Electrochemical kinetics is described for understanding electrochemical measurement methods. Rate equations when the rate-determining steps are the charge transfer and diffusion are derived in an equilibrium system, and then the rate equations for a corrosion system are derived from those for the equilibrium system. Furthermore, Tafel extrapolation and polarization resistance methods to estimate the exchange current and corrosion current are described.
The behavior of atmospheric corrosion monitoring （ACM） sensors composed of various anodic substrates were tested in aqueous salt solutions and through humidity cycle tests using salts. The result showed that the ACM sensors could be used in solution, and the humidity cycle tests using NaCl solution revealed a correlation of output with concentration. The result also showed that the outputs depended on the types of anode constituting the substrate used for the sensor. Meanwhile, in a test simulating atmospheric corrosion, sensors using other types of substrate showed behavior similar to that of the Fe/Ag galvanic couple sensor. However, when Al or stainless steel was employed the resulting outputs which had no relationship with the relative humidity and it seemed to be specific to the metal type. These results suggested that material corrosiveness can be directly measured by the ACM sensor.
There is oxygen free copper （hereinafter called OFC） as a corrosion resistant material to ant's nest corrosion. We exposed OFC to various corrosion conditions, compared corrosion resistance of phosphorus deoxidized copper （hereinafter called PDC） and OFC, and then presumed the real environment in which ant's nest corrosion occurs.
Corrosion in the depth direction was confirmed as same as PDC by exposing OFC to a high concentration formic acid aqueous solution.
We confirmed that ant's nest corrosion occurs even in OFC under a high concentration of corrosive medium. That's why, we presumed that the condensed water in the actual environment has dilute concentration organic acid.
Permeated hydrogen from scratches （0 mm2, 0.3 mm2 and 1.5 mm2） formed on zinc coated steels was measured by electrochemical hydrogen permeation technique with wet and dry cycle corrosion tests. Independent of the area of the formed scratches, the hydrogen permeation current with similar shape was measured. The white corrosion products were observed after the tests. The hydrogen permeation charges increased with cycle number up to 3, and thereafter it was decreased with the cycle number. The corrosion products around the formed scratches were simonkolleite （Zn5（OH）8Cl2･H2O）. It was suggested that the formation of simonkolleite is the possible reason for decreasing the hydrogen permeation current for longer wet and dry corrosion tests. Comparing hydrogen permeated charge from 1st to 3rd cycle and scratch area, it was suggested that generated hydrogen does not uniformly permeated into steel substrate at the scratch.
Immersion tests, polarization curve measurement, and electrochemical impedance measurement were conducted in order to investigate the effect of Sn alloying on the corrosion resistance of ferritic stainless steels in sulfuric acid solutions. The addition of Sn to 14Cr ferritic stainless steels and the addition of Sn2＋ ions in the solutions were effective in decreasing the corrosion rate in sulfuric acid solutions. Sn was an effective alloying element for suppressing the anodic dissolution near the corrosion potential and Sn2＋ acted as effective ions for inhibiting both anodic and cathodic reactions in sulfuric acid solutions. The addition of Sn to 14Cr ferritic stainless steels was quite effective in decreasing the anodic current densities in the acidic sodium sulfate solutions of pH 0.5―2 and in the potential range where Sn2＋ ions are thermodynamically stable. It was thought that Sn in the ferritic stainless steels dissolved as Sn2＋ ions in sulfuric acid solutions and the active dissolution was suppressed by the surface adsorption of Sn chemical species originated from the dissolved Sn2＋ ions.