Range Of Hydrogen Concentrations Research Articles

238 微小試験片によるステンレス鋼高圧水素ガス曝露材の強度特性評価(OS8-2 水素環境が金属強度特性に及ぼす影響,OS8 水素環境が金属強度特性に及ぼす影響)

Tensile and fatigue properties of stainless steels exposed to highly pressurized hydrogen gaseous environment are investigated using small specimen. The hydrogen content distribution in the small specimen is nearly uniform, because the thickness of the specimen is very small (0.3mm). Metastable austenitic stainless steel SUS304 and SUS304L show the degradation of tensile ductility and the fatigue life by exposure to hydrogen gas environment. Even stable austenitic stainless steel SUS316L shows the little degradation of the tensile ductility in the high hydrogen content range, but doesn't show the degradation of the fatigue life.

1H NMR spectra and echoes in Pd–H and Pd–Ag–H alloys

The paper presents the experimental results of rigid-lattice proton magnetic resonance spectra and second moments in Pd–H, Pd 0.90Ag 0.10–H, Pd 0.80Ag 0.20–H, Pd 0.75Ag 0.25–H, and Pd 0.65Ag 0.35–H alloys at T = 2.4 K in a wide hydrogen concentration range. Free induction decay (FID), solid and inhomogeneous echoes were detected and interpreted. The interpretation based on dipole–dipole interaction of homogeneously distributed proton spin system is satisfactory at high hydrogen concentration, but an inhomogeneous field of paramagnetic origin (most probably coming from Fe impurities) plays the dominant role at small hydrogen content. An unexpected correlation was found between the macroscopic magnetic susceptibility and the second moment coming from the inhomogeneous internal field.

Boron-Doped Si0.8Ge0.2 Thin Film Deposited by Helicon Sputtering for Microthermoelectric Hydrogen Sensor

A boron-doped thin film of thickness was deposited by helicon sputtering. Thermal annealing was carried out to crystallize as-deposited amorphous-like thin films. The thermoelectric properties of the films, such as an electrical conductivity, a carrier concentration, a mobility, and a Seebeck coefficient, were investigated. As a result, the films by helicon sputtering exhibited finer grains and smoother surface than those of the film deposited by conventional radio frequency (rf) sputtering. The film deposited by helicon sputtering with an rf induction coil power of and annealed at for showed a resistivity of , a Seebeck coefficient of , a Hall mobility of , and a carrier concentration of at . A microthermoelectric hydrogen sensor (micro-THS) with the boron-doped thin film and annealed at for showed high sensitivity for hydrogen gas in air. This sensor could have wide detection range of hydrogen concentration from to 3%. At an operating temperature of , for the low hydrogen concentration of , clear response was shown by the micro-THS with the film deposited by helicon sputtering and annealed at for .

SOFC characteristics along the flow path

Solid oxide fuel cells (SOFCs) in metallic housings were integrally and locally characterised. The tests were performed in counter flow operation for hydrogen concentrations from 2% to 100%, to identify concentration limitations and to optimise fuel utilisation. Cell characterisations were performed by spatially resolved electrochemical impedance spectroscopy (EIS), current density/voltage ( i– V) and temperature measurements as well as gas chromatography measurements at 16 distinct points across the cell. The results show a substantial variation of current density and voltage distribution along the flow path with varying hydrogen content and fuel utilisation. The fuel utilisation was calculated from the local current densities and compared to the values measured by gas chromatography. Both sets of results showed good agreement. At low hydrogen inlet concentrations the voltage at the fuel outlet drops to values that might be harmful for the stability of the anode since reoxidation of nickel can occur. The impedances obtained by local EIS did not show an overall coherent dependency on the hydrogen concentration. EIS under load revealed two distinct domains: in the range of hydrogen concentrations of 2–10% H 2 the impedance decreased significantly with increasing hydrogen content whereas at higher hydrogen contents the impedance was hardly affected. This indicates significant concentration and diffusion overpotential at low hydrogen concentrations. The local data showed differing behaviour in the middle of the cell compared to the fuel outlet. Leakage at the sealing could be identified as a possible reason. As an additional method of investigation, the voltage drop over the contact resistance of the cathode side was measured. Temperature measurements show that local temperatures differ significantly depending on the load applied to the cell. This observation emphasizes the importance of a thermal management adapted to the characteristics on operation conditions of the cells, particularly when the stack itself has only a low mass.

Strain-induced effects in H: Ti: LiNbO3 single-crystal layers

The parameters of proton-exchange waveguide H: LiNbO3 layers and doubly doped H: Ti: LiNbO3 layers were comparatively analyzed by x-ray diffractometry and optical mode spectroscopy. It was established that the change in the lattice parameter in hybrid H: Ti: LiNbO3 layers is significantly smaller than that in proton-exchange H: LiNbO3 layers formed under the same proton exchange conditions. The behavior of the optical and structural parameters of H: Ti: LiNbO3 layers was studied in a wide hydrogen concentration range.

Micro-Thermoelectric Hydrogen Sensors with Pt Thin Film and Pt ∕ Alumina Thick Film Catalysts

Micro-thermoelectric hydrogen sensor (micro-THS) was fabricated to operate with its unique working principle of the combination of the thermoelectric effect of SiGe thin film and the Pt-catalyzed exothermic reaction of hydrogen oxidation. We focused on improving sensitivity and response speed of micro-THS using a new catalyst deposition method. Comparing with the two catalysts of thin and thick film technology, sensitivity of the micro-THS with thick film catalyst was 5 times higher than that of the sensor with Pt thin film catalyst. The of thick film catalyst was large enough for a wide detection range of hydrogen concentration from 25 ppm to 3%, although its size was small, 35% of the Pt thin film one. At operating temperature of 100°C, for the low hydrogen concentration of 25 ppm, clear response of 0.03 mV the micro-THS with thick film catalyst was observed.

Magnetic Properties of Palladium and Palladium–Platinum Alloy of Various Hydrogen Content

Magnetic properties of palladium and palladium-platinum alloy (Pd-Pt) of different hydrogen content were measured in a hydrogen atmosphere at ambient temperature using a superconducting quantum interference device (SQUID) magnetometer. It was found that the magnetic susceptibility of Pd and Pd-Pt alloy decreased with increasing hydrogen content. These results were attributed to a change in the electronic structure of the valence band. Increasing hydrogen content in Pd and Pd-Pt alloy causes the Fermi level to rise and the density of states at Fermi level to decrease. Since the magnetic susceptibility is proportional to the density of states at the Fermi level, the magnetic susceptibility decreases with increasing hydrogen content. The magnetic susceptibility of Pd-Pt was smaller than that of Pd over the whole hydrogen content range. This was ascribed to the higher position of the Fermi level of Pd-Pt than that of Pd. [doi:10.2320/matertrans.47.2373]

Large negative magnetoresistance in the hydride halidesGdI2Hx: A system with competing magnetic interactions

We have studied the magnetic and magnetoresistance properties of $\mathrm{Gd}{\mathrm{I}}_{2}{\mathrm{H}}_{x}$ samples within a hydrogen concentration range $0.24\ensuremath{\leqslant}x\ensuremath{\leqslant}0.45$. A large negative magnetoresistance ($\ensuremath{\sim}95%$ in a $70\text{\ensuremath{-}}\mathrm{kOe}$ field at $150\phantom{\rule{0.3em}{0ex}}\mathrm{K}$) has been observed in ferromagnetic $\mathrm{Gd}{\mathrm{I}}_{2}{\mathrm{H}}_{x}$ samples $(x=0.24,0.26)$ near the magnetic transitions ${T}_{\mathrm{C}}\ensuremath{\approx}170\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. These layered compounds exhibit thermally activated conduction, accompanied by a gradual decrease of the activation energy below ${T}_{\mathrm{C}}$. The magnetoresistance is remarkably large ($\ensuremath{\sim}50%$ at $70\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$) already at room temperature and continuously increases with decreasing temperature, reaching saturation in the ferromagnetic region. The magnetic studies reveal the presence of competing ferromagnetic and antiferromagnetic interactions, which result in a spin freezing at low temperatures. These results suggest that the large magnetoresistance effect is governed by magnetic disorder present in the system.

Effect of Pd additions on phase stability and hydrogen-induced internal friction of TiZrCuNi glassy alloys

The effects of additions of Pd below 10 at.% on the stability and hydrogen-induced internal friction behavior of Ti 34 Zr 11 Cu 47 Ni 8 glassy alloys have been investigated. Thermal analyses indicate that the supercooled liquid region decreases distinctly with increasing Pd content. It was found that internal friction peak temperatures of Ti 34 Zr 11 Cu 47 Ni 8 –Pd hydrogenated glassy alloys (HGAs) in the hydrogen content range below approximately 30 at.% H were higher than those of the original Ti 34 Zr 11 Cu 47 Ni 8 HGAs, especially at hydrogen contents below ∼10 at.% H. It was also found that the internal friction peaks of Ti 34 Zr 11 Cu 47 Ni 8 –Pd HGAs increased with increasing hydrogen content below ∼15 at.% H, after which they tended to saturate. These results are in contrast to the effects of Si addition as previously reported. The effects of Pd are discussed from the viewpoint of the interstitial site distribution for hydrogen and local atomic structure of the glassy alloy.

Response to hydrogen of a metal/AlN/Si thin film structure: Effects of composition and structure of a combination Pd–Cr gate

The effect of Cr addition to the gate of a Pd/AlN/Si Hydrogen gas sensor was investigated by modifying the gate composition and structure. A device with a pure Pd gate responds to hydrogen concentrations as low as 1 ppm, with saturation at about 60 ppm. However, with a Pd 0.96Cr 0.04 alloy gated device, although the response amplitude was reduced, the dynamic range was considerably enhanced, with useful response up to 50,000 ppm and with quite satisfactory signal to noise down to 50 ppm. Interestingly, in 10% Cr alloyed to the gate, the response was lost. To investigate the mechanism responsible for this effect, two gate structures were studied where a thin layer of pure Pd was added to the 4% alloy gate, one at its outer surface and the other at the gate/AlN interface. The response of the former saturated at 60 ppm and in general behaved comparably to the device with a pure Pd gate, whereas the latter showed the expanded dynamic range. For all these cases the maximum magnitude of the electrical response is in the range of 0.1–0.5 V, even though the hydrogen concentration range varies by three orders of magnitude. This indicates that saturating electrical response is highly sensitive to the properties of the gate outer surface, whereas hydrogen sensitivity is highly dependent on the amount of hydrogen reaching the interface between metal gate and insulator.

Development of a hydrogen sensor based on solid polymer electrolyte membranes

A compact hydrogen gas sensor based on solid polymer electrolyte (Nafion 117), working under amperometric conditions at room temperature with minor water maintenance, has been developed. Electrodes were prepared chemically by using the impregnation–reduction method. The polymer was platinized by using a platinum chloro amino complex and sodium tetrahydro borate as impregnating salt and reducing agent, respectively. The thin Pt films were characterized by XRD, infrared spectroscopy, optical microscopy, scanning electron microscopy and EDAX. Sensor measurements were performed under amperometric short-circuit current conditions. A maximum sensitivity of about 0.01 μA cm −2 ppm −1 was obtained. The response time was observed to be in the range of 10–50 s. A reproducible response with an approximately linear current versus P H 2 has been observed for the range of hydrogen concentration from 1 to 10%.

Hysteresis and related irreversible phenomena in CeNi 5-based intermetallic hydrides: Effect of substitution of Co for Ni

The phase relationships and thermodynamics of hydride formation and decomposition in the CeNi 5− x Co x –H 2 ( x = 1, 1.5, 2.5) systems have been studied by means of pressure–composition isotherm measurement and XRD analysis. Special attention has been paid to the first hydrogenation. A significant reduction of hysteresis, especially within the first cycle, has been observed in all studied alloys as compared with non-substituted CeNi 5. The effect of temperature and reaction direction on the isotherm shape and plateau splitting has been revealed for CeNi 3.5Co 1.5. The CeNi 2.5Co 2.5–H 2 system has demonstrated an exceptional phenomenon of oscillating dynamics of equilibrium achievement within the hydrogen concentration range of 3–5 atoms H per formula unit. Some suggestions on the CeNi 5− x Co x peculiarities have been proposed.

Behavior of Pre-hydrided Zircaloy-4 Cladding under Simulated LOCA Conditions

To promote a better understanding of high burn-up fuel rod behavior in a loss-of-coolant accident, laboratory-scale experiments were performed varying sample and test conditions with non-irradiated Zircaloy-4 claddings. Short test rods, fabricated with claddings having a wide range of hydrogen concentrations (about 100 to 1,450 ppm), were heated, isothermally oxidized at 1,220 to 1,500 K in steam flow, and quenched in flooding water. Axial shrinkage of the rods during the quench was restrained, controlling the maximum restraint load at four different levels. Test rods ruptured during the heat-up, and slight hydrogen concentration effects were seen on rupture temperature and strain. Depending primarily on the oxidized fraction of the cladding thickness, a part of claddings sustained circumferential cracking and fractured into two pieces during the quench. The fracture/no-fracture threshold of the oxidized fraction decreases as both the initial hydrogen concentration and axial restraint load increase. Consequently, when the restraint load is below 535 N, the fracture threshold is higher than 20% cladding oxidation, irrespective of the hydrogen concentration. This is sufficiently higher than the limit in the Japanese ECCS acceptance criteria.

Influence of Hydride Re-orientation on BWR Cladding Rupture under Accidental Conditions

Hydride precipitation along the radial-axial plane increases in high burn-up boiling water reactor (BWR) fuel claddings. The radially-oriented hydrides may have an important role during fuel behavior in a reactivity-initiated accident and may reduce ductility of the cladding under pellet-cladding mechanical interaction (PCMI) conditions. In order to promote a better understanding of the influence of the radial hydrides on cladding failure behavior under the PCMI conditions, tube burst tests were conducted for unirradiated BWR claddings charged with 200 to 650 ppm of hydrogen. About 20 to 30% of hydrides were re-oriented and precipitated along the radial-axial plane. The claddings exhibited large rupture openings with an axial crack at room temperature and 373 K. The crack penetrated through cladding wall preferentially along the radial hydrides, and radial cross section showed cladding failure in a brittle manner. However, reduction in residual hoop strain by precipitation of the radial hydrides was very small. It is accordingly expected that ductility of high burn-up BWR cladding is significantly reduced not only by precipitation of radial hydrides as far as hydrogen concentration and radial hydride fraction range in the present study.

Acoustic investigations of the ZrV 2–H system

Elastic modulus and internal friction of the ZrV 2H x system have been measured by the method of low-frequency acoustics (∼1 kHz) in a wide range of hydrogen concentrations (0 ≤ x ≤ 6) and temperatures (65 K < T < 300 K). It is established that an increase of the hydrogen concentration shifts the structural phase transformation from the rhombohedral to the cubic phase of the ZrV 2 compound towards high temperatures and leads to its suppression. An anomaly of the elastic modulus in the concentration range 0.7 < x ≤ 6 with a corresponding peak of the internal friction was detected at a temperature of ∼200 K, characteristic of the phase transition. The relaxation peak of the internal friction observed above 200 K is caused by dissipation of elastic energy on interphase boundaries.

Hydrogen and hydride detection in metallic glasses

Different methods for the detection of hydrogen dissolved in the structure of metallic glasses and the detection of hydrides eventually present in these materials are presented and discussed. It includes a conventional procedure, the electrochemical hydrogen permeation test and two alternative ones: a new method herein named proton elastic recoil track analysis (p-ERTA) and another one based on Hall Effect measurements. These methods were applied in samples of Fe40 Ni38Mo4B18 and Ni81P19 metallic glasses. The electrochemical hydrogen permeation tests were described and discussed based on results of the two metallic glasses used so as to support the results obtained with the new methodologies. The p-ERTA technique was proposed as a combination of two well known and established techniques, namely the elastic recoil detection analysis and the solid state nuclear track detection. It permitted the observation that the spatial localization of hydrogen in the structure of the metallic glass possesses a heterogeneous distribution. The easy-to-perform Hall Effect measurements were useful to detect hydride formation in the structure of a metallic glass and the variation of the hydrogen diffusion coefficient over a wide range of hydrogen concentrations, even in regions where hydrogen-hydrogen interactions are likely to occur.

Argon–hydrogen rf plasma study for carbon film deposition

In this work the effect of hydrogen addition on the physical properties and the sputtering efficiency of an radio-frequency (rf) (13.56 MHz) Ar plasma was investigated. The discharges in Ar–H2 were used to sputter-deposit carbon films from a graphite cathode, with a hydrogen concentration in the feed gas ranging from 0 to 100% (the useful range for film growth was however limited to 0–85%). The physical plasma parameters were determined using a Langmuir probe, which, coupled with a chemical modelling of the ion–molecule and electron–molecule reactions in gas phase, enabled us to define the energy flux conditions at the cathode. The results show that hydrogen exerts a positive effect on the film deposition rate at the lowest end of the hydrogen concentration range, an enhancing deposition effect correlated with a high density of ArH+ ions in the plasma and a high energy flux carried by the ions to the cathode. Nonetheless, an analysis of the processes at the cathode indicates that the sputtering mechanism was essentially physical in the low [H2] range (3–20%) but that a chemical assistance of the process should be considered too for the remaining [H2] range. Besides, even in the physical sputtering regime, the target material removal occurred with a reactive sputtering mechanism, which implies a chemical modification of the target surface layers and surface binding energy.

An investigation on structure, deformation and fracture of hydrides in titanium with a large range of hydrogen contents

The deformation and fracture behaviors of δ hydrides in cyclic strained titanium containing 350, 720 and 930 ppm hydrogen were investigated and compared to that of γ hydrides in 77 ppm hydrogen specimens. It was found that the γ and δ hydrides, respectively, in 77 and 350 ppm hydrogen specimens could be plastically deformed readily along with the matrix without fracture, while the δ hydrides at hydrogen contents more than 720 ppm can be either plastically deformed or cleavage fractured, depending on their sizes, orientations, and interactions with localized matrix deformation. The crystallographic, microstructural and micromechanical mechanisms for hydride behavior were discussed.

An investigation on structure, deformation and fracture of hydrides in titanium with a large range of hydrogen contents

An investigation on structure, deformation and fracture of hydrides in titanium with a large range of hydrogen contents

Medium range ordering of amorphous silicon-carbon alloys studied by GISAXS, optical spectroscopy and IBA

The nano-structural properties of non-stoichiometric hydrogenated amorphous silicon carbide thin films, deposited by magnetron sputtering and PECVD (plasma enhanced chemical vapour deposition) in a wide range of hydrogen and carbon concentration, were analysed by GISAXS (grazing incidence small angle X-ray scattering), optical spectroscopy and IBA (ion beam analysis). The GISAXS was performed on ELETTRA synchrotron radiation source, Trieste (Italy). All of the measured specimens showed the presence of ‘particles’ with mean dimensions between 1.5 and 4.5 nm while the size distribution of ‘particles’ varied from sample to sample between 1 and 2.5 nm. In order to determine the constitution of the ‘particles’, the specimens were examined by vibrational spectroscopy (Raman and IR spectroscopy) when estimating the local structural and chemical ordering and IBA (ion beam analysis) e.g. RBS (Rutherford back scattering) and ERDA (elastic recoil detection analysis) when estimating the composition of films. The results suggest that the ‘particles’ are agglomerates of small voids, whose size increases with carbon to silicon ratio and whose distribution broadens with hydrogen concentration.