Rapid Diffusion Of Hydrogen Research Articles

Hydrogen-assisted fatigue crack propagation behavior of selective laser–melted Inconel 718 alloy

Hydrogen-assisted fatigue crack propagation behavior of selective laser melted Inconel 718 alloy was investigated under in situ electrochemical hydrogen charging, and by multi-scale microstructural analysis. Results suggest that hydrogen significantly increases the fatigue crack growth rate (FCGR), and such an effect is intensified for the post-heat-treatment sample by an acceleration of 2.8 times. Rapid hydrogen diffusion along grain boundaries, and planar-dislocation-slip-induced local hydrogen concentration induced abundant of intergranular cracking, and a decrease of deformation expansion. The suppressed dislocation emission and mobility by hydrogen significantly confine the plastic deformation ahead of the crack tip, thus accelerated the FCGR in the presence of hydrogen.

The defect structure evolution in magnesium hydride/metal-organic framework structures MIL-101 (Cr) composite at high temperature hydrogen sorption-desorption processes

This paper describes the microstructural changes in the process of high temperature hydrogen sorption of composite based on MgH2 and metal-organic framework structures (MOFs) MIL-101 (Cr). The microstructure of the composite was analyzed by X-ray diffraction, electron microscopy and positron annihilation spectroscopy (PAS). The PAS complex allows in situ measurements in a vacuum chamber at elevated temperature and pressure ranges during hydrogenation or dehydrogenation. Based on the results obtained, the composite structure represents a core-shell in which nano-sized particles of chromium oxide and MIL-101(Cr) residues are evenly distributed on the surface of larger magnesium hydride particles. The MOFs MIL-101(Cr) is partially retained after mechanical synthesis and remains relatively stable when heated to 340 °C. The defect structure formed as a result of the synthesis contributes to the rapid diffusion of hydrogen into the bulk of magnesium particles. This defect structure affects the absorption of hydrogen by composites at temperatures up to 400 °C and have a negligible effect at 450 °C.

Sound velocities and single-crystal elasticity of hydrous Fo90 olivine to 12 GPa

Nominally anhydrous minerals (NAMs) may contain significant amounts of water and constitute an important reservoir for mantle hydrogen. The colloquial term ‘water’ in NAMs is related to the presence of hydroxyl-bearing (OH−) point defects in their crystal structure, where hydrogen is bonded to lattice oxygen and is charge-balanced by cation vacancies. This hydrous component may therefore have substantial effects on the thermoelastic parameters of NAMs, comparable to other major crystal-chemical substitutions (e.g., Fe, Al). Assessment of water concentrations in natural minerals from mantle xenoliths indicates that olivine commonly stores ∼0–200 ppm of water. However, the lack of samples originating from depths exceeding ∼250 km coupled with the rapid diffusion of hydrogen in olivine at magmatic temperatures makes the determination of the olivine water content in the upper mantle challenging. On the other hand, numerous experimental data show that, at pressures and temperatures corresponding to deep upper mantle conditions, the water storage capacity of olivine increases to 0.2–0.5 wt%. Therefore, determining the elastic properties of olivine samples with more realistic water contents for deep upper mantle conditions may help in interpreting both seismic velocity anomalies in potentially hydrous regions of Earth's mantle as well as the observed seismic velocity and density contrasts across the 410-km discontinuity.Here, we report simultaneous single-crystal X-ray diffraction and Brillouin scattering experiments at room temperature up to 11.96(2) GPa on hydrous [0.20(3) wt% H2O] Fo90 olivine to assess its full elastic tensor, and complement these results with a careful re-analysis of all the available single-crystal elasticity data from the literature for anhydrous Fo90 olivine. While the bulk (K) and shear (G) moduli of hydrous Fo90 olivine are virtually identical to those of the corresponding anhydrous phase, their pressure derivatives K′ and G′ are slightly larger, although consistent within mutual uncertainties. We then defined linear relations between the water concentration in Fo90 olivine, the elastic moduli and their pressure derivatives, which were then used to compute the sound velocities of Fo90 olivine with higher degrees of hydration. Even for water concentrations as high as 0.5 wt%, the sound wave velocities of hydrous and anhydrous olivines were found to be identical within uncertainties at pressures corresponding to the base of the upper mantle. Contrary to previous claims, our data suggest that water in olivine is not seismically detectable, at least for contents consistent with deep upper mantle conditions. In addition to that, our data reveal that the hydration of olivine is unlikely to be a key factor in reconciling seismic velocity and density contrasts across the 410-km discontinuity with a pyrolitic mantle.

A review on pitting corrosion and environmentally assisted cracking on duplex stainless steel

Duplex stainless steel is widely used in the petrochemical, maritime, and food industries. However, duplex stainless steel has the problem of corrosion failures during use. This topic has not been comprehensively and academically reviewed. These factors motivate the authors to review the developments in the corrosion research of duplex stainless steel. The review found that the primary reasons for the failure of duplex stainless steels are pitting corrosion and chloride-induced stress corrosion cracking. After being submerged in water, the evolution of the passive film on the duplex stainless steel can be loosely classified into three stages: nucleation, rapid growth, and stable growth stages. Instead of dramatic rupture, the passive film rupture process is a continuous metal oxidation process. Environmental factors scarcely affect the double-layer structure of the passive film, but they affect the film's overall thickness, oxide ratio, and defect concentration. The six mechanisms of alloying elements on pitting corrosion are summarized as stabilization, ineffective, soluble precipitates, soluble inclusions, insoluble inclusions, and wrapping mechanisms. In environments containing chlorides, ferrite undergoes pitting corrosion more easily than austenite. However, the pitting corrosion resistance reverses when sufficiently large deformation is used. The mechanisms of pitting corrosion induced by precipitates include the Cr-depletion, microgalvanic, and high-stress field theories. Chloride-induced cracks always initiate in the corrosion pits and blunt when encountering austenite. Phase boundaries are both strong hydrogen traps and rapid hydrogen diffusion pathways during hydrogen-induced stress cracking.

Effect of open pore and pore interconnectivity in the Ni-SDC cermet anode microstructure on the performance of solid oxide fuel cells

In nickel-samarium-doped ceria (Ni-SDC) cermet anode layers, the open pores and interconnected pores in the microstructure are the main factors that affect the mechanical and electrical properties. In this work, porous Ni-SDC cermet anode layers are fabricated using various quantities of potato starch (0 to 25 wt.%) as a pore forming in the anode powders. The properties of the Ni-SDC cermet anode layers were characterised by FESEM-BSE microscopy, Archimedes method for density measurement, Vickers hardness, flexural strength, and DC four-point electrical conductivity. The findings revealed that the different content of potato starch greatly affected the percentage of porosity and pore interconnectivity in the microstructure and consequently altered the mechanical and electrical properties of the Ni-SDC cermet anode. The degree of shrinkage, relative density, mechanical strength and electrical conductivity of the Ni-SDC cermet anodes decreased as their pore former content increased. Furthermore, the research shows that the large porosity (> 40%) in the Ni-SDC cermet anode microstructure affected the continuity of Ni-Ni, SDC and Ni-SDC phases and thereby affected the mechanical and electrical properties. The Ni-SDC cermet anode with 10 wt.% exhibited sufficient porosity, Vickers hardness, flexural strength and electrical conductivity of 34%, 48 MPa, 72 MPa and 2028 S/cm (at 800 °C), respectively. Therefore, optimisation of porosity in the Ni-SDC cermet anode microstructure strongly contributes to the well-connected pore channels for the rapid diffusion of hydrogen for oxidation and mechanical strength.

In-situ infrared spectra of OH in rutile up to 1000 °C

The infrared spectra of hydrous, oriented single crystals of synthetic Al-doped and pure rutile were measured from room temperature to 1000 °C at 1 bar using a heating stage. At room temperature, the spectra show only one band at ~3278 cm−1 in pure rutile, and two additional bands at ~3303 and 3323 cm−1 in Al-doped rutile. The main band associated with Al at ~3323 cm−1 loses intensity as temperature increases and nearly disappears already at 300 °C. This suggests that the corresponding defect only forms during cooling and, therefore, water speciation in rutile at room temperature is not representative of subduction zone or upper mantle conditions. All OH bands shift to lower wavenumbers at elevated temperatures with dν/dT = −0.0831 cm−1 K−1 for the main band at 3278 cm−1. This strong low-frequency shift is unexpected for an OH bond involved in hydrogen bonding, indicating decreasing O–O distance for the OH band. Together with the extreme broadening of the band at high temperature, it suggests some weakening of the OH bond strength and a rapid exchange of protons, consistent with rapid hydrogen diffusion in rutile.

Hydrogen diffusion in bulk MgB2

The diffusion of hydrogen in MgB2 is crucial to the kinetics of rehydrogenation of Mg(BH4)2. We report a comprehensive combination of first-principles calculations and Kinetic Monte Carlo Simulations to examine the energetics of diffusion of hydrogen atoms through bulk MgB2. From these calculations we find that diffusion is fast for the neutral interstitial hydrogen defect and that the overall migration barrier for hydrogen diffusion in MgB2 is 0.22eV, showing that rapid diffusion of hydrogen is possible even at moderate temperatures. The interstitial hydrogen defect formation energy is around 0.8eV at 0K, indicating a low hydrogen solubility at moderate temperatures.

Zinc-Oxide Thin-Film Transistor With Self-Aligned Source/Drain Regions Doped With Implanted Boron for Enhanced Thermal Stability

Because of the rapid diffusion of hydrogen in zinc oxide even at a relatively low temperature, zinc-oxide-based thin-film transistors (TFTs) with hydrogen-doped source/drain regions suffer from degraded thermal stability. The use of boron, which is a heavier and a more slowly diffusing dopant, is systematically investigated as a replacement of hydrogen. Its effectiveness as a dopant has been studied in terms of a range of process conditions, including its implantation dosage and the subsequent heat treatment temperature, time, and ambience. The lowest resistivity of 2 mΩ-cm has been obtained at a boron dose of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Self-aligned top-gated zinc-oxide TFTs with source/drain regions doped with implanted boron are shown to be more stable than those doped with hydrogen, even when subjected to the relatively high temperature needed for the formation of a good-quality passivation layer.

Suspended sub-50 nm vanadium dioxide membrane transistors: fabrication and ionic liquid gating studies

We demonstrate a robust lithographic patterning method to fabricate self-supported sub-50 nm VO(2) membranes that undergo a phase transition. Utilizing such self-supported membranes, we directly observed a shift in the metal-insulator transition temperature arising from stress relaxation and consistent opening of the hysteresis. Electric double layer transistors were then fabricated with the membranes and compared to thin film devices. The ionic liquid allowed reversible modulation of channel resistance and distinguishing bulk processes from the surface effects. From the shift in the metal-insulator transition temperature, the carrier density doped through electrolyte gating is estimated to be 1 × 10(20) cm(-3). Hydrogen annealing studies showed little difference in resistivity between the film and the membrane indicating rapid diffusion of hydrogen in the vanadium oxide rutile lattice consistent with previous observations. The ability to fabricate electrically-wired, suspended VO(2) ultra-thin membranes creates new opportunities to study mesoscopic size effects on phase transitions and may also be of interest in sensor devices.

Characterization of hydrogen-induced crack initiation in metastable austenitic stainless steels during deformation

Hydrogen-induced crack initiation in hydrogen-charged metastable austenitic stainless steels during deformation at 295 K is characterized by performing a combined tensile and hydrogen release experiment and scanning probe microscopy. Strain-induced martensite (α′) not only provides a path for rapid hydrogen diffusion in austenite (γ) but also promotes crack initiation. Hydrogen rapidly diffuses from α′ and accumulates at the boundary between the α′-rich and γ-rich zones during deformation due to the high hydrogen diffusivity and low hydrogen solubility in α′, resulting in crack initiation at the boundary between the α′-rich and γ-rich zones. The hydrogen-induced crack initially grows along the boundary between the α′-rich and γ-rich zones and then propagates in the α′-rich zone.

Protection of the Retina by Rapid Diffusion of Hydrogen: Administration of Hydrogen-Loaded Eye Drops in Retinal Ischemia–Reperfusion Injury

Retinal ischemia-reperfusion (I/R) injury by transient elevation of intraocular pressure (IOP) is known to induce neuronal damage through the generation of reactive oxygen species. Study results have indicated that molecular hydrogen (H(2)) is an efficient antioxidant gas that selectively reduces the hydroxyl radical (*OH) and suppresses oxidative stress-induced injury in several organs. This study was conducted to explore the neuroprotective effect of H(2)-loaded eye drops on retinal I/R injury. Retinal ischemia was induced in rats by raising IOP for 60 minutes. H(2)-loaded eye drops were prepared by dissolving H(2) gas into a saline to saturated level and administered to the ocular surface continuously during the ischemia and/or reperfusion periods. One day after I/R injury, apoptotic cells in the retina were quantified, and oxidative stress was evaluated by markers such as 4-hydroxynonenal and 8-hydroxy-2-deoxyguanosine. Seven days after I/R injury, retinal damage was quantified by measuring the thickness of the retina. When H(2)-loaded eye drops were continuously administered, H(2) concentration in the vitreous body immediately increased and I/R-induced *OH level decreased. The drops reduced the number of retinal apoptotic and oxidative stress marker-positive cells and prevented retinal thinning with an accompanying activation of Müller glia, astrocytes, and microglia. The drops improved the recovery of retinal thickness by >70%. H(2) has no known toxic effects on the human body. Thus, the results suggest that H(2)-loaded eye drops are a highly useful neuroprotective and antioxidative therapeutic treatment for acute retinal I/R injury.

Polymer Membranes for Hydrogen Separations

AbstractThe development of a hydrogen-based economy would generate a substantial necessity for efficient means of collecting hydrogen with a relatively high purity. Membrane separations play a major role in the separation of hydrogen gas from various gas mixtures, and this article discusses the use of polymeric materials to produce these membranes. After a review of the historical use of polymeric membranes and some background information regarding mechanisms of gas transport in membranes, this article will review the work that has been done in the two major classes of hydrogen separation membranes: hydrogen-selective membranes and hydrogen-rejective membranes. In hydrogen-selective membranes, the very small size of the hydrogen molecule is exploited to allow rapid diffusion of hydrogen through the membrane while excluding other gases. Hydrogen-rejective membranes use the significantly higher sorption of other gases to overcome the advantages of the small size of the hydrogen molecule. The discussion of these two types of membranes will be followed by a presentation of the current state of the art with regard to polymeric membranes for hydrogen separation and a discussion of the predictions for future applications and advancements in this area.

Effects of intentionally introduced hydrogen on the electrical properties of ZnO layers grown by metalorganic chemical vapor deposition

Unintentionally doped ZnO layers grown epitaxially on a sapphire substrate have been exposed either to a hydrogen or deuterium plasma. Secondary ion mass spectroscopy measurements performed subsequently showed a rapid diffusion of hydrogen in these layers. Furthermore, the presence of hydrogen in the ZnO samples is found to be responsible for nearly a factor of 3 increase in the free electron concentration. This effect is attributed to the hydrogen passivation of compensating acceptor impurities present in the as-grown ZnO layers.

X-ray diffraction, neutron scattering and NMR studies of hydrides formed by Ti 4Pd 2O and Zr 4Pd 2O

The oxygen-stabilized Ti 4Pd 2O and Zr 4Pd 2O alloys with the cubic E9 3-Ti 2Ni type structure have been reacted with hydrogen gas. Powder X-ray diffraction (XRD) has shown that the hydride phase retains a face-centered-cubic unit cell with an expansion of lattice parameter that is dependent on hydrogen content. The crystal structure has been solved for Zr 4Pd 2OD 3.5 by neutron diffraction. NMR measurements of proton relaxation times were made on Ti 4Pd 2OH 5.0 to assess diffusion behavior. Although the activation energy of 0.39 eV derived for Ti 4Pd 2OH 5.0 was nearly identical to the value found for hydrogen diffusion in oxygen-free Ti 2PdH 1.47, the spin-lattice ( T 1d) and rotating-frame ( T 1ρ) relaxation times minima were at much lower temperatures for Ti 4Pd 2OH 5.0, which implies more rapid hydrogen diffusion rates in the oxygen-stabilized phase. The nearest neighbor coordination sites that are involved in proposed hydrogen diffusion path ways are discussed and compared to the deuterium sites of Zr 4Pd 2OD 3.5.

The effect of annealing on hardness, microstructure and delayed hydride cracking in Zr–2.5Nb pressure tube material

The effect of annealing at 400 °C on hardness, microstructure and velocity of delayed hydride cracking (DHC) in Zr–2.5 pressure tube material in both the axial and radial directions was investigated. DHC velocity tests were performed at temperatures from 120 to 240 °C on specimens which had been annealed up to 1000 h. The β-phase initially was a thin, continuous film between α-grains providing a path for rapid hydrogen diffusion. Since the β-phase pathways were closely spaced in the axial direction but not in the radial direction, DHC velocity is 1.9 times faster in the axial direction initially. During annealing, the β-phase decomposed to discrete particles, the room temperature hardness dropped 10% and the axial DHC velocity decreased by a factor of five. The radial crack velocity decreased by a factor of three and the ratio of axial to radial DHC velocity decreased to 1.2. The decrease of this ratio corresponded to the large disruption of the β-phase caused by prolonged annealing. The activation energies for DHC velocity in these tests lay between 33 and 47 kJ/mol, suggesting that the existing theories for activation energy are incomplete.

Hydrogen embrittlement of titanium during microwave plasma assisted CVD diamond deposition

During diamond deposition on a titanium substrate using a gas mixture of H2–CH4 (196 : 4), hydrogen easily diffused into the substrate and led to significant microstructural coarsening and a severe loss in Charpy impact energy. In order to prevent the rapid diffusion of hydrogen into the substrate during diamond deposition, three techniques were studied. The first method was to use a post-vacuum annealing treatment to achieve dehydrogenation of a diamond coated titanium specimen. However, the Charpy impact energy could not be restored significantly even after a few hours of annealing. The second method was to apply a barrier interlayer between the diamond coating and titanium substrate. Results showed that even though the sputtered TiN coating and plasma nitrided layer could prevent the rapid diffusion of hydrogen and carbon into the titanium substrate, the deposited diamond coatings had poor adhesion to the substrate. A graded interlayer produced by plasma nitriding followed by plasma carbonitriding was effective in preventing the rapid diffusion of hydrogen and also improving the nucleation rate and adhesion of the diamond coating. The third method was to use a gas mixture of Ar–H2–CH4 instead of the conventional H2–CH4 . With the use of an Ar–H2–CH4 (180 : 16 : 4) mixture, a smooth and nanocrystalline diamond coating was deposited, and there was little change in the substrate microstructure or Charpy impact energy after diamond deposition.

Effects of pre-treatments and interlayers on the nucleation and growth of diamond coatings on titanium substrates

During diamond deposition on titanium substrates, two processes exist: (1) diffusion of hydrogen into a titanium substrate and the formation of hydride thereby degrading the mechanical properties of the substrate; and (2) competition among the rapid diffusion of carbon atoms into substrates, the formation of carbide and the nucleation of diamond crystals (thereby affecting the nucleation and growth rate of the diamond coating). To increase the diamond nucleation rate and prevent the rapid diffusion of hydrogen and carbon into the substrate, different surface treatments and interlayers were studied in this paper. Results showed that polishing with diamond pastes and ultrasonic pre-treatment in diamond suspensions will significantly increase the nuclei density of diamond crystals. However, the diffusion of hydrogen into the substrate could not be prevented . Pre-etching of the titanium substrate using hydrogen plasma for a short time significantly increased the nuclei density of diamond crystals. Results showed that on a TiN interlayer, there was no significant improvement in diamond nucleation and growth, and the deposited diamond coatings showed poor adhesion. New diamond crystals were formed on the DLC interlayer in which DLC acted as the precursor for diamond nucleation. However, the so-formed diamond coating showed spallation. The plasma nitrided layer could prevent the rapid diffusion of hydrogen and carbon into the titanium substrate, but results showed a relatively low nucleation density of diamond crystals and poor adhesion. A graded interlayer combining plasma nitriding followed by plasma carbonitriding was effective in preventing the rapid diffusion of hydrogen and carbon into the substrate and improving the nucleation rate and adhesion of diamond coating.

A Two-Step Low-Temperature Process For A P-N Junction Formation Due To Hydrogen Enhanced Thermal Donor Formation In P-Type Czochralski Silicon

ABSTRACTThe incorporation of hydrogen into standard p-type Czochralski (Cz) silicon (≥1 Ωcm) by a 110 MHz plasma treatment at 260°C leads to the formation of an n-type region due to hydrogen enhanced thermal donor (TD) formation in hydrogenated regions of the wafer, if a subsequent annealing in air is applied at 450°C. Spreading resistance probe (SRP) and light beam induced current (LBIC) measurements were used for the experimental analysis. The p-n junction depth, i. e. the counter doping by TDs, depends on the initial doping level of the p-type substrate, and therefore on the post-hydrogenation annealing time. The penetration of the n-type region into the wafer bulk is driven by a rapid hydrogen diffusion. The essential process for a TD generation is the creation of metastable hydrogen molecular species around 260°C and their decay at 450°C.

Ion beam analysis of edge effects in Al/M/Al stripes

Abstract Al/M/Al stripes (with M = Hf, Ti or TiW) having widths from 0.5 to 200 μm were annealed in N2 and H2 gas. The interdiffusion between layers and hydrogen diffusion in from edges were studied by RBS and nuclear reaction analysis. For Hf and Ti systems, rapid hydrogen diffusion in from the edge was observed. However, this hydrogen did not affect interdiffusion between layers. Al/Hf/Al samples showed an edge-enhanced diffusion, which was likely caused by reactive ion etching (RIE) during processing. For the Ti-W system, the edge diffusion was reduced in H2 during annealing.

Low Temperature Crystallization of Amorphous Silicon Films Using an Excimer Laser

ABSTRACTIn an effort to enhance the electrical properties of silicon thin films, we have performed recrystallization experiments on a variety of amorphous silicon films using an excimer laser. The intense, pulsed UV produced by the laser (308nm, using XeCl gas) is highly absorbed by the amorphous material and thus provides intense localized heating in the near surface region. Two types of starting films were studied: plasma CVD a-Si:H and LPCVD a-Si. The subsequent modification produces crystallites whose structure and electrical characteristics vary due to starting material and laser scan parameters. The treated films have been characterized using Raman, x-ray diffraction, TEM, SIMS and transport measurements. The results indicate that crystallites nucleate in the surface region. The degree of crystallization near the surface increases dramatically as a function of deposited laser energy density and less so as a function of laser shot density. The hall mobility of the highly crystallized samples exhibit an increase of 2 orders of magnitude over the amorphous starting material. In the PECVD material, the rapid diffusion of hydrogen causes voids to be formed at intermediate laser energy densities and removal of film at higher energy densities. The LPCVD material withstands the high laser energies to produce well crystallized films with crystallite sizes greater then 1000Å.