The impedance of stainless steel electrodes in neutral aqueous solutions containing sulphate and chloride ions have been measured under anodic polarization. The types of steels used are 18Cr-8Ni, 17Cr-13Ni, 17Cr-13Ni-3Mo, 20Cr-25Ni, 20Cr-25Ni-1Mo, 20Cr-25Ni-3Mo, 20Cr-25Ni-5Mo and 18Cr. The conclusions obtained are summarized as follows.
(1) In 1M-Na₂SO₄ solution, two minimum values (at+0.40V and +0.95V vs. SCE) and one maximum value (at +0.75V vs. SCE) appear in the capacitive component-potential curves of all the specimens used, and these curves can be devided into four regions at these potentials, i. e. region I: -0.18V (corrosion potential)-+0.40V, region II: +0.40V- +0.75V, region III: +0.75- +0.95V, and region IV: +0.95V- +1.50V (V vs. SCE). It is thought that the region I corresponds mainly to the growth of passive films with potential and the regions II to IV probably resulted not only from the changes of passive films but also from the changes of Faradaic impedances caused by the dissolution of electrodes.
(2) In 1M-NaCl solutions, the pitting potentials of the steels used, except for the 20Cr-25Ni-5Mo steel, are wholly in the region I. The 20Cr-25Ni-5Mo steel does not sustain pitting corrosion by the anodic polarization in IM-NaCl solution, and in this case all regions I to IV appear in the capacitive component-potential curves. The changes of capacitances in the region II and III, however, are not clear in comparison with the changes in the same regions obtained with the 20Cr-25Ni steel in 1M-Na₂SO₄ solution. The same phenomenon is found in the capacitive component-potential curve of 17Cr-13Ni steel obtained in the solution of 0.1M-NaCl+0.2M-Na₂MoO₄. These phenomena are thought to result from the adsorption of MoO₄^2- ions.

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From our studies on organic corrosion inhibitors, it has been proposed that water molecule was adsorbed on metallic surface by the donation of electron pairs of its oxygen atom and organic corrosion inhibitors could be adsorbed by displacing the water, as shown in followings,
M: O-H-H RNH₂→M: O-H-H…NH₂R→M
+O-H-H…NH₂R→M: NH₂R
+O-H-H…NH₂R
This theory was applied to Ni-catalysts, often used for hydrogenations. Ni is stored in water or in alcohol as usual. The surface of Ni in water should be adsorbed by water molecule and one in alcohol by its molecule, as illustrated in next formulae,
Ni: O-H-H(I) and Ni: O-H-C₂H₅ (II)
Hydrogenation of acetone to isopropylalcohol with these two types of catalysts was carried out, and with I the reaction proceeded at room temperature, while with II it could not at less than 50°C. For these, it was concluded that acetone couldbe reduced by its displacing ability with the adsorbed water.
Ni: O-H-H…OC-CH₃-CH₃→Ni: OC-CH₃-CH₃
H₂→Ni+HOCH-CH₃-CH₃
But ethyl radical in II could block the approach of acetone to metal and it could not be adsorbed. Then it should be needed to pull off alcohol molecule from the surface by heating to be adsorbed with acetone. Immediately after acetone was adsorbed the hydrogenation reaction should take place.
When isooctene was reduced to isooctane with these catalysts, heating was necessary. But with II the reaction was more promptly carried out than with I, as the alcohol could be more easily desorbed than the water.
As the active site on metallic surface was adsorbed by the water, desorption of the water will make the active site open for the reactants. Strong electron-donating substances, such as acetone or triethylamine, will promote hydrogenation reaction by pulling the water apart from the active site, as following manners,
Ni: O-H-HCH₃COCH₃→Ni+O-H-H…OC-CH₃-CH₃,
Ni: O-H-H(C₂H₅)₃N→Ni+O-H-H…N(C₂H₅)₃
These promoters have been tried in the isooctenehydrogenation with water-dipped Ni, and have found that they, only in the limited amounts (7×10^-5mol/g Ni), could lower the reaction temperature, and that the addition in the amounts increased the reaction rate at the same temperature. This showed that the active site of Ni should be best open for isooctene when electron-donating substances were just equimolecular with the adsorbed water.

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