The history of studies on metallic corrosion inhibitors is reviewed. Most of fundamental adsorption and oxidation inhibitors were developed by the 1950s while precipitation inhibitors were mainly thereafter. It is important to be noted that novel environmentally acceptable (green) inhibitors were investigated mostly after 1970. The quality of inhibitor investigation was gradually changed from finding a new, effective inhibitor for metallic corrosion to elucidating inhibition mechanism by discussing data of electrochemical experiments and surface analyses and also using physical and chemical properties of inhibitors since the 1960s. The linear free energy relationship, the hard and soft acids and bases principle, and quantum chemical calculations were introduced for discussing mechanisms of corrosion inhibition. In future, effective green inhibitors will be developed by derivation from naturally occurring substances.

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To examine the applicability of the cathodic protection, which is accompanied with calcareous deposition, to ferrous structures in estuary areas, a study has been made concerning the effects of seawater dilution on the amount, the composition and the structure of the deposit. The dilution resulted in few effects on the amount of the deposit, until the dilution decreased the salinity to 1/10 of the original value. On the other hand, the Mg/Ca ratio of the deposit was greatly influenced by the dilution. As for the structure, the deposit thickness was sharply increased when the dilution decreased the salinity less than 1/10 of the original value. These results were discussed on the basis of the difference in the crystallization rate and the hydrophilic character between CaCO₃ and Mg(OH)₂.

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To estimate a proper anodes arrangement in the cathodic protection of a gigantic marine structure, quite a simple method was proposed, and the validity and applicability of the method was examined. The method was based on the assumption that the electric resistance between an anode and the structure mainly come from the part of seawater in catholic protection of a gigantic marine structure. To examine the validity of this assumption, the potentials of the anode and cathode under the catholic protection at a constant current density were measured using seawaters diluted to various salinities. The results showed that the dilution method is valid for the estimation of the anodes arrangement in the catholic protection of gigantic marine structures.
To show how to apply the dilution method to a concrete design problem in protecting a gigantic marine structure cathodically, the electric current distributions on a structure during catholic protection were measured in seawater diluted to 1/10 with fresh water. A close relation was found between the distribution of current density and that of accompanying calcareous deposit amount. The current density data were treated statistically, and a dimensionless number was introduced to evaluate quantitatively the unevenness of the calcareous deposit distribution. It was found that the dimensionless number is very useful for designing the arrangement of electrodes for the catholic protection of a gigantic marine structure accompanied with calcareous deposition.

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我々は新しく開発した塗装系-これは鋼材の上に絶縁層, 導電層, 上塗り層で構成されている-を用い, 大気中の鋼材のカソード防食を試みてきた.
工業環境兼海浜環境の曝露を日本の千葉県で行った. 電圧を印加した欠陥の赤錆発生面積比率は, 電圧を印加しない欠陥よりも小さかった. 曝露開始2週間後, 炭酸マグネシウムを含有する白色析出物によって欠陥が被覆され, カソード電流が減少した. 白色電解析出皮膜は欠陥の耐食性を高めると考えられる. 欠陥に形成された電解質液膜及び白色析出皮膜を均質で連続した抵抗薄膜とみなすことにより, 測定された欠陥のカソード電流は, 分布定数型モデルに従うことを示した. このモデルによると, 我々の開発している新しい塗装系は腐食環境が厳しいほど欠陥の耐食性が高くなる.

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我が国では, チタンが高レベル放射性廃棄物地層処分用オーバーパックの候補材料の一つに挙げられている. オーバーパックは, 長期間地層処分後には, 還元性のベントナイト接触水によって腐食されると推定されている. 本研究においては, 大気中生成皮膜を有するチタンを模擬ベントナイト接触水中でカソード分極したときに皮膜に生じる光学的および組成的変化をエリプソメトリーおよびXPSで調べた. 電位を下げていったとき, 屈折率, 消衰係数および膜厚の中で屈折率の変化が最も早く生じる. これは皮膜中のTi⁴⁺イオンがTi³⁺イオンに還元されるためである. 屈折率の変化が生じる電位から判断すると, 35～75%RHの大気中で形成された皮膜の内, 75%RH大気中生成皮膜がカソード分極による変質に対して最も抵抗性が高いと考えられる.

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