Effective Hydrogen Diffusion Coefficient Research Articles

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.

Measurements of effective diffusion coefficients of helium and hydrogen through gypsum

An experimental apparatus, which was based on the ¼-scale garage previously used for studying helium release and dispersion in our laboratory, was used to obtain effective diffusion coefficients of helium and hydrogen (released as forming gas for safety reasons) through gypsum panel. Two types of gypsum panel were used in the experiments. Helium or forming gas was released into the enclosure from a Fischer burner11Certain commercial entities, equipment, or materials may be identified in this document in order to describe an experimental procedure or concept adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the entities, materials, or equipment are necessarily the best available for the purpose. located near the enclosure floor for a fixed duration and then terminated. Eight thermal-conductivity sensors mounted at different vertical locations above the enclosure floor were used to monitor the temporal and spatial gas concentrations. An electric fan was used inside the enclosure to mix the released gas to ensure a spatially uniform gas concentration to minimize stratification. The temporal variations of the pressure difference between the enclosure interior and the ambience were also measured. An analytical model was developed to extract the effective diffusion coefficients from the experimental data.

Hydrogen permeation behaviour and associated phase transformations in annealed AISI304 stainless steels

The effective diffusion coefficient and subsurface concentration of hydrogen in annealed AISI304 austenitic stainless steels have been measured by the electrochemical permeation method. The effects of different cathodic current densities on the effective diffusion coefficient, hydrogen concentration beneath the cathodic surface and steady state permeation current density have been studied. The value of the effective diffusion coefficient for the permeated specimens increases with increasing charging current density. The hydrogen subsurface concentration and steady state permeation current density first increase with increasing charging current density, then decrease with increasing current density. X-ray diffraction analyses were used to investigate the phase transformation during hydrogen charging. The results revealed that cathodic charging resulted in the formation of a considerable amount of e and α′ martensites, which will increase with charging time.

Behaviour of hydrogen in gas nitrided iron studied by electrochemical permeation and desorption techniques

Hydrogen permeation through and desorption from cathodically charged iron membranes with nitrides γ′, (ε+γ′) and ε layers have been studied. On the basis of the nonstationary permeation, the effective diffusion coefficients of hydrogen for the nitrided membranes, and hence the real diffusion coefficients in each nitride layer were evaluated. After cessation of charging, desorption rate of hydrogen was measured at both sides of the membrane. An analysis of the desorption rates enabled to distinguish the diffusible (mobile) hydrogen from the reversibly trapped one. Hydrogen trapping was enhanced by the γ′ precipitates and especially by the nitrided compound layers.

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.

Hydrogen permeation in Fe-40 at.% Al alloy at different temperatures

The electrochemical permeation technique for studying transport and trapping of hydrogen in Fe-40 at.% Al alloy at temperatures of 5, 25, 45 and 65 °C was used in the paper. The influence of temperature on the effective hydrogen diffusion coefficient, hydrogen permeation rate and hydrogen solubility was determined. The activation energy of hydrogen diffusion in iron aluminide in the studied temperature range was also determined.

The study of removing hydroxyl from silica glass

The removal of hydroxyl from silica glass produced by melting quartz powder under an atmosphere containing hydrogen was investigated. After heat-treatment at the temperature range (700–1200 °C) in nitrogen atmosphere, the effective hydrogen diffusion coefficients were evaluated based on the law of nonsteady-state diffusion. The activation energy obtained is 254 kJ mol −1 for the dehydroxylation process in the heat-treatment temperature range of 700–900 °C, and a different activation energy calculated is 32 kJ mol −1 in the temperature range of 900–1200 °C. The activation energies for the dehydroxylation process at the temperature (700–900 °C) and the higher temperature (900–1200 °C) correspond to the binding energy of SiO–H bond and the activation energy for the diffusion of hydrogen in silica glass respectively, which indicate there is a change of mechanism for dehydroxylation with heat-treatment temperature.

Consecutive-Parallel Reactions in Nonisothermal Polymeric Catalytic Membrane Reactors

This work reports the development of a nonisothermal and nonadiabatic pseudo-homogeneous model to study a completely back-mixed membrane reactor with a polymeric catalytic membrane, for conducting the consecutive hydrogenation of propyne to propene and then to propane. The performance of the reactor is analyzed in terms of the propyne concentration in the permeate stream (the only outlet stream from the reactor), the conversion of propyne and hydrogen, and the selectivity and overall yield to the intermediate product propene. The operating and system parameters considered are the Thiele modulus, the dimensionless contact time, the Stanton number, and the effective hydrogen sorption and diffusion coefficients. To define the regions where the catalytic membrane reactor may perform better than a conventional reactor, a comparison between both reactors is made. For the range of parameter values considered, the reactor model in this study demonstrates that the catalytic membrane reactor performs better than th...

Interaction of water diffusion and hydrogen diffusion in silica glass at high temperatures

Both water diffusion and hydrogen diffusion in silica glass at high temperatures involve molecular diffusion and reaction with the glass network. One of the reaction products, hydroxyl, is common in both reactions and, therefore, the effective diffusion co-efficients of the two molecular species may not be independent of each other when both molecular species co-exist. The extent of the interaction was investigated by determining the effective diffusion co-efficients of water and hydrogen from hydroxyl profiles in a silica glass, prepared by melting in a hydrogen atmosphere, after heat-treatment at 750 °C in a wet atmosphere. In this case, water diffuses into the glass while hydrogen diffuses out of the glass. These diffusion co-efficients were compared with values obtained in the absence of other diffusing species: water without hydrogen and hydrogen without water. It was found that the effective hydrogen diffusion co-efficient was reduced by more than an order of magnitude by the presence of water vapor, while the effective water diffusion co-efficient was unaffected, within experimental error, by the presence of hydrogen.

Quantification of hydrogen diffusion and trapping in 2.25Cr-1Mo and 3Cr-1Mo-V steels with the electrochemical permeation technique and melt extractions

The electrochemical permeation technique was used to investigate the effect of microstructure, hydrogen activity, and stationary dislocations generated by tensile straining on the permeation and degassing of hydrogen. A conventional 2.25Cr-1Mo steel, with which the existing hydrotreating reactors are made, and a 3Cr-1Mo-V steel, which is a candidate material for the future generation of reactors, were selected for this study. The effective diffusion coefficient of hydrogen derived from permeation and degassing transients shows a slower diffusivity in the V-containing steel at room temperature, regardless of the hydrogen activity. A large plastic deformation obtained by tensile straining in the homogeneous deformation domain only leads to a moderate decrease of the hydrogen diffusivity in both steels. The results are compared with the literature data on hydrogen permeation in iron and ferritic steels. On the other hand, the hydrogen content was measured with the melt extraction method after cathodic charging and subsequent aging at room temperature for different times to determine the diffusible (lattice+reversibly trapped) hydrogen concentration. It was shown that the latter is larger in 3Cr-1Mo-V steel, which contains, in addition, a large fraction of “strong reversible” traps. A good concordance was found between the diffusible hydrogen concentration values computed from steady-state permeation measurements and from graphical integration of decay transients. The validity of the quantification, from permeation experiments, of the diffusible hydrogen concentration in materials with complex microstructures is discussed.

Electrochemical kinetics of hydrogen intercalation in gadolinium switchable mirrors

Potential-step experiments on gadolinium thin-film electrodes provide current and optical transmission transients, whose time constants are related to effective hydrogen diffusion coefficients according to a standard diffusion model. The diffusion coefficients and switching kinetics depend on temperature, hydrogen concentration, potential, and film thickness. A thickness dependence of the kinetics is observed in which the diffusion coefficient and optical switching time are linearly dependent.

Hydrogen diffusion in fused silica at high temperatures

Hydrogen diffusion in a silica glass at high temperature (750–1500 °C) was investigated. The starting material was a silica glass that was melted in hydrogen atmosphere and contained a high concentration of hydroxyl and hydride. After heat treatment at various temperatures in air, the effective hydrogen diffusion coefficients were evaluated from the removal rates of hydroxyl and hydride. The obtained diffusion coefficients exhibited an unusual temperature dependence, with the lower diffusion coefficient being observed at higher temperature in the temperature range of 1000–1500 °C. This was attributed to the higher reactivity of hydrogen with the glass network at higher temperatures, effectively slowing down the hydrogen mobility. Below 1000 °C, the effective hydrogen diffusion coefficient exhibited a normal temperature dependence. This reversal of the temperature dependence of the effective hydrogen diffusion coefficient appears to be related to the reversal of the temperature dependence of the hydroxyl (or hydride) solubility in silica glass.

Electrode materials based on hydrogen-sorbingalloys of AB2 composition (A = Ti, Zr; B = V, Ni, Cr)

The alloy Zr 0.5Ti 0.5V 0.5Ni 1.3Cr 0.2 with structure of C14 Laves phase was prepared by arc melting under argonatmosphere. Sorption and electrocatalytical properties of electrodes based on the alloy withCu-binder were investigated. Optimal conditions for treatment of the electrode surface in analkaline electrolyte were identified. Alkaline activation of electrodes was more effective thanabsorption-desorption. Rate of reaction of evolution and ionization of absorbed hydrogen wasincreased by an order of ∼1.5–2 by alkaline treatment. The effective diffusion coefficient ofhydrogen was estimated as 10 −8 cm 2/s.

Intraparticle Diffusion Limitations in the Hydrogenation of Monounsaturated Edible Oils and Their Fatty Acid Methyl Esters

Intraparticle diffusion limitation in the hydrogenation and isomerization of fatty acid methyl esters (FAMEs) and edible oils (triacylglycerol, TAG) in porous nickel catalyst was investigated both under reactive and under inert conditions. Under reactive conditions, the diffusion coefficients were determined from the best fits of the model simulations applying the intrinsic reacting kinetics of monounsaturated FAME hydrogenation to experiments under diffusion limited conditions. For 0.02 < PH2 < 0.50 MPa, an effective hydrogen diffusion coefficient of De,H2 = (1.6 ± 0.7) × 10-10 m2/s (T = 443 K) was obtained in Pricat 9910 (sample 1992). TAG hydrogenations, at 373 < T < 443 K and 0.30 < PH2 < 0.50 MPa, appear to be limited by diffusion limitation of TAG, yielding De,TAG = (4.5 ± 2.2) × 10-13 (T = 373 K), (2.0 ± 0.9) × 10-12 (T = 403 K), and De,TAG = (3.3 ± 1.1) × 10-12 m2/s (T = 443 K). The temperature dependency of De follows the relation Deη/T = 2 × 10-7 (m2 Pa)/K (η is the fluid viscosity, Pa s) for 37...

A method for determination of the diffusion coefficient of hydrogen in titanium alloys by chemical etching

We propose a model of absorption of hydrogen by titanium alloys in the process of chemical etching. We obtained a solution that describes the amount of absorbed hydrogen and its distribution in the metal as a function of the rate and time of etching. On the basis of the equations obtained, we developed a method for determination of the diffusion coefficient of hydrogen in a metal. The essence of the method is a sequential etching of a specimen in hydrogenated and nonhydrogenated solutions and determination of the amount of hydrogen which remains in the metal. The effective diffusion coefficients of hydrogen in titanium alloys with various structures are found.

Reactivation kinetics of boron acceptors in hydrogenated silicon during zero bias anneal

The reactivation kinetics of passivated boron acceptors in hydrogenated silicon during zero bias annealing in the temperature range of 65–130 °C are reported. For large annealing times and high annealing temperatures, the reactivation process follows second-order kinetics and is rate limited by a thermally activated H̃2 complex formation process. For short annealing times and low annealing temperatures, the reactivation rate is found to be larger than that due to H̃2 complex formation alone. We conclude that the faster reactivation is caused by the diffusion of the liberated hydrogen atoms into the bulk as well as H̃2 complex formation. The effective diffusion coefficient of hydrogen is measured and found to obey the Arrhenius relation with an activation energy (1.41±0.1) eV.

Hydrogen Diffusion and Accumulation in Automotive Fasteners

Abstract Permeation, plating, and baking tests were carried out to determine the susceptibility of a newly developed steel (BHS-1) to absorb and diffuse hydrogen in comparison to the currently used type 1022 (UNS G10220) and type 4037 (UNS G40370) steels. The effective diffusion coefficient (Deff) of hydrogen in BHS-1 was slightly lower than in the traditional steels; however, the ability to absorb hydrogen during plating and to release hydrogen during baking was comparable. Acidic and alkaline zinc-plating processes dissolved similar amounts of hydrogen into all of the studied steels.

Intraparticle diffusion in hydrogenation of 3‐hydroxypropanal

AbstractStrong intraparticle diffusion resistance was observed and the apparent effectiveness factors were measured for the hydrogenation of 3‐hydroxypropanal (HPA) to 1,3‐propanediol (PD) over Ni/SiO2/Al2O3 catalyst pellets at 45 to 80°C and 2.60 to 5.15 MPa in a stirred reactor with a spinning basket. A mathematical model was proposed to describe the intraparticle diffusion and to estimate the effective diffusion coefficients of HPA, PD and hydrogen under reaction conditions by a maximum likelihood function of the apparent effectiveness factors of HPA and PD. The calculated concentration distributions of HPA, PD and hydrogen in catalyst particles reveal an excess of hydrogen at 80°C and higher temperatures, but an excess of HPA at 45°C. It results in a weak dependence of the consumption formation rate of HPA and PD on the partial pressure of hydrogen at high temperature.

Diffusion-limited self-discharge reaction in the Hubble space telescope battery

The self-discharge rate of aerospace flight-quality nickel-hydrogen batteries is limited by hydrogen diffusion within the nickel electrode active material. A diffusion-limited reaction model is developed which accounts for the observed self-discharge behavior. Effective hydrogen diffusion coefficients were calculated from the open-circuit self-discharge data on Hubble space telescope flight-quantified nickel-hydrogen cells and ranged from 1.12×10 −10 cm 2/sec at 25°C to 7.45×10 −12 cm 2/sec at 0°C.

Diffusion-elastic phenomena in nickel and cobalt electrodeposits plated on to strip cathodes

A quantitative analysis was made of the post-deposition increase of the internal tensile stress in nickel and cobalt electrodeposits using an approach based on the diffusion-elastic phenomena. Equations were derived for the determination of the amount and the effective diffusion coefficient of hydrogen, which leaves the deposit immediately after plating. The experimental results are processed using these equations and the results are compared with data in the literature. The role played by hydrogen desorption in increasing the tensile stress after the electrodeposition current is switched off was confirmed.