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We investigated the influence of two fillers-CB (carbon black) and silica-on the H

We have investigated the volume effects on hydrogen diffusion properties in both sorption and desorption processes by employing a volumetric analysis technique. The total uptake (𝐶∞), total desorbed content (𝐶0), sorption diffusion coefficient (Ds), desorption diffusion coefficient (Dd), sorption and desorption equilibrium time of hydrogen in two rubbery polymers are determined relative to the diameter and thickness of the cylindrical sample in the two processes. 𝐶∞ and 𝐶0 do not demonstrate the appreciable volume dependence for all rubbers. The identical values in 𝐶∞ and 𝐶0 indicate the reversibility between sorption and desorption, which is interpreted by the occurrence of physisorption rather than chemisorption by introducing hydrogen molecules. The larger Dd values in the desorption process than Ds may be attributed to increased amorphous phase and volume swelling caused by increased hydrogen voids and polymer chain scission after decompression. The time to reach equilibrium in both sorption and desorption processes was found to be linearly proportional to the square of thickness above an aspect ratio of 3.7, which is consistent with the numerical simulations based on the solution of Fick’s law. This finding could be used to predict the equilibrium adsorption time depending on the sample size in the polymer.

An in-situ small punch (SP) test method has recently been developed as a simple screening technique for evaluating the properties of metallic materials used in high-pressure hydrogen environments. With this method, the test conditions including temperature and gas pressure can easily be adjusted to those used in practice. In this study, specimens of STS316L steel and 18 wt% Mn steel were prepared at two different surface roughness, fabricated using wire-cutting and mechanical polishing. Their effects on hydrogen embrittlement (HE) were evaluated using in-situ SP testing at both room temperature and a lower temperature where HE was shown to occur under 10 MPa hydrogen. Both steels were evaluated using two variables obtained from in-situ SP testing, the SP energy, and the relative reduction of thickness (RRT), to quantitatively determine the effect of specimen surface roughness on HE susceptibility. Their fracture characteristics due to HE under 10 MPa hydrogen showed little difference with surface finish. Surface roughness had a negligible influence on these quantitative factors describing HE, indicating that it is not a dominant factor to be considered in in-situ SP testing when it is used to screen for HE compatibility in steels used in high-pressure hydrogen environments.

We report volumetric analysis techniques to analyze the transport properties of hydrogen dissolved in cylindrical-shaped polymers. The techniques utilize the volume measurement of the released hydrogen from rubber by gas collection in a graduated cylinder after charging sample with high-pressure hydrogen and subsequent decompression. We further improve the graduated cylinder with some modifications, such as reading the electrical capacitance of the water level using electrodes and changing the sample loading position. From the measurement results, the uptake (C∞), diffusion coefficient (D), and solubility (S) of hydrogen are quantified with an upgraded diffusion analysis program. These methods are applied to three cylindrical rubbers. Dual adsorption behaviors with increasing pressure are observed for all the samples. C∞ follows Henry's law up to ~15 MPa, whereas Langmuir model applies up to 90 MPa. D shows Knudsen and bulk diffusion behavior below and above pressure, respectively. A COMSOL simulation is compared with experimental observations.

Nondestructive impedance spectroscopy (IS) was developed and demonstrated to detect the effects of hydrogen on nitrile butadiene rubber exposed to hydrogen gas (H2) at high pressures up to 10 MPa. IS was applied to obtain an in situ and real-time quantification of H2 penetration into and its desorption out of rubber under high pressure. The diffusion coefficients of H2 were also obtained from the time evolution of the capacitance, which were compared with those obtained by thermal desorption gas analysis. The in situ measurements of the capacitance and the dissipation factor under various pressures during cyclic stepwise pressurization and decompression demonstrated the diffusion behaviour of H2, the phase of the rubber under high pressure, the transport properties of H2 gas, and the physicochemical interaction between H2 and the rubber. These phenomena were supported by a COMSOL simulation based on the electric current conservation equation and scanning electron microscopy (SEM) observations.

Rubber materials play a key role in preventing hydrogen gas leakage in high-pressure hydrogen facilities. Therefore, it is necessary to investigate rubber materials exposed to high-pressure hydrogen to ensure operational safety. In this study, permeation, volume swelling, hydrogen content, and mechanical characteristics of acrylonitrile butadiene rubber (NBR), ethylene propylene diene monomer (EPDM), and fluorocarbon (FKM) samples exposed to pressures of 35 and 70 MPa were investigated. The results showed that the volume recovery and hydrogen desorption behavior of EPDM with the highest permeation were fast whereas those of FKM with the lowest permeation were slow. The volume of NBR with the highest hydrogen content expanded after decompression. In contrast, FKM swelled the most despite having the lowest hydrogen content. After exposure to high-pressure hydrogen, the compression set (CS) slightly increased due to internal cracks, but the tensile strength decreased significantly with increasing pressure despite the absence of cracks in the fracture area of all tensile specimens. It was concluded that the decrease in tensile strength is closely related to the volume increase because of the relationship between the relative true strength and the volume ratio.

The strain-controlled low-cycle fatigue behavior of P91 steel is investigated under various strain amplitudes ranging from 0.20% to 1.0% at 25, 538, and 566 °C. The fatigue life decreases with an increase in the test temperature; however, a clear reduction is observed at low strain amplitudes, resulting in the degradation of the fatigue limits. The amount of cyclic softening increases with an increase in the strain amplitude and is significantly higher at elevated temperatures. Based on experimental results, Basquin-Coffin-Mason models are established to express the relationship between the strain amplitude-fatigue life curves and the cyclic stress-strain. The transition fatigue life increased from 6677 reversals at 25 °C to approximately 12000 reversals at the elevated temperatures of 538 and 566 °C. The more pronounced effect of temperature at the very low strain amplitude condition is attributed to the occurrence of multiple oxidation-enhanced crack initiations after long-term exposure to elevated temperatures.

We established an ex-situ technique for evaluating hydrogen gas permeability by thermal desorption analysis (TDA) gas chromatography (GC) and by self-developed diffusion analysis software. Absorbed hydrogen mass in rubber, related to the GC-peak area, is recorded as a function of elapsed time after decompressing the hydrogen under high-pressure. From the charging amount (CH0) and diffusivity (D) obtained by the developed diffusion analysis program, the solubility(S) and permeability(P) is evaluated via Henry’s law and P = SD, respectively. The techniques were applied to ethylene propylene diene monomer (EPDM) rubber, sealing material candidates in hydrogen infrastructures. EPDM sample mixed with carbon black fillers showed dual hydrogen diffusion behaviors, whereas EPDM sample without carbon black showed a single hydrogen diffusion behavior. There was no appreciable pressure or size dependence on D, S and P. P are consistent with that measured by different researcher within the expanded uncertainty.

The influence of hydrogen embrittlement on the fatigue behaviors of AISI 304 stainless steel is investigated. The fatigue endurance limits of the untreated and hydrogen-embrittled materials were almost the same at 400 MPa, and hydrogen embrittlement had little influence even though the sample contained about 8.1 times more hydrogen. Thus, the sensitivity of hydrogen gas in this material is very low. A surface crack initiation, growth, coalescence, and micro ridge model is proposed in this study. Slip line formation ⇒ microcrack formation ⇒ increases in the crack width, and blunting of the crack tip as it grows ⇒ formation of many slip lines because of deformation in the shear direction ⇒ growth of the crack in the shear direction, forming micro ridges, coalescence with adjacent cracks ⇒ continuous initiation, growth, coalescence, and ridge formation of surface cracks and specimen breakage.

Paper-based sensors fabricated using the pencil-on-paper method are expected to find wide usage in many fields owing to their low cost and high reproducibility. Here, hydrogen (H2) detection was realized by applying palladium (Pd) nanoparticles (NPs) to electronic circuits printed on paper using a metal mask and a pencil. We confirmed that multilayered graphene was produced by the pencil, and then characterized Pd NPs were added to the pencil marks. To evaluate the gas-sensing ability of the sensor, its sensitivities and reaction rates in the presence and absence of H2 were measured. In addition, sensing tests performed over a wide range of H2 concentrations confirmed that the sensor had a detection limit as low as 1 ppm. Furthermore, the sensor reacted within approximately 50 s at all H2 concentrations tested. The recovery time of the sensor was 32 s at 1 ppm and 78 s at 1000 ppm. Sensing tests were also performed using Pd NPs of different sizes to elucidate the relationship between the sensing rate and catalyst size. The experimental results confirmed the possibility of fabricating paper-based gas sensors with a superior sensing capability and response rate.

The system for producing magnetic field constitutes an important component of magnetic refrigerator. Many researchers have directed significant effort to increase the magnetic field intensity, because the magnetocaloric effect at the Curie temperature increases with the power of 2/3 of the magnetic field. In this study, we report the simulation of the magnetic field intensity at polar axis of a Halbach cylinder (HC) by i) changing the length and thickness of the HC, ii) having with or without gap of the HC, and iii) surrounding the HC with a soft magnet shell, acting as a shielding. We simulated the field distribution of a HC with a finite size. Furthermore, the detailed numerical results of the magnetic field distribution and its dependence on shielding are presented in this study.

Hydrogen penetration into a metal leads to damages and mechanical degradations and its content measurement is of importance. For a precise measurement, a sample preparation procedure must be optimized through a series of studies on sample washing and drying. In this study, two-step washing with organic solvents and thermal soaking in inert gas were tried with a rod-shaped, API X65 steel sample. The samples were machined from a steel plate and then washed in acetone and etyl-alcohol for 5 minute each and dried with compressed air. After then, the samples were thermally soaked in a home-made nitrogen gas chamber during 10 minute at different heat gun temperatures from 100 to and corresponding temperature range in the soaking chamber was from 77 to according to the temperature calibration. Hydrogen residue in the samples was measured with a hot extraction system after each soaking step; hydrogen residue of wppm after the thermal soaking at decayed with increase of the soaking temperature. By adopting the heat transfer model, decay behavior of the hydrogen residue was fitted into an exponential decay function of the soaking temperature. Saturated value or lower bound of the hydrogen residue was 0.36 wppm and chamber temperature required to lower the hydrogen residue about 95% of the lower bound was . Furthermore, a thermal desorption spectroscopy was done for the fully soaked samples at . Weak hydrogen peak was observed for whole temperature range and it means that hydrogen-related contaminants of the sample surface are steadily removed by heating. In addition, a broad peak found around means that parts of the hydrogen residue are irreversibly trapped in the steel microstructure.

This study reports the micro-structural and electrochemical properties of metal-supported solid oxide fuel cells (MS-SOFCs) with an La0.8Sr0.2MnO3−d (LSM)/8 mol% yttria-stabilized zirconia (8YSZ) composite cathode, fabricated at room temperature using the aerosol deposition process (ADP). The composite cathode fabricated with the ADP technique shows uniform distribution of components and pores and the interface between the cathode and the electrolyte displays excellent joining properties. The area specific resistance (ASR) of the ADP-LSM/8YSZ sample is approximately 1.50 Ω cm2 at 800 °C, so this sample shows a significantly lower ASR value than the values usually reported for samples fabricated by the in-situ treatment method for MS-SOFCs. The power density of the cells with the ADP-LSM/8YSZ cathode coated on MS-SOFCs shows a maximum value of 0.38 mW cm−2 at 800 °C and stable performance in the severe thermal durability test. Therefore, these research results can broaden the opportunities for adoption of the ADP coating processes to fabricate cathode materials in MS-SOFCs.

보일러 튜브용 크롬강의 열화기구에 대해 고찰하였다. 크롬강의 열화는 경도 및 응력-파단 수명의 변화를 동반하는데, 이는 주로 탄화물 분해 거동에 의존한다. 그런데 2Cr강인 T22의 열화는 이러한 탄화물 거동에 따르지만 12Cr강인 X20의 열화는 마르텐사이트 래쓰 성장거동에 따르기도 한다. T22와 X20의 열화에 의한 경도값과 응력-파단수명 변화현상을 미세조직적인 측면에서 고찰하였다.

Peak interval for reversible permeability is presented for nondestructively evaluating the remanent life of 1Cr-0.5Mo steel. The method to measure the peak interval of reversible permeability is based on the value of reversible permeability is the same as the differential value of the hysteresis loop. The measurement principle is based on the first harmonics voltage induced in a sensing coil using a lock-in amplifier tuned to a frequency of the exciting voltage. Results obtained for the peak interval of reversible permeability and Rockwell hardness on the aged samples decrease as aging time and the Larson-Miller parameter increase. We could estimate the remanent life of 1Cr-0.5Mo steel by using the relationship between the peak interval of reversible permeability and the Larson-Miller parameter, nondestructively.

The effect of He-injection on irradiation-induced segregation of aging treated Fe–12%Cr–15%Mn austenitic steels, which are candidate materials as the reduced radio-activation of structure material for nuclear and/or fusion reactors was investigated by using the 1250 kV high voltage electron microscope (HVEM) connected with an ion accelerator. The Fe–Mn–Cr steel has been irradiated at 573 K by three irradiation modes of single electron-beam irradiation, electron-beam irradiation after He-injection and electron/He+-ion dual-beam irradiation in a HVEM. Irradiation-induced segregation analyses were carried out by an energy dispersive X-ray analyzer (EDX) in a 200 kV FE-TEM with beam diameter of about 0.5 nm. Dislocation loops with strain contrast were formed during irradiation and the loop numbers density increased rapidly with irradiation dose for He-pre-injected specimens. Voids were not observed after irradiations with three irradiation modes up to 5.4 dpa at 573 K. Irradiation-induced segregations of Cr and Mn near grain boundary were observed in each irradiation condition, but the amounts of Mn segregation decreased in the cases of electron/He+-ion dual-beam irradiation compared with single electron-beam and electron-beam irradiation after He-injection conditions.

The Ultrasonic Nanocrystal Surface Modification (UNSM) technology improves the fatigue life of a torsion bar by inducing compressive residual stress on the surface layer. The UNSM is applied to replace the presetting method and shot peening technology. The torsion bar must be changed periodically because of a lack of durability and a phenomenon related to the stress relaxation. The torsion fatigue test specimens were made of DIN17221 material, and the results showed that the fatigue life was 5 times more than under durability test conditions. A comparison test between the commercial vehicles' presetting method and shot peened torsion bar and the UNSM torsion bar showed that the UNSM could replace the presetting method and shot peening.

Many researchers have been interested in the nondestructive measurement methods for estimating components damage in order to assure the safe service of steel structures. It is recognized that the evaluating techniques based on magnetic measurement can offer a great potential because of high susceptibility to the change of several metallurgical factors. Magnetic property such as coercive force was measured. The coercive force at room temperature monotonously increased with the increase of frequency. The correlation between the magnetic properties of used material and that of un-used material was studied. The coercive force gradient at room temperature increased with the increase of aging. Hence the estimating method using magnetic properties allows one to evaluate the extent of material aging for reactor pressure vessel.

A nanocontact deformation method was used to measure the local and graded residual stresses around contact damages. By analyzing influences of the residual stress on nanocontact deformation itself instead of measuring the secondary crack emanated from it, 0.65 μm spatial resolution, which was superior to the highest level 1.8 μm attained by previous indentation fracture mechanics tests with an acute cube-corner indenter, was obtained with a general Berkovich indenter. However, a stress model combined with the nanocontact deformation provided only average stress variation around the contact damages. Thus, a resolution of two principal components from the residual stress in a biaxial state has been attempted in this study. By introducing radial microcracks around artificial microVickers damages, a crack-normal circumferential stress component disappeared and a series of nanoindentations close to the microcrack line yielded a variation of the radial stress component. By comparing this result with the average stress variation mentioned above, the crack-opening circumferential stress was measured and showed a good consistency with the previous study in soda-lime glass. In addition, distinctive features of present method were compared with previous indentation fracture mechanics method.