Effects of water, chloride ion and formic acid on galvanic corrosion of mild steel coupled to noble metal in methanol have been investigated by the amount of galvanic current with zero impedance ammeter and by weight loss measurement. The corrosion rate of mild steel in methanol containing chloride ion and water was found to increase as compared to the aqueous solution containing equivalent chloride ions. The corrosion rate of mild steel in methanol containing formic acid was extremely accelerated due to the lower pH. The corrosion products consisted of C₃H₃FeO₆·H₂O and C₂H₂FeO₄·2H₂O at the concentration up to 1.5% formic acid. These products, when exposed to atmosphere, turned into a brownish amorphous substance through oxidation, which changed into Fe₃O₄ and Fe₂O₃ as the temperature increased. At the formic concentration of 1.5% or more, as the corrosion products dissolved by formic acid, the corrosion rate of mild steel showed a slight decrease. Furthermore, we proved it was possible to monitoring of the corrosion rate of steel in methanol by the galvanic current flowing from galvanic couple.

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In saké, silver-brazed joints of stainless steel have corroded preferentially at the interface of stainless steel and filler metal, thereby exfoliated at that interface. The α-Cu phase in the filler metal and sensitized grain boundary of the steel were anodic to α₁-Ag phase in the filler metal. Therefore, corrosion in the interface of steel and filler metal progressed. In anodic polarization and immersion tests, it was found that copper and stainless steel were easily corroded in saké, and eluted Fe ions accelerated greatly discoloration of saké.

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Pitting potentials in sodium chloride solution have been measured potentiodynamically for Ni-Cr-Fe overlay weld alloys with dispersed NbC on a carbon steel formed by plasuma transferred arc method. The presence of NbC in the alloys with Fe content more than 40% caused an electronegative shift in pitting potential, and the morphology of the localized attack was found hemisphere or heneycomb. With Fe content less than 5%, the pits of the alloys containing no NbC had crystallographic attack with Cr-rich phases undissolved. As NbC content was increased, the pitting potential shifted in electropositive direction and the anodic dissolution was uniform with no pitting. The Ni-Cr-Fe overlay weld alloys with dispersed 40% NbC was coverded with a Cr-Nb-Fe-C composition film after anodizing at 1.0V vs. Ag/AgCl and then had higher resistance to pitting corrosion.

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Transport of water and ionic species through coating films during blistering of epoxycoated steels under electric current was studied in a sodium chloride solution by a mass gain method and a chemical analysis. Areas of cathodic delamination were compared with each other in some alkali and alkali earth metal chloride solutions. In the presence of an anodic current, the apparent transport numbers across the film were determined as 0.5 for both Cl^- and Fe²⁺ ions. Mass increase of the specimen, due to the penetration of water, corresponded to a water transport of 1 to 3mol/F. On the other hand, in the presence of a cathodic current, the apparent transport number for Na⁺ was 0.5, and the residual electricity would be transported by H⁺ and/or OH^- ions. The mass increase of the specimen corresponded to the water penetration of 20 to 60mol/F. These water penetrations were attributed to an osmotic pressure of concentrated FeCl₂ and NaOH solutions in the blisters, and the degree of water penetration depended upon the solubilities of salts and hydroxides. Because of high solubility of NaOH, the area of cathodic delamination was always several ten times larger than that of anodic one. Alkali metal chlorides accelerated the cathodic delamination, since the solubilities of their hydroxides are usually very large and the pH of the solutions are very high.

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Recently there is a strong tendecy toward lighter weight and smaller size in recent electric appliances, while they are assembled from more components than ever, including metallic ones. Although appropriate consideration is made during the design of those metallic components, there sometimes happen problems of unexpected corrosion depending on environments and conditions of operation. In this report, examples of corrosion classified according to components in electric appliances are described including their control methods.

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