Deuterium Desorption Research Articles

Determination of activation energy of ion-implanted deuterium release from W-Y2O3**Project supported by the National Magnetic Confinement Fusion Energy Research Project, Ministry of Science and Technology of China (Grant No. 2015GB109002), the Innovation Fund of Postgraduate, Xihua University, China (Grant No. ycjj2018017), and the National Natural Science Foundation of China (Grant No. 21401173).

The retention and release of deuterium in W–2%Y2O3 composite materials and commercially pure tungsten after they have been implanted by deuterium plasma (flux ∼ 3.71 × 1021 D/m2⋅s, energy ∼ 25 eV, and fluence up to 1.3 × 1026 D/m2) are studied. The results show that the total amount of deuterium released from W–2%Y2O3 is 5.23 × 1020 D/m2(2.5 K/min), about 2.5 times higher than that from the pure tungsten. Thermal desorption spectra (TDS) at different heating rates (2.5 K/min–20 K/min) reveal that both W and W–2%Y2O3 have two main deuterium trapped sites. For the low temperature trap, the deuterium desorption activation energy is 0.85 eV (grain boundary) in W, while for high temperature trap, the desorption activation energy is 1.57 eV (vacancy) in W and 1.73 eV (vacancy) in W–2%Y2O3.

Implantation of Deuterium and Helium Ions into a Tungsten-Coated Composite Structures

The capture, retention, and thermal desorption of deuterium and helium ions with medium energies implanted into tungsten-coated multilayer functional structures and the formation of corresponding radiation-induced damages in the crystal lattice of the tungsten coatings of those structures have been studied making use of the thermal desorption spectroscopy and electron microscopy methods. The behavior of deuterium and helium in the examined materials and its dependence on the post-implantation heating temperature, the dose of irradiation with D+ and He+ ions, and the irradiation condition – separate (making use of ions of only one kind) or sequential (making use of ions of both kinds) – are analyzed. A classification of radiation-induced defects and mechanisms of their annealing are proposed.

Cathode and plasma phenomena in vacuum-arc sources of hydrogen isotope ions: I. Desorption of hydrogen isotopes during the operation of vacuum arc cathode spots

A model is proposed to describe the desorption of deuterium from a deuterated cathode during the operation of the vacuum arc cathode spot. The model treats a cathode spot as consisting of individual cells and involves a numerical simulation of the temperature fields that arise during the hydrodynamic processes responsible for the formation of microcraters on the cathode surface. Using a deuterated ZrD0.67 cathode as an example, it is shown that the amount of deuterium desorbed immediately from the crater formed during the operation of the cathode spot cells is several times smaller than the total amount of desorbed deuterium. The main portion of deuterium is desorbed from the hot cathode region adjacent to the crater and from the crater at the stage of its cooling. For a deuterated ZrD0.67 cathode, the percentage of desorbed deuterium can reach 80% of the total number of evaporated atoms, and it can be even greater if the cathode spot cells operate in the immediate vicinity of each other.

Hydrogen trapping in tungsten: impact of helium irradiation and thermal cycling

The impact of helium (He) plasma exposure with He fluxes relevant for ITER and WEST on the near-surface microstructure of polycrystalline tungsten (W) is investigated by coupling transmission electron microscopy (TEM) analysis and thermal desorption spectrometry (TDS) measurements. The samples were exposed in the PSI-2 linear plasma device to 75 eV He ions up to the fluence of 3 × 1023 He m−2 with the surface temperature in the range 1053–1073 K. The obtained He bubbles–enriched W samples are subsequently probed with sequences of low flux and low fluence 250 eV deuterium (D) ion implantations and TDS measurements in an ultra-high-vacuum setup to study the effects of the near-surface morphology changes due to the helium irradiation on fundamental mechanisms of deuterium retention. The results obtained for two different near-surface layer He bubbles morphologies revealed that the effects of He irradiation on D retention in W strongly depend on its subsequent thermal cycling. For annealing below 900 K, deuterium retention is similar to the one measured in pristine W. In contrast, for annealing above 1150 K, deuterium retention in the He bubbles-enriched W is increased 3–8 fold as compared to non-damaged W. Additionally, the deuterium desorption peak shifts from 540 to 450 K. This increase of D trapping in the He bubbles-enriched W annealed above 1150 K is presumably associated with a modification of the near-surface microstructure concurrent with an outgassing of He.

Destabilizing the Dehydrogenation Thermodynamics of Magnesium Hydride by Utilizing the Immiscibility of Mn with Mg.

Hydrogen storage is a key technology for the advancement of hydrogen and fuel cell power technologies in stationary and portable applications. MgH2, an example of a high-capacity hydrogen storage material, has two major material challenges for practical applications: slow hydrogen desorption kinetics and high hydrogen desorption temperature. Numerous studies have reported enhancements in kinetics but only a few in thermodynamics. Here, we present a simple but effective way to improve upon both the kinetic and thermodynamic aspects of desorption by utilizing the immiscibility of Mn, a non-hydrogen absorbing metal, with Mg. Mg0.25Mn0.75, prepared through ball milling MgH2 and Mn powders, is a nanocomposite where the nanometer-sized MgH2 domains are randomly embedded in a Mn matrix. This sample readily and reversibly absorbs and desorbs deuterium even at a temperature of 200 °C without the addition of any catalysts. This is nearly 180 °C lower than the typical operating temperature of conventional bulk Mg. Furthermore, at a given temperature, its deuterium desorption pressure is clearly elevated compared to that of pure Mg, indicating the destabilization of MgD2. The average crystallite size of MgD2 in deuterated Mg0.25Mn0.75 determined from X-ray diffraction data is around 9 nm. Nuclear magnetic resonance spectroscopy studies show that MgD2 domains are heavily strained and some of the D atoms are coordinated by a few Mn atoms, suggesting that a large number of lattice defects, including the partial substitution of Mg with Mn, are introduced during ball milling. Furthermore, the Mn matrix firmly locks nanosized MgD2, preventing the agglomeration of MgD2 below 250 °C. Our study suggests that a synergistic effect created by nanosizing, large lattice distortions, and robust interfaces between MgD2 and the Mn matrix can effectively and concurrently improve the kinetics and thermodynamics of MgD2 in Mg0.25Mn0.75. Our work demonstrates the possibility of utilizing the immiscibility of metals with Mg to synthesize a robust nanostructure that can alter the kinetics and stability of MgH2.

Modeling the sharp deuterium release from beryllium co-deposits

Many studies have shown a sharp deuterium desorption from beryllium at around 450 K. In an attempt to model this sharp release, a new model was developed, describing the formation and decomposition of beryllium deuteride. Such a model was found to reproduce the sharp desorption peak in the thermal desorption spectrum. Moreover, in contrast to other models, the new model was able to reproduce the constant deuterium desorption from beryllium held at a constant elevated temperature. Fitting the modeling results to experimental data allowed us to determine the deuterium solubility limit in beryllium, which indicated an endothermic formation of beryllium deuteride. New values of the deuterium surface recombination coefficient were also obtained, differing from the ones found in the literature.

Comparison of dynamic deuterium retention in single-crystal and poly-crystals of tungsten: The role of natural defects

The time evolution of fuel retention in materials relevant for future fusion reactors is compared for two different tungsten microstructures: single-crystal versus recrystallized poly-crystals. The initial retention of both types of sample is similar. It decays exponentially with a time constant of ~18 h at 300 K (the so-called short-term retention). After 48 h at room temperature, a constant deuterium retention is measured (long-term retention) with the single-crystal containing systematically less deuterium than poly-crystals. Macroscopic rate equations models are built with density functional theory inputs to reproduce deuterium desorption observables with the MHIMS-R code. We found that the native oxide layer could explain the desorption peak located at ~450 K as well as most of the short-term retention in the single-crystal. The native oxide together with, dislocations for single-crystal and grain boundaries for poly-crystals, are responsible for the long-term retention. Dislocations should explain the desorption peak located at ~815 K for mechanically polished samples. The dual role of most of tungsten defects is related to their multi-trapping properties with filling-level-dependent detrapping energies. Finally, the use of an effective diffusivity of deuterium through the native oxide layer, i.e. its diffusion barrier character, is evaluated.

Hydrogen Desorption Kinetics Derived from Electrochemical Ni-B Compositions

The paper studies how boron concentration exerts its influence on the structure of nickel-boron-hydrogen composites. An increase in the concentration of the alloying component of boron in nickel increases the dispersion and leads to the alignment of the micro-profile surface and the formation of the nano-sized structures. Boron is an impurity trap for hydrogen atoms in Ni–B electrochemical composites. The paper also presents the results of the studies of the kinetics of hydrogen desorption from Ni-B electrochemical composites. The hydrogen content in the Nix-By-Hz samples (9 at.% Boron), measured by the vacuum extraction method, was 600 cm3/100 g, which significantly exceeds the corresponding value for electrochemical nickel ~ 100 cm3 per 100 g. In this respect, deuterium thermal desorption spectrums from Ni–B composites preimplanted with various doses of deuterium ions at T ~ 100 K were studied. It has been confirmed that the structure of the deuterium thermal desorption spectrum is the implantation dose function. The deuterium content for nickel corresponds to the following ratio: Ni: D = 1:1, whereas the ratio for the composite is Ni95B5 [Ni95:B5]:D = 1:1.25. Distinct peak with a maximum temperature of 325 K is formed for the nickel. Whereas for the Ni–B composite, the thermal desorption spectrum has a diffuse peak with a maximum temperature of 325 K and a deuterium desorption region where the temperature ranges from 250 to 500 K.

Recent studies of tungsten-based plasma-facing materials in the linear plasma device STEP

This contribution summarized the recent studies of tungsten-based plasma-facing materials in the linear plasma device like the simulator for tokamak edge plasma (STEP), focusing on the examination of newly developed tungsten (W)-based materials and plasma-induced defects in pure W. Pure W, W-V, W-Y2O3 and W-ZrC samples were exposed to a high-flux plasma of ~ 1021–1022 m−2 s−1 with a fluence up to 1026 m−2 at a surface temperature below 500 K. The investigation of fundamental evolution of plasma-induced defects in pure W indicated a critical role of hydrogen-dislocation interactions. Suppressed surface blistering was observed in all W-based materials, but deuterium desorption behavior and retention were distinct with respect to different materials. The studies showed that the linear plasma device like the STEP was indispensable in the understanding of plasma-material interactions and the qualification of new materials for future fusion reactors.

Deuterium concentration’s in austenitic stainless steel by deuterium irradiation. Effects temperature irradiation

Using the deuterium thermodesorption spectra from the 18Cr10NiTi steel samples exposed to different doses, we have plotted the total amount of deuterium desorbed from the sample as a function of the radiation dose and the irradiation temperatures. Temperature 100 K. The maximum attainable concentration of deuterium in steel is C=1 (at.D/at.met.= 1/1). At C≥0.5, two hydride phases are formed in the steel, the decay temperatures of which are 240 K and 275 K. The hydride phases are formed in the bcc structure resulting from the martensitic structural transformation in steel [1]. Temperature 295 K. The medium-dose region is characterized by radiation induced action on the steel in the presence of hydrogen. The process results in the formation of the energy-stable crystalline nanostructure of steel, having a developed network of intercrystalline boundaries. The basis for this developed network of intercrystalline boundaries is provided by the amorphous state. The total concentration of the accumulated deuterium in the region of medium implantation doses makes 7 to 8 at.% [2]. Temperature 380; 420; 600 and 900 K. In a deuterium thermodesorption spectra the extended area of deuterium desorption in a range of temperatures 450-900 K is observed, caused by formation of local structure in a radiation induced layer. Formation of local structure can be caused by a segregation of a steel component in the course of deuterium implantation (radiation induced local structure at deuterium presence).The total concentration of the accumulated deuterium in the region of medium implantation doses makes 1 to 3 at.%.

The long-term stability of deuterated thin titanium films

Using neutron reflectometry, we investigated the deuterium desorption of Pd-covered Ti films that have been deuterated at 1 bar deuterium at room temperature and then exposed to air. The deuterium content was monitored continuously for the first two days. Thereafter, measurements were conducted periodically, spanning a period of up to 2 years. The films were in the thickness range of 10–300 nm and the desorption behaviour showed a strong dependence on the film thickness. The smaller the Ti film thickness the faster the Ti films desorbed the stored deuterium.

Stabilization of defects by the presence of hydrogen in tungsten: simultaneous W-ion damaging and D-atom exposure

The possible mutual influence and synergistic effect between defect production and the presence of hydrogen isotopes in the crystal lattice of tungsten is studied. For this purpose, we perform modeling of experimental data where polycrystalline tungsten samples were in one case sequentially irradiated by 10.8 MeV tungsten ions followed by low-energy deuterium exposure and in the other case simultaneously irradiated by tungsten ions, while exposed to deuterium atoms. Modeling of the measured deuterium depth profiles and thermal-desorption spectra for different irradiation temperatures is performed by the MHIMS (migration of hydrogen isotopes in materials) code. A model of trap creation due to tungsten ion irradiation during the deuterium atom exposures is implemented. In both experimental series, the deuterium desorption peaks corresponding to defects induced by tungsten irradiation are described by the same two de-trapping energies of 1.83 and 2.10 eV. The experiments give unambiguous proof that the presence of deuterium increases the overall trap density. The modeling reveals that the two trap concentrations are affected differently by the temperature and presence of deuterium: the concentration of the low-energy trap is significantly higher in the case of simultaneous exposure compared to sequential exposure, especially at high temperature (2.2 times higher at 1000 K). The concentration of the high-energy trap is only weakly affected by the presence of hydrogen.

Influence of the presence of deuterium on displacement damage in tungsten

The influence of the presence of deuterium on displacement damage in tungsten is studied by implanting 20 MeV tungsten ions into displacement-damaged tungsten already containing 1.7 at.% deuterium. SDTrimSP calculations reveal that for the tungsten implantation fluence used, on average each D atom is recoiled once and hence mobile deuterium should be present simultaneously while displacing tungsten atoms. Nuclear reaction analysis after the tungsten implantation shows that no deuterium is lost from the sample and the depth profile is unchanged. However, deuterium must have been de-trapped and is effectively re-trapped again because temperature programmed desorption spectroscopy reveals that deuterium is redistributed from the low temperature de-trapping peak to the high temperature de-trapping peak. Rate equation modelling can describe the measured deuterium desorption with the same de-trapping energies as for the initial material but with increased trap densities only. Decorating the samples after the additional tungsten ion implantation again with a low energy deuterium plasma shows increased deuterium retention beyond the saturation value that is known for initially deuterium free, displacement-damaged tungsten by nearly a factor of two. Both observations together indicate that deuterium is stabilizing the defects created within the collision cascade.

Influence of Preliminary Irradiation by a High Heat Flux on the Re-emission and Thermal Desorption of Deuterium Implanted from Reduced Activation Steels

The deuterium release from reduced activation Eurofer steel samples is investigated by measuring the re-emission directly during ion irradiation and via thermal desorption spectroscopy without contact with air. A part of the experiments are carried out using a sample previously subjected to high-power pulsed thermal action using the QSPA-T setup, Troitsk Institute of Innovative and Thermonuclear Research. Subsequent irradiation is performed using a 5-keV D 3 + ion beam to a fluence of up to 1021 m–2 at room temperature. In all cases, a major part of the implanted deuterium is released from the sample already at the irradiation stage. A significant part of the deuterium also desorbs in the interval between irradiation and spectroscopic measurements. Deuterium re-emission from damaged samples reaches a maximum value more slowly than that from undamaged ones, and deuterium release during holding is more intense. This can be explained by the structure of the damages caused by the heat flux: the hydrogen-trap concentration grows in the material, and the surface area participating in desorption increases.

Effect of exposure temperature on deuterium retention and surface blistering of tungsten exposed to sequential nitrogen and deuterium plasma

Rolled tungsten (W) was sequentially exposed to nitrogen (N) and deuterium (D) plasma at different surface temperatures to investigate the influence of N pre-irradiation on D retention and surface blistering of W. Surface imaging revealed that significant amounts of blisters are formed after D exposure at 230 and 370 K. However, no blisters were found in the case of 520 K D exposure. In addition, N pre-irradiation increases the areal density of blisters, in particular that of small blisters. This effect becomes more significant for 500 K N exposure compared with 300 K N exposure. D depth profiles show that N pre-irradiation leads to an increase of the D concentration in the near surface. Thermal desorption spectra show that only one main desorption peak appears for the case of 230/520 K, while two peaks are found for 370 K D exposure. Though N pre-irradiation does not change the deuterium desorption peak positions, it slightly changes the total D retention. These phenomena indicate a temperature dependence of the effect of N pre-irradiation on the D behavior in W.

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.

Formation and thermal stability of subsurface deuterium in Ni(110)

A unique feature of plasma-enhanced catalysis compared to thermal catalysis is the presence of reactive hydrogen radicals and ions in the gas phase above the catalyst surface. The uptake and subsequent thermal desorption of deuterium on a Ni(110) surface have been measured using incident gaseous D2 molecules, D atoms, and D2+ ions. Molecular D2 exposures on Ni(110) at 90 K form adsorbed D adatoms at the surface, but do not populate subsurface deuterium binding states under UHV conditions. In contrast, such subsurface states on Ni(110) are readily populated at 90 K by incident D atoms and D2+ ions. Subsurface D atoms recombine to desorb as D2 gas in temperature programmed desorption (TPD) measurements to create new characteristic subsurface-derived D2 thermal desorption peaks near 175 K for incident D atoms and 190–260 K, depending on the energy of the incident D2+ ions used, along with a new peak at 435 K for incident ions. While there are small differences for adsorbed D adatoms on Ni(110) and Ni(111) surfaces regarding their thermal stability and subsequent D2 TPD curves, the thermal stability and D2 TPD peaks from subsurface D atoms are nearly the same for these two substrates. This information will be helpful for a fuller understanding of the role of subsurface hydrogen and its reactivity in hydrogenation for plasma-enhanced catalysis over Ni-based catalysts.

Deuterium desorption from ion-irradiated tantalum and effects on surface morphology

Compared to tungsten (W), tantalum (Ta) has shown superior resistance to helium (He)-induced surface morphology changes under fusion-relevant irradiation conditions. However, Ta is also expected to have a stronger interaction with hydrogen isotopes, potentially limiting its use as a plasma-facing material. Despite these concerns, detailed investigations on hydrogen irradiation effects on Ta are scarce. In this study, pristine and fuzzy (He+ ion-irradiated) Ta samples are irradiated with 120 eV deuterium (D) ions at various temperatures and examined with a combination of thermal desorption spectroscopy (TDS), scanning electron microscopy (SEM), and optical reflectivity. TDS reveals discrete D desorption temperatures at 660 and 760 K, corresponding to trapping energies of 1.82 and 2.11 eV, respectively. Although D is retained in Ta both in higher quantities and at higher temperatures compared to W, extreme surface temperatures expected in tokamak divertors may exceed these desorption temperatures and counteract retention. Furthermore, this study indicates that Ta is relatively resistant to adverse surface structuring under D+ ion irradiation. In fact, D+ is shown to prevent and suppress Ta fuzz formation in sequential D+/He+ ion irradiation experiments. While further investigations are needed to elucidate this behavior, these initial investigations show a strong potential for the use of Ta as a PFC material.

Deuterium diffusion and retention in tungsten coated with barrier layer during ion irradiation

The results of the comparative analysis of low-temperature desorption of deuterium from tungsten coated with aluminum and yttrium films under the irradiation by hydrogen plasma with oxygen impurity are presented. The irradiation of aluminum or yttrium coating by H2+1%O2 plasma leads to the desorption of implanted deuterium from the samples. It was shown that the number of atoms desorbed depends on the sign of enthalpy of hydrogen solution in the metal film.

Effects of cold deformation, electron irradiation and extrusion on deuterium desorption behavior in Zr-1%Nb alloy

The present article introduces the data of analysis of ranges of ion-implanted deuterium desorption from Zr-1% Nb alloy. The samples studied underwent plastic deformation, low temperature extrusion and electron irradiation. Plastic rolling of the samples at temperature ∼300 K resulted in plastic deformation with the degree of ε = 3.9 and the formation of nanostructural state with the average grain size of d = 61 nm. The high degree of defectiveness is shown in thermodesorption spectrum as an additional area of the deuterium desorption in the temperature ranges 650–850 K. The further processing of the sample (that had undergone plastic deformation by plastic rolling) with electron irradiation resulted in the reduction of the average grain size (58 nm) and an increase in borders concentration. As a result the amount of deuterium desorpted increased in the temperature ranges 650–900 K. In case of Zr-1% Nb samples deformed by extrusion the extension of desorption area is observed towards the temperature reduction down to 420 K. The formation of the phase state of deuterium solid solution in zirconium was not observed. The structural state behavior is a control factor in the process of deuterium thermodesorption spectrum structure formation with a fixed implanted deuterium dose (hydrogen diagnostics). It appears as additional temperature ranges of deuterium desorption depending on the type, character and defect content.