Deuterium Diffusion Research Articles

In situ observation and kinetic modeling of the fundamental mechanisms underlying hydrogen sorption in forged Mg–Mg2Ni composites

While Mg–Mg2Ni composites are promising for hydrogen storage, their implementation is hindered by our incomplete understanding of absorption/desorption kinetics. Here, we combine in situ neutron diffraction with kinetic and microstructural analyses to uncover the sorption mechanism of deuterated hydrogen D2 in a Mg–Mg2Ni composite processed by fast forging. Phase transitions upon first absorption are found to be different from subsequent absorptions. The first absorption involves rapid formation of Mg2NiD0.3-x followed by simultaneous formation of MgD2 and Mg2NiD4. Kinetic modeling indicates that surface nucleation of the magnesium hydride is rate-limiting. Subsequent absorptions involve two phases, Mg and Mg2NiD0.3-x, which promote absorption. Kinetic modeling and microstructure analysis indicate that (1) MgD2 nucleation occurs at the Mg–Mg2NiD0.3-x interface and (2) Mg2NiD4 formation is kinetically controlled by deuterium diffusion through the growing Mg2NiD4 plate. In all desorptions, deuterium release starts by rapid decomposition of Mg2NiD4 into Mg2NiD0.3-x, followed by slower MgD2 decomposition.

Deuterium permeation studies through bare and Er2O3 coated SS 316L

Hydrogen isotope permeation through the structural walls of a fusion reactor poses concern for both fuel loss and safety. A primary focus in the International Thermonuclear Experimental Reactor (ITER) is the reduction of hydrogen isotopes, particularly tritium permeation through structural materials. In this work, an experimental setup has been developed to study the permeation of deuterium through thin samples such as bare and erbia (Er2O3) coated 100 µm thick stainless steel (SS 316 L). Permeation results through a bare SS 316 L sample yielded deuterium diffusivity and permeability of SS 316 L. Erbia coating on SS 316 L was developed using dip coating technique and its performance was tested as a permeation reduction barrier (PRB). A permeation reduction factor of ∼87 and 359 have been achieved with coating thickness ∼ 100 and ∼200 nm respectively. No measureable permeation flux was obtained for coating thickness of 492 nm. These results indicate the effectiveness of erbia coating in reducing deuterium permeation through SS 316 L.

Deuterium permeation performance of V4Cr4Ti/RAFM steel joint with in-situ formed carbide interlayer during diffusion bonding

Vanadium alloy (V4Cr4Ti) is a structural material used in future fusion reactors owing to its inherent advantages of high-temperature strength and neutron irradiation resistance. Oxygen pickup and high hydrogen isotope permeability are the two major concerns for their application in various types of blankets. To solve these issues, a bimetallic joint was designed with a CLF-1 layer of reduced-activation ferritic/martensitic (RAFM) steel to resist corrosion and a CLF-1/V4Cr4Ti bonding interface to suppress hydrogen isotope permeation. Samples were prepared from joints bonded via solid-state diffusion under hot isostatic pressing (HIP). Deuterium (D) gas permeation tests were performed at various temperatures in the range 400–600 °C at 100 kPa. After deuterium permeation tests, the thermal desorption spectra (TDS) of the samples were analyzed. And the permeation behavior of deuterium atom across the joints was schematically discussed. The results showed that bonding with steel could be an effective solution for resisting hydrogen isotope permeation through the V4Cr4Ti alloy. Thermal desorption spectrum (TDS) analysis of the tested samples revealed a desorption peak temperature equivalent to that of TiC. The formation of a 1 µm-wide B2 ordered α'- [Fe, (V, Ti)] phase layer, together with a large number of dispersed carbides around the interface, played a significant role in the deuterium permeation resistance. In addition, microstructural changes in the steel base material after the 900 °C bonding process were beneficial for suppressing deuterium diffusion.

Effect of pre-deformation on hydrogen diffusion and hydrogen induced damage in commercially pure titanium

This work aims to elucidate the interaction between hydrogen atoms and pre-introduced dislocations in commercially pure titanium (CP-Ti). Positron annihilation spectroscopy supplemented by the first-principle calculations was utilized to reveal the effects of dislocation densities on the formation of hydride types and the concentration of hydrogen-induced defects in CP-Ti. Results show that, in the hydrogen-charged sample with 40 % deformation, hydrogen-induced damage gradually decreases when the hydrogen enters the sample at a depth of about 350 nm. This finding suggests that the high-density dislocations present in deformed specimens effectively trap hydrogen atoms and inhibit their diffusion, which ultimately mitigate damage within the samples. γ-TiH and δ-TiH2 hydrides are observed in the hydrogen-charged sample. The thermal desorption spectroscopy results show that the desorption amount of deuterium decreases from 1.14 × 1018 D/cm2 to 5.10 × 1017 D/cm2 with an increase in dislocation density because dislocations inhibit the diffusion of deuterium. In samples with higher deformation, the high dislocation density inhibits the formation of δ-TiH2 hydrides and promotes the formation of γ-TiH hydrides, which significantly reduce the hardening of samples. These results provide insight into the interaction of hydrogen with pre-introduced defects and provide strong theoretical support for the development and improvement of more damage-resistant materials.

Experiments on Hydrogen Uptake and Diffusion in LiNb<sub>0.15</sub>Ta<sub>0.85</sub>O<sub>3</sub> Single Crystals by Infra-Red Spectroscopy

Hydrogen is an impurity that is often present in LiXO3 (X= Nb, Ta) single crystals and related materials. In this context, the diffusion of hydrogen is an important process because it may influence the overall conductivity of the material. We investigated the diffusional hydrogen uptake in LiNb0.15Ta0.85O3 single crystals at 600 °C. For the experiments, O2 is bubbled through liquid deuterated water (D2O), which leads to a saturation of the gas atmosphere with D2O that is incorporated into the crystal during isothermal annealing. The diffusivities of deuterium during uptake were determined by infra-red spectroscopy. We identified a fast process that can be associated with tracer diffusion and a second slower process with an almost three times lower diffusivity.

Hydrogen and deuterium permeation in Hastelloy N

Hastelloy N was chosen as the fluoride salt-contacting structural material for the Molten Salt Reactor Experiment due to its excellent compatibility with the fuel salt FLiBe. FLiBe is currently investigated for several advanced fusion and fission reactor concepts where tritium generation in the FLiBe is anticipated. Knowledge of hydrogen transport properties through Hastelloy N is important to understand how tritium would permeate through this material and result in an unintentional release. In this study, the hydrogen and deuterium permeability, diffusivity, and solubility were measured from 500 to 700 °C at a primary-side pressure of 10 kPa in a well-characterized sample of Hastelloy N. The prepared polycrystalline Hastelloy N had C and O impurities present on the surface. These impurities were investigated using Auger Emission Spectroscopy and Ar depth profiling. The adventitious C was removed upon the first Ar sputter cycle whereas O persisted deeper into the sample. For permeation experiments, applied deuterium pressures ranged from 13 Pa to 100 kPa and deuterium transport remained in the diffusion-limited regime (J ∝ P0.5) throughout the pressure range examined. Two methods are employed to measure the effective hydrogen and deuterium diffusivity: rise and decline. The decline method produced improved statistical model fits for calculating the effective diffusion coefficient compared to the rise method. The resultant transport properties compared well to published values for other nickel alloys.

Modelling of deuterium diffusion and thermal desorption in tungsten exposed to high-flux deuterium plasma

In nuclear fusion, hydrogen isotopes transportation in tungsten has been identified as a crucial process which could affect various key processes in the operation of a fusion device, such as tritium self-sustaining and operational safety. To enhance the understanding of deuterium diffusion and trapping in millimeter-thick tungsten under high-flux plasma conditions, we carried out a systematic simulation investigation on the deuterium plasma exposure and subsequent thermal desorption using the TMAP7 code based on experimental results. The simulation reveals that the defect concentration with a low de-trapping energy , as estimated solely from simulating thermal desorption, is lower than its actual density due to the temperature history of plasma exposure and subsequent cooling processes. Moreover, the growth rate of deuterium mobile concentration exhibits nonmonotonic behavior over time during plasma exposure, which strongly depends on the ratio of defect concentration with a high de-trapping energy to that with a low de-trapping energy. Additionally, we observed that the maximum deuterium diffusion depth does not follow a proportional relationship with the square root of exposure time, which is attributed to the growing number of plasma-induced defects and the reducing injection coefficient with increasing fluences. This work provides valuable insights into the understanding of deuterium transportation in tungsten during high-flux plasma exposure which could contribute to understanding and modelling of hydrogen isotopes recycling in future fusion devices.

Deuterium permeation through liquid tin supported by a nickel substrate

A model of deuterium permeation through liquid (liq.) Sn supported by a nickel (Ni) substrate is proposed as follows; deuterium dissolves in liq. Sn according to the Sieverts’ law and its concentration immediately becomes uniform through the liq. Sn layer due to large diffusivity of deuterium in liq. Sn. A thin intermediate Sn-Ni alloy layer is formed at an interface of liq. Sn and the Ni substrate in a transient of deuterium permeation. Deuterium concentration and diffusivity in the alloy layer would be lower than those in liq. Sn and pure Ni, resulting in lower deuterium permeability. Consequently, the intermediate Sn-Ni alloy layer could control total deuterium permeation through the liq. Sn supported by the Ni substrate.

In situ analysis of phase constituents evolution upon hydrogen cycling of cold-forged Mg-Ni powders

Development of hydrogen storage in metal hydrides requests efficient, simple and safe processes such as room temperature forging. Samples elaborated in this way from Mg and Ni powders result in bulk pellets whose only identified phases are Mg and Ni. Deuterium absorption occurs from 250 °C in these samples due to the co-existence of basal fiber texture and structural defects, both induced by forging. In situ neutrons diffraction analysis shows the progressive formation of the Mg2NiD0.3 / Mg2NiD4 phases upon deuterium cycling and allows to identify the multi-step absorption and desorption mechanisms at temperatures as low as 270 °C. The growth of the Mg2NiD0.3 / Mg2NiD4 phases occurs in a short time during the second step of the deuterium absorption – as Mg2NiD0.3 transformed into Mg2NiD4 – and progresses from the periphery of the initial Ni particles towards their center. The mechanism is controlled simultaneously by deuterium diffusion and migration of Mg atoms through the already formed Mg2NiD4 deuteride. The reaction between Mg and Ni is not observed in the absence of deuterium, even after annealing at 285 °C for 48 h, thus we evidence a deuterium-induced mobility of the metal atoms.

Numerical simulation of cathode-spot crater formation and deuterium desorption process on hydrogen titanium cathode with flux boundary conditions and different impregnation degree

In this paper, the crater formation process of single cathode spot on hydrogen titanium electrode is modeled. In this model, combined with the deuterium diffusion equation, the flux boundary condition was considered to calculate the cathode spot desorption rate with different impregnation degree, and the deformation process of the cathode spot crater was simulated by a hydrodynamic model. The simulation results show that the current, size, and depth of a single cathode spot crater tend to decrease with increasing impregnation degree, which is consistent with many related experimental results. The simulation result shows that the desorption of deuterium in a single cathode spot crater mainly occurs in the ignition stage, and the positions of desorption are successively distributed in the liquid metal flow area on the side wall of the crater and the high temperature area in the center of the crater. The desorption rate of deuterium drops rapidly after cathode spot quenching. At the same time, the increase of arc current and impregnation degree can improve the deuterium desorption rate of a single cathode spot.

First Observation of Quantum Diffusion in Non-Cubic Metal: Deuterium Diffusion in In

Diffusion of deuterium in indium is studied herein. In the temperature range 200–350 K, mass transfer is controlled predominantly by the mechanism of overbarrier atomic jumps; at temperatures from 80 to 120 K, by tunneling; whereas in the range from 120 to 200 K, there takes place a gradual transition from one migration mechanism to the other. These results are of fundamental significance since it is shown for the first time that quantum diffusion can be observed in a metal with a crystal lattice other than the body centered cubic one. Conditions are specified that are necessary for the observation of quantum diffusion of hydrogen: low values of Debye temperature, density of atomic packing in the lattice, and distance between the nearest equilibrium positions of hydrogen atoms. Moreover, data on the influence of point defects on hydrogen tunneling in solids are gained for the first time as well. The quantum diffusion coefficient is twice as high in the sample with enhanced vacancy concentration.

Hydrogen and Deuterium Solubility, Diffusivity and Permeability from Sorption Measurements in the Ni33Ti39Nb28 Alloy.

The hydrogen/deuterium sorption properties of Ni33Ti39Nb28 synthesized by the vacuum induction melting technique were measured between 400 and 495 °C for pressure lower than 3 bar. The Sieverts law is valid up to H(D)/M < 0.2 in its ideal form; the absolute values of the hydrogenation/deuteration enthalpy are ΔH(H2) = 85 ± 5 kJ/mol and ΔH(D2) = 84 ± 4 kJ/mol. From the kinetics of absorption, the diffusion coefficient was derived, and an Arrhenius dependence from the temperature was obtained, with Ea,d = 12 ± 1 kJ/mol for both hydrogen isotopes. The values of the alloy permeability, obtained by combining the solubility and the diffusion coefficient, were of the order of 10-9 mol m-1 s-1 Pa-0.5, a value which is one order of magnitude lower than that of Ni41Ti42Nb17, until now the best Ni-Ti-Nb alloy for hydrogen purification. In view of the simplicity of the technique here proposed to calculate the permeability, this method could be used for the preliminary screening of new alloys.

Density functional theory study of formation and diffusion of hydrogen, deuterium, and tritium in Pd-V intermetallic compounds

Permeation of hydrogen isotopes in palladium/vanadium bimetallic membranes is known to deteriorate over time because of Pd-V interdiffusion. Intermetallic compounds may form in the interdiffusion region. Density functional theory is employed to study how Pd-V compounds may affect the permeation. Three compounds Pd8V, α-Pd2V, and PdV4 are explored in this study. Formation and migration energies of hydrogen, deuterium, and tritium are calculated and subsequently compared to the data in pure Pd and V metals. The calculations show that both the formation and migration energies in the compounds are higher than in the pure metals. Thus, the permeation of these isotopes in the compounds is lower than in the pure metals. In addition, the least permeable compound is the one near the middle of the composition range, i.e. the α-Pd2V. The results provide atomistic insight for the permeation reduction in Pd/V membranes as interdiffusion progresses.

Dynamics of deuterium retention and desorption from plasma-facing materials in fusion reactor-relevant conditions

Hydrogen isotopes retention and desorption during and after discharges in fusion devices are still not well understood due to the complex device conditions and limitations of in-situ diagnostics and measurements. We simulated well-diagnosed recent experiments at the DIII-D facility to benchmark our ITMC-DYN integrated package of modeling deuterium diffusion, retention, and desorption during and after D discharge irradiation. Modeling results were compared with detail experimental data of D desorption fluxes for various irradiation conditions. We predicted the temporal evolution of free and trapped D distribution in tungsten (W) plasma-facing material (PFM). Effects of key parameters namely diffusion coefficient, recombination rate, trapping energies against different defect types, were examined in these simulations. Existing experimental data of these parameters in literature varies significantly which makes it harder to identify key mechanisms and physics responsible for hydrogen isotope retention and desorption. The purpose of this work is to accurately simulate recent well-diagnosed reactor experiments given the uncertainties in such parameters and identify mechanisms responsible for the retention and desorption. We implemented the best identified diffusion, recombination, and trapping parameters in ITMC-DYN package that integrate both various collisional and thermal processes. We predicted, for example, that sample cooling between discharges in DIII-D operations can significantly affect the spatial distribution of trapped D in W under reactor irradiation conditions. Correct prediction of desorption spectra from samples irradiated during 10 DIII-D discharges showed that up to 35% of D can be retained in high binding energy defects such as vacancy clusters or voids.

Deuterium permeability of Russian fusion structural materials

Nowadays, three classes of materials are considered the most relevant as the structural materials for fusion facilities: the austenitic steels, reduced activation ferritic-martensitic steels (RAFMS) and V-Cr-Ti alloys. In Russian Federation, the materials of all three types are developed and industrially produced: the ChS-68 austenitic steel, the Ek-181 RAFMS, and the V-4Cr-4Ti alloy. In this work, the deuterium permeability was studied of the fusion-relevant structural materials produced in Russia. Gas-driven permeation measurements were performed in a pressure range of 0.1÷5⋅104 Pa and in a temperature range of 290÷600 °C. Deuterium diffusion and permeation coefficients for the ChS-68 steel were found out. Permeability of the V-4Cr-4Ti alloy was estimated. At the same membrane temperature and D2 pressure at the inlet surface, the deuterium flux permeating through the oxidized Ek-181 RAFMS is the lowest, the flux through the ChS-68 austenitic steel is several times higher, and the flux through vanadium alloy is 3–4.5 orders of magnitude higher.

Deuterium permeation behavior in a FeCrAl-based alloy containing Mo, Nb and Ta elements for LWR cladding application

The deuterium permeation behavior of a FeCrAl-based alloy containing Mo, Nb and Ta elements was investigated by gas-phase deuterium permeation testing, transmission electron microscopy, X-ray diffraction and electron backscatter diffraction methods. The results show that the higher the test temperature, the greater the steady-state permeation flux of the FeCrAl-based alloy. As the upstream deuterium pressure increases, the steady-state permeation flux of the FeCrAl-based alloy also increases. The pressure exponent n is between 0.5 and 1, indicating that deuterium permeation in the FeCrAl-based alloy is controlled by a combination of bulk diffusion and surface processes. This phenomenon is caused by the oxide film generated on the surface of the FeCrAl-based alloy during deuterium permeation test. The deuterium permeability of the FeCrAl-based alloy is about 37 times that of 316 L and 95 times that of Zircaloy-4 at the typical operating temperature of 300 °C. At 360 °C, the deuterium permeability of the FeCrAl-based alloy is about 25 times that of 316 L, and about 32 times that of Zircaloy-4. Compared with 316 L and Zircaloy-4 alloy, the activation energy of deuterium permeation of the FeCrAl-based alloy is smaller, indicating that deuterium permeates more easily in the FeCrAl-based alloy. The activation energy of deuterium diffusion in the FeCrAl-based alloy is also smaller, indicating that deuterium diffuses more easily in the FeCrAl-based alloy.

High hydrogen isotopes permeation resistance in (TiVAlCrZr)O multi-component metal oxide glass coating

Developing ceramic coating with high hydrogen isotopes permeation resistance is an urgent task in many fields such as fusion reactor systems, hydrogen storage/transportation, and fuel cell. In this work, a (TiVAlCrZr)O multi-component metal oxide glass (MCMOG) coating is developed as a new type of hydrogen isotopes permeation barrier (HIPB), and the diffusion behavior of deuterium in MCMOG is studied for the first time. Compared with the deuterium permeation reduction factor (DPRF) of 51 for amorphous alumina coating (at 587 °C in 0.65 µm), the 29 nm dense MCMOG coating has around 27 times enhancement with DPRF of 1420 at 550 °C. Based on first-principles calculations, we show that the significantly suppressed deuterium permeation in MCMOGs is attributed to the sluggish diffusion of deuterium arising from the highly rugged energy landscape, which is induced by the diversity of electronic band structures near the Fermi level. In addition, oxygen vacancies strongly affect PRF, where the PRF of the fully oxidized MCMOG layer (29 nm) is around 200 times compared to that of MCMOG with the same thickness containing oxygen vacancies. Therefore, dense MCMOG is a new promising HIPB material.

EFFECT OF IRRADIATION AND DEUTERIUM BEHAVIOR IN LI-BASED TRITIUM BREEDING CERAMICS

The behavior of implanted deuterium in advanced lithium orthosilicate (Li4SiO4) pellets with addition of lithium metatitanate (Li2TiO3), and in reference Li4SiO4 pellets, has been investigated. Thermal desorption (TD) spectroscopy was used to study the deuterium interaction with radiation defects in materials. Computational evaluation of deuterium desorption within the framework of the diffusion-trapping model allowed to associate characteristics of experimental TD spectra with specific trapping sites in the material. It was found that deuterium desorption is limited mainly by intragranular diffusion of deuterium and its trapping by radiation defects associated with Li-vacancy traps. Deuterium gas release from both ceramics demonstrated similar trend indicating weak dependence of deuterium trapping behavior on phase composition. The change of the morphology and elemental composition of the pellets surface has been analyzed. SEM examination indicated that ion irradiation and subsequent thermal desorption annealing of two-phase ceramics leads to an increase in surface destruction processes.

Deuterium permeability and diffusivity in FeCrAl alloys for LWR cladding application

FeCrAl alloys, one of the promising ATF (Accident Tolerant Fuel) claddings, have been widely researched because of their superior oxidation resistance. However, compared with zirconium-based cladding, the higher tritium permeability of FeCrAl alloys could result in a higher tritium concentration in the primary coolant water. Deuterium transport through ferrite FeCrAl alloys compared with 316L-SS was investigated using a permeation apparatus. Deuterium permeability, diffusivity and solubility in FeCrAl alloys were measured. A 2D finite element method model was built based on updated test results to analyze the tritium release from LWRs fuel rods. Deuterium diffusivity in FeCrAl alloys is more than one order of magnitude higher than 316L-SS, but the solubility is much lower. In addition, the impact of all these data on LWRs operation was discussed. The diffusion rate significantly affects the time to reach steady state. Still, even if the diffusion rate is reduced by a factor of 0.01, it does not affect the steady-state tritium permeability from the fuel rods. FeCrAl fuel rods would experience a considerable tritium flux release rate because of the high diffusivity.

Debye Temperature and Quantum Diffusion of Hydrogen in Body-Centered Cubic Metals.

Diffusion of deuterium in potassium is studied herein. Mass transfer is controlled predominantly by the mechanism of overbarrier atomic jumps at temperatures 120–260 K and by the tunneling mechanism at 90–120 K. These results together with literature data allowed us to determine conditions under which the quantum diffusion of hydrogen in metals can be observed, which is a fundamental problem. It is established that in metals with a body-centered cubic lattice tunneling can be observed only at temperatures below the Debye temperature θD solely for metals with θD < 350 K. Predictions are made for metals in which quantum diffusion of hydrogen can be experimentally registered. Metals for which such results cannot be obtained are specified as well. Among them are important engineering materials such as α-Fe, W, Mo, V, and Cr.