Highly pressurized hydrogen gas is one of the most effective media for storage and transport of hydrogen for fuel cells. Mechanical properties of an aluminum alloy and austenitic stainless steels were investigated by Slow Strain Rate Testing (SSRT) in hydrogen environment pressurized at 45MPa, for ensuring the safety of materials used for the compressed hydrogen system. A6061-T6 aluminum alloy and stable austenitic stainless steel 316L showed no evidence of embrittlement even at extremely low strain rates (3×10-7-3×10-6s-1). In contrast, metastable austenitic stainless steel 304L showed considerable degradation of ductility in the hydrogen environment due to strain-induced martensitic transformation. Susceptibility to hydrogen environment embrittlement (HEE) could be discussed based on hydrogen content absorbed into the materials and threshold stress.
We used time-of-flight secondary ion mass spectrometry to get a better understanding of the carbon-containing layer formed in summer and winter on copper exposed to an urban atmosphere. The positive ion mass spectra of as-exposed surfaces revealed that the chemical composition of the carbon-containing layer formed in summer was essentially the same as that formed in winter. However, the intensities of ion fragments originating from volatile organic compounds adsorbed in winter were stronger than those in summer. This is attributed to the temperature dependence of the physisorption of the compounds, assuming that the amounts of hydrocarbon contamination in the analytical instrument were the same for both samples. The positive ion mass spectra of sputtered surfaces (5 nm from the uppermost surface) showed that the chemical composition of the sputtered surface was different than that of the as-exposed surfaces. The only compound found on the sputtered surfaces was dicapryl phthalate (DCP), based on a comparison of the standard mass spectra of DCP with the observed ones. The peaks arising from DCP observed on the copper exposed in winter were higher than those in summer. This is attributed to the higher particulate organic carbon concentration observed in winter. The thicker carbon-containing layer formed on the copper exposed in winter possibly retarded the atmospheric corrosion by acting as a barrier to water adsorption on the copper patina.
As for the weathering steel, it is important to judge whether to suit the environment when applying to the structure. The authors presented the expression that allowed the environmental factor and amount of corrosion loss based on the results of the atmospheric exposure tests for weathering steel (JIS-SMA) and the Ni-added high corrosion resistant weathering steels in nationwide various places. In the present paper, the method to estimate the corrosion loss that had been proposed up to now was arranged. The characteristics of a domestic environment were clarified based on the results of the atmospheric exposure tests. In addition to the corrosion examination results of these steels in the laboratory, the corrosion estimation curve was proposed. As a result, the corrosion resistance of the weathering steel was in good agreement with the corrosion loss estimated with the past knowledge. The Ni-added high corrosion resistant weathering steel had the possibility to show higher corrosion resistance against salinity than the result estimated with weathering alloy index V-value that had been proposed up to now. In addition, the amount of corrosion loss can be decreased by giving the structure receiving the rainfall and the rust stabilization assistance processing.