO4 containing 0.5 mol · dm-3 NaCl. However, in both cases of 16Cr-14Ni-2Mo-0.17N SS and 18Cr-2Mo-1N SS, the concentration of Cr was not higher than that of Type 316L SS. Crevice corrosion tests and repassivation tests were conducted on Type 316L SS and 18Cr-2Mo-1N SS. The lowest value of potentials, at which crevice corrosion was initiated and propagated in synthetic seawater at 35°C, for 18Cr-2Mo-1N SS was still nobler than that for Type 316L SS. Repassivation potentials for crevice corrosion did not depend on the crevice corrosion depth in the case of Type 316L SS. On the other hand, the repassivation potential for 18Cr-2Mo-1N SS decreased with increasing crevice corrosion depth and came equivalent to that for Type 316L SS at a crevice corrosion depth of 0.3 mm.
To elucidate the local wet atmospheric environment surrounding a weathering steel girder of bridge in a mountainous region, atmospheric temperature, relative humidity near on steel surface and steel surface temperature were measured by a monitoring device at each site simultaneously for two years. The time of dew condensation (TOC) at the six sites was calculated from the above data. To compare the obtained TOC to the characteristic of the rust, the rust layers formed on the representative sites were characterized by XRD, electrochemical potential of steel with rust layer, rust thickness and observation of the surface appearance, respectively. The obtained values of TOC at all sites were less than 10% of the time of wetness (TOWISO) according to ISO 9223. These low levels of the TOC corresponded to the thin thickness of the rust layers. The values of TOC also affected to the mass fraction of γ-FeOOH constituent, the potential and the surface appearance. In this case on the local site of the bridge girder in a mountain region, it was concluded that the TOC was a better indicator for wet atmospheric environment than the TOWISO.