Effective Hydrogen Diffusivity Research Articles

Cracks in Martensite Plates as Hydrogen Traps in a Bearing Steel

It is demonstrated that a macroscopically homogeneous distribution of tiny cracks introduced into a martensitic bearing steel sample can provide powerful hydrogen traps. The phenomenon has been investigated through thermal desorption spectroscopy and hydrogen permeation measurements using both cracked and integral samples. The effective hydrogen diffusion coefficient through the cracked sample is found to be far less than in the un-cracked one. Similarly, when samples are charged with hydrogen, and then subjected to thermal desorption analysis, the amount of hydrogen liberated from the cracked sample is smaller due to the trapping by the cracks. Theoretical analysis of the data shows that the traps due to cracks are so strong, that any hydrogen within the cracks can never in practice de-trap and cause harm by mechanisms that require the hydrogen to be mobile for the onset of embrittlement.

Quantitative Analysis of the Effect of Hydrogen Diffusion from Silicon Oxide Etch-Stopper Layer into Amorphous In–Ga–Zn–O on Thin-Film Transistor

To investigate the effect of hydrogen diffusion from the silicon oxide etch-stopper (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> ES) layer into the amorphous In–Ga–Zn–O (a-IGZO) on thin-film transistor (TFT) properties and stabilities, we fabricated a-IGZO TFTs with a SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> ES layer deposited by plasma-enhanced chemical vapor deposition at various silane (SiH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) partial pressures (P[SiH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ]). Then, quantitative analysis was performed to investigate the relationship between the hydrogen content of the a-IGZO and electrical properties and stability of the TFTs. We found that a low resistance region was formed at the backchannel of the TFT, when the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> ES layer was deposited at higher P[SiH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ], leading to a drastic negative threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm {\textbf {th}}}$ </tex-math></inline-formula> ) shift. In addition, it was also found that at the frontchannel, the increase in the carrier concentration of a-IGZO was proportional to the increase in the amount of hydrogen in a-IGZO. On the other hand, when P[SiH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ] was increased, the subthreshold swing, hysteresis, and gate-bias stability of the TFT improved. The results indicate that hydrogen diffused from the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> ES layer passivates the electron traps at the a-IGZO and/or gate insulator/a-IGZO interface, and almost all of the hydrogen also acts as shallow-donor in a-IGZO.

Assessment of Hydrogen Uptake and Permeation in AHSSs

This study aims to develop novel experimental procedure that quantifies response of AHSSs with different microstructures, deformation status, and strength levels to hydrogen. The capacity for trapped hydrogen, kinetics of hydrogen absorption and loss, and hydrogen mobility are measured and analyzed by permeation tests. The experimental findings are discussed in terms of microstructural features for an interstitial free (IF) and a dual phase (DP) steels. Further, the density of trap sites and its effect on effective diffusivity of hydrogen in the steel are analyzed by means of a diffusion model.

High temperature proton transport in BaCe0.95Yb0.05O3−δ perovskite

The phase transitions and proton transport in BaCe0.95Yb0.05O3−δ perovskite were studied by Raman spectroscopy, X-ray diffraction and synchrotron radiation X-ray diffraction. Proton mobility in this material appears to be intimately associated to the crystal phases of the framework host. Therefore, in the present paper the phase transformations of the BaCe0.95Yb0.05O3−δ perovskite were studied during heating and under hydrogen diffusion. One of the objectives of the present research was to establish the expanse across the phase fields. But, more significantly, the effect of hydrogen diffusion on structure applying a careful structural refining analysis was studied with the help of the Pawley and Rietveld methods.

Analysis of Fishscaling Resistance of Low Carbon Heavy Plate Steels

The precipitates and hydrogen permeation behavior in three kinds of hot rolled low carbon heavy plate steels for enameling were analyzed; then, both sides of the steels were enameled. The experimental results show that a large amount of coarse Ti4C2S2 and fine Ti(C, N) particles exist in the optimized Ti-bearing steel, quite a lot of fine Ti(C, N) particles exist in the optimized carbon steel, but only a little bit fine Ti(C, N) particles exist in the carbon steel. The fishscaling resistance of the steels can be correlated to the effective hydrogen diffusion coefficient, and a model of correlation between the effective hydrogen diffusion coefficient and the volume fraction of the precipitates was established and verified. The effective hydrogen diffusion coefficient should be lower than 3. 96 × 10 6 cm2/s to avoid fishscaling in heavy plate steels.

Electroplating of Rhodium/Si(111) Junctions for Solar Fuel Generation: Effects of Hydrogen Diffusion

Surface chemical and electronic properties of electroplated Rh/Si(111)-interfaces were investigated by cyclovoltammetry, HRTEM, electrochemical impedance and synchrotron radiation photoelectron spectroscopy (SRPES). The strong adsorption of hydrogen onto (photo)-electrochemical deposited Rh crystallites brings about a source of atomic hydrogen, which diffuses into the silicon substrate. The incorporation of hydrogen turns the underlying substrate amorphous and passivates dopant energy states. This inverts the conduction type of the semiconductor with the formation of an apparent surface pn-junction which controls the electronic behavior of the metal/semiconductor contact.

Effect of Nitriding on the Hydrogen Diffusion Coefficient through AISI 4340

The effect of plasma nitriding on hydrogen permeation through AISI 4340 was studied both experimentally and theoretically. Effective hydrogen diffusion coefficients were measured for three different AISI 4340 membrane specimens: as-received, nitrided, and nitrided specimens with the compound layer removed by mechanical abrasion. The as-received specimen had a higher diffusion coefficient (2.8 × 10−6 cm2/sec) than the nitrided specimens. The nitrided specimen with the compound layer intact had a much lower hydrogen diffusion coefficient (0.65 × 10−6 cm2/sec) than the specimen without the compound layer (1.9 × 10−6 cm2/sec). These results demonstrate that the γ′-Fe4N rich compound surface layer and the N that diffuses more deeply into AISI 4340 during plasma nitriding both reduce the effective hydrogen diffusion coefficient. Multiple permeation transients yield evidence for the presence of only reversible trap sites in as-received specimens and the presence of both reversible and irreversible trap sites in nitrided specimens, with and without the compound zone intact. In addition, density functional theory-based molecular dynamics simulations yield hydrogen diffusion coefficients through γ′- Fe4N (1.5 × 10−5 cm2/sec) one order of magnitude lower than through α-Fe (1.2 × 10−4 cm2/sec), which supports the experimental measurements of hydrogen permeation.

Measurement of effective hydrogen diffusivity using the Scanning Kelvin Probe

Effective hydrogen diffusivity (DH,eff) was determined utilizing the Scanning Kelvin Probe (SKP) to measure the SKP voltage on cross-sectioned, hydrogen pre-charged samples at 25°C. Two secondary hardened martensitic steels, Fe–13Co–11Ni–3Cr–1.2Mo–0.2C–0.02Mn and Fe–11Ni–12Cr–1Mo–0.005C–0.02Mn (wt%) were evaluated. DH,eff was 1.5 to 2×10−8cm2/s. Results compared well to previously reported measurements for Fe–13Co–11Ni–3Cr–1.2Mo–0.2C–0.02Mn steel using isothermal Thermal Desorption (TDS) and an Arrhenius relationship to obtain an average DH,eff of 8.96×10−9cm2/s at 25°C (Thomas et al., 2002).

Hydrogen diffusion coefficients through Inconel 718 in different metallurgical conditions

We report hydrogen permeation studies through cold rolled, solutionized, and precipitation hardened Inconel 718 foils. The effective hydrogen diffusion coefficient is considerably higher (5.3–6.8×10−11cm2/s) for the solutionized Inconel 718 than for either the cold rolled (3.3–4.2×10−11cm2/s) or precipitation hardened (2.1–2.9×10−11cm2/s) specimens. Microstructural studies indicate that the reduced hydrogen diffusion coefficients in the latter specimens arise from hydrogen trapping at dislocations and precipitates that are present at much lower concentrations in the solutionized specimens. Also, repeated permeation transients provide evidence for irreversible hydrogen trapping in the cold rolled and precipitation hardened specimens, but such effects are insignificant in the solutionized specimens.

Effective Hydrogen Diffusion in Aluminum Alloy 5083-H131 as a Function of Orientation and Degree of Sensitization

The effective hydrogen diffusivity in aluminum alloy (AA)5083- H131 (UNS A95083) for various orientations and degrees of sensitization (DoS) was investigated using AA5083/Pd bilayer membranes. Sensitization produced β-phase (Al3Mg2) precipitates. A modified Devanathan-Stachurski permeation method was used with hydrogen charging by open-circuit exposure to 0.01 M sodium hydroxide (NaOH) and detection via Pd hydride formation. The measured hydrogen diffusivity (DH,eff) in the longitudinal (L) or short transverse (S) direction was almost independent of AA5083 foil thickness, indicating bulk diffusion control. DH,eff was not sensitive to the DoS, ranging from 2 mg/cm2 to 49 mg/cm2. The average room temperature diffusivities of hydrogen, DH,eff (25°C), for the initial H charging cycle of as-sensitized foils, were determined by the slope (Lcorr2/6 vs. t) method to be 8.5 (±1.4) × 10−11 cm2/s along the S direction and 1.4 (±0.2) × 10−10 cm2/s along the L direction, with a 95% confidence level. By averaging individual measured data points, DH,eff (25°C) was found to be 1.0 (±0.3) × 10−10 cm2/s along the S direction and 1.5 (±0.4) × 10−10 cm2/s along the L direction. The effective diffusivity of hydrogen increased by one to two orders of magnitude during the second and third hydrogen charging cycles. This charge cycle dependency was interpreted to result from extensive hydrogen trapping in uncharged foils and remaining trap site occupancy after initial precharging. The implication of these results toward intergranular stress corrosion involving hydrogen-controlled cracking of inter-β ligaments between closely spaced, quickly dissolving β-phase precipitates on grain boundaries is discussed.

Quantification of hydrogen effective diffusion coefficients and effusion behavior in duplex stainless steel weld metals

Modern methods like carrier gas hot extraction enable the quantification of dissolved hydrogen as well as the determination of the hydrogen trapping and diffusion behavior. This method was applied in order to compare for the first time the hydrogen diffusion and trapping behavior in electrochemically charged and welded duplex stainless steel (1.4462). Characteristic extraction temperatures (400, 650, and 900 °C) were used to quantify the amounts of diffusible hydrogen and trapped hydrogen for the base material and the weld metal, and in order to calculate the effective diffusion coefficients corresponding to the specific temperature. The comparison of the charging methods showed that electrochemically charged samples have a higher content of diffusible hydrogen than the welded samples. In addition, the effusion times increase in welded samples, which indicate a higher amount of trapped hydrogen. In electrochemically charged weld samples, a significant lower concentration of hydrogen was determined than in the base material. In addition, the effective diffusion coefficients were calculated for every microstructure and charging method. It was found that the base material has a higher effective hydrogen diffusion coefficient than that of the weld metal. This effect is due to the tortuous path of hydrogen diffusion in the weld metal.

Hydrogen Isotope Investigation of Amphibole and Glass in Dacite Magmas Erupted in 1980–1986 and 2005 at Mount St. Helens, Washington

In active, shallow, sub-volcanic magma conduits the extent of the dehydrogenation^oxidation reaction in amphibole phenocrysts is controlled by energetic processes that cause crystal lattice damage or conditions that increase hydrogen diffusivity in magmatic phases. Amphibole phenocrysts separated from dacitic volcanic rocks erupted from 1980 to 1986 and in 2005 at Mount St. Helens (MSH) were analyzed for dD, water content and Fe3þ/Fe2þ, and fragments of glassy groundmass were analyzed for dD and water content. Changes in amphibole dD values through time are evaluated within the context of carefully observed volcanic eruption behavior and published petrological and geochemical investigations. Driving forces for amphibole dehydrogenation include increase in magma oxygen fugacity, decrease in amphibole hydrogen fugacity, or both. The phenocryst amphibole (dD value c. ^57o and 2 wt % H2O) in the white fallout pumice of the May 18, 1980 plinian eruptive phase is probably little modified during rapid magma ascent up an 7 km conduit. Younger volcanic rocks incorporate some shallowly degassed dacitic magma from earlier pulses, based on amphibole phenocryst populations that exhibit varying degrees of dehydrogenation. Pyroclastic rocks from explosive eruptions in June^October 1980 have elevated abundances of mottled amphibole phenocrysts (peaking in some pyroclastic rocks erupted on July 22, 1980), and extensive amphibole dehydrogenation is linked to crystal damage from vesiculation and pyroclastic fountain collapse that increased effective hydrogen diffusion in amphibole. Multiple amphibole dD populations in many 1980 pyroclastic rocks combined with their groundmass characteristics (e.g. mixed pumice textures) support models of shallow mixing prior to, or during, eruption as new, volatile-rich magma pulses blended with more oxidized, degassed magma. Amphibole dehydrogenation is quenched at the top surface of MSH dacite lava lobes, but the diversity in the dDamph populations in original fresh lava flow surfaces may occur from blending magma domains with different ascent histories in the sub-volcanic environment immediately before eruption. Multi-stage open-system magma degassing operated in each parcel of magma rising toward the surface, whereas the magma below 7 km was a relatively closed system, at least to the October 1986 eruption based on the large population of minimally dehydrogenated, rim-free amphibole in the lavas. Magma degassing and possibly H isotope exchange with low-dD fluids around the roof zone may have accompanied the 1·5 km upward migration of the 1980 magma body. The low-dDamph (c. ^188 to ^122o) oxy-amphibole phenocrysts in lava spines extruded in May 2005 reflect dehydrogenation as ascending viscous magma degassed and crystallized, and fractures that admitted oxygen into the hot solidified lava spine interior facilitated additional iron oxidation.

Pore network effects under the reduction of catalyst size at elevated temperatures

To evaluate the pore network effect due to variation in catalyst size, adsorption/desorption isotherms of N2 at 77.3K were measured for γ-Al2O3 particles of 4.0, 1.0, 0.5 and 0.04mm in diameter with ASAP 2020 by Micromeritics. It shows the desorption knee is obvious for the 4.0mm particle, while it is not found for the others. Nevertheless, the loops of isotherm hysteresis are decreasing when the particle size is reduced from 1.0 to 0.04mm. Under elevated temperatures with benzene hydrogenation as the working system, it shows the hysteresis in adsorption and reaction rate are remarkable for the 2.0 and 4.0mm particles, but is much less evident when the particle size is reduced to 1.0 and 0.5mm. With the increase of reaction temperature, the hysteresis loop tends to move to the region of high relative vapor pressures, due to the unstable vapor condensation condition in small pores. To inspect how the reaction rate is affected by the variation of catalyst condition, the internal wetting fraction and the internal effectiveness factor are measured and evaluated over a wide vapor pressure range, and an almost linear relationship is found between them. It shows the effective diffusivity of hydrogen under full vapor condensation in the catalyst is about 13 times that filled with bulk liquid, which suggests the catalyst pore can be considered being filled with vapor–liquid mixture rather than with bulk liquid.

Hydrogen Diffusivity During Corrosion of High-Purity Aluminum

The effective diffusivity of hydrogen in as-annealed (550°C for 5 h) 99.999% purity polycrystalline aluminum was determined using Al/Pd bilayer membranes following the procedure of K.R. Hebert. Bulk diffusion control was verified by the foil thickness variation method. The room temperature diffusivity of hydrogen was determined to be 1.6 ± 0.4 × 10−10 cm2/s during initial hydrogen charging in 0.01 M sodium hydroxide (NaOH) solution. The effective diffusivity of hydrogen increased by two orders of magnitude during the second hydrogen charging and approaches the literature for gas phase egress from precharged material. This difference was interpreted to be the result of extensive trapping in freshly annealed foils and high residual trap site occupancy after initial precharging. The activation energy for lattice hydrogen egress was analyzed through constant heating rate thermal desorption spectra. This activation energy was 17.0 ± 0.6 kJ/mol. The experimental results also demonstrated that the measured hydrogen diffusivity is sensitive to the NaOH concentration speculated to be related to its influence on hydrogen production rate, hydrogen overpotential, and solid-state hydrogen concentration.

Improved conductivity of aluminum-doped ZnO: The effect of hydrogen diffusion from a hydrogenated amorphous silicon capping layer

Plasma-deposited aluminum-doped ZnO (ZnO:Al) demonstrated a resistivity gradient as function of the film thickness, extending up to about 600 nm. This gradient decreased sharply when the ZnO:Al was capped by a hydrogenated amorphous silicon layer (a-Si:H) and subsequently treated according to the solid phase crystallization (SPC) procedure at 600 °C. The resistivity reduced from 1.2 · 10−1 to 2.6 · 10−3 Ω · cm for a film thickness of 130 nm, while for thicker films the decrease in resistivity was less pronounced, i.e., a factor of 2 for a film thickness of 810 nm. While the carrier concentration was not affected, the mobility significantly increased from 7 to 30 cm2/V · s for the thick ZnO:Al layers. This increase was ascribed to the passivation of grain boundary defects by hydrogen, which diffused from the a-Si:H toward the ZnO:Al during the SPC procedure. The passivation effect was more pronounced in thinner ZnO:Al layers, characterized by a smaller grain size, due to the presence of large grain boundaries. For thicker films with grain sizes up to 200–300 nm the mobility became progressively less affected by the presence of grain boundaries. Therefore, the hydrogen-induced improvement in conductivity was less significant for the thick ZnO:Al films.

Welding heat input effect on the hydrogen permeation in the X80 steel welded joints

In this study, the effect of microstructure at the base metal (BM), the fine grain heat affected zone (FGHAZ), the coarse grain HAZ (CGHAZ) and weld metal (WM) under different welding heat input on hydrogen permeation in X80 steel weldments have been investigated. Base metal showed the highest effective diffusivity. With each heat input, the effective hydrogen diffusivity in FGHAZ is comparable to that of the base metal. The effective hydrogen diffusivity in weld metal was lower than that in CGHAZ. With increasing the welding heat input, the effective diffusivity in different zones of the weldment decreased correspondingly. Non-metallic inclusions were not detected in each specimen. Constituents in microstructure under low heat input are likely to agglomerate during accelerated cooling. The retained hydrogen may create an unpredictable susceptibility to hydrogen cracking at the CGHAZ even existing during service.

Assessment of pH and temperature effects on stress corrosion cracking of 1018 low carbon steel

Stress corrosion cracking tests (SCC) were performed on 1018 low carbon steel into 0·5M NaCl solution at different pH values and temperatures of 25, 50 and 70°C using the slow strain rate testing technique. Evaluations were complemented with hydrogen permeation measurements and electrochemical impedance spectroscopy. Studies show hydrogen diffusion effects depending on temperature and pH. The maximum hydrogen diffusion was observed at 70°C (pH<1). The SCC susceptibility was measured as the percentage reduction in area and the time to failure and was maximal at pH<1 at the temperatures studied. The most likely mechanism for the cracking susceptibility of 1018 steel in the chloride solutions seems to be hydrogen assisted anodic dissolution assisted by hydrogen embrittlement. After failure, the fracture surfaces were observed by scanning electron microscopy and chemical analysis was obtained by X‐ray energy dispersive spectroscopy. The specimens tested in air exhibited a ductile type of failure, whereas, in the corrosive solution the specimens showed a brittle fracture.

Effective hydrogen diffusion coefficient for solidifying aluminium alloys

An effective hydrogen diffusion coefficient has been calculated for two solidifying Al – 4.5 wt.% Cu and Al – 10 wt.% Cu alloys as a function of the volume fraction of solid. For this purpose, in situ X-ray tomography was performed on these alloys. For each volume fraction of solid between 0.6 and 0.9, a representative volume element of the microstructure was extracted. Solid and liquid voxels were assimilated to solid and liquid nodes in order to solve the hydrogen diffusion equation based on the chemical potential and using a finite volume formulation. An effective hydrogen diffusion coefficient based on the volume fraction of solid only could be deduced from the results of the numerical model at steady state. The results are compared with various effective medium theories.

Effects of Hydrogen Diffusion on the Mechanical Properties of Austenite 316L Steel at Ambient Temperature

This study examined how the strain rate affects the room-temperature tensile behavior of hydrogen-charged 316L stainless steels. A hightemperature homogenization treatment was applied to the specimens after hydrogen charging and copper electroplating to remove the hydrogen concentration gradient. A softening phenomenon was observed in the hardening behavior of the H-charged and homogenized specimen at a strain rate of 2 � 10 � 3 /s. The observation was further confirmed by an inspection of the fracture surface of the tensile test specimen. [doi:10.2320/matertrans.M2010273]

On the estimation of hydrogen diffusion parameters in amorphous and crystalline irons

We present a new simulation technique and apply it to study the hydrogen diffusion in amorphous and crystalline iron. For amorphous model we obtain a broad continuous distribution of site and transition energies. The site energy distribution is well fitted to the Gauss form, but the transition energy distribution has the asymmetrical character. Furthermore, the activation energy for amorphous iron is close to that for fcc crystalline iron, but its pre-exponential factor has the same order of magnitude as for bcc crystalline iron. The concentration effect of hydrogen diffusion has been also examined and it demonstrates the qualitative agreement with experimental data.