Thermal Desorption Spectroscopy Spectra Research Articles

Cluster dynamics modeling of hydrogen retention and desorption in tungsten with saturation and multi-trapping effect of sinks

Abstract Hydrogen (H) retention and desorption in tungsten (W)-based plasma-facing materials (PFMs) are still not well understood, largely due to the limitations of ex-situ observations in experimental detection methods like thermal desorption spectroscopy (TDS). In order to reveal the fundamental mechanisms behind H retention and desorption, we developed a cluster dynamics (CD) model, IRadMat-TDS, for theoretical modeling of depth distribution and TDS of deuterium (D) in polycrystalline W. The model newly includes the saturated absorption and emission of D in inherent sinks like grain boundaries (GBs), as well as the multi-trapping effect of D in various types of GBs with different trapping energies. The simulated TDS spectra are in agreement with experimental ones. For polycrystalline W under D ion irradiation within keV-energy range, two typical thermal desorption peaks in TDS at around 490 and 550 K are explicitly attributed to D emission from GBs and vacancies, respectively. And GBs play a major role in D retention. Moreover, the broad peaks in TDS come from the convolution of multi-trapping of D in sinks with different types of trapping sites rather than a single-site approximation.

Influence of sample extraction location on thermal desorption spectroscopy from a heat-resistant 13CrMo4-5 steel plate and correlation with microstructure features

Thermal desorption spectroscopy (TDS) is a highly sensitive and widely used method to directly measure the total hydrogen concentration and indirectly assess the hydrogen trapping sites and mechanisms from the spectra features in steels. Thus, there is a need to investigate the influence of sample location from a 5 mm plate of hot-rolled heat-resistant structural steel on TDS spectra. Via a new highly sensitive and specific correlation coefficient (microToH), the TDS results are correlated with low-angle grain boundaries volume fraction, grain size with different misorientation thresholds, microhardness, and geometrically necessary dislocations at different densities.The results indicate that sample location influences 133% and 62% in the hydrogen desorption of peak 1 (at 515 K), and total hydrogen concentration via the influence of peak 2 (at 634 K), respectively. Thus, sample location needs to be considered as one relevant aspect in a research plan based on TDS analysis. The influence on peak 3 (at 762 K) was found to be negligible as it is related to the first exothermic peak of the heating cycle, associated with carbide precipitation phenomena. The individual grain analysis performed with high-resolution adaptive DMM and GND maps emphasizes the accumulation of the deformation in the ferritic domain at the vicinity of the pearlite structures.

Evaluation of microstructural and environmental effects on the hydrogen uptake and desorption in high-strength carbon steels: A thermal desorption spectroscopy study

The hydrogen uptake in three high-strength carbon steels is studied after exposure to three different environments: an aqueous solution with CO2 bubbling, CO2/H2S bubbling, and cathodic charging without external gassing. The hydrogen uptake is substantially higher in CO2/H2S environment compared to CO2 environment for all materials. The lamellar cementite morphology absorbs higher hydrogen than the material with spheroidite microstructure with similar carbon content. The corrosion layer formed on the steels in CO2 environment strongly affects the hydrogen effusion and the thermal desorption spectroscopy spectrum in all materials, while the corrosion layer formed in CO2/H2S environment does not show this effect.

Effect of neutron dose on the tritium release behavior of Li2TiO3–0.5Li4SiO4 biphasic ceramic

Neutron irradiation with different fluence and flux on the Li2TiO3-0.5Li4SiO4 biphasic ceramic powders was conducted. The tritium release behavior was studied by thermal desorption spectroscopy (TDS) with different heating rates and isothermal heating at various temperatures. It was found that the tritium TDS spectra were shifted toward the higher temperature side as the neutron fluence was reduced. The tritium migration in the biphasic ceramic was governed by diffusion and de-trapping processes with the activation energies of 0.29–0.50 eV and 1.00–1.13 eV for the neutron-irradiated samples with the fluence of 8.25 × 1015 and 3.96 × 1016 n cm−2. For isothermal heating, there is another tritium desorption peak when the sample was continually heated to higher temperatures after isothermally heating at 690 K and 800 K, indicating that tritium still remained in the ceramic under isothermal heating conditions. The intensity of the second peak was decreased at the higher isothermal heating temperatures. The diffusion model with detrapping reaction can fit the experimental data, suggesting that both the detrapping and diffusion processes should be considered to estimate tritium release characteristics for the tritium breeding biphasic ceramics.

Helium isotope exchange in tungsten irradiated sequentially with 4He and 3He ions

Helium (He) isotope exchange in tungsten (W) during sequential irradiation by 3 keV 4He and 3He ions at room (RT) and elevated temperatures (700-1200 K) was investigated. The total He fluence was in the range of 5 × 1021–1.8 × 1022 He/m2 to provide a saturation of the surface layer. The amount of He retained in W after irradiation was measured using in-situ (up to 1500 K) and ex-situ (up to 2500 K) thermal desorption spectroscopy (TDS). Air exposure influenced TDS spectra, but clear were no noticeable differences between 3He and 4He TDS spectra after single irradiation. Subsequent irradiation with different He isotopes demonstrated a very efficient isotope exchange already at room temperature. The substitution of He atoms goes even faster with increasing irradiation temperature. Mechanisms of observed processes are discussed on the base of a simple model.

Reaction–diffusion simulations of hydrogen isotope trapping and release from cavities in tungsten, II: Array of cavities

We present a reaction–diffusion model of hydrogen (H) trapping and release from a metal containing an array of cavities. The model is based on a kinetic description of H trapping in chemisorption sites at the cavity surface and H2 gas precipitation in the cavity volume. Significant differences compared to the case of a single cavity (Zibrov and Schmid, 2022) are observed at high cavity number densities due to retrapping effects. They affect the shape of thermal desorption spectroscopy (TDS) curves, the variation of the TDS peak position with the heating rate, and the desorption at a fixed temperature. The TDS spectra from cavities exhibit features that are very difficult to describe with conventional models but are readily observed in experiments: Sharp rising edges of desorption peaks and constant desorption at a fixed temperature. Also the dynamics of H transport and trapping in the material containing cavities differs from that for point defects, especially at low temperatures. The non-equilibrium effects in the interaction of H with cavities are particularly important for metals with low H solubility, such as tungsten and beryllium.

Deuterium retention and desorption behavior of W-Ta-Cr-V high entropy alloy

Deuterium retention and desorption behavior of W-Ta-Cr-V films under deuterium plasma irradiation were studied. The W-Ta-Cr-V films were prepared on the molybdenum (Mo) substrate by magnetron sputtering. Subsequently, all films annealed at 1000 °C were exposed to deuterium plasma at a flux of 8.13 × 1019 D/m2·s for 9 h to achieve an irradiation fluence of 2.63 ×1024 D/m2. Electron backscattered diffraction (EBSD) was used to characterize the texture and average grain size of films. Doppler broadening spectrometry of positron annihilation (DBS-PA) was carried out with an energy-variable slow positron beam to detect the concentration of vacancy-type defects in the films. The results suggest that there are fewer vacancy-type defects inside W-Ta-Cr-V grains. Deuterium retention and the desorption behavior of W-Ta-Cr-V were studied by compared to pure tungsten films. In the 300–800 K temperature range, the peaks of thermal desorption spectroscopy (TDS) of W-Ta-Cr-V films are substantially consistent with that of the W films. Notably, in the range of 800 K-1000 K, W-Ta-Cr-V film has no thermal desorption peak. We attribute this to the large lattice distortion and low vacancy formation energy, which inhibit the growth of voids inside the grains of W-Ta-Cr-V films. The total deuterium retention of W-Ta-Cr-V films is compared with that of W films. It is measured by TDS that the deuterium retention of W-Ta-Cr-V films is nearly 5 times that of W films. Based on the analysis of the TDS spectra, the higher deuterium retention in W-Ta-Cr-V films is due to the more grain boundary defects.

Tungsten fuzz annealing effect on deuterium retention in polycrystalline tungsten

Using a beam-plasma discharge device operating on helium (He), tungsten with the fuzz on the surface (Wf) has been formed by irradiating polycrystalline tungsten (W) samples with He ions with an energy of ∼150 eV and the fluence of ∼6 × 1024 He/m2 at the temperature of 1273 K. The deuterium (D) retention in Wf annealed at different temperatures was studied by thermal desorption spectroscopy (TDS). Before and after annealing at temperatures of 1000,1200,1400 and 1600 K, Wf was irradiated at room temperature by 2 keV D3+(667 eV/D) ions with the fluence of 1021 D/m2, then in-situ TDS was performed after each irradiation. Annealing W above 1200 K clearly changes the retention mechanism of D: the TDS spectrum consisting of multiple peaks changes to an almost single-peak spectrum. Annealing at 1600 K leads to surface smoothing and the decrease of the D retention by a factor of two compared to the annealing at 1000 K. This can be explained by an increase of the reflection coefficient for the flat W surface. However, the D retention in Wf is significantly higher compared to that in W without He plasma exposure even after annealing at 1600 K, because there are still He bubbles in Wf that effectively trap D

Investigation of the effect of carbon on the reversible hydrogen trapping behavior in lab-cast martensitic Fe C steels

The present study evaluates the active hydrogen trapping sites of three martensitic Fe C alloys with a carbon content of 0.2 wt%, 0.4 wt% and 1.1 wt% by thermal desorption spectroscopy (TDS). The absence of additional alloying elements reduces the microstructural complexity and allows focussing on the carbon effects only. The TDS spectra are extrapolated towards cryogenic temperatures, enabling to deconvolute the desorption spectrum in Gaussian curves corresponding with H detrapping from lattice positions, dislocations, high angle grain boundaries and cementite. The activation energy for hydrogen desorption and the amount of H trapped at each site is further profoundly evaluated. It is found that the carbon content controls the amount of hydrogen trapped at dislocations and its activation energy for detrapping decreases with increasing carbon content. The trap density of the high angle grain boundaries is controlled only by the prior austenitic grain size and the corresponding activation energy for H desorption is independent of the carbon content. Hydrogen trapping at cementite was only detected in the samples with the highest carbon content (Fe-1.1C). • Interaction between hydrogen and martensitic Fe C steels is investigated by TDS. • The main hydrogen trapping sites are dislocations and high angle grain boundaries. • C content strongly influences the H trapping characteristics at dislocations. • Amount of H trapped at HAGBs merely depends on the prior austenitic grain size. • H trapping at cementite is only relevant for hypereutectoid compositions.

Critical verification of the Kissinger theory to evaluate thermal desorption spectra

Multiple types of hydrogen trapping sites in advanced high-strength steels (AHSS) are often experimentally characterized by means of thermal desorption spectroscopy (TDS). The evaluation is regularly based on the peak deconvolution procedure combined with Kissinger's theory, which provides distinctive desorption energies of hydrogen trapping sites at microstructural defects. However, the desorption energies published in literature are often non-conclusive and from time to time contradictive in nature. Therefore, it is of utmost importance to verify the evaluation procedures according to Kissinger's theory for multiple types of hydrogen trapping sites. For that purpose, theoretical TDS spectra were simulated using a bulk diffusion model according to Oriani's theory. Binding energies and trap densities were chosen for providing TDS spectra with clearly separated as well as overlapping TDS peaks. Finally, the desorption energies according to Kissinger's theory were compared with the theoretical trapping energies used in the models. Based on this theoretical work, it is strongly recommended to apply the Kissinger theory only for the evaluation of single or well separated TDS peaks. If peaks overlap, complementary microstructural variation and characterization are a perquisite to correctly evaluate the TDS spectra.

Cesium polytungstate in sputtered solar control films. II. Electronic structure and water-induced defects

The origin of low conductivity and high near-infrared absorption observed in sputtered Cs-polytungstate (CPT) thin films was studied using x-ray photoelectron spectroscopy (XPS), thermal desorption spectroscopy (TDS), and first-principles calculations. The film's resistivity was directly correlated with the intensity of XPS W5+4f peaks, and the mobility of the conduction band (CB) electrons was evaluated as 1.27 × 10−7 cm2 V−1 s−1, both implying the dominance of W5+-trapped electrons in the CB. The presence of H2O residue in the films was detected from XPS O 1s and TDS spectra, suggesting that the incorporation of water upon film deposition induced numerous W/Cs defects reported in Part I. The two representative types of optical profiles were reproduced by first-principles calculations with W-deficient CPT and H2O-incorporated pyrochlore, respectively. We conclude that water-induced W/Cs defects annihilated free electrons in the films, causing loss of conductance and plasma reflection, whereas W5+-trapped electrons generated by O and W vacancies underwent polaronic excitations that generated large near-infrared absorption.

Deuterium trapping in the subsurface layer of tungsten pre-irradiated with helium ions

The effect of He-induced defects in tungsten on the efficiency of trapping of deuterium ions in the subsurface layer was studied using thermal desorption spectroscopy (TDS). The W sample was pre-irradiated with 3 keV helium ions at room temperature and various fluences in the range of 1019 – 5 × 1021 He/m2. Then, it was exposed to a probe fluence of 1019 D/m2 of 2 keV D3+ (670 eV/D) ions, and in-situ TDS was performed. The de-trapping energy for D atoms increased with the increase of the He pre-irradiation fluence. On the other hand, a strong decrease in the D retention was observed if the He fluence increased above 1021 He/m2. At the highest He fluence of 5 × 1021 He/m2 deuterium trapping was possible only after partial release of He atoms. By comparison of experimental TDS spectra with modeling, the de-trapping energies of D atoms from various defects were estimated.

Evaluation of hydrogen retention behavior in tungsten exposed to hydrogen plasma in QUEST

Abstract The W (tungsten) samples were placed at Top, Equator and Bottom plasma facing walls of QUEST (Q-shu University Experiment with Steady-State-Spherical Tokamak) device and exposed to 754 shots of hydrogen plasma during 2017A/W (Autumn/Winter) campaign. Thereafter, their surface morphologies and chemical states were evaluated by TEM (Transmission Electron Microscope) and XPS (X-ray photoelectron spectroscopy). The XPS results showed that a thick carbon layer about 3–18 nm has formed throughout the wall surface. Among them, the Bottom wall had the deposition layer with the thickness of 2 nm, which was thinner than the top wall, namely erosion-dominated. On the other hand, a thick C layer about 18 nm was deposited on the Equator wall. The additional 1 keV D2+ was implanted into these samples and the D (deuterium) retention enhancement was estimated. The D2 TDS (Thermal Desorption Spectroscopy) spectra for all the samples had two major desorption stages at 400 K and 650 K, namely the desorption of D trapped by irradiation damages and deposition layer. The erosion/deposition profile would be caused by wall position and plasma condition, like a current start-up experiment. The desorption temperature of H2 (hydrogen) was shifted toward higher temperature side compared to that exposed to previous plasma campaign (2016 A/W), suggesting that H was mainly accumulated in the deposition layer with forming C–H bonds.

Thermal desorption spectroscopy evaluation of hydrogen-induced damage and deformation-induced defects

ABSTRACT Thermal desorption spectroscopy (TDS) was performed on ultra-low carbon (ULC) steel with various degrees of hydrogen-induced damage and deformation-induced defects. First, the extent to which hydrogen-induced damage manifests itself in TDS measurements was evaluated. Application of multiple test conditions on cold deformed ULC steel with and without the presence of hydrogen-induced damage showed that such damage did not appear as a hydrogen signal on the TDS spectra. Second, interesting features observed on the TDS spectra of cold deformed ULC steel were further investigated by assessing the TDS spectra of recrystallised and annealed ULC steel. As such, the four peaks in the TDS spectra were linked to microstructural features: interstitial lattice positions, grain boundaries, dislocations and microvoids.

Thermal desorption spectroscopy studies of hydrogen desorption from rare earth metal trihydrides REH3 (RE=Dy, Ho, Er)

Abstract Rare earth (RE) metals form two stoichiometric hydrides, REH2 and REH3, and for the yttrium group of RE transformation of a FCC (REH2) into an HCP (REH3) lattice takes place during the second step of hydrogenation REH2 + ½ H2 → REH3. Earlier studies of the hydrogen desorption properties of the rare earth hydrides were limited to Y and RE = La, Ce, Pr, Nd, Sm, Gd, Tb and Er. The present work is focused on the studies of the kinetics and mechanism of hydrogen desorption from trihydrides of heavy rare earths, DyH3, HoH3, and ErH3. The Thermal Desorption Spectroscopy (TDS) studies were performed at pressures below 1 × 10−5 mbar during linear heating from room temperature to 1173 K at different heating rates ranging from 1 to 5.5 K/min. Hydrogen desorption traces show the presence of two main events with the low-temperature peak appearing below 573 K, while the second peak is positioned at 1083–1159 K, with the peak temperatures gradually increasing following the rise of the heating rate. Fitting of the peak temperatures in the TDS spectra using the Kissinger method yielded activation energies of hydrogen desorption for both hydrogen desorption events. For DyH3 and ErH3, the shapes of the TDS spectra appear to be well described by a phase-stuctural transformation following a model of nucleation and growth, while for HoH3 the dehydrogenation mechanism includes a phase boundary reaction. This applied model of phase-structural transformations shows differences in dimensionality and rate-limiting steps as related to the studied compound and the desorption events, REH3 → REH2 or REH2 → RE.

Critical assessment of the evaluation of thermal desorption spectroscopy data for duplex stainless steels: A combined experimental and numerical approach

The present study evaluates thermal desorption spectroscopy (TDS) data measured for UNS S32205 duplex stainless steel. Variations in the TDS spectra are obtained by electrochemical hydrogen charging for different times and by applying different heating rates for desorption to evaluate the desorption activation energy. Good agreement is found when comparing the experimental TDS curves with the desorption flux based on a numerical diffusion model using a homogeneous average hydrogen diffusion coefficient for the two-phase (ferrite-austenite) duplex microstructure. Trapping cannot be distinguished from the experimental TDS data since hydrogen diffusion in austenite is the rate-determining process during desorption. An average diffusion activation energy of 43.4 kJ/mol is determined from the experiments. Moreover, similar findings are obtained with a finite-element model that includes the heterogeneous hydrogen-related properties of the two phases of this duplex stainless steel.

Helium retention in tungsten under plasma and ion beam irradiation and its impact on surface morphology

Helium (He) is a product of deuterium-tritium (DT)-fusion reaction and will be a natural impurity in DT plasma in future fusion devices. He retention in tungsten irradiated by plasma and mass-separated ions in a wide temperature range (300–1200 K) was investigated by means of thermal desorption spectroscopy (TDS). He retention did not exceed the level of 1.5 × 1021 He m−2 for all investigated samples. A significant effect of air exposure on TDS spectra was demonstrated. In contrast to in situ TDS measurements, He release after interaction with the air started from ∼400 K, even in the case of high temperature irradiation. Changes in surface morphology were analyzed by secondary electron microscopy. Blisters were found at the surface after ion irradiation at low temperatures. Acceleration of surface modification and more complex surface morphology was observed in the case of irradiation at temperatures above 1000 K.

Changes in surface morphology of helium-induced tungsten nanostructure during high-temperature annealing

Abstract When exposed to high-flux helium plasmas, tungsten is known to develop a surface nanostructure called tungsten fuzz. Although there exists a consensus for the general mechanisms that lead to this nanostructure, a number of questions regarding its formation have yet to be addressed. One common approach to investigate helium-tungsten interactions is thermal desorption spectroscopy (TDS), as TDS can offer insight into the trapping of helium in tungsten that ultimate drives the nanostructure growth. However, during TDS, the surface morphology of the tungsten nanostructure can change dramatically at temperatures substantially lower than those required to fully desorb the trapped helium. For a comprehensive interpretation of TDS spectra, the helium release from trapping sites should be disentangled from complications that may arise from the changing surface morphology. In this work, we characterize the effects of high-temperature annealing on the surface morphology of tungsten nanostructure during TDS. Six ITER-grade W samples were exposed to helium plasma under identical conditions (a He ion fluence Φ i = 8.6 × 10 24 m − 2 , ion energy of 90 eV, and sample temperature of 1123 K) to generate similar surface nanostructures on each sample. Samples were then annealed at various temperatures for different durations to determine the impact of annealing temperature and duration on the surface nanostructure. During annealing, TDS spectra of the He release rate were obtained using a quadrupole mass spectrometer, yielding He release peaks near 373 K and 1123 K. Changes to the surface morphology were observed on samples annealed at temperatures as low as 1173 K, using a combination of spectroscopic ellipsometry and helium ion microscopy with focused ion beam profiling.

Helium desorption behavior and growth mechanism of helium bubbles in FeCrNi film

Abstract He-charged FeCrNi films were prepared by radio frequency (RF) magnetron sputtering technique, and helium desorption behavior, growth process and evolution mechanism of helium bubbles in FeCrNi film were studied by thermal desorption spectroscopy (TDS) spectra combined with microstructure analysis under different annealing treatments. Three different He desorption peaks were observed in TDS spectra, which can be related to the release of interstitial helium atoms from the near-surface regions, helium-vacancy clusters with different sizes in FeCrNi film. TEM analysis showed that helium bubbles can be uniformly distributed in He-charged FeCrNi nanocrystalline films. Under annealing treatments at different temperatures, the size of helium bubbles obviously increases with increasing annealing temperature, corresponding to the significantly decrease in the number density of helium bubbles in FeCrNi films, and the growth mechanism of helium bubbles was suggested to originate from the migration and coalescence (MC) mechanism.

Chloroform desorption from poly(lactic acid) nanocomposites: a thermal desorption spectroscopy study

Abstract Biopolymer nanocomposites were prepared by solvent casting dispersing lauryl-functionalized cellulose nano-fibrils (CNF) in a poly(lactic acid) matrix (PLA). The release of residual chloroform (CHCl3) solvent molecules was studied by Thermal Desorption Spectroscopy (TDS) analysis. TDS spectra of the PLA matrix show a single desorption peak at T P = 393 K with FWHM ~10 K, compatible with a zero-order desorption kinetics. This narrow TDS peak was accurately reproduced assuming that: (i) the rate limiting step is given by the CHCl3 de-trapping from sites in the PLA matrix where residual solvent molecules form small aggregates and (ii) the activation energy for desorption linearly decreases from 1.19 eV for saturated traps to 1.11 eV when the traps occupancy by solvent molecules approaches zero. The balance energy term ϵ D = −0.08 eV is due to the attractive interactions between trapped CHCl3 molecules. Adding CNF particles to the PLA matrix the zero-order peak shifts to lower temperatures and a second peak with FWHM ~60 K appears at higher temperatures. This second peak is compatible with a first-order desorption kinetics and is attributed to the release of dispersed CHCl3 molecules from trapping sites in PLA-CNF interface region. The obtained information are of interest for applications in food and electronic packaging and for the development of medical materials.