Permeation Reduction Factor Research Articles

Deuterium permeation studies through bare and Er2O3 coated SS 316L

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

Effects of Internal Stress and Hydrogen Penetration on the Performance of Er2O3 Coatings as Hydrogen Permeation Barriers.

Ceramic coatings that can effectively prevent hydrogen permeation have a wide range of applications in hydrogen energy and nuclear fusion reactors. In this study, for the first time, the internal stress of Er2O3 coatings was found to be a key factor that could determine their hydrogen permeation resistance and lifespan. The internal stress was controlled by designing layered Er2O3 coatings. The internal stress increased with an increasing number of Er2O3 layers. When the number of layers was below 15, the increased internal stress did not adversely affect the coating performance and might help to increase its hydrogen permeation resistance. Although the overall thickness of the 15-layer Er2O3 coating was only 97 nm, its hydrogen permeation reduction factor (PRF) reached the highest value of 626, whereas a further increase in the internal stress detrimentally affected the ability of the coating to reduce hydrogen permeation. In addition, the experimental observations and simulation results revealed that the performance of the Er2O3 coatings was related to the hydrogen atoms that penetrated the coating, which weakened the Er-O bonds and consequently decreased the Er2O3 fracture limit. This study provides insights into the effects of internal stress and hydrogen penetration on the performance of ceramic coatings as hydrogen permeation barriers and will help guide strategies for the structure design of hydrogen permeation barriers possessing high PRFs and long lifespans.

Improving hydrogen isotope permeation resistance of (TiVAlCrZr)O multi-component metal oxide coating by O+ Ion implantation

Oxygen vacancy can greatly affect the performance of metal oxide to hydrogen isotope permeation resistance. In this work, we report a new strategy to improve the permeation resistance by oxygen ion implantation. A (TiVAlCrZr)O multi-component metal oxide film was prepared as a tritium permeation barrier on a 316 L substrate by RF magnetron sputtering deposition, and then implanted by oxygen ions to fill the oxygen vacancies inside. The grazing incidence X-rays (GIXRD) analysis showed that the pristine and the oxygen-implanted coatings were in an amorphous phase. The deuterium permeation resistance of the four coatings was tested by a gas-driven device. The result showed that the pristine coating had a permeation reduction factor (PRF) of 5,610 at 500 °C, while there was a 13.6 times of increase in PRF with an oxygen concentration of 11.4 at.% with the best-reported value of 76,500, and more oxygen ions implanted, the better the deuterium permeation resistance of the coating. The GIXRD showed that after the test the pristine coating remained amorphous, while some crystals were formed in the oxygen-implanted coating with an oxygen concentration of 11.4 at.%. Oxygen ion implantation enhanced the deuterium permeation resistance by filling the oxygen vacancies and forming of more stable state of amorphous multi-component metal oxide, which is expected to be a new type of deuterium permeation barrier.

A novel method for preparing α-Al2O3 (Cr2O3)/Fe–Al composite coating with high hydrogen isotopes permeation resistance

α-Al2O3 as a preferred material for hydrogen isotopes permeation barrier (HIPB) can effectively prevent hydrogen embrittlement in structural steel and has higher thermal stability. However, its application is limited by the issue that it is hard to prepare α-Al2O3 at relatively low temperature and its formation temperature is too high (>1000 °C) to damage the mechanical properties of structural steel. To overcome this issue, this paper presents a novel method (combining Al electrodeposition, aluminizing, Cr deposition and air oxidation) for the preparation of α-Al2O3 (Cr2O3)/Fe–Al composite coating on 316 L stainless steel for the first time. The formation temperature of α-Al2O3 was successfully reduced to 800 °C. The post-oxidation samples were characterized by SEM, XPS, XRD, EDS and TEM. The results showed that the oxide film was composed of highly crystalline α-Al2O3 and Cr2O3 nanoparticles, where the later were diffusely distributed in the internal α-Al2O3 film. And there was an epitaxial growth relationship between α-Al2O3 and Cr2O3. The low-temperature formation of the α-Al2O3 film was due to the fact that the Cr2O3 nanoparticles formed during the oxidation process acted as templates and nucleation sites, which reduced the nucleation barrier of α-Al2O3. Deuterium permeation tests showed that its deuterium permeation reduction factor (DPRF) was 8892 at 500 °C, which met the standard for practical application.

Optimization of alumina tritium permeation barrier with consideration of the thickness and the surface coverage

Alumina is considered as one of the most promising candidates for tritium permeation barrier. Coating preparation parameters such as the thickness and the surface coverage both affect the hydrogen isotope resistant performance of TPBs. Alumina coatings with thickness in the nanometric scale are considered in this work. Reduced thickness in the coatings leads to an improvement in the thermal conductivity and the reduction of mismatch problems with the substrate due to differences in the thermal expansion coefficients. Alumina coatings with different thickness were prepared on differentiated manufactured substrate by radio frequency magnetron sputtering with varying sputtering time. Deposited alumina layers are maximal 104.2 nm in thickness. Gas-driven permeation experiments have been performed to investigate the deuterium permeation behavior of the coating samples. It is noted that the alumina coating with only approximately 100 nm in thickness whose permeation reduction factor could achieve 1784 at 823 K and maintain its excellent performance at elevated temperatures, which indicates that the coating at nanometer scale with high surface coverage is capable of possessing extraordinary hydrogen permeation resistance property.

Presentation and Preliminary Test of APRIL: A New Facility for the Characterization of Antipermeation Coatings for Fission and Fusion Applications

Antipermeation and anticorrosion coatings are being developed to reduce tritium permeation from liquid metal [LiPb of the water-cooled lithium-lead breeding blanket and Pb for lead-cooled fast reactors (LFRs)] to primary heat transfer systems. The facility APRIL (Alumina-coating for tritium Permeation Reduction for Innovative LFR) was designed and installed at ENEA Brasimone R.C. to characterize the permeation reduction factor (PRF) of the candidate coatings in static conditions. In the current configuration, APRIL is composed of three pipes, closed at one end, that simulate the heat exchangers of the ALFRED LFR. Two of the pipes are coated with 3 µm of alumina with pulsed laser deposition techniques, the reference method for a fission reactor. The third pipe is uncoated. During the tests, all the pipes are filled with pressurized steam at 100 bar and 480°C, the steam generator condition of the ALFRED LFR. The tests are made in the gas phase; indeed, the three pipes are installed in a chamber filled with helium with a known concentration of deuterium that simulates tritium. Deuterium permeates inside the pipes, allowing for the evaluation of the PRF by means of the ratio between the measured permeated flux in the uncoated pipe and in the coated ones. A first test with 0.5% of deuterium was carried out and the evaluated PRF was about 13.5.

Thermochemically synthesized α‐Al2O3 composite coating with high bonding strength and deuterium permeation resistance

AbstractHydrogen isotope permeation in structural steels can cause severe issues, including steel brittleness, fuel loss, and radioactive pollution in fusion reactors. To tackle this issue, we report a simple synthesis of α‐Al2O3/AlPO4 composite coating by the thermochemical reaction method to serve as an effective barrier hampering hydrogen isotope permeation. This coating was formed at 500°C and composed of α‐Al2O3 and AlPO4 phases. A relatively uniform and compact structure with thickness of ∼35 μm made its corrosion resistance reaching above 3000 times that of the 321 steel substrate. With just one‐side coated, the α‐Al2O3/AlPO4 coating achieved a considerable deuterium permeation reduction factor of 1935 at 450°C, three orders of magnitude higher than 321 steels. What's more, after the deuterium permeation test, no pores or cracks were generated. The excellent bonding between the coating and the substrate was resulted from the formation of CrxPy at their interface induced by Cr diffusion from the substrate. The results obtained from the current study shed new light on seeking reliable and viable ceramic coatings to tackle hydrogen permeation issues.

Direct Fabrication and Characterization of Zirconia Thick Coatings on Zirconium Hydride as a Hydrogen Permeation Barrier

The present work attempted to produce thick zirconia coatings formed by micro-arc oxidation as a hydrogen permeation barrier on zirconium hydride alloy. A novel multiphase zirconia coating was achieved, exhibiting superior hydrogen permeation barrier performance. The growth dynamics, formation mechanism, and phase evolution behavior of thick zirconia coatings were explored, and the hydrogen permeation barrier performance was evaluated by means of vacuum dehydrogenation experiment. The hydrogen desorption quantity was monitored by analyzing pressure changes with a quadruple mass spectrometer (QMS). Experimental results show that the multiphase coatings were composed of monoclinic ZrO2 (m-ZrO2), tetragonal ZrO2 (t-ZrO2), and a trace of cubic ZrO2 (c-ZrO2). The coatings were generally divided into a dense and uniform inner, intermediate layer, and a porous top layer. The quantitative analysis indicates an increased amount of m-ZrO2 toward the coating surface and an increased amount of t-ZrO2 toward the oxide/metal interface. This novel multiphase thick zirconia coating can noticeably improve hydrogen permeation resistance, and the permeation reduction factor (PRF) value is improved by nearly 13 times compared with bare zirconium hydride. It is demonstrated that hydrogen desorption is retarded to some extent in the presence of thick zirconia coating. Hydrogen desorption of the sample with ceramic coating started at 660 °C, which was apparently higher than that of the sample without coating.

An Al2O3/Ni–Al tritium permeation barrier coating for the potential application in thorium-based molten salt reactor

The Al2O3/Ni–Al composite coating was formed on the outside surface of GH3535 superalloy by pack aluminizing and subsequent in-situ oxidation, and deuterium permeation tests were carried out to assess the tritium permeation barrier performance of the coating. Scanning Electron Microscopy (SEM) showed that the surface of Al2O3 films was dense, homogeneous, and crack-free. Transmission Electron Microscopy (TEM) photos manifested that the interface between γ-Al2O3 film and Ni–Al interlayer was distinct without micropores, and the thickness of Al2O3 film with the structure of γ-phase is approximately 80 nm. The Arrhenius equation for permeability of GH3535 was obtained as Φ=1.37·10−7·exp(−57.92(KJ mol−1)/RT) by deuterium permeation tests. The deuterium permeation reduction factor of Al2O3/Ni–Al coating kept 2–3 orders of magnitudes at a temperature from 400°C to 700°C. The D-permeation resistant performance of this coating still has the potential to be further improved.

Impact of surface oxide on hydrogen permeability of chromium membranes

Hydrogen permeation through pure and oxidised bulk chromium membranes was measured by the classical gas technique to get insight into oxide as a hydrogen permeation barrier (HPB). An additional palladium-coated reference chromium membrane was tested to avoid the influence of native Cr oxide. Key parameters for Cr permeability: P0 = 3.23 × 10−7 mol H2/s/m/Pa0.5 and Ea = 0.68 eV and Cr diffusivity D0 = 9.0 × 10−5 m2/s and Ea = 0.59 eV. In the sample preparation stage, a thin ∼2 nm thick oxide was formed. Additional oxidation in pure oxygen at 400 °C increased the thickness from 20 to 50 nm. At this temperature, its efficiency as HPB was evaluated by comparing permeation rates to the reference chromium membrane. The highest permeation reduction factor of ∼3900 corresponded to only a ∼28 nm thick Cr oxide layer. Surface morphology and oxide thickness were investigated by SEM, while the thickness and type of chromium oxide by XPS.

Effect of Cr2O3 nanosheet insertion on the deuterium permeation behavior of a Cr-Zr-O coating

In this study, a Cr2O3 nanosheet (Cr2O3 NS) inserted Cr-Zr-O coating was developed as a hydrogen isotope permeation barrier. The Cr2O3 NSs, fabricated by rapid heat treatment, were amorphous with a thickness of only several nanometers. These Cr2O3 NSs were then incorporated into a Cr-Zr-O multi-metal oxide composite coating via a dip-coating method to form a coating. The effect of the Cr2O3 NS concentration on the morphology, microstructure and deuterium permeation resistance of the coating was studied. With the addition of 1.0 g l−1 Cr2O3 NSs, compared with the Cr-Zr-O coating without NSs, the permeation reduction factor of the resultant coating was enhanced from 249 °C to 575 °C at 500 °C. The coating, with a thickness of nearly 193 nm, achieved a comparable deuterium resistance that was above two orders of magnitude higher than the steel substrate. The results show that ceramic NSs can serve as effective fillers for enhancing the coating performance when functioning as a hydrogen isotope barrier.

Layer-structured Cr/CrxN coating via electroplating-based nitridation achieving high deuterium resistance as the hydrogen permeation barrier

Hydrogen isotope permeation through structural materials is a key issue for developing nuclear fusion energy, which will cause fuel loss and radioactive pollution. Developing ceramic coatings with high thermal shock and hydrogen resistance is an effective strategy to solve this issue. In this work, a layer-structured Cr/CrxN coating was successfully fabricated by a facile electroplating-based nitridation technique, which is easy, facile, and applicable to coating complex-shaped substrates. The Cr/CrxN coating, composed of a bottom Fe/Cr interdiffusion zone, a middle Cr layer, and a top CrxN layer, exhibits high bonding strength, high anti-thermal-shock ability, and high deuterium permeation resistance. Its bonding strength achieves 43.6 MPa. The Cr/CrxN coating remains intact even after suffering 300 thermal shock cycles under a 600 °C-water condition. Through optimizing the nitridation temperature, the Cr/CrxN coating achieves a deuterium permeation reduction factor (PRF) as high as 3599 at 500 °C. Considering its scalable fabrication technique and considerable properties, the developed Cr/CrxN coating may serve as a novel high-performance hydrogen permeation barrier in various fields.

First-principles insight of hydrogen dissolution and diffusion properties in γ-Al2O3

First-principles theory is applied to identify the structure of γ-Al2O3 first. Then, hydrogen dissolution and diffusion behavior was further studied to reveal the reason that permeation reduction factor (PRF) of γ-Al2O3 is lower than that of α-Al2O3. Our calculations show that the formation energy for Al vacancy at the octahedral interstitial site (VAl−OIS−3) is lower than that at the tetrahedral interstitial site (VAl−TIS−3), and are far lower than those of other defects in both defective spinel and non-spinel γ-Al2O3. Thus, the stability of VAl−OIS−3 is higher than that of VAl−TIS−3 in both Al-rich and O-rich environments. However, when hydrogen atoms are introduced into γ-Al2O3, the stability of [VAl-TIS-H]−2 is higher than that of [VAl-OIS-H]−2 in the defective spinel γ-Al2O3 structure, while the opposite is true for the non-spinel γ-Al2O3 structure. The vibrational frequencies for OH− in [VAl-TIS-H]−2 and [VAl-OIS-H]−2 for defective γ-Al2O3 are calculated to be 3608 cm−1 and 3374 cm−1, respectively, which is in excellent agreement with the infrared (IR) absorption peaks observed at ∼3500 and ∼3300 cm−1. The defective spinel model is more suitable for describing the γ-Al2O3 structure. In defective spinel γ-Al2O3, there are many native Al vacancies, which are arranged in a straight line along the [21¯1¯0] direction. The migration barrier for H diffusion along these native Al vacancies is so low that these Al vacancies can provide a rapid diffusion channel for H. Thus, the permeability of H in γ-Al2O3 is much higher than that in α-Al2O3 leading to a lower permeation reduction factor (PRF). Our results can provide not only a sound theoretical explanation for the low PRF of γ-Al2O3 but also a direction to improve the efficiency in preventing H permeation through FeAl/Al2O3 tritium permeation barriers (TPBs).

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

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

Corrosion behavior and deuterium permeability of aluminide coating in high-temperature carbon dioxide atmosphere

In the thermionic space nuclear power, the hydrogen released by the moderator ZrH2 penetrates into the core and affects the power generation performance. Therefore, it is necessary to prepare hydrogen permeation barrier materials such as aluminide coatings on the surface of structural components. In this study, the aluminide coating was prepared by a composite low-temperature aluminizing process. Since the working environment was a mixture of helium (He) and carbon dioxide (CO2), the corrosion behavior of aluminide coatings in this atmosphere at 600 °C for 1000 h was studied. The results showed that an oxide layer of about 1–2.3 μm was formed on the surface, which was mainly composed of alumina, mixed with a small amount of chromia. There was a carbon-containing layer in the outer part of the oxide layer. The aluminide coating surface morphology was significantly improved, and CO2 gas had a repairing effect on the coating surface. In addition, the effect of CO2 gas on the hydrogen permeation resistance of aluminide coatings was comparatively investigated in pure D2 and D2 + CO2 atmospheres. The permeation reduction factors (PRF) under pure D2 and D2 + CO2 were 7.76 and 77.4, respectively, indicating that CO2 gas improved the PRF of the aluminide coatings by an order of magnitude.

A dense Fe-Al/Al2O3 coating as tritium permeation barrier on CLAM steel by hot-dipping aluminizing

Exploring tritium permeation barriers with high permeation reduction factor (PRF) by an industrial scale process is crucial for tritium systems in fusion reactors. Herein, we fabricated a dense Fe-Al/Al2O3 coating by a simple hot-dipping aluminizing (HDA) method and optimized oxidation strategy. The microstructure, chemical composition, and crystallographic characteristic of obtained samples were investigated. And the permeation of deuterium through the sample was determined by gas-driven permeation (GDP) experiments. The results show that the obtained oxide coating mainly consisted of γ-Al2O3 layer and FeAl gradient transition layer. Notably, the Al2O3 layer formed by the oxidation of FeAl alloy coating possessed a high PRF value of 2394 at 550 °C. Compared with the direct oxidation of HDA sample, the oxide coating prepared by the alloy topcoat oxidation strategy was denser and had less defects. Meanwhile, the effect of Al topcoat and different FeAl alloy topcoats on the microstructure and performance of the oxide coating were investigated, respectively. And the formation mechanisms of oxide coatings prepared by different oxidation strategies were also analyzed.

Hydrogen Permeation Behavior of Zirconium Nitride Film on Zirconium Hydride.

Hydrogen permeation barrier plays an important role in reducing hydrogen loss from zirconium hydride matrix when used as neutron moderator. Here, a composite nitride film was prepared on zirconium hydride by in situ reaction method in nitrogen atmosphere. The phase structure, morphology, element distribution, and valence states of the composite film were investigated by XRD, SEM, AES, and XPS analysis. It was found that the composite nitride film was continuous and dense with about 1.6 μm thickness; the major phase of the film was ZrN, with coexistence of ZrO2, ZrO, and ZrN0.36H0.8; and Zr-C, Zr-O, Zr-N, O-H, and N-H bonds were detected in the film. The existence of ZrN0.36H0.8 phase and the bonds of O-H and N-H revealed that the nitrogen and oxygen in the film could capture hydrogen from the zirconium hydride matrix. The hydrogen permeation performance of nitride film was compared with oxide film by permeation reduction factor (PRF), vacuum thermal dehydrogenation (VTD), and hydrogen permeation rate (HPR) methods, and the results showed that the hydrogen permeation barrier effects of nitride film were better than that of oxide film. The zirconium nitride film would be a potential candidate for hydrogen permeation barrier on the surface of zirconium hydride.

Hydrogen permeation from F82H wall of ceramic breeder pebble bed: The effect of surface corrosion

Understanding the permeation behavior of tritium from a pebble bed breeding blanket is essential for establishing a self-sufficient fuel cycle in a nuclear fusion reactor. It is known that double corrosion layers forms on reduced activation ferritic-martensitic (RAFM) steel surface by gas release from a ceramic breeder material, however, its effect on hydrogen permeation behavior has not been elucidated. Herein, in-situ measurement of hydrogen permeation through an F82H RAFM wall of a ceramic breeder pebble bed was performed under H2-added sweep gas conditions. The corrosion layer formed on the F82H sample had a dense microstructure, which reduced hydrogen permeation flux at least by one order of magnitude. The permeation reduction factors were 20–50 at the water-coolant temperature of a blanket. A self-repairing ability is expected for the surface oxide layer as the corrosion occurs spontaneously inside a breeding blanket.

Study of deuterium permeation, retention, and desorption in SiC coatings submitted to relevant conditions for breeder blanket applications: thermal cycling effect under electron irradiation and oxygen exposure

In this paper we report on the performance as deuterium permeation barriers of sputtered amorphous, dense and not fully stoichiometric SiC coatings under relevant conditions for breeder blanket applications in fusion reactors. To do that, we investigate the following effects on permeation values: (i) thermal cycling at 450 °C, (ii) combined thermal cycling and e− irradiation (1.8 MeV up to a total dose of 1 MGy), as well as (iii) oxygen exposure at a temperature of 450 °C during e− irradiation. Data show that the permeation reduction factor (PRF) for the as-deposited SiC coated is ∼10 4, even at the predicted operation temperature for the breeder and it is slightly reduced either by thermal cycling without and during e− irradiation. However, the exposure to oxygen at 450 °C during e− irradiation leads to degradation of the coating and of its PRF of about three orders of magnitude. The origin of the coating degradation is discussed.

Development of anti-permeation and corrosion barrier coatings for the WCLL breeding blanket of the European DEMO

Tritium permeation from breeder material to the Water Coolant System (WCS) in Water Cooled Lithium Lead (WCLL) Breeding Blanket (BB) is one of the technological issues to be solved in the design of the European DEMO. Since the tritium extraction from the Water Coolant System is more challenging and expensive than the extraction from the eutectic alloy PbLi, it is mandatory to use of a protective coating on the blanket wall to minimize the permeation rate. Moreover, a protective coating can prevent the corrosion of EUROFER steel by the action of PbLi.alumina-based coatings are considered as reference for barriers thanks to their good chemical compatibility with the PbLi alloy and their capability to reduce permeation. Three coating technologies were selected in the frame of the EUROfusion project: electrochemical ECX (chemical deposition) process, Pulsed Laser Deposition (PLD) and Atomic Layer Deposition (ALD) coating. The coatings were developed and optimized in order to satisfy the design requirements of good mechanical compatibility with steels, strong adhesion, corrosion compatibility in PbLi at relevant BB design conditions and a Permeation Reduction Factor at least of 200 under neutron irradiation. The present paper aims to describe the status of the technologies and the main results obtained.The final objectives of the R&D activities are to demonstrate the applicability of the coating to WCLL BB and therefore the scale-up of the technologies from laboratory scale to the BB scale.