Metallic materials used in electronic components and devices corrode in the same ways as automobiles and bridges, but their small dimensions make them orders of magnitude more susceptible to corrosion failure. The corrosion involves interactions with environment. These interactions can be put to use under control. This article presents the tarnishing film formation characteristics of silver as the first part of a series of articles describing corrosion behavior of silver in electronics application. The mechanisms and processes of tarnishing are discussed and indoor tarnishing film formation rates are presented.

A test specimen simulating a pier, which is a harbor structure with a series of reinforced concrete members from the atmospheric to the tidal zone, was fabricated and tested for exposure to seawater. The potential and current density of the reinforcing bars in each environmental category were observed to investigate the effect of tidal fluctuations on the corrosion of the reinforcing bars in the concrete. As a result, changes in the rebar potential and current density were observed in synchronization with tidal fluctuations. The formation of different macrocells was observed depending on the tidal level, and the macrocell characteristics changed with the lengthening of the exposure period.

A non-destructive method for measuring the fiber embedment depth of an optical fiber sensor used to detect degradation of an FRP hydrochloric acid storage tank was investigated. Ultrasonic and optical coherence tomography （OCT） measurements were performed on sensors with various fiber depths, and their accuracies were compared. As a result, it was determined that the OCT measurement was more accurate and relatively effective. The validity of the hydrochloric acid penetration rate calculated from the fiber depth measured by OCT and the discoloration start time of the sensor module when immersed on one side was also examined.

Gamma-radiolysis experiments with gas-liquid coexistent samples were carried out to investigate effects of gas-phase radiolysis on corrosive environment for materials in solutions under irradiation. After gamma-ray irradiation, hydrogen peroxide, nitrate ion, nitrite ion were detected in the liquid phase. The production yields of nitrate ion and nitrite ion increased with increasing gas-phase volume and oxygen concentration. This result indicated that chemical reactions including oxygen and nitrogen in the gas phase were required for the production of nitrate ion and nitrite ion. To magnify the effects of gas-phase radiolysis in the gas-liquid coexistent samples, absorption dose rate in the liquid phase was reduced by one-hundredth using lead shield. The concentration of hydrogen peroxide and the pH in the shielded liquid phase were similar to those in the irradiated pure water, which did not contact with gas phase. This result indicated that the effects of nitrate ion and nitrite ion dissolved in the liquid phase on water radiolysis were not important in the current experimental system, in which the effects of gas-phase radiolysis were increased by 100-times.

A thermodynamic model （U-Cal model） has been developed that predicts fugacities and water content in the CO₂ phase （gas or supercritical fluid）, and CO₂ solubility and pH in aqueous solution in CCS environment, which is a CO₂ environment in a supercritical state. The values predicted by the U-Cal model agreed well with the measured values. The water content in the CO₂ phase increases to 1-10 g/L due to the mutual dissolution of CO₂ and H₂O. The increase in the solubility of CO₂ in aqueous solution and the decrease in pH with increasing pressure are small. The CO₂ corrosion behavior of carbon steel was discussed by using the U-Cal model. In iron dissolution dominant CO₂ corrosion in aqueous solution of carbon steel, the corrosion rate could be understood as a function of pH. In FeCO₃ formation dominant CO₂ corrosion, it was considered that the corrosion progressed as FeCO₃ dissolves to supersaturation and then FeCO₃ precipitated on the surface of the material. The FeCO₃ precipitation behavior was predicted from the crystal growth rate equation. Corrosion of carbon steel in the CO₂ phase involves similar mechanisms to corrosion in aqueous solution, but the corrosion rate is lower.