The constant current interrupter method has been applied to the study of irreversible polarization of cathodic deposition of nickel.
The interrupter was constructed by a mercury wetted electromagnetic relay combined with thyratron. Its performance characteristics were checked by the electrodeposition of nickel from nickel sulfate bath as well as from Watt's type plating bath.
The resistance polarization, the differential capacity of electric double layer, and also the activation overpotential were determined by the analysis of potential decay curves.

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By the oscillographic determination of the potential decay curves, analysis was made on the resistance polarization, the differential capacity of double layer, and the activation overpotential with respect to the inhibitor action of naphthalene sulfonates in the electrodeposition of nickel from nickel sulfate bath.
It was found that naphthalene sulfonates had no specific effects on the resistance polarization as well as on the activation overpotential in the electrodeposition of nickel. However, the dependence of the differential capacity of double layer upon the electrode potential in the presence of naphthalene sulfonates was very significant even though there were no special relations between the differential capacity and the number or positions of sulfonategroups in naphthalene ring.

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Study was made on the inhibitor action of addition agents in the electrodeposition of nickel from nickel chloride bath.
For the examination of the adsorption phenomena of the addition agents on the nickel surface, the capacity of double layer and the polarization potential during the hydrogen discharge on the nickel electrode in 0.1N HCl solution were measured with respect to the concentration of the addition agents.
During the hydrogen discharge reaction, saccharin, thiourea, β-naphthoquinoline, and N-ethyl quinolium iodide reduced the differential capacity of double layer in 0.1N HCl solution.
It was found that saccharin and thiourea decreased the overpotential of hydrogen discharge at lower concentrations. On the other hand, β-naphthoquinoline and N-ethyl quinolium iodide increased the overpotential, but gave rise to the lower limit of currents at higher concentrations in 0.1N HCl solution.
The results would be explained by the strong adsorption of these compounds on the nickel cathode surface.
Comparative study was made on the inhibitor action in terms of the increase or decrease of over-voltage (ΔE) due to the addition agents in the electrodeposition of nickel.
The increase of ΔE was observed with the increase of current density by the addition of disodium 1.5-naphthalene sulfonate, thiourea, or coumarin (conc. of 2m M/l), but the decrease of ΔE was observed by the addition of butynediol under the same conditions.
The addition of saccharin gave no change of ΔE at the current density of 0.5-50mA/cm².

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It is widely known on the effects of inorganic anions and organic ions on the corrosion behaviors of iron. Since these ions inhibit corrosion by the adsorption on iron surface, it is valued for their adsorption capacity to determine it as a function of electrode potential. Adsorption capacity of inorganic ions was found to be arranged in ascending order of ClO₄^-<Cl^-<Br^-<I^- by C-E curves. Whereas, adsorption-desorption potentials of these anions were indicated by several peaks on the above curves. Synergism and antagonism between inorganic anions and organic ions were interpreted in terms of ionic adsorption at the interface between iron and acid solution.

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The degree of surface coverage (μ) obtained from electrical double layer capacity and inhibition efficiency (η) determined gravimetrically in organic and inorganic corrosion inhibitors-such as amines, halides, and propionate-were determined with regard to iron-acid solution systems. Each of the values of μ and ηwas also measured as a function of inhibitor concentration (m).
There was a significant difference between HCl-amines and HCl-halides (or propionate) systems. That is, a maximum appeared on μ- or η-m curves prior to attaining to a definite value in the former system; while in the latter system, the curves obtained were typical Langmuir adsorption isotherms.
Linear correlationship was observed between μ and η, but the correlation factor varied according to the concentration ranges of each inhibitor. The above facts and the appearance of maximum on μ- or η-m curves suggest that the inhibition mechanism of corrosion inhibitors is not a simple one, but probably is a complex type of adsorption at active centres, overall adsorption, and film-forming mechanisms, or their mixed type.

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