The equilibrium distribution of hydrogen at trapping sites is shown putting emphasis on the effect of the binding energy. Trapping effects on hydrogen diffusivity derived from both the solution of diffusion equation and statistical thermodynamics are reviewed. Analytical and experimental estimations of the kinetics of trapping are reviewed. Dislocation transport of hydrogen by moving dislocations is critically examined.
A new electrode, Mo/Mo/MoO2 has been proposed for the purpose of better control of corrosion inhibition of constructive materials in adsorption refrigeration systems. The electrode is prepared by heating a molybdenum rod in air at 873K followed by reduction in hydrogen at 723K. The potential of the electrode was stable in LiBr solutions of wide range of temperature (298-428K), concentrations of LiBr (2, 17.3mol kg-1), LiOH (10-3-10-1mol kg-1), Li2MoO4 (10-4-10-2mol kg-1) and LiNO3 (0-10-2mol kg-1). The potential of the electrode responded to the concentration of LiOH while not to those of Li2MoO4 and LiNO3. The electrode potential was changed sharply by introducing oxygen into the solution at 353K in 2mol kg-1 LiBr solution. But it became less clear at 428K in 17.3mol kg-1 LiBr solution. The electrode can be used as a sensor for the concentration of LiOH. Another application of the electrode would be a quasi internal reference electrode in a commercial machine for the monitoring of corrosion potential of steels.
Acoustic emission (AE) from external stress corrosion cracking (ESCC) on a butt-weld 4 inch SUS 304 steel pipe of 4mm thickness was monitored as a function of internal hydrostatic pressure. AEs were detected by the resonant sensors with center frequencies of 50kHz and 450kHz and analyzed using the signal processing system developed. Among three types of AEs detected by the 50kHz sensors, Lamb wave AEs with broad frequency band were located near the ESCCs and found to be generated during pressure rise and reducing. Radiation pattern analyses of zero-th order symmetric Lamb mode suggested AEs from surface friction, crack of the rust in ESCC and falling-off grains of IG-ESCC. AEs monitored by the sensors with 450kHz center frequency were possibly produced by the falling-off of grains along IG-SCC. Though the primarily AEs from TG-SCC can hardly be detected by conventional AE system, we can detect secondary AEs associated with ESCC. This paper also discussed how to detect the secondary AEs from ESCC in process plants.
To prevent severe corrosion of steel bridges arisen by deicing salts, water washing of girders of two bridges made of weathering steel in Shikoku Island has been performed. Before confirming the effect of the water washing on prevention against the severe corrosion, the influence of deicing salts on the rust of the steel girders was examined. The thicknesses and weight per unit area of the rust layer on the girders were measured. The rust powder sampled from the girders was characterized by ion-chromatograph, XRD and N2 adsorption, i. e., BET analysis. Concentration of chloride ions soluble to water from the rust changed with seasons, revealing a peak in winter. The concentration of the soluble chloride ions exceeded approximately 0.2 mass% in winter season and the high concentration of chloride ions introduced formation of heavy and flaky rusts in summer. The rust formed under the environment containing the higher concentration of chloride ions exhibited the smaller specific BET surface area. It is conceivable that the large amount of chloride ions adsorbed on the surfaces of the rust particles enlarges the size of the particles. It is strongly suggested that chloride ions in the agglomerates of large size of particles in the rusts accelerate corrosion and introduce high growth rate of the rust layer.
To prevent the deicing salt-induced severe corrosion of weathering steel bridges, shikoku Regional Bureau of Japan Highway Public Co. (JH-Shikoku) performed water washing test of 2 bridge girders for 3 years. The supplied water pressure was 2-4MPa and the flow rate was 3-5.5l/min. The periodical water washing was done at the beginning of April after the seasonal sprinkling of deicing salts in every year. The rust layer formed on the washed part was characterized in a manner similar to the previous paper and was compared to the rust layer on no-washed part. The rust layers were characterized at two times, i. e.: the day (beginning of April) after the water washing was finished and the day (beginning of November) before the seasonal sprinkling of deicing salts. After the water washing, the concentration of soluble chloride ion of the rust layer decreased to approximately half of the seasonal peak in winter. The increase of rust layer thicknesses and the mass of rust per unit area on the washed parts were constantly suppressed during the experimental period. The corrosion loss of the steel with washed rust layer was smaller than the steel with no-washed rust layer. The specific surface area (SA) of the rust particles formed on the washed part was kept larger even in summer, when SA decreases in general by the high concentration of residual chloride ion. It is suggested that water washing has preserved the protectiveness of rust layer by the suppression of size growth of rust particles owing to chloride ion. Periodical water washing as a prevention technique to deicing salt-induced corrosion is useful for the maintenance of weathering steel bridges.