The piezo-electric detection was applied to nickel electrode in 0.5mol/dm³ sulfate solutions (pH=3.0 and 5.8) to measure the potential of zero charge (PZC) and to investigate the active dissolution/passivation.
The PZC of nickel electrode in pH 3.0 sulfate solution directly measured from the piezo-electric signals was -0.15V (SHE). The frequency analysis of piezo-electric response to the active dissolution/passivation was performed on basis of the proposed reaction mechanism to provide the separated two terms of q_M and Q; the former is a surface charge density of nickel electrode and the latter is an apparent charge density caused by adsorption. The total constant, k_a, involving dissolution and passivation processes, evaluated from the frequency analysis was about 6×10²s^-1 and 3×10³s^-1 for the solution of pH 3.0 and pH 5.8, respectively.
The value of Q was derived as a function of rate constant of elemental reaction step and coverage of intermediate adsorbates. The competitive processes of active dissolution and passivation was discussed from the potential dependence of Q.

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In order to evaluate the effect of dissolved oxygen (DO) on corrosion of ferrous materials, test specimens were oxidized in high temperature (288°C) and high purity water for 1000 hours. Weight loss and metal release of each specimen were measured after removing the oxide films. Characteristics of the oxide films were elucidated by EDX, SIMS and XPS. The weight loss increased in the following order regardless of DO: Type 316 LSS<Type 304 SS<carbon steel. Metal release was observed in all materials in deaerated pure water. Carbon steel corroded more at low DO than at high DO. On the other hand, Type 304 SS showed corrosion inhibition due to its Cr-rich oxide films, at low DO. The same effect was seen for the oxide films containing Mo, Ni and Cr on Type 316 LSS. At high DO, Fe and Ni ferrite caused a decrease in corrosion of stainless steels. The metal distributions in the oxide films on stainless steels varied with immersion time and DO. These results could be explained by the metal solubilities and the diffusion of oxygen containing species, based on the oxide film characterizations.

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Marine clay beds in Japan are often distributed in coastal plains and inland basins. This clay is composed of marine sediments and is very corrosive. We tried to predict the degree of external corrosion of water main exposed to agressive soils containing marine clay. It is used in the equation of prediction model that the growing rate of the pitting depth (P) follows a power law equation of time (t): P=ktⁿ. Parameter “k” and “n” were decided by the results of regression analysis. By assuming that “k” means the corrosiveness of environment, “n” could be given by the statistical analysis. Parameter “n” did not depend on the environmental factors. The corrosion of cast iron pipes installed in areas where marine clay is distributed is statistically described in terms of environmental factors in the present paper. We established the correlation between the depth of corrosion pit and the period after the installation of mains, and found a useful equation for predicting the depth of corrosion pit.

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Attempt has been made to clarify the effects of Cl^- concentration on galvanic corrosion between aluminium alloy 5052 and tin plate for can stocks. Electrochemical polarization measurements have been carried out to make the electrochemical evaluation of corrosion resistance of aluminium alloys. Behavior of galvanic corrosion was understood by the taking into acount of a corrosion model which has linearity between electrochemical potential and galvanic current. The possibility of aluminium alloy 5052 pitting could be estimated in terms of the values of Cl^- concentration and anode/cathode area.

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The type of corrosion and cracking of metals, and a point of view at inspection of plants having those damages are described. The technique of measurements on corrosion and cracking for metals by non-destructive methods such as magnetic, ultranic, X-ray, eddy current etc. are explained, further the method for life-estimation of corroded chemical plant by the extreme value statistical analysis are discussed.

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Some theoretical approaches were reviewed for understanding the passive behaviour of iron electrode. On the thermodynamic approach the electrochemical equilibrium of chemical species was assumed at any interface, resulting in a potenital difference in the passive film which should be accompanied by a difference of chemical potentials. On the ionic conductor approach the high-field-assisted ion migration connected with the ionic charge transfer at the passive film/solution interface originates a potential difference in the film. The prediction from the approach for the thickness-potential relation dependent on solution pH is in agreement with the experimental result. On the semiconductive oxide electrode approach the electronic equilibrium plays an important role, which yields a depletion layer for free electric carrier in the film. The depletion layer functions as a dielectric layer which sustains a potential difference in the film.

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