The inhibition efficiency of polar organic inhibitors is correlated with the hard and soft acids and bases principle. It has been reported that an inhibitor acting as a soft base was readily chemisorbed on various transition and non-transition metals, resulting in a high efficiency of corrosion inhibition. Effect of the polar organic compounds was studied on anodic polarization curves of Ni electrode in a 3M HClO₄ solution. The compounds used as the inhibitors were those of which polar atoms belong to elements of 4B, 5B, 6B, and 7B groups in the periodic table. Similar relationship between the inhibition efficiency and the HSAB principle, as shown in the previous papers, was also obtained from the results in the active region of polarization curves. The passivation potential shifted toward a noble potential and the critical current density increased with the concentration of the inhibitor and with its softness as the base. The passive current density was enhanced by the addition of the inhibitors of which polar atoms were of the 6B and 7B groups, while lowered by the addition of those of the 5B group. From the discussion of the relationship between the chemical adsorption and the HASB principle, it was concluded that the inhibitors of the 7B and 6B group elements were adsorbed on the metallic Ni surface. However, the inhibitors of the 5B group elements were adsorbed on the passive film of the Ni electrode and reinforced the passive film. No significant difference was observed in the curves of the transpassive region for the electrodes uninhibited and inhibited with the inhibitors.

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In order to develop standard testing method for evaluating anodic behaviors of magnesiumm alloy galvanic anodes serviced in underground, the galvanostatic dissolution experiments were conducted at a current density of 0.03mA/cm² for 10 days and various factors influencing on parameters such as closed circuit potential and current efficiency were studied.
In test solutions containing Na₂SO₄, open and closed circuit potentials of the anode became less noble with increasing salt concentration. The increase in concentration of Na₂SO₄ promoted passivation and nonuniform dissolution on anode surface and the resulting localized dissolution led to the lowering of current efficiency. The tendency of passivation was not affected by exclusion of dissolved oxygen from test solution or addition of bentnite, but the addition of chloride more than 1 percent was considerably effective to uniform dissolution.
The results obtained in pH controlled solutions containing MgSO₄ or MgCl₂ showed that the current efficiency remarkably depended on pH value of test solution. The corrosion pattern of the anode being enveloped in backfil or CaSO₄ paste in sulfate solution was slightly more smooth than those of the anode without paste. It was assumed that the lowering of pH on surface by accumulation of magnesium ions due to an enclosure of the paste inhibited passivation, and that the inhibition in this case might be insufficient to produce uniform dissolution. Finally, owing to strong passivation of anode surface in such sulfate test solutions, it was considered that it is difficult to reproduce the dissolution provided under field conditions.
On the other hand, the current efficiency in artificial sea water was varied with pH of sea water like in sulfate solutions, but uniform dissolution was presented and reasonable values of potential and current efficiency were gained in short time test owing to chloride enough for depassivation and good stability of pH by saturation of Mg(OH)₂. According to these results, it was concluded that artificial sea water saturated with Mg(OH)₂ is the most suitable media for testing anode performance of magnesium galvanic anode revealed in practical use.

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The electrical conductivity of mixtures of synthetic α-, β-, γ-FeOOH, and Fe₃O₄ crystals has been measured to elucidate the high-order structure in the FeOOH/Fe₃O₄ systems as model rusts. The electrical conductivity of FeOOH/Fe₃O₄ binary systems showed minimum values for the samples containing less than 50% volume fraction of Fe₃O₄. The electrical conductivity change in low Fe₃O₄ content range was characteristic to each FeOOH polymorph. The electrical conductivity change suggests that FeOOH cyrstals form an aggregate which is loosened by coexisting Fe₃O₄ crystals. Above 50% of the Fe₃O₄ fraction, the electrical conductivity of the binary system increased steeply with the Fe₃O₄ content, implying that a chain-like structure of Fe₃O₄ crystals is formed. Electrical conductivity changes for the systems of α-FeOOH/γ-FeOOH/Fe₃O₄ and α-FeOOH/β-FeOOH/Fe₃O₄ also suggest the roles of each component played in the high-order structure of the ternary systems. The correlation between the electrical conductivity and high-order structure was discussed with reference to properties of the rust layer formed in atmospheric corrosion.

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Feasibility of repassivation potential, E_R, as a crevice corrosion characteristic has been studied for the stainless steel/barnacle-crevice which is well known to cause corrosion problems in marine environment. Specimens of Type 316 steels were exposed to live sea water from June, July and August in 1982 for 1 to 5 months to deposit barnacles of various growth stages on specimen surfaces. E_R measurements were conducted in the laboratory keeping the barnacles alive. Two types of specimens were utilized. The type M specimen has as many barnacles as deposited. The type S specimen has single barnacle left alone on its surface. The E_R values obtained did not depend on maximum penetration depth as an extent of preceding growth of crevice corrosion. Various conditions of barnacles in size of bottom shell diameter, the starting month and duration of exposure in sea seemed to give minor influences to E_R values. These facts confirm that the concept of E_R as a well defined characteristic can be applied also to Type 316 steel/barnacle-crevice. The least noble E_R value for the crevice is -0.3--0.2V. SCE and less noble than +0.4V. SCE as the spontaneous potential of passivated stainless steel in live sea water. This does not extrude the practical experiences that Type 316 steel corrodes under deposited barnacles in marine environment.

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