The hydrogen compatibility of metallic materials is often evaluated by conducting tensile tests of H-charged specimens in air or inert gas at ambient temperature; however, it is not clear whether the H distribution calculated with hydrogen diffusivity under a diffusion-controlled process is consistent with the actual distribution. This study estimated the hydrogen distribution in a H-charged nickel maintained in air at ambient temperature for a few months after exposure to hydrogen gas by using the Vickers hardness test and secondary ion mass spectrometry. Both methods provided similar H distributions, which were fitted by the solution of a diffusion equation under a diffusion-controlled process, and the hydrogen diffusivity was also determined. The estimated H distributions were successfully fitted by the solution of the diffusion equation, and the determined hydrogen diffusivity of nickel was consistent with literature data, indicating that the calculated H distribution reproduced the actual one.

The paper presents the hydrogen-entry, tensile, and fatigue properties of a precipitation-hardened martensitic stainless steel, JIS-SUS630, with a newly developed coating, whose thickness ranges from 10 to 20 μm. The newly developed coating consists of alumina, aluminum, and ferroaluminum, and has an excellent resistance to hydrogen entry in 100-MPa hydrogen gas at 270°C. The hydrogen entry in the coated specimen occurred under a diffusion-controlled process and the effective hydrogen diffusivity was approximately one thousandth of that of the base steel. Although the hydrogen diffusivity of JIS-SUS630 was two orders of magnitude larger than that of JIS-SUS304, the effective hydrogen diffusivity of the coated JIS-SUS630 was nearly equal to that of the coated SUS304. In our previous study with secondary-mass ion spectroscopy (SIMS), the coating’s excellent resistance to hydrogen entry was attributed to interfacial hydrogen trapping between the aluminum and ferroaluminum layers. The experimental result obtained in this study suggested that the excellent resistance to hydrogen entry demonstrated by the developed coating can be attributed to the reduction in the permeation area induced by the interfacial trapping of hydrogen. The tensile tests of a smooth, round-bar specimen and fatigue tests of a circumferentially notched specimen with exposure to 100-MPa hydrogen gas at 270°C were performed in air at room temperature (RT). The test results showed that the tensile and fatigue properties of the coated specimens were not degraded by hydrogen exposure, whereas those for the non-coated specimens were significantly degraded. Hydrogen-pressure cycle tests of the coated, tubular specimens with an inner notch were also carried out with 95-MPa hydrogen gas at 85°C, demonstrating that the fatigue life of the tubular specimen was improved by the developed coating.

Hydrogen (H-1) trapped at intermetallic particles (IPs) in an aluminum alloy, 6061-T6, was visualized with secondary ion mass spectrometry (SIMS) by precisely excluding the false signal which is caused by background hydrogen (H-BG). The interference of the H-BG was avoided by a unique continuous pre-sputtering (pre-digging) by a primary ion beam of SIMS into a sample in combination with silicon sputtering prior to the SIMS measurement of the sample and we succeeded in visualizing the exact signal of H-1 trapped by IPs at subsurface layer of the sample charged in high-pressure hydrogen gas. The thermal desorption analysis clarified that the desorption energy (E-d) of the IPs was 200 kJ/mol or higher, which was extremely higher than Ed for lattice interstice, dislocations, and vacancies. High density hydrogen was concentratedly trapped at IPs in the subsurface layer in contact with the hydrogen gas. This nature causes an extremely low effective hydrogen diffusivity of 6061-T6 of the order of 10(-14) m(2)/s even at 200 degrees C and may eventually give a high HE resistance to 6061-T6. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

The hydrogen atom interacts various lattice defects and secondary particles in a material, causing a degradation in the tensile strength and elongation, well-known as hydrogen embrittlement (HE). Such material-hydrogen interaction should be extensively investigated to elucidate a precise mechanism of the HE. This study investigated hydrogen-entry properties and hydrogen state of an aluminum alloy 6061-T6 exposed to high-pressure hydrogen gas by means of thermal desorption analysis (TDA) and secondary ion mass spectrometry (SIMS). The TDA revealed that the hydrogen entry in the alloy occurred under the present hydrogen-exposure condition and the hydrogen was trapped by an extremely-deep trapping site, compared to ordinary trapping sites (lattice, dislocation, and vacancy) previously reported. To detect reliable signals of hydrogen trapped in the alloy by SIMS, removal of background-originated hydrogen derived from water or hydrocarbon molecules and verification of false signals produced due to a difference in sputtering rate between the phases were thoroughly conducted. Consequently, it was revealed the hydrogen was trapped by micrometer-sized intermetallic particles.

Pressure cycle tests were performed on two types of Cr–Mo steel pressure vessels with notches machined on their inside under hydrogen-gas pressures, between 0.6 and 45 MPa at room temperature. Fatigue crack growth (FCG) and fracture toughness tests of the Cr–Mo steels samples from the vessels were also carried out in gaseous hydrogen. The Cr–Mo steels showed accelerated FCG rates in gaseous hydrogen compared to ambient air. The fracture toughness of the Cr–Mo steels in gaseous hydrogen was significantly smaller than that in ambient air. Four pressure vessels were tested with gaseous hydrogen. All pressure vessels failed by leak-before-break (LBB). The LBB failure of one pressure vessel could not be estimated by using the fracture toughness in gaseous hydrogen KIC,H; accordingly, the LBB assessment based on KIC,H is conservative and there is a possibility that KIC,H does not provide a reasonable assessment of LBB. In contrast, the fatigue lives of all pressure vessels could be estimated by using the accelerated FCG rates in gaseous hydrogen.

The apparent hydrogen diffusivity and the saturated hydrogen content of Cr-Mo and Ni-Cr-Mo steels were determined with high-pressure hydrogen gas. Surface effects on hydrogen entry and exit were also investigated by using palladium-coated samples and by diffusion analysis using the finite-element method. Hydrogen contents of hydrogen-exposed cylindrical specimens of various sizes were measured by means of gas chromatography mass spectrometry to obtain the saturated hydrogen content. The diffusivity was determined by fitting the solution of a diffusion equation to the experimental hydrogen contents determined by desorption at various constant temperatures. In the specimens examined, surface effects were significant at room temperature. The temperature dependences of the diffusivity were reasonably consistent with reference data mainly measured with electrochemical charging. These results were interpreted in terms of hydrogen trapping. Ordinary electrochemical charging represents a more severe condition than exposure to high-pressure hydrogen, for example, at 100 MPa. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

This study presents a precise hydrogen-barrier mechanism of a newly developed three-layer (alumina/aluminum/ferro-aluminum) aluminum-based coating in high-pressure gaseous hydrogen. After exposure to high-pressure gaseous hydrogen, the hydrogen content of the specimen with a palladium-sputtered aluminum-based coating was the same as that of the specimen with aluminum-based coating, but without palladium. Furthermore, the hydrogen content of the coated specimens increased with a decrease in the specimen size. These results indicate that the hydrogen entered by a diffusion-controlled process. The effective diffusivity of the coated specimen was approximately one thousandth of that of base steel (type 304 stainless). Such excellent resistance could not be obtained with a two-layer coating (alumina/ferro-aluminum). Analysis of local hydrogen concentrations by secondary ion mass spectroscopy demonstrated that the extremely low effective hydrogen diffusivity of the three-layer-coated specimen was attributed to hydrogen trapping at the aluminum–ferro-aluminum interface, and not to the hydrogen-entry obstruction by the aluminum layer.

Hydrogen uptake in a ferritic steel was investigated through secondary ion mass spectrometry (SIMS) at 83 K, where hydrogen diffusion is sufficiently suppressed. Additionally, the SIMS was operated with cold trap and Si sputtering to reduce the back ground effect. Thanks to the suppression of hydrogen diffusion during the measurements, the cryogenic SIMS could demonstrate reproducible results which showed a significant difference in hydrogen content between hydrogen-charged and uncharged specimens. Namely, hydrogen in the ferritic steel was successfully detected similarly to austenitic steels.

Hydrogen contained in austenitic stainless steel is classified as diffusible or nondiffusible. The hydrogen distribution in austenitic stainless steel changes with time owing to hydrogen diffusion at room temperature, and such changes in hydrogen distribution cause the mechanical properties of the steel to change as well. It is therefore important to analyze the time variation of the hydrogen distribution in austenitic stainless steel at room temperature to elucidate the effects of hydrogen on the steel's mechanical properties. In this study, we used secondary ion mass spectrometry (SIMS), a highly sensitive detection method, to analyze the time variation of the distribution of hydrogen charged into 316L austenitic stainless steel. SIMS depth profiles of hydrogen that were acquired at the three measurement times were analyzed, and the results were compared among the measurement times. 1H− intensities and distribution of the intensities changed with time due to diffusion of hydrogen in the hydrogen-charged 316L steel sample at room temperature. Moreover, the time variation of the hydrogen concentration distribution of the hydrogen-charged 316L sample was calculated using a one-dimensional model based on Fick's second law. The time variations of the measured hydrogen intensities and of the calculated values are compared.

Pressure cycle tests were performed on two types of Cr-Mo steel pressure vessels with inner diameters of 306 mm and 210 mm and notches machined on their inside under hydrogen-gas pressures, varied between 0.6 and 45 MPa at room temperature. One of the Cr-Mo steels had a fine microstructure with tensile strength of 828 MPa, while the other had a coarse microstructure with tensile strength of 947 MPa. Fatigue-crack growth (FCG) and fracture-toughness tests of the Cr-Mo steels were also carried out in gaseous hydrogen. The Cr-Mo steels showed accelerated FCG rates in gaseous hydrogen compared to ambient air with an upper bound corresponding to an approximately 30-times higher FCG rate. Furthermore, in gaseous hydrogen, the fracture toughness of the Cr-Mo steel with coarse microstructure was significantly smaller than that of the steel with fine microstructure. Four pressure vessels were tested; then, all of the pressure vessels failed by leak-before-break (LBB). Based on the fracture-mechanics approach, the LBB failure of one pressure vessel could not be estimated by using the fracture toughness in gaseous hydrogen. The fatigue lives could be estimated by using the upper bound of the accelerated FCG rates in gaseous hydrogen.

The microstructure immediately beneath the fracture surface produced during fully-reversed fatigue loading of uncharged and hydrogen-charged 304 and 316 stainless steels has been investigated by using focused ion beam machining in conjunction with transmission electron microscopy. The microstructure beneath striations on the fracture surface is dependent on the presence/absence of hydrogen and varies as a function of distance from the surface. The underlying microstructure also is dependent on the morphology of the fracture surface and is distinctly different beneath striations and flat regions. The differences in evolved microstructure are considered in terms of mechanisms by which hydrogen modifies deformation processes.

Epoxy resin attached to a fatigue fracture surface of Ti-Al-Nb alloy was removed using a removal method for hardly soluble organic material attached to metallic material, which has been developed by the author. In the removal method process, the epoxy resin attached to the fracture surface was treated with an organic solvent, `tetrahydrofuran', and cold concentrated sulfuric acid of nearly 100% purity. After the epoxy resin was removed from the fracture surface with the removal method, damage of the microscopic feature of the fracture surface was investigated using a scanning electron microscope (SEM). For the first time, the degree of the removal of the epoxy resin with the method was investigated by energy dispersive X-ray spectroscopy (EDS) in this research. After the removal, no damage of the fracture surface was found with SEM observation. In addition, C Kα derived from the epoxy resin was not detected with the EDS after removal. The result of the EDS analysis clarified that the epoxy resin was completely removed with the removal method.

Secondary ion mass spectrometry (SIMS) is used to detect local distributions of hydrogen in various materials. However, it has been well-known that it is extremely difficult to analyze net hydrogen (H(N)) in metals with SIMS. This was because hydrogen, which is originated from moisture (H(2)O), hydrocarbon (C(x)H(y)) or other organic materials (C(x)H(y)O(z)) existing on a sample surface or in the SIMS chamber, is simultaneously detected in the SIMS measurement of the H(N), and the H(N) and the background-originated hydrogen (H(BG)) cannot be distinguished in a SIMS profile. The effective method for reductions and determinations of the H(BG) in hydrogen measurements of metallic materials with the SIMS method has not been established. The present paper shows an effective method for reduction and estimation of H(BG) in SIMS analyses of hydrogen charged into type 316 L austenitic stainless steel, and an accurate estimation method of the net charged hydrogen. In this research, a silicon wafer is sputtered by a primary ion beam of a SIMS near an analyzed area (silicon sputtering method) to reduce H(BG). An uncharged type 316 L sample was prepared for estimation of H(BG) in SIMS measurements of the hydrogen-charged sample. The gross intensities of hydrogen between the hydrogen-charged sample and the uncharged sample were compared. The gross intensities of hydrogen of the uncharged sample (26.8-74.5 cps) were much lower than the minimal gross intensities of hydrogen of the hydrogen-charged sample (462-1140 cps). Thus, we could reduce the H(BG) enough to estimate the hydrogen charged into the type 316 L sample. Moreover, we developed a method to determine intensities of H(BG) in the measurement of the hydrogen-charged sample by estimating the time-variation of hydrogen intensities in the measurements of the uncharged sample. The intensities of the charged hydrogen can be obtained by subtracting the estimated intensities of the H(BG) from the gross intensities of hydrogen of the hydrogen-charged sample. The silicon sputtering method used to reduce H(BG) and the determination method for H(BG) in this research can be applied to the accurate hydrogen analysis for other various metallic materials.

Secondary Ion Mass Spectrometry (SIMS) analyses were carried out on type 304 austenitic stainless steel. On annealed specimen exposed to hydrogen (10 MPa, 358 K), Element Depth Profiles SIMS mode was able to describe quantitatively the hydrogen profile content computed by the Fick's law. Based on SIMS analyses on the wake of a fatigue crack (propagation in hydrogen gas at 0.6 MPa and RT), it was possible to compute an apparent diffusivity and solubility in the crack tip region. The apparent solubility and diffusivity in the deformed regions were two times and five orders of magnitude higher than the ones on annealed material, respectively. High hydrogen content was found around the crack tip, where the plastic deformation was well developed (pronounced slip activity). The high apparent diffusivity is presumed to result from enhanced hydrogen transport induced by cyclic plastic activity at the crack tip. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

If human beings or animals repeatedly ingest plant leaves contaminated with minute quantities of hazardous metals (Pb, As, Hg, Cd, etc.), the metals will gradually accumulate in their bodies. When the quantities of the metals in the bodies reach toxic levels, they may cause serious symptoms of poisoning. Therefore, it is significant to detect and analyze the minute quantities of hazardous metals that attach to plant leaves in terms of epidemiology and disease prevention. We developed grazing exit micro X-ray fluorescence analysis (GE-micro-XRF), which was expected to analyze the localized surface of an aqueous plant leaf with a much faster and simpler sample treatment than with conventional analytical methods, to detect Pb attached to a surface of a leaf of Camellia hiemalis. A micro X-ray beam was produced by using a polycapillary X-ray lens. GE-v-XRF is a grazing exit X-ray analysis (GE-XA) method in which X-rays emitted from only the near-surface region of a specimen are selectively detected under a grazing exit angle condition (extremely low exit angle near 0 degrees). In any GE-XA method, X-rays emitted from inside the specimen must be absorbed inside the specimen and attenuated when X-rays pass through the specimen. However, we deduced that X-rays emitted from inside aqueous organic material such as a plant leaf are scarcely absorbed because X-ray absorption in any aqueous organic material is much smaller than that in most metallic and semiconductor materials, which was analyzed with GE-XA methods. Therefore, we have developed a novel GE-micro-XRF method in which a chip of a silicon wafer is placed between the analyzed leaf and an X-ray detector as an absorber of the X-rays emitted from inside the leaf. As a result of GE-XRF analysis of a leaf dipped in Pb standard solution using the X-ray absorber, we have for the first time selectively detected X-rays emitted from the near-surface region of an aqueous plant leaf. Therefore, we have detected X-rays emitted from Pb with much higher peak/background ratios (P/B ratios) as compared to those of conventional XRF analysis. In the analysis, we also found a difference in element distributions between the leaf surface and its interior. Therefore, we observed and analyzed a cross section of the leaf with a SEM-EDX to confirm the validity of this result. The result of the analysis of the cross section has been in excellent agreement with that of the XRF analysis.

Grazing exit micro X-ray fluorescence analysis (GE-mu-XRF) using an X-ray absorber method was applied to an analysis of Pb attached to an aqueous leaf of Cammelia hiemalis. As a result of the analysis, we found that X-rays emitted from the surface region of the leaf could be detected selectively and then X-rays of Pb could be detected with low background using this analytical method. In this research, an effect of the X-ray absorber was indicated by comparing between X-ray spectra gained with and without use of that. However, since Pb was not attached to a leaf analyzed for this comparison, peak/background ratios of the X-rays of Pb using the X-ray absorber were not compared with those without use of the X-ray absorber. Moreover, X-ray exit angles did not correspond with each other between with and without use of that. We, therefore, applied the GE-1 -XRF to an analysis of As attached to a leaf of Cammelia hiemalis, and then investigated the effect of the X-ray absorber at identical X-ray exit angles with and without use of that. As a result of that, we found peak/background ratios of X-ray peaks of As with use of the X-ray absorber drastically increased at grazing exit angles as compared to those without use of that.

High yield (100%) of C60 fullerene nanotubes have been successfully produced by the liquid-liquid interfacial precipitation method in a small-scale experimental set-up. These nanotubes were. grown in the irradiated C60-saturated pyridine and isopropyl alcohol (IPA) system combined at different ratios (1:10, 1:9, 1:8, 1:6 C60-pyridine:IPA) and incubated at varying temperatures (15°C, 10°C, 5°C). Solutions irradiated under visible light (436 nm) produces higher yield of production and higher reproducibility compared with that illuminated with ultraviolet light (302 nm). The volume of nanotubes grown also increases with increasing ratio of C60-pyridine:IPA and decreasing temperature of incubation. Scanning electron microscopic observations show thinner nanotubes prepared with lower amount of IPA. At present, the process of scaling up the procedure to obtain gram quantities of nanotubes is under investigation. Such work will prove beneficial in obtaining more information on its physical and mechanical properties.