Thermal Desorption Spectroscopy Experiments Research Articles

TDS Simulator: A MATLAB App to model temperature-programmed hydrogen desorption

We present TDS Simulator, a new software tool aimed at modelling thermal desorption spectroscopy (TDS) experiments. TDS is a widely used technique for quantifying key characteristics of hydrogen-material interactions, such as diffusivity and trapping. However, interpreting the output of TDS experiments is non-trivial and requires appropriate post-processing tools. This work introduces the first software tool capable of simulating TDS curves for arbitrary choices of material parameters and hydrogen trap characteristics, using the primary hydrogen diffusion and trapping models (Oriani, McNabb-Foster). Moreover, TDS Simulator contains a specific functionality for loading experimental TDS data and conducting the inverse calibration of a selected transport model, providing automatic estimates of the density and binding energy of each hydrogen trap type in the material. In its first version, TDS Simulator is provided as a MATLAB App, which is made freely available to the community and provides a simple graphical user interface (GUI) to make use of TDS Simulator straightforward. As reported in the present manuscript, the outputs of TDS Simulator have been extensively validated against literature data. Demonstrations of automatic determination of trap characteristics from experimental data through the optimisation tool are also provided. The present work enables an efficient and straightforward characterisation of hydrogen-material characteristics relevant to multiple applications, from nuclear fusion to the development of hydrogen-compatible materials for the hydrogen economy. TDS Simulator can be downloaded from https://mechmat.web.ox.ac.uk/codes (To be uploaded immediately after the review process).

Hydrogen isotope permeation and retention behavior in the RAFM steel manufactured by laser powder bed fusion

Laser powder bed fusion (LPBF) has emerged as a promising additive manufacturing technique for producing complex components across various industries. This method is particularly instrumental in fabricating reduced activation ferritic/martensitic (RAFM) steel, a candidate structural material for the tritium breeding blanket. Hydrogen transport behaviors in the conventional RAFM steel have been largely investigated; however, they are not well understood in the LPBF-RAFM steel. In this work, we studied the hydrogen isotope permeation and retention behavior in the RAFM steel fabricated by LPBF, utilizing the deuterium gas driven permeation and thermal desorption spectroscopy experiments. The results show that the hydrogen isotope permeability of the LPBF-RAFM steel is close to the conventionally fabricated RAFM steel, but the diffusion coefficient is greatly lower and the retention is markedly higher in the LPBF-RAFM steel compared to the conventional RAFM steel. The large number density of microvoids and TiC precipitates in the LPBF-RAFM steel could be the predominant factors that result in the decrease in hydrogen isotope diffusion coefficient and the increase in the total amount of deuterium retention.

Study of hydrogen sorption and desorption processes of zirconium beryllide ZrBe2

One of the promising intermetallic compounds for use in nuclear and fusion reactors, as well as in hydrogen energy technology, are intermetallic compounds of beryllium with metals such as Ti, V, Zr and Nb. Beryllium-based intermetallics are not only a promising material for blankets of future fusion reactors, but can also be utilized in other areas of the nuclear industry, including fission reactor reflectors, rocket and space technology. The interest in studies of the interaction of hydrogen isotopes with beryllides is related to the accumulation of tritium and helium in the material, formed as a result of nuclear reactions under neutron irradiation, and is caused by the need for understanding the processes arising from such interaction.In this work, hydrogen sorption and desorption processes of zirconium beryllide ZrBe2 produced by industrial technologies at JSC “Ulba Metallurgical Plant” (JSC UMP) were investigated. The experiments were performed by the Sievert’s and thermal desorption spectrometry (TDS) methods. In TDS experiments deuterium was chosen for samples saturation to reduce the possible error in determining fluxes associated with the release of hydrogen from the elements of the vacuum chamber.An equation for hydrogen solubility in zirconium beryllide ZrBe2 was obtained by processing the experimental data obtained by the Sievert’s method:S=0.46±0.1molm3∙Pa12∙exp-13.3±0.5kJmolRTThe temperature intervals of formation and decomposition of two different hydride phases (deuterides) of zirconium beryllide ZrBe2 at ∼ 600 K and ∼ 900 K have been established in TDS experiments.

Initial study on thermal stability of cold spray tantalum coating irradiated with deuterium for fusion applications

Removal of neutral hydrogen atoms in the plasma edge reduces the number of charge exchange events and thus, the net energy losses in the plasma, significantly improving performance of fusion devices. Effective control of the residual pressure of hydrogen isotopes (HIs) in the plasma edge may be achieved by utilizing a hydrogen absorbing first wall interface capable of withstanding the harsh fusion environment. In this study, we have investigated tantalum (Ta) coating deposited by cold spray technology on 316L stainless steel substrate as a potential plasma-facing material surface. High fluence low energy deuterium plasma irradiation experiments and subsequent thermal annealing cycles associated with thermal desorption spectrometry (TDS) demonstrated superior structural stability of the Ta coating. TDS experiments revealed the outgassing of deuterium (as measure of its retention) for cold spray Ta coatings to be three times higher than bulk Ta and two orders of magnitude greater than bulk polycrystalline W. X-ray photoelectron spectroscopy revealed evolution of oxidation states upon deuterium irradiation and a partial recovery of the metallic signature of Ta after the thermal treatment at 1100 K.

Onto the role of copper precipitates and reverted austenite on hydrogen embrittlement in 17-4 PH stainless steel

High strength materials are of interest for hydrogen powered mobility where structural components can be exposed to high pressure (350–700 bars) of dihydrogen. However, high strength stainless steels such as 17-4 PH grade with a martensitic matrix are known to be more prone to hydrogen embrittlement (HE). The mechanisms affecting this type of grade have not been completely elucidated yet. In particular, in this work, the role of copper rich precipitates (Cu-pp) and reverted austenite (γrev) on mechanical behavior in presence of hydrogen was investigated. At first, advanced structural characterizations (Synchrotron-XRD, ACOM/TEM) were performed on different metallurgical conditions. Then, hydrogen trapping ability of Cu-pp and γrev was investigated using thermal desorption spectroscopy (TDS). Hydrogen embrittlement susceptibility was qualified through slow strain rate tensile testing. The results showed that the formation of tiny Cu-pp (< 10 nm) during ageing was deleterious for the HE resistance of the steel, since it increased the ultimate tensile strength. In addition to their role in the steel hardening, tiny Cu-pp actively trapped hydrogen at the Cu-pp/matrix interfaces. The nature of Cu-pp/matrix interfaces, which affects their surface energy and therefore the binding energy of hydrogen, impacted clearly the HE resistance. In particular, TDS experiments showed that tiny ‘slightly coherent’ Cu-pp acted as a low energy hydrogen trap contrary to tiny ‘incoherent’ fcc Cu-pp which strongly trapped hydrogen. The former was found to have a deleterious effect while the latter had a rather beneficial effect. Besides, a high fraction of reverted austenite was beneficial for the HE resistance since it softened the material, and trapped rather strongly hydrogen at the γrev/matrix. The fcc (Cu-pp or γrev)/martensitic matrix interfaces seemed to play a major role in hydrogen trapping in 17-4-PH stainless steel. When hydrogen is tightly bound to these interfaces, it happens to reduce the hydrogen embrittlement susceptibility of the material, 17-4 PH that is generally ‘H fragile’ because of its martensitic matrix.

Interaction of water and carbon monoxide with MnO(001) thin films on Au(111).

Atomically defined MnO(001) thin films were grown on an Au(111) substrate, and their interaction with water (D2O) was investigated by infrared reflection absorption spectroscopy (IRAS) and thermal desorption spectroscopy (TDS). Carbon monoxide adsorption experiments were performed to probe surface atoms and defects on oxide films. Next, water interaction was investigated from which an associative binding pathway and a dissociative binding pathway were revealed, where the water molecules adsorb at terraces and water dissociation takes place at oxygen vacancies mediated by nearby Mn2+ sites. The IRAS data are supported by TDS experiments, which also manifest the importance of defects in the adsorption characteristics of MnO.

Recovery and recrystallization of warm-rolled tungsten during helium thermal desorption spectroscopy annealing

Tungsten has been perceived as one of the most promising plasma-facing materials for future fusion reactors. Its behavior under helium irradiation has been extensively studied. In this work, we focus on the recovery and recrystallization of helium-implanted surface grains in warm-rolled polycrystalline tungsten. Mechanically polished specimens with and without 40 keV helium implantation were heated to 1650 °C during helium thermal desorption spectroscopy experiment. Our results suggest that recovery and recrystallization occurred via subgrain coarsening and removal of low-angle grain boundaries in as-polished specimen. Its average grain size increased from 1.70 to 8.89 μm, and its fraction of low-angle grain boundary decreased from 0.77 to 0.29. By contrast, little changes of grain size and grain boundary misorientation angle were found in helium-implanted surface grains. Such enhanced thermal stability is attributed to the pinning effect of helium bubbles on grain boundaries, and the underlying mechanism is discussed based on the proposed model of cellular microstructure.

Desorption measurements of accelerator-related materials exposed to different stimuli

High-energy particle accelerators require low desorbing components to minimize beam-induced pressure rises leading to serious beam intensity losses. To better understand the specific mechanisms of desorption and outgassing processes, a new UHV setup was developed that allows us to apply different stimuli such as temperature, electrons and energetic ions. The different stimuli probe different sample depths and enable the identification of surface and bulk contributions. Data on thermal desorption spectroscopy (TDS) and electron-stimulated desorption (ESD) are presented for a series of pure metals, stainless steel and gold-coated copper samples. TDS experiments with ex-situ preannealing at 400 °C under UHV conditions for about 4 h indicate that this procedure is most appropriate to significantly reduce bulk-related desorption.

Atomic-scale investigation of deep hydrogen trapping in NbC/α-Fe semi-coherent interfaces

The precipitation of niobium carbide (NbC) is a superior approach to mitigating hydrogen embrittlement (HE). The role of the semi-coherent interface between NbC and α-Fe on hydrogen trapping and HE resistance in high-strength tempered martensitic steel was investigated in this study. High-resolution transmission electron microscopy observations are performed to reveal the atomic-scale crystallographic orientation relationship, atomic arrangements, and associated crystalline defects in the NbC/α-Fe semi-coherent interface. We observed the Kurdjumov–Sachs orientation relationship with (11¯1¯)NbC//(101)α−Feand [01¯1]NbC//[1¯11]α−Febetween the NbC and α-Fe phases. Noticeably, two sets of misfit dislocations with Burgers vectors of b(1)=ab/2[111]on (011¯)α-Fe planes and b(2)=ab/2[11¯1]on (110) α-Fe planes (ab is the lattice constant of α-Fe), which would be the deep hydrogen trapping sites, were characterized in the NbC/α-Fe semi-coherent diffuse interface. In addition, density functional theory-based first-principles calculations revealed that the deep binding energy between the NbC/α-Fe semi-coherent interface and hydrogen is 0.80 eV, which well matches the hydrogen desorption activation energy of 81.8 kJ/mol determined via thermal desorption spectroscopy experiments. These demonstrate that the nature of the deep hydrogen trapping sites of the NbC/α-Fe semi-coherent interface is the misfit dislocation core. Distinguished HE resistance was obtained and ascribed to the deep hydrogen trapping of uniformly dispersed NbC nanoprecipitates with an average diameter of 10.0 ± 3.3 nm. The strategy of deep hydrogen trapping in the NbC/α-Fe semi-coherent interface is beneficial for designing HE-resistant steels.

Characterization of the energetics and configurations of hydrogen in vacancy clusters in tungsten

We have explored the retention of hydrogen (H) in tungsten (W) by investigating its dissolution and aggregation in vacancy clusters (VCs) using a first-principles method and thermodynamic models. The solution energy of a single H in the VCs is in the range of −0.99 to −0.64 eV, much lower than that at a mono-vacancy (~ −0.37 eV) and interstitial site (~1.01 eV) in W. Such a remarkable discrepancy is rationalized on the electronic interaction of H with its neighboring W atoms, which varies from repulsion to attraction with H moving from perfect crystal to vacancy/VCs. Specifically, the solution/trapping energies of H in VCs can be well categorized by the coordination number of its neighboring W atoms, i.e. the lower the coordination number of W, the stronger the H–W attraction and the lower the H solution/trapping energy. Furthermore, taking the cluster as an example, it is observed that the multiple H atoms form a multilayer nested cage configuration at the VC surface initially, and then the stable H2 molecules form in the center of the VCs. Interestingly, the pre-existing H atoms in the VC inner surface have a shielding effect on the H–W interaction, decreasing the electron density of the central region of the VCs and facilitating the formation of H2 molecules. Moreover, the desorption temperatures of H in the VCs are also predicted based on the Polanyi–Wigner equation, and are in good agreement with the available thermal desorption spectroscopy experiments. Our calculations provide a good reference to understand the influence of VCs on the retention and evolution of H in W.

Surface coverage dependent mechanisms for the absorption and desorption of hydrogen from the W(1 1 0) and W(1 0 0) surfaces: a density functional theory investigation

Herein we investigate absorption and desorption of hydrogen in the sub-surface of tungsten via density functional theory. Both the near-surface diffusion and recombination of a bulk hydrogen atom with a hydrogen atom adsorbed upon the W(1 1 0) and W(1 0 0) surfaces are investigated at various surface adsorption coverage ratios. This study intends to model the desorption processes occurring during thermal-desorption spectroscopy experiments and the absorption of hydrogen during gaseous or low energy atomic exposure. Since the diffusion and recombination processes are expected to change as the hydrogen coverage of the surface varies, different coverage ratios were investigated on both surfaces. We found that at a saturation coverage of hydrogen on both surfaces, the activation barriers for the recombination of molecular hydrogen are below 0.8 eV. On the contrary, below saturation, the activation barriers for recombination rise to 1.35 eV and 1.51 eV depending on the coverage and on the orientation of the surface. Regarding the absorption of atomic hydrogen from the surface into the bulk, the activation barrier raises from less than 1.0 eV at saturation to around 1.7 eV below saturation on both surfaces. These results indicate that surface mechanisms certainly play a significant role in the kinetics of desorption of hydrogen from tungsten; it is also expected that surface mechanisms affect the total amount on hydrogen absorbed in tungsten during implantation.

Systematic Experimental Study on Quantum Sieving of Hydrogen Isotopes in Metal-Amide-Imidazolate Frameworks with narrow 1-D Channels.

Quantum sieving of hydrogen isotopes is experimentally studied in isostructural hexagonal metal‐organic frameworks having 1‐D channels, named IFP‐1, −3, −4 and −7. Inside the channels, different molecules or atoms restrict the channel diameter periodically with apertures larger (4.2 Å for IFP‐1, 3.1 Å for IFP‐3) and smaller (2.1 Å for IFP‐7, 1.7 Å for IFP‐4) than the kinetic diameter of hydrogen isotopes. From a geometrical point of view, no gas should penetrate into IFP‐7 and IFP‐4, but due to the thermally induced flexibility, so‐called gate‐opening effect of the apertures, penetration becomes possible with increasing temperature. Thermal desorption spectroscopy (TDS) measurements with pure H2 or D2 have been applied to study isotope adsorption. Further TDS experiments after exposure to an equimolar H2/D2 mixture allow to determine directly the selectivity of isotope separation by quantum sieving. IFP‐7 shows a very low selectivity not higher than S=2. The selectivity of the materials with the smallest pore aperture IFP‐4 has a constant value of S≈2 for different exposure times and pressures, which can be explained by the 1‐D channel structure. Due to the relatively small cavities between the apertures of IFP‐4 and IFP‐7, molecules in the channels cannot pass each other, which leads to a single‐file filling. Therefore, no time dependence is observed, since the quantum sieving effect occurs only at the outermost pore aperture, resulting in a low separation selectivity.

Effects of high-energy C ions irradiation on the deuterium retention behavior in V-5Cr-5Ti

Vanadium alloys are attractive candidate structural materials in future fusion reactors. To evaluate the effects of irradiation on the deuterium retention behavior in vanadium alloys, samples made of V-5Cr-5Ti were irradiated by 5.5 MeV carbon ions. Doppler broadening measurements of the positron annihilation radiation tests were carried out to investigate the defect properties in the irradiated samples. Then the irradiated and virgin samples were implanted with deuterium in an ECR (electron-cyclotron resonance) linear plasma device followed by thermal desorption spectroscopy experiments. It was found that the irradiation process introduced large density of vacancy-type defects and subsequently increased the deuterium retention in the V-5Cr-5Ti, which remains as a serious concern for the vanadium alloys in the application as the structural materials of the fusion blanket.

The Effect of Pulsed Current and Organic Additives on the Hydrogen Incorporation in Electroformed Copper Used in High Vacuum Applications

The trend in electron accelerators design consists in approaching the poles of the steering magnets close to the electron beam. This implies reducing the bore hosting the vacuum chamber and using very small diameter vacuum pipes [1]. The application of functional thin films by physical vapour deposition in such small diameter chambers becomes then very difficult. A new approach relies on copper electroforming to build the vacuum chamber onto a pre-deposited thin film coating [2]. In this method, unlike the usual process, the pipe is built from the inside out. An aluminium mandrel is coated with a functional thin film first, then by a copper film and finally followed by a thick electroplated copper (1-3mm) structural layer. The replacement of high-purity copper parts by electroformed ones may nevertheless lead to the incorporation of various impurities among which hydrogen, which is generated by solvent reduction and thus trapped into the coating. The aim of the present study is the evaluation of the effect of two main triggers, namely polarization wave modulation and copper electrolyte composition by the addition of organic additives. For this purpose, transient curves in response to pulsed currents have been studied for various cathodic current densities. Two main patterns have been observed as shown in figure 1a in the absence of additive. At low current densities, i.e. below 50 A/dm2, the potential increases rapidly and reaches an average constant value. For higher current densities, two characteristic plateaux can be observed: the first one corresponds to the faradic reduction of copper below the diffusion limit, and the second one, at higher potential, is attributed to the diffusion-limited range that is well known for promoting the hydrogen generation. When adding 33 mg/L of d-xylose, it is possible to reach higher current densities before the occurrence of the transition between the faradic reduction of copper, near the electrode, and the diffusion-limited mechanism. The d-xylose acts clearly by inhibiting the hydrogen discharge. Thank to this, four singular situations have been identified on the curves (marked by the stars on figure 1). They correspond to four pulse sequences (40A/dm2, Ton=20 ms), (40A/dm2, Ton=80 ms), (70A/dm2, Ton=20 ms), (70A/dm2, Ton=80 ms), which were used to prepare samples for characterization in terms of hydrogen outgassing by Thermal Desorption Spectroscopy (TDS) and X-Ray Diffraction (XRD) measurements. TDS experiments show two peaks (figure 2), corresponding to the release of hydrogen trapped into the copper under different forms. The temperature of desorption of the first peak (around 420°C for a ramp of 10K/min) corresponds well to hydrogen interstitial diffusion in the copper deposit [3]. The nature of the second peak (around 600°C) is not yet understood. [1] C. Steier, A. Anders, D. Arbelaez, J.M. Byrd, K. Chow, S. De Santis, R.M. Duarte, J.-Y. Jung, T.H. Luo, A. Madur, H. Nishimura, J.R. Osborn, G.C. Pappas, L.R. Reginato, D. Robin, F. Sannibale, D. Schlueter, C. Sun, C.A. Swenson, W.L. Waldron, E.J. Wallen and W. Wan, "Progress of the R&D towards a diffraction limited upgrade of the Advanced Light Source", in Proceedings of IPAC, Richmond, USA (2015), p. 1840. [2] L. Lain Amador, P. Chiggiato, L. M.A Ferreira, V. Nistor, A. T. Perez Fontenla, M. Taborelli, W. Vollenberg, M-L Doche, J-Y Hihn “Development of copper electroformed vacuum chambers with integrated non-evaporable getter thin film coatings” Journal of Vacuum Science and Technology A, accepted. [3] Y. Fukai “Formation of superabundant vacancies in M–H alloys and some of its consequences: a review” Journal of Alloys and Compounds 356–357 (2003) 270–273. Figure 1

Effects of grain size and deformation temperature on hydrogen-enhanced vacancy formation in Ni alloys

Positron annihilation spectroscopy and thermal desorption spectroscopy experiments were combined to ascertain the role of hydrogen on generation of vacancies and vacancy clusters in Ni alloys. The effects of grain size and deformation temperature are emphasized for pure Ni single crystals and polycrystalline Ni-201 alloy samples with two grain sizes that were thermally pre-charged with 3000 appm hydrogen. Variation in positron lifetime and intensity suggests that hydrogen enhances and stabilizes vacancies and vacancy clusters. Additionally, grain boundaries and the regions adjacent to them are preferential sites for vacancy and cluster formation. Hydrogen-altered vacancies and vacancy clusters are manifest in yield behavior differences: uniform vacancy distributions augment strength increases after hydrogen charging; enhanced yield strength during cryogenic deformation is ascribed to an ‘Orowan type’ strengthening mechanism while cross-slip restriction dominates hardening behavior at room temperature.

Ab initio study of interaction of helium with edge and screw dislocations in tungsten

The interaction of a single He atom with edge and screw dislocations in tungsten has been studied using ab initio calculations. It was revealed that He is strongly attracted to the core of both dislocations with the interaction energy of −1.3 and −3.0eV for screw and edge dislocations, respectively, which corresponds to the detrapping temperature in thermal desorption spectroscopy experiments of about 500K and 1050K, respectively. The lowest energy positions for He around the dislocation cores are identified and the atomic structures are rationalized on the basis of elasticity theory considerations. Both types of dislocations exhibit a higher binding energy for He as compared to the He-He binding (known as self-trapping) and are weaker traps as compared to a single vacancy. It is, thus, concluded that the strong attraction to dislocation lines can contribute to the nucleation of He clusters in the temperature range which already excludes He self-trapping.

Release behavior of hydrogen isotopes in deuterium-irradiated Li2TiO3

The release mechanism of tritium in breeding materials is one of the critical issues in fusion reactor. In this study, thermal desorption spectroscopy (TDS) experiments were performed at heating rates of 5, 10, and 15K/min to elucidate the release kinetics of deuterium from trapping sites. The deuterium spectra for Li2TiO3 irradiated by deuterium ions in different heating rates featured an obvious peak at temperature ranging from 550K to 800K. The activation energy of deuterium release from Li2TiO3 is 0.53eV. X-ray diffraction (XRD) results indicate that Li2TiO3 crystals are damaged by D+ irradiation, but no new phases are produced. After TDS experiments, the crystallinity of Li2TiO3 crystals recovers as that of unirradiated samples. Li2TiO3 samples become dark blue after annealing in vacuum and become white again after annealing in air. According to X-ray Photoelectron Spectroscopy (XPS), the surface compounds of colored Li2TiO3 have changed. This may be attributed to the formation of oxygen defect in reduction atmosphere.

Combined microtomography, thermal desorption spectroscopy, X-ray diffraction study of hydrogen trapping behavior in 7XXX aluminum alloys

In the present study, combined thermal desorption spectroscopy (TDS), microtomography and X-ray diffraction study has been carried out to identify the hydrogen trap sites in 7XXX aluminum alloys. Through constant heating rate TDS experiments, three distinct trap states have been identified. It is revealed that micropores are the predominant hydrogen trap site in alloys with medium hydrogen content, whereas grain boundaries is the major hydrogen trap site in alloys with low and high hydrogen content. We have clarified that the rate of trap site occupancy in grain boundaries is high compared to dislocations and vacancies. Such high hydrogen coverage at grain boundaries indicates that the hydrogen-assisted fracture would be intergranular.

Revisited reaction-diffusion model of thermal desorption spectroscopy experiments on hydrogen retention in material

Desorption phase of thermal desorption spectroscopy (TDS) experiments performed on tungsten samples exposed to flux of hydrogen isotopes in fusion relevant conditions is analyzed using a reaction-diffusion model describing hydrogen retention in material bulk. Two regimes of hydrogen desorption are identified depending on whether hydrogen trapping rate is faster than hydrogen diffusion rate in material during TDS experiments. In both regimes, a majority of hydrogen released from material defects is immediately outgassed instead of diffusing deeply in material bulk when the evolution of hydrogen concentration in material is quasi-static, which is the case during TDS experiments performed with tungsten samples exposed to flux of hydrogen isotopes in fusion related conditions. In this context, analytical expressions of the hydrogen outgassing flux as a function of the material temperature are obtained with sufficient accuracy to describe main features of thermal desorption spectra (TDSP). These expressions are then used to highlight how characteristic temperatures of TDSP depend on hydrogen retention parameters, such as trap concentration or activation energy of detrapping processes. The use of Arrhenius plots to characterize retention processes is then revisited when hydrogen trapping takes place during TDS experiments. Retention processes are also characterized using the shape of desorption peaks in TDSP, and it is shown that diffusion of hydrogen in material during TDS experiment can induce long desorption tails visible aside desorption peaks at high temperature in TDSP. These desorption tails can be used to estimate activation energy of diffusion of hydrogen in material.

Macroscopic rate equation modeling of trapping/detrapping of hydrogen isotopes in tungsten materials

Relevant parameters for trapping of Hydrogen Isotopes (HIs) in polycrystalline tungsten are determined with the MHIMS code (Migration of Hydrogen Isotopes in MaterialS) which is used to reproduce Thermal Desorption Spectrometry experiments. Three types of traps are found: two intrinsic traps (detrapping energy of 0.87 eV and 1.00 eV) and one extrinsic trap created by ion irradiation (detrapping energy of 1.50 eV). Then MHIMS is used to simulate HIs retention at different fluences and different implantation temperatures. Simulation results agree well with experimental data. It is shown that at 300 K the retention is limited by diffusion in the bulk. For implantation temperatures above 500 K, the retention is limited by trap creation processes. Above 600 K, the retention drops by two orders of magnitude as compared to the retention at 300 K. With the determined detrapping energies, HIs outgassing at room temperature is predicted. After ions implantation at 300 K, 45% of the initial retention is lost to vacuum in 300 000 s while during this time the remaining trapped HIs diffuse twice as deep into the bulk.