An ultrathin （nm order of the thickness）, two-dimensional polymer coating was prepared on the passive film formed in a borate buffer at pH 8.49 by modification of 16-hydroxyhexadecanoate anion HO（CH₂）₁₅CO₂^－ self-assembled monolayer with 1, 2-bis（triethoxysilyl）ethane （C₂H₅O）₃Si（CH₂）₂Si（OC₂H₅）₃ and octadecyltriethoxysilane C₁₈H₃₇Si（OC₂H₅）₃. The electrode covered with the passive film and two-dimensional polymer was treated in 0.1 M NaNO₃ to heal the passive film. The time for passive film breakdown of the complex film, t_bd was markedly long, expecting more than 1000 h and the protection efficiency, P（％） was extremely high, more than 99.9％, unless the passive film breakdown occurred. Complete protection against passive film breakdown and markedly high value of P can be investigation of ultimate protective coatings for SDGs in future.

In order to analyze the effect of β-rays on corrosion, the effect of dissolved ⁹⁰Sr on the corrosion potential of Type 316L stainless steel was investigated. The ⁹⁰Sr-containing HCl was dropped into the diluted artificial seawater while the corrosion potential was measured. The solution was dropped in two times and the radioactivity of the solution was adjusted to be 0.15 MBq and 1.5 MBq, respectively. As a result, it was found that the potential of Type 316L stainless steel was increased by the drop of ⁹⁰Sr-containing HCl.

For accurately evaluating the risk of hydrogen embrittlement in steels, the hydrogen concentration near the steel surfaces needs to be determined. An electrochemical hydrogen permeation method to measure sub-surface hydrogen concentration can use steel sheets but not steel bars. Because iron oxide and working strain generated in the manufacturing process that affects hydrogen permeability are present on the sub-surface of steel bars, we need to evaluate steel bars directly. In this report, we research an electrochemical hydrogen permeation method and method to determine the surface hydrogen concentration for steel bars.

The effect of solution layer thickness on the atmospheric corrosion of carbon steel was investigated using novel devices fabricated by a 3D printer. These novel devices allowed us to control the solution layer thickness precisely. Potentiodynamic polarization measurements were performed under thickness-controlled solution layer, and oxygen diffusion limiting current density（j_lim） and anodic current density（j_anode） were measured. As the solution layer becomes thinner, j_lim increased and j_anode decreased. This result indicates that corrosion accelerates when the solution layer becomes thinner. The diffusion coefficient of oxygen was calculated as 3.20×10^－5 cm² s^－1 from the relationship between j_lim and solution layer thickness, and the critical diffusion thickness was estimated to be 0.87 mm.