Diffusion Coefficients Of Deuterium Research Articles

A comprehensive study on the kinetics and isotherms of D2/H2 adsorptive separation using pure and composite Cu-BDC-NH2 MOFs at 77 K

Pure and composite Cu-Amino-terephthalate MOF has been produced by ultrasound wave to evaluate the adsorption capacity and adsorptive separation of D2 and H2 at 77 K up to 1000 mbar. The frameworks are characterized by XRD, SEM, FTIR, ICP, BET, and EDX analysis. Separation studies were performed using idealized adsorption solution theory (IAST) and direct measurements. Isotherm studies showed the data had good agreement with the Langmuir model and the adsorption capacity of deuterium was greater than hydrogen in all samples. Linear Driving Force (LDF) model was applied to investigate the effective diffusion coefficients of deuterium and hydrogen in the frameworks. The LDF model showed hydrogen molecules diffused faster than deuterium molecules in all frameworks. In the adsorption enthalpy studies, there was a slight difference between deuterium and hydrogen adsorption energy. In this regard, Cu-BDC-NH2@rGO showed a higher adsorption enthalpy difference compared to Cu-BDC-NH2. Finally, the D2/H2 selectivity of the composite framework was greater than the pure one. Regarding this matter, the Cu-BDC-NH2@rGO MOF showed a maximum selectivity factor of about 2.2 at 77 K and 1000 mbar based on the IAST model.

Low-temperature sorption of hydrogen by porous carbon material containing palladium nanoclusters

The sorption of hydrogen isotopes by a composite nanostructured carbon material containing palladium clusters with an average size of 3–5 nm was studied in the temperature range of 8–290 K. The total amount of sorbed hydrogen strongly depends on the method of manufacturing the composite and is 2–4.5% of the sample mass. In the kinetics of hydrogen sorption and desorption by a composite, two processes with characteristic times differing by more than an order of magnitude are identified. The relatively fast process seems to be related to the filling of the cavities of the carbon matrix with hydrogen molecules, the longer one corresponded to the diffusion of hydrogen into the crystal lattice of palladium nanoclusters. Two temperature regions are found for the temperature dependences of the diffusion coefficients of hydrogen and deuterium in composite samples. Above 60 K, the diffusion activation energies in the sample containing palladium nanoclusters were more than twice the values obtained for the pure carbon matrix. Below 60 K, the diffusion coefficients of deuterium in the pure carbon matrix weakly depended on temperature. In the case of diffusion of hydrogen and deuterium into palladium nanoclusters, a change in the character of the temperature dependence was observed at a lower temperature (∼30 K). Below this temperature the activation energy decreased by approximately an order of magnitude.

Characterisation of deuterium distributions in corroded zirconium alloys using high-resolution SIMS imaging

Hydrogen diffusion through the oxide grown on Zr alloys by aqueous corrosion processes plays a critical role in determining the rate of hydrogen pickup (HPU) which can result in embrittlement of fuel cladding and limit the burnup of the nuclear fuel it encapsulates. Mapping the hydrogen/deuterium distributions in these oxide layers, especially in the barrier layer close to the metal/oxide interface, is a powerful way to understand the mechanism of both oxidation and hydrogen pickup. Here we have characterised by high-resolution SIMS analysis the deuterium distribution in oxide layers on a series of Zr alloys, including autoclave-oxidised Zircaloy-4, Zr-1Nb and Zr-2.5Nb alloys, and in-flux and out-of-flux corroded Zr-2.5Nb samples. Pre-transition Zircaloy-4 samples show a high deuterium trapping ratio in the oxide and a higher diffusion coefficient than in oxides on the Nb-containing samples. Neutron irradiation increases the deuterium diffusion coefficient, the deuterium concentration in the oxide and the pickup fraction in Zr-2.5 Nb samples. Comparative NanoSIMS and EDX/SEM analysis demonstrates that the deuterium is not preferentially trapped at second phase particles in the oxides on any of the alloys studied, but there is direct evidence for trapping at the surfaces of small oxide cracks especially in Zircaloy-4 samples. The high resolution mapping of these hot-spots in 3D can provide unique information on the mechanisms of hydrogen uptake, and suggests that the development of interconnected porosity in the oxide may be the critical rate-determining mechanism that controls HPU in the aqueous corrosion of zirconium alloys in water-cooled reactors.

Characterisation of Deuterium Distributions in Corroded Zirconium Alloys Using High-Resolution SIMS

Hydrogen diffusion through the oxide grown on Zr alloys by aqueous corrosion processes plays a critical role in determining the rate of hydrogen pickup which can result in embrittlement of fuel cladding and limit the burnup of the nuclear fuel it encapsulates. Mapping the hydrogen/deuterium distributions in these oxide layers, especially in the barrier layer close to the metal/oxide interface, is a powerful way to understand the mechanism of both oxidation and hydrogen pickup. Here we have characterised by high-resolution SIMS analysis the deuterium distribution in oxide layers on a series of Zr alloys, including autoclave-oxidised Zircaloy-4, Zr-1Nb and Zr-2.5Nb alloys, and in-flux and out-of-flux corroded Zr-2.5Nb samples. Pre-transition Zircaloy-4 samples show a high deuterium trapping ratio in the oxide and a higher diffusion coefficient than in oxides on the Nb-containing samples. Neutron irradiation increases the deuterium diffusion coefficient, the deuterium concentration in the oxide and the pickup fraction in Zr-2.5 Nb samples. Comparative NanoSIMS and EDX/SEM analysis demonstrates that the deuterium is not preferentially trapped at SPPs in the oxides on any of the alloys studied, but there is direct evidence for trapping at the surfaces of small oxide cracks especially in Zircaloy-4 samples. The high resolution mapping of these hot-spots in 3D can provide unique information on the mechanisms of hydrogen uptake, and suggests that the development of interconnected porosity in the oxide may be the critical rate-determining mechanism that controls HPU in the aqueous corrosion of zirconium alloys in water-cooled reactors.

Quantum Diffusion of Deuterium in Sodium.

The online nuclear reaction analysis technique has been applied to study the temperature dependence of deuterium diffusion coefficients for deuterium in sodium at temperatures ranging between 110 and 240 K, and at cryogenic temperatures, below 160 K, tunneling of deuterium atoms in the metal lattice has been observed. Above 160 K, diffusion occurs by the classical mechanism of overbarrier atomic jumps. Results of quantum diffusion of deuterium in a metal have been obtained for the first time; they used to be known only for the lightest hydrogen isotope, protium, in niobium and tantalum. The analysis has shown that the necessary condition for carrying out the quantum mechanism of deuterium migration is low Debye temperature of a metal, below 200 K. Experimental data on diffusion of hydrogen isotope in an alkali metal have also been obtained for the first time in this paper.

3D-characterization of deuterium distributions in zirconium oxide scale using high-resolution SIMS

In pressurised water reactors (PWRs), fuel rods are clad with zirconium alloy tubes chosen for their low neutron capture cross section and good oxidation resistance. Understanding cladding-water corrosion reactions at 280–350 °C and the correlated hydrogen pickup into these Zr alloys is crucial to the safe operation of PWRs and to increasing the burnup of the fuel. Here we describe a method based on 3D mapping by high resolution SIMS to measure the distribution of deuterium in oxidised Zircaloy-4 alloy samples. Two analysis directions, depth-profiling and cross-sectional, were used to ensure we understand possible imaging artefacts during sputtering of the complex microstructure in these samples. The topography of the sputtering carter and sputtering rate have been calibrated by Focused Ion Beam (FIB)/Scanning Electron Microscopy (SEM) analysis. The deuterium diffusion coefficients at 360 °C is calculated suing the depth profile in both samples. The results show that the 3D deuterium distribution can be successfully measured in isotopically spiked samples, but that care has to be taken to understand the effect of deuterium outgassing and surface diffusion during Cs+ primary ion bombardment, which results in a degraded lateral resolution, which distorts the apparent deuterium distribution. The detection method in this paper can be a useful tool in the analysis of the distribution of hydrogenic species in zirconium fuel cladding materials in service, and can also provide other engineering materials.

Kinetic D/H fractionation during hydration and dehydration of silicate glasses, melts and nominally anhydrous minerals

The distribution of hydrogen isotopes during diffusion-driven aqueous processes in silicate glasses, melts and crystals was investigated. Hydration/dehydration experiments were performed on silica glasses at 1000 °C and 1 bar total pressure. Dehydration triggered by decompression-driven bubble nucleation and growth was performed on rhyolitic melts at 800 °C and a few hundred MPa. Hydrogen extraction from a nominally anhydrous mineral (grossular) single crystal was carried out at 800 °C and ambient pressure. After these three series of experiments, pronounced water (sensu lato) concentration profiles were observed in all recovered samples. In the grossular single-crystal, a large spatial variation in H isotopes (δD variation > 550‰) was measured across the sample. This isotopic distribution correlates with the hydrogen extraction profile. The fit to the data suggests an extreme decoupling between hydrogen and deuterium diffusion coefficients (DH and DD respectively), akin to the decoupling expected in a dilute ideal gas (DH/DD ≈ 1.41). Conversely, no measurable spatially- and time-resolved isotopic variations were measured in silicate glasses and melts. This contrasted behavior of hydrogen isotopes likely stands in the different water speciation and solution mechanisms in the three different materials. Glasses and melts contain essentially hydroxyl and molecular water groups but the mobile species is molecular water in both cases. Protonated defects make up most of the water accommodated in grossular and other nominally anhydrous minerals (NAM). These defects are also the mobile species that diffuse against polarons. These results are crucial to accurately model the degassing behavior of terrestrial and lunar magmas and to derive the initial D/H of water trapped in fluid inclusions commonly analyzed in mantle NAMs, which suffered complex geological histories.

Retention and release of hydrogen isotopes in carbon materials priorly charged in gas phase

Thermal desorption of deuterium from isotropic graphites and a CFC material priorly charged with deuterium gas has been investigated to obtain quantitative information on hydrogen recycling and tritium inventory in fusion experimental devices and future reactors. The spectra of thermal desorption spectrometry (TDS) appear to have five peaks, which are defined as peaks 1–5 in order of the increase of temperature. Diffusion coefficients of deuterium for the absorption process are evaluated for the samples charged with deuterium gas for various absorption times. Absorption pressure dependence of TDS spectra shows a unique change in the temperatures of peak 2. As for the absorption temperature dependence of TDS spectra, peak 4 has a drastic change in the shape of spectra and also in the peak temperatures. The mechanism of desorption for peak 5 will be associated to a detrapping process with a dispersion of energies in the range of 4.0–4.9 eV.

Application of the Nuclear Reaction Analysis Online Technique to Study the Diffusion of Deuterium in Metals

Nuclear reaction analysis online technique has been applied to study the diffusion of deuterium in metals. Investigations ensuring the application of the new method have been performed. These investigations include the development of a device for diffusion annealing of samples in the chamber of an accelerator and an algorithm for taking into account the effect of radiation defects on the diffusion coefficients. Test measurements of the diffusion coefficients of deuterium in nickel in the temperature range from 130 to–60°С have been performed. For negative temperatures, experimental data on the diffusion of a hydrogen isotope in a metal have been obtained for the first time by a direct method and it has been shown that the online nuclear reaction analysis provides reliable data.

First-principles molecular dynamics study of deuterium diffusion in liquid tin.

Understanding the retention of hydrogen isotopes in liquid metals, such as lithium and tin, is of great importance in designing a liquid plasma-facing component in fusion reactors. However, experimental diffusivity data of hydrogen isotopes in liquid metals are still limited or controversial. We employ first-principles molecular dynamics simulations to predict diffusion coefficients of deuterium in liquid tin at temperatures ranging from 573 to 1673 K. Our simulations indicate faster diffusion of deuterium in liquid tin than the self-diffusivity of tin. In addition, we find that the structural and dynamic properties of tin are insensitive to the inserted deuterium at temperatures and concentrations considered. We also observe that tin and deuterium do not form stable solid compounds. These predicted results from simulations enable us to have a better understanding of the retention of hydrogen isotopes in liquid tin.

Hydrogen diffusivity in oxide layers formed in Zr alloy in air or steam

The effect of the oxidation conditions on hydrogen diffusion in oxide layers in Zr alloy was experimentally studied. Samples of GNF-Ziron (high-iron Zircaloy-2-type alloy) sheets were oxidized in air or steam and then exposed to deuterium plasma to charge them with deuterium. Deuterium depth profiles in each sample were observed by nuclear reaction analysis during plasma exposure, and the deuterium diffusion coefficient D was estimated. The results showed that the D values of the steam-oxidized samples were high, whereas that of a steam-oxidized sample that was subsequently heated in vacuum was as low as those of air-oxidized samples. The difference in D was not attributed to the structure but is probably due to the presence of OH groups absorbed during steam oxidation.

Deuterium diffusion in proton conductors La0.9Sr0.1ScO3-δ and BaZr0.9Y0.1O3-δ at room temperature

Abstract Room-temperature measurements of diffusion coefficients for deuterium in proton conductors La0.9Sr0.1ScO3 -δ and BaZr0.9Y0.1O3 -δ which contain dissolved H2O vapor have been performed. The concentration of oxygen structure vacancies in oxides after treatment in vapor was close to zero. A diffusion source of deuterium was created by ion implantation; measurement of the concentration–distance distribution of deuterium in samples was performed in situ during implantation. The NRA technique and 2H(d,p)3H reaction at an energy of the incident beam of 650 keV were used. For the initial and boundary conditions of the diffusion problem which were realized in the work, a solution of the inhomogeneous Fick equation was obtained. Using the technique developed, measurements of the diffusion coefficients for hydrogen in proton conductors were for the first time performed directly. For the BaZr0.9Y0.1O3 -δ oxide, the directly gained values of diffusion coefficients agree rather well with those obtained from the proton conductivity with the use of Nernst–Einstein equation.

Evaluating the hydrogen isotope absorption/diffusion coefficient of CVD-SiC at high temperature

Deuterium diffusion coefficient measurements of CVD-SiC were carried out using a solubility and diffusivity measurement apparatus to investigate the permeation mechanism of the hydrogen isotope through CVD-SiC. Experiments were conducted with thin-sheet-type samples with thicknesses of 0.1mm, 1mm, and 2mm at 1073–1183K. Total amount of occluded gas into or released gas from different thickness but same weight sample were expected to be the same, but unexpectedly differed by more than 50%. As the release rates after sufficient time had passed were almost the same, and the 1-mm-thick sample had twice the surface area of the 2-mm-thick sample, the measurements were probably affected by adsorbed gas on the surface. The value of D/L2 (the diffusion coefficient divided by the square of the thickness), obtained by fitting to the theoretical formula but ignoring the early phase of discharge, was in good agreement for samples of different thickness at the same temperature, and was more than 5 orders of magnitude smaller than that obtained from the permeability measurement experiments. Therefore, we believe that the deuterium permeation through CVD-SiC is primarily dependent on the permeation rate through the grain boundaries.

Hydrogen traps in ion-irradiated F82H steel observed by NRA

Characteristics of irradiation-induced trapping of hydrogen were investigated for quantitative evaluation of tritium retention in F82H steel. Before and after irradiation of 0.8-MeV 4He or 0.3-MeV H ions, deuterium depth profiles near the surface of a disk sample were observed by nuclear reaction analysis under continuous exposure of deuterium plasma. One type of trap, with a trapping energy of 0.66eV, was observed after each irradiation. The ratio of trap production rate to atomic displacement was 0.0046 and 0.0014 for He and H irradiation, respectively. Annihilation occurred around 600K for H irradiation but was not observed even at 691K for He irradiation. Traps are likely to be interstitial-like sites associated with dislocation loops. This study also indicates that helium plays a role in inhibiting trap annihilation. In addition, the deuterium diffusion coefficient in non-irradiated F82H was determined by a time-lag permeation experiment.

Deuterium diffusion in oxide layers of Zr–2.5Nb alloy

In situ diffusion measurements of the hydrogen isotope deuterium in the oxide layers formed on Zr–2.5Nb alloy have been carried out at 523 and 573K by using a combined technique of deuterium plasma exposure and nuclear reaction analysis for the D(3He,p)4He reaction. The oxide layers were prepared in two environments, 1M LiOH-containing water at 563K and steam at 673K, and their thicknesses ranged from 1.6 to 1.9μm. The deuterium profile evolution in the oxides showed a combined process of absorption and dissolution in the surface region, and subsequent bulk diffusion in the deeper region. The diffusion coefficients of deuterium were evaluated for the two formation environments from the transient deuterium profiles of the oxide layers. The diffusion coefficients in the LiOH–water oxide were significantly larger than the values in the steam oxide. Compared with previously obtained data for three kinds of Zircaloy-type alloys (Zry-2, GNF-Ziron and VB), both of the Zr–2.5Nb oxides possessed the smallest diffusivities among the four alloys. Moreover, the surface concentrations of deuterium in the Zr–2.5Nb oxides were distinctly lower than those in the other Zircaloy-type alloy oxides. The superior hydrogen absorption performance of Zr–2.5Nb alloy observed in the out-of-pile corrosion tests was attributed to the smaller diffusivity and the smaller concentration gradient. The mechanism for the lower hydrogen diffusion flux of Zr–2.5Nb alloy was discussed in terms of the dissolution effect of niobium with variable valences of Nb2+–Nb5+ from the β-Nb precipitates into the ZrO2 lattice.

ERD studies of D-ion depth distributions after implantation into some pure metals and alloys

This paper presents a report on experimental results of depth distributions of deuterium ions implanted with 25 keV energy at a fluence interval of (1.2–2.3) × 1022 m−2 into samples of pure metals (Cu, Ti, Zr, V, Pd) and diluted Pd alloys (Pd-Ag, Pd-Pt, Pd-Ru, Pd-Rh). The post-treatment depth distributions of deuterium and hydrogen atoms were measured within a few hours after implantation with the use of elastic recoil detection (ERD) analysis. After three months the measurements were repeated. The comparison of the obtained results in both series of studies allowed us to make an important observation of the desorption rates of implanted deuterium atoms from pure metals and diluted Pd alloys. The maximum measured concentrations of deuterium atoms in pure Zr and Ti foils with relatively small desorption rate of deuterium atoms within three months after implantation were observed. Also a very high spreading of deuterium atom distributions was observed in all the measured pure metals and alloys. It can be explained by the large diffusion coefficients of deuterium and extremely fast kinetics.

Deuterium diffusion in steam-corroded oxide layer of zirconium alloys

In situ diffusion experiments of the hydrogen isotope deuterium in the oxide layer formed on zirconium alloys were carried out to clarify the hydrogen diffusion mechanism in the layer. The experiments were done in deuterium plasma for the temperature range from 523 to 673 K by using a nuclear reaction analysis for D( 3He,p) 4He. The zirconium alloys used were GNF-Ziron (high iron Zircaloy-2 type alloy) and VB (high iron and chromium alloy), which had been corroded in 673 K H 2O- or D 2O-steam for 10–15 days. The oxide thickness ranged from1.4 to 1.7 μm of pre-transition condition. The results showed that the steam oxides had a double-layer structure composed of the outside non-protective oxide with faster diffusivity and the inside barrier layer with slower diffusivity. The barrier layer thickness was about 0.8–0.9 μm and unchanged for the two alloys. For the in situ deuterium plasma diffusion experiments, the diffusion coefficient of deuterium in the barrier layer of GNF-Ziron was given as, D (cm 2/s) = 4.5 × 10 −13exp (−17,000/RT). The diffusion coefficient in the VB oxide at 573 K was approximately half of that in the GNF-Ziron oxide. This factor for the diffusivity was roughly consistent with their hydrogen absorption performance. For the deuterium release experiments in a vacuum subsequent to the in situ deuterium diffusion experiments, the diffusion in the barrier oxide layer was further retarded, suggesting lower diffusivity than for the case of the in situ deuterium plasma atmosphere.

Hydrogen Absorption Mechanism of Zirconium Alloys Based on Characterization of Oxide Layer

Abstract In order to get a better understanding of the mechanism governing hydrogen absorption behavior in Zr-based alloys, various characterization techniques were applied to the oxide layers of three alloys: Zry-2, GNF-Ziron (Zry-2-based alloy with ∼0.26 wt % Fe), and VB (Zr-based alloy containing ∼0.5 wt % Sn, ∼0.5 wt % Fe, and ∼1 wt % Cr). Out-of-pile corrosion tests were carried out in 400 °C steam and 290 °C LiOH water. For both tests, the hydrogen absorption decreased with higher iron content in the alloys, in the order of Zry-2>GNF-Ziron>VB, despite different kinetics of a parabolic law in the former test and a linear law in the latter test. The acceleration of hydrogen absorption in the LiOH water was ascribed to the formation of degraded or open grain boundaries up to locations very near the metal/oxide interface. The pre-transition steam oxides of 1.4–1.7 μm had a double layer structure composed of the outside non-protective oxide of monoclinic ZrO2 with faster diffusivity and the inside barrier layer of predominantly tetragonal ZrO2 with slower diffusivity. The thickness of the barrier layer of about 0.8–0.9 μm was not changed for the different alloys. The diffusion coefficient of deuterium in the VB oxide was approximately half of that in the GNF-Ziron oxide. This factor for the diffusivity was consistent with their hydrogen pickup performance. The higher compressive stress in the barrier layer was directly linked to the higher hydrogen pickup resistance of the alloys. Preferential dissolution of alloy elements from the second-phase particles (SPPs) into the oxide matrix was evinced for iron, and was very limited for chromium and nickel. These two elements had a tendency to exist as precipitates in the oxide layers, chromium mainly as oxide, and nickel mainly as metal. The superior hydrogen absorption performance of VB containing higher iron content and the SPPs with larger size and number density was attributable to the dissolved iron effect and higher compressive stress state generated from the delayed oxidation of the SPPs in the barrier layer.

Hydrogen tracer diffusion in LiBH4 measured by spatially resolved Raman spectroscopy

The hydrogen tracer diffusion in LiBH(4) has been determined by spatially resolved Raman spectroscopy. The measurements give direct evidence of a macroscopic diffusion of BH ions as well as atomic exchange of hydrogen between the anions. An effective tracer diffusion coefficient of deuterium in LiBH(4) of D approximately 7 x 10(-14) m(2) s(-1) at 473 K is derived. The direct exchange rate of hydrogen between BH(4) units is 10 orders of magnitude slower, i.e. the relatively fast effective hydrogen diffusion has its origin in the fast diffusion of BH(4) units.

Deuterium diffusion in a chemical densified coating observed by NRA

Ceramic coatings on structural material are expected as a barrier for tritium permeation in fusion devices. A Cr 2O 3–SiO 2–CrPO 4 coating on stainless steel by use of a chemical densified coating (CDC) method was experimentally studied. The sample disk was exposed to a deuterium plasma and an analyzing beam of 3He ions irradiated the sample to observe deuterium concentration profiles. It was found that a very long time, typically 10 ks at 563 K, was needed for deuterium to diffuse from the surface to a few μm in depth. The profiles were analyzed with a diffusion model to obtain the diffusion coefficient of deuterium, which was expressed by 1.1 × 10 −10exp(−0.71 eV/kT) [m 2 s −1] between 470 and 723 K. The diffusion coefficient was about 5 orders of magnitude smaller than that in type 304 stainless steel at 563 K. The CDC coating is expected to significantly delay tritium permeation.