Method of forming hydrogen permeation barrier on metal substrate

Abstract

A method of forming a hydrogen permeation barrier on a metal substrate by heating the substrate and exposing the substrate to a mixed gas supply is provided. The method is beneficial and effective to provide a thin layer that inhibits hydrogen permeation. The invention also relates to an article for storing or transporting hydrogen and to the use of a sheet comprising a specific layer for storing or transporting hydrogen.

Description

Field of the Invention

[0001] The present invention relates to a method for forming a thin hydrogen permeation barrier on a metal substrate. Such a barrier is particularly suitable for use in articles for storing or transporting hydrogen, such as containers and pipes, to which the present invention also relates. background

[0002] Hydrogen permeates relatively freely through most metals, which poses a significant obstacle to many technological applications. In particular, effectively reducing the penetration of gaseous hydrogen or its isotopes into metal walls by introducing barriers is necessary in two main areas: preventing hydrogen embrittlement of steel and controlling tritium inventories in future nuclear fusion reactors.

[0003] In a hydrogen-based energy economy, the large-scale distribution of gaseous hydrogen will require a dense network of pipelines to safely deliver the gaseous hydrogen [Jones et al. (2007)]. Coating and painting bulk metals with relatively thick, impermeable layers is a widely used solution for preventing steel corrosion. These techniques are successfully used in many projects, from automobiles to long pipelines, where an air atmosphere is harmful. Hydrogen affects steel differently than oxygen and water because it causes hydrogen embrittlement. In addition to developing new steel grades that are less susceptible to embrittlement, an effective hydrogen permeation barrier (HPB) on the inside of the pipe will remain an important issue.

[0004] The situation with nuclear fusion is slightly different. Most recent research has focused on future fusion reactors using tritium as fuel [Causey et al. (2012)]. Small amounts of tritium are produced in situ and fused with deuterium to form helium or recycled within the fusion reactor. Unfortunately, some tritium can penetrate the subsurface of the reactor walls in either neutral or ionized form, accumulate, and slowly escape through the cooling system into the atmosphere. Because tritium decays with a half-life of 12.3 years, a significant portion of tritium can accumulate in the reactor walls, becoming a permanent source of radiation. The radiation intensity of tritium must be kept below certain critical limits.

[0005] In the case of the Demonstration Power Plant ("DEMO"), a proposed class of experimental fusion reactors designed to demonstrate net production of electric power from nuclear fusion, the walls will be made of a specific low-reactivity steel known as "Eurofer" [Esteban et al. (2007)]. This is a martensitic steel with high hydrogen permeability. As a safety precaution, all interior surfaces must be clad with highly impermeable HPB to prevent tritium from being trapped in the walls and from penetrating into the environment outside the reactor.

[0006] Due to the high permeability of hydrogen through most metals, polymers, and even many dielectrics, the requirements for HPBs are more specific than those for corrosion protection coatings. Therefore, suitable materials can only be selected from those with the lowest overall hydrogen diffusivity and solubility, with further limitations imposed by chemical inertness and high operating temperatures. Besides only a few specific metals, candidates for dielectrics include some oxides, carbides, and nitrides.

[0007] The coating technique used to create a well-adhering, flawless barrier is just as important as the material selection. Techniques that form the ad layer solely through oxidation are particularly attractive. Other methods require specialized gas environments with strong electric and magnetic fields, limiting uniform ad layer coverage over large, inhomogeneous areas. Evaluating the achieved barrier performance is another challenging task. Several new methods can track very low concentrations of hydrogen isotopes in large quantities, but they are generally unable to determine their mobility. Furthermore, they do not reveal the role of barrier defects.

[0008] Using modern vacuum instrumentation, even the most efficient barriers can be well characterized using dynamic or gas accumulation methods. The classic gas permeability method remains the most reliable option for determining actual HPB efficiency. Hydrogen permeability is recorded at elevated temperatures on the downstream side of the cladding membrane, exposed to significantly higher upstream hydrogen pressures. There is no single, definitive definition of HPB efficiency, as it is always associated with the specific experimental evaluation setup.

[0009] Previous attempts to introduce barriers typically involve depositing a layer with a thickness of one or more microns (≥1 μm) on the metal wall. For example, US20130171442 A1 discloses a method for modifying a porous substrate, which comprises coating a metal hydroxide layer on the substrate and subsequently calcining to convert the metal hydroxide layer into a continuous metal oxide layer, thereby forming a modified porous substrate. In particular, the document discloses a stainless steel substrate coated with a lithium-containing aluminum hydroxide layer (about 3 μm thick), which is then converted into an Al2O3 layer before adding a Pd film (about 11.5 μm thick) on top.

[0010] at the same time, et al. (2023) published an experimental study using a chromium membrane with an oxide layer obtained by controlled oxidation and having a thickness of 20 nm to 50 nm. The publication studied and discussed the permeation reduction factor (PRF) of such a layer.

[0011] It would be beneficial to reduce the thickness of such a barrier layer while achieving similar or improved reduction in hydrogen permeation.The present invention has been devised in light of the above considerations. SUMMARY OF THE INVENTION

[0012] A first aspect of the present invention is a method for forming a hydrogen permeation barrier on a metal substrate, the method comprising the steps of:

[0013] (i) heating the metal substrate to a temperature between 25° C. and 500° C.;

[0014] (ii) exposing the heated metal substrate to a mixed gas supply comprising hydrogen and an oxygen-containing gas; and

[0015] (iii) generating a hydrogen permeation barrier comprising one or more layers, wherein the one or more layers comprises a hydroxide layer.

[0016] The present invention provides a method for forming a thin layer (such as an ultrathin layer) on a metal surface, resulting in a highly impermeable hydrogen barrier. Compared to known methods, the method advantageously provides a lower thickness layer (such as a metal hydroxide layer having a thickness of approximately 0.1 nm) that is produced with significantly greater efficiency. An additional advantage is that the barrier can be converted back to its original permeable state by exposing it to dry hydrogen.

[0017] In some embodiments, the metal substrate comprises chromium.

[0018] In some embodiments, the metal substrate comprises iron. The iron may optionally be contained in steel, such as carbon steel.

[0019] Thus, in some embodiments, the metal substrate comprises steel.

[0020] In some embodiments, the metal substrate comprises chromium and iron.

[0021] In some embodiments, the metal substrate comprises chromium and steel.

[0022] In some embodiments, the metal substrate comprises a chromium layer.

[0023] In some embodiments, the metal substrate comprises a chromium layer and iron. In some embodiments, the metal substrate comprises a chromium layer and an iron-containing layer.

[0024] In some embodiments, the iron-containing layer is an iron layer or a steel layer. The iron layer may consist essentially of iron. The steel layer may consist essentially of steel.

[0025] In some embodiments, the metal substrate comprises a chromium layer and an iron layer. In some embodiments, the metal substrate consists essentially of a chromium layer and an iron-containing layer.

[0026] In some embodiments, the metal substrate comprises a chromium layer and steel. In some embodiments, the metal substrate comprises a chromium layer and a steel layer. In some embodiments, the metal substrate consists essentially of a chromium layer and a steel layer.

[0027] Preferably, the chromium layer is the outermost layer - ie the chromium layer is exposed to the mixed gas supply in step (ii) of the method.

[0028] In some embodiments, the metal substrate comprises carbon steel.

[0029] In some embodiments, the metal substrate comprises stainless steel.

[0030] In some embodiments, the metal substrate comprises martensitic stainless steel.

[0031] In some embodiments, the metal substrate comprises Eurofer 97 (which may alternatively be referred to simply as "Eurofer").

[0032] In step (i) of the method of the invention, the metal substrate is heated to a temperature of between 25° C. and 500° C. Suitably, in step (ii) of the method, the metal substrate is exposed to a mixed gas supply at this temperature.

[0033] In some embodiments, in the heating of step (i), the metal substrate is heated to a temperature of at least 30°C, or at least 50°C, or at least 75°C, or at least 100°C, or at least 150°C, or at least 200°C, or at least 250°C, or at least 300°C, or at least 350°C, or at least 400°C.

[0034] In some embodiments, in the heating of step (i), the metal substrate is heated to a temperature of at least 50°C, or at least 150°C, or at least 300°C.

[0035] In some embodiments, in the heating of step (i), the metal substrate is heated to a temperature of at least 300°C.

[0036] In some embodiments, in the heating of step (i), the metal substrate is heated to a temperature of at most 475°C, or at most 450°C, or at most 425°C, or at most 400°C.

[0037] In some embodiments, in the heating of step (i), the metal substrate is heated to a temperature of at most 400°C.

[0038] In some embodiments, in the heating of step (i), the metal substrate is heated to a temperature between 50°C and 500°C, or between 200°C and 450°C, or between 300°C and 400°C.

[0039] In some embodiments, in the heating of step (i), the metal substrate is heated to a temperature between 300°C and 400°C.

[0040] In some embodiments, in step (i), the metal substrate is additionally placed under a pressure below atmospheric pressure. That is, in addition to being heated, the metal substrate may also be placed under a pressure below atmospheric pressure. That is, the heated metal substrate may be under a pressure below atmospheric pressure when exposed to the mixed gas supply in step (ii). The metal substrate may be heated first, and then the heated metal substrate may be placed under a pressure below atmospheric pressure; or the metal substrate may be placed under a pressure below atmospheric pressure first, and then heated at a pressure below atmospheric pressure; or heating and decompression may be performed simultaneously.

[0041] In these embodiments, "pressure below atmospheric pressure" means that in step (i), the metal substrate is placed in a space or system with a pressure below atmospheric pressure, such as a pressure of less than 1 atmosphere, or at most 100,000 Pa, or at most 50,000 Pa, or at most 10,000 Pa, or at most 1,000 Pa, or at most 100 Pa, or at most 10 Pa, or at most 1 Pa, or at most 10 - 1 Pa, or at most 10 -2 Pa, or at most 10 -3 Pa, or at most 10 -4 Pa, or at most 10 -5 Pa, or at most 10 -6 Pa.

[0042] In some embodiments, the pressure below atmospheric pressure is a vacuum. That is, in some embodiments, in step (i), the metal substrate (in addition to being heated) is placed in a vacuum. In these embodiments, "vacuum" means that in step (i), the metal substrate is placed in a space or system with a pressure significantly below atmospheric pressure, such as a pressure of at most 10 Pa, or at most 1 Pa, or at most 10 -1 Pa, or at most 10 -2 Pa, or at most 10 -3 Pa, or at most 10 -4 Pa, or at most 10 -5 Pa, or at most 10 -6 In some embodiments, the vacuum has a pressure of at least an ultra-high vacuum, i.e., a vacuum having a pressure of at most 10 -6 Pa(10 -8 mbar) pressure.

[0043] It should be understood that step (ii) of the method of the present invention is carried out in the same space or system as step (i). For example, the space or system can be a sealed unit. The space or system can have an upstream portion relative to the metal substrate (mixed gas supply is provided in the upstream portion) and a downstream portion relative to the metal substrate. The downstream portion can be separated from the upstream portion in such a way (for example, by the presence of the metal substrate) that the mixed gas supply can basically only travel between the upstream portion and the downstream portion by permeating through the (heated) metal substrate. Therefore, if necessary, permeation can be measured in the downstream portion.

[0044] In some embodiments, prior to step (i), the method includes the step of adding a chromium layer to the metal substrate precursor. For example, the chromium layer can be deposited on the metal substrate precursor, such as by triode sputtering. The metal substrate precursor can comprise iron or steel or consist essentially of iron or steel. The metal substrate precursor can include an iron-containing layer, such as an iron layer or a steel layer.

[0045] In some embodiments, the chromium layer has a thickness of at most 15 μm, or at most 10 μm, or at most 8.0 μm, or at most 6.0 μm, or at most 4.0 μm, or at most 2.0 μm, or at most 1.0 μm.

[0046] In some embodiments, the chromium layer has a thickness of at least 0.01 μm, or at least 0.1 μm, or at least 0.5 μm, or at least 1.0 μm, or at least 1.5 μm, or at least 2.0 μm, or at least 2.5 μm, or at least 3.0 μm.

[0047] In some embodiments, prior to step (ii) (i.e., prior to exposing the heated metal substrate to the mixed gas supply), the method includes exposing the heated metal substrate to an initial hydrogen supply. Suitably, the initial hydrogen supply is a gas supply comprising or consisting essentially of H2 (hydrogen). This step may be preferred in order to determine the initial permeability of the metal substrate.

[0048] Suitably, the mixed gas supply is a gas supply comprising or consisting essentially of H2 (hydrogen) and an oxygen-containing gas.

[0049] Suitably, the oxygen-containing gas is a gas that serves as a source of oxygen atoms. The oxygen-containing gas may be a gas that contains OH or forms OH. In some embodiments, the oxygen-containing gas is O2 (oxygen) or H2O (water, i.e., steam).

[0050] In some embodiments, the mixed gas supply comprises or consists essentially of H2 and O2. In some embodiments, the mixed gas supply comprises or consists essentially of H2 and H2O. In some embodiments, the mixed gas supply comprises or consists essentially of H2 and H2O. In some embodiments, the mixed gas supply comprises or consists essentially of H2, O2, and H2O.

[0051] In some embodiments, the mixed gas supply comprises hydrogen and oxygen in an atomic ratio (H:O) of at least 80:20, or at least 85:15, or at least 90:10, or at least 95:5.

[0052] In some embodiments, the mixed gas supply comprises hydrogen and oxygen in an atomic ratio (H:O) of at least 80:20.

[0053] In some embodiments, the mixed gas supply comprises hydrogen and oxygen in an atomic ratio (H:O) of at least 95: 5. For safety reasons (to reduce the risk of explosion), an atomic ratio (H:O) of at least 95: 5 may be preferred.

[0054] In some embodiments, the mixed gas supply comprises hydrogen and oxygen in an atomic ratio (H:O) of at most 99.9:0.1, or 99.7:0.3, or 99.5:0.5, or at most 99:1, or at most 97:3, or at most 95:5.

[0055] In some embodiments, the mixed gas supply comprises hydrogen and oxygen in an atomic ratio (H:O) of at most 99.7:0.3. In some embodiments, the mixed gas supply comprises hydrogen and oxygen in an atomic ratio (H:O) of at most 99:1.

[0056] In some embodiments, the mixed gas supply comprises hydrogen and oxygen in an atomic ratio (H:O) between 95:5 and 99.7:0.3.

[0057] In some embodiments, the oxygen-containing gas is O2 or H2O, and the mixed gas supply comprises hydrogen and oxygen in an atomic ratio (H:O) between 95:5 and 99.7:0.3.

[0058] In some embodiments, the mixed gas supply is supplied at about atmospheric pressure, such as from 80 kPa to 120 kPa, or from 90 kPa to 110 kPa, or from 95 kPa to 105 kPa. In some embodiments, the mixed gas supply is supplied at a pressure above atmospheric pressure, such as at least 120 kPa.

[0059] Suitably, step (iii) of the method occurs simultaneously with step (ii) of the method. That is, when the metal substrate is exposed to the mixed gas supply, this will result in the creation of a hydrogen permeation barrier on the metal substrate.

[0060] It is generally found that as the oxygen content in the mixed gas supply increases, the amount of time it takes to create a hydrogen permeation barrier on the metal surface is shorter. In some embodiments, the metal substrate is exposed to the mixed gas supply for at least 1 second, or at least 10 seconds, or at least 1 minute, or at least 2 minutes, or at least 5 minutes. In some embodiments, the metal substrate is exposed to the mixed gas supply for at most 20 minutes, or at most 10 minutes, or at most 5 minutes, or at most 2 minutes, or at most 1 minute, or at most 10 seconds.

[0061] Suitably, a hydrogen permeation barrier is created on the metal substrate, effectively shielding the surface of the metal substrate from the surrounding atmosphere.

[0062] In some embodiments, the hydrogen permeation barrier comprises at least two layers, or at least three layers, or at least four layers.

[0063] In some embodiments, the hydrogen permeation barrier comprises one layer, or two layers, or three layers, or four layers.

[0064] At least one of the layers of the hydrogen permeation barrier is a hydroxide layer. Preferably, the hydroxide layer is the outermost layer of the hydrogen permeation barrier. For example, in the case where the hydrogen permeation barrier comprises a hydroxide layer and one other layer, preferably, the one other layer is formed on the metal substrate, and the hydroxide layer is formed on the one other layer. For example, in the case where the hydrogen permeation barrier comprises a hydroxide layer and one or more other layers, preferably, the hydroxide layer is separated from the metal substrate by the one or more other layers.

[0065] In some embodiments, the hydroxide layer has a thickness of at most 1 nm, or at most 0.8 nm, or at most 0.6 nm. In some embodiments, the hydroxide layer has a thickness of at most 1 nm. The thickness can be estimated by X-ray photoelectron spectroscopy (XPS).

[0066] In some embodiments, the hydroxide layer has a minimum thickness corresponding to a monolayer. In some embodiments, the hydroxide layer is a monolayer. That is, the layer is effectively two-dimensional, being substantially one molecule thick.

[0067] In some embodiments, the hydroxide layer is a chromium hydroxide layer. For example, where the metal substrate comprises chromium, such as a chromium layer, at least a portion of the chromium can react with the mixed gas supply to form a chromium hydroxide layer.

[0068] In some embodiments, one or more layers of the hydrogen permeation barrier further include an oxide layer.

[0069] In some embodiments, the oxide layer is a chromium oxide layer.

[0070] In some embodiments, the hydrogen permeation barrier comprises a hydroxide layer and an oxide layer.

[0071] In some embodiments, the hydrogen permeation barrier consists of a hydroxide layer and an oxide layer.

[0072] In some embodiments, the hydrogen permeation barrier comprises a chromium hydroxide layer and a chromium oxide layer.

[0073] In some embodiments, the hydrogen permeation barrier consists of a chromium hydroxide layer and a chromium oxide layer.

[0074] In some embodiments, a hydroxide layer (such as a chromium hydroxide layer) is formed on an oxide layer (such as a chromium oxide layer), and the oxide layer (such as a chromium oxide layer) is formed on a metal substrate (such as a chromium layer).

[0075] Preferably, the thickness of the hydroxide layer (such as the chromium hydroxide layer) is lower than the thickness of the oxide layer (such as the chromium oxide layer).

[0076] Permeability Reduction Factor (PRF) [as defined herein, see also V. (2019)] is a convenient parameter by which barrier efficiency is expressed as the quotient between the hydrogen permeability through an uncoated metal substrate (without a hydrogen permeability barrier) and the hydrogen permeability through a metal substrate coated with a hydrogen permeability barrier. In some embodiments, the hydrogen permeability barrier on the metal substrate provides a PRF of at least 1000, or at least 2000, or at least 3000, or at least 4000, or at least 5000, or at least 6000, or at least 7000. In some embodiments, the hydrogen permeability barrier on the metal substrate provides a PRF of at least 1000. In some embodiments, the hydrogen permeability barrier on the metal substrate provides a PRF of at least 5000.

[0077] In some embodiments, the method further comprises the step of removing the hydroxide layer by exposing the hydrogen permeation barrier to a dry hydrogen supply. "Dry" hydrogen supply means that the gas supply does not contain oxygen-containing gas. The dry hydrogen supply contains hydrogen, and preferably consists essentially of hydrogen. The hydrogen reacts with the hydroxide groups on the surface (and thus removes the hydroxide groups) to form water. This step advantageously allows the method to be reversible, as desired.

[0078] Preferably, during the step of removing the hydroxide layer, the hydrogen permeation barrier is exposed to a supply of dry hydrogen at a temperature of at least 300°C or at least 400°C.

[0079] A second aspect of the present invention is an article for storing or transporting hydrogen, wherein the article comprises a wall having an iron-containing layer, a chromium layer, a chromium oxide layer, and a chromium hydroxide layer. The chromium oxide layer and the chromium hydroxide layer may collectively represent a hydrogen permeation barrier formed on the chromium layer and the iron-containing layer (which may collectively represent a metal substrate).

[0080] In some embodiments, all of the walls of the article have an iron-containing layer, a chromium layer, a chromium oxide layer, and a chromium hydroxide layer.

[0081] In some embodiments, the iron-containing layer is an iron layer or a steel layer.

[0082] In some embodiments, the article is a hydrogen storage tank, a nuclear fusion reactor, or a pipeline.

[0083] A third aspect of the present invention provides the use of a sheet material comprising an iron-containing layer, a chromium layer, a chromium oxide layer, and a chromium hydroxide layer for the storage or transportation of hydrogen. Such a sheet material exhibits excellent properties for significantly reducing or preventing hydrogen permeation and can therefore be used in applications such as hydrogen storage tanks, nuclear fusion reactors, or pipelines.

[0084] In the second and third aspects (and, where applicable, the first aspect), preferably, the chromium hydroxide layer is formed on the chromium oxide layer; and / or preferably, the chromium oxide layer is formed on the chromium layer; and / or preferably, the chromium layer is formed on the iron-containing layer (such as an iron layer or a steel layer).

[0085] The present invention includes the combination of the described aspects and preferred features, unless such a combination is clearly impermissible or explicitly avoided.Preferred features mentioned in relation to the first aspect of the invention may apply equally to the other aspects. Summary of the Figures

[0086] Embodiments and experiments illustrating the principles of the present invention will now be discussed with reference to the accompanying drawings, in which:

[0087] Figure 1 A schematic diagram of the permeability assessment setup is shown;

[0088] Figure 2 shows the effect of a hydrogen permeation barrier comprising chromium oxide compared to a reference sample containing palladium;

[0089] Figure 3 shows the effect of a hydrogen permeation barrier comprising chromium oxide and chromium hydroxide compared to a reference sample containing palladium;

[0090] Figure 4 A FIB-SEM cross section of a chromium film is shown;

[0091] Figure 5An XPS depth profile study of the chromium oxide surface layer is shown;

[0092] Figure 6 Shown are deconvoluted high-resolution XPS spectra just after a permeation cycle with hydrogen and 5% O2;

[0093] Figure 7 The results show that CrO x Time-resolved in situ DRIFT (Drift Reflectance Infrared Fourier Transform) spectroscopy;

[0094] Figure 8 Details of the membranes used to evaluate hydrogen permeation barrier efficiency are shown. Detailed description

[0095] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying drawings. Additional aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0096] The following set of examples of the present invention relates to the in-situ formation and decomposition of ultrathin barriers on metal substrates, including the measurement of hydrogen permeability. In this set of examples, five samples were produced, each of which deposited a dense and defect-free chromium film onto a solid martensitic steel substrate to form a bilayer film. Subsequently, a hydrogen permeation barrier was produced on the metal substrate.

[0097] Sample preparation

[0098] A 0.5 mm thick sample of optically polished Eurofer 97 (40 mm OD) was selected. Eurofer 97 is a low-activation tempered martensitic steel that is a particularly suitable structural material for future nuclear fusion reactors and has the following chemical composition (wt %): 0.11 C, 8.7 Cr, 1.0 W, 0.10 Ta, 0.19 V, 0.44 Mn, 0.004 S, and the balance Fe. Eurofer 97 is strong and highly permeable.

[0099] The thin chromium films were deposited in a Balzers Spruton experimental cell, which uses the principle of triode sputtering, in which a hot plasma arc is formed between an ionization chamber with a hot filament and an auxiliary ring-shaped anode. The arc parameters were 40 V x 50 A at an argon pressure of 0.2 Pa. The chromium target (PI-KEM, 99.95%) was the cathode placed in the center of the anode ring. The cathode voltage was 1800 V, and a current of 0.7 A was maintained. The typical deposition temperature was 130°C. The chromium deposition rate was approximately 0.8 μm / h. The duration of all depositions was 4 h, resulting in a chromium layer thickness of approximately 3.3 μm.

[0100] As a reference sample, an additional film was prepared using a palladium film (having a thickness of approximately 100 nm) sputtered on a 3.3 μm chromium film.

[0101] Initial penetration

[0102] Next, the membranes were installed in the permeation cells of each sample in turn and sealed on both sides with gold gaskets. An all-metal ultra-high vacuum (UHV) system was applied to the permeation cells for all permeability evaluations and intermediate oxidation cycles (i.e., all hydrogen and oxygen tests were performed without removing the seals). The membranes specifically studied separated the upstream and downstream sections. This Figure 1 Depicted in Figure 1 A schematic diagram of the permeability evaluation setup is shown, where CM1 , CM2 and CM3 are capacitance manometers, IMG is an inverted magnetron vacuum gauge, and QMS is a quadrupole mass spectrometer.

[0103] The permeation cell was then heated to 400° C. over a period of 4 hours. Next, pure hydrogen (99.999%) was passed into the upstream part of the cell and the membrane was exposed to the gas in a controlled manner at a high temperature of 400° C. and a pressure of 1 bar (the pressure was monitored by a capacitance manometer CM3).

[0104] A thin chromium oxide is formed during this process (except in the reference membrane comprising a palladium membrane).The pressure rise in the closed downstream section reveals the initial permeability value of the membrane. Figure 2 Calculated permeation reduction factor (PRF) values ​​for the five samples and a Pd-containing reference sample are shown, with each bar in the figure representing an individual sample. Figure 2 A schematic diagram of the layers and H2 permeation is also depicted (CrO x In this case, when pure hydrogen was used, a modest suppression of hydrogen permeability by chromium oxide was observed, with PRF values ​​ranging from about 4.5 to about 39 compared to a Pd-containing reference film (which, by definition, has a PRF value of 1).

[0105] The differences in PRF among these samples are believed to be caused by different native oxide thicknesses and slight variations in local water pressure, inducing oxidation during the high vacuum 400 °C pretreatment.

[0106] Hydroxide-containing barriers

[0107] Subsequently, the gas content of the permeation cell was changed by introducing oxygen. This was done by preparing a mixture of approximately 4 kPa of oxygen and approximately 80 kPa of hydrogen (with an atomic ratio of approximately 95:5 H:O) in the upstream section. Otherwise, the conditions were the same as above (i.e., the membrane was exposed to the gas supply at a temperature of 400°C and a pressure of 1 bar).

[0108] Under these conditions, an ultrathin layer of chromium hydroxide formed on the chromium oxide surface for all five samples. This resulted in a complete, immediate, and permanent blockage of hydrogen permeation. It is assumed that the hydroxyl groups form a barrier to hydrogen dissociation, the first step in the permeation process. In contrast, no change in hydrogen permeability was observed for the Pd-containing reference sample.

[0109] Figure 3 PRF values ​​calculated for five samples and a Pd-containing reference sample are shown, with each bar representing an individual sample. Figure 3 A schematic diagram of the layers and H2 permeation is also depicted (shown in the CrO x In this case, with the addition of an oxygen source to the hydrogen in the gas supply, a PRF of at least 5000 was observed compared to a Pd-containing reference film (which had a PRF value of 1).

[0110] The beneficial results observed in the present invention are surprising. The subject of hydrogen / water interactions on catalytic surfaces is well described by theoretical models and supported by experiments with noble metals (Pt, Pd, etc.). Theoretical descriptions of the phenomena leading to "site blocking" have been published [e.g., see Henderson et al. (2002)]. Experimental evidence for this effect has been observed at low temperatures due to CO. However, in contrast, no known prior art demonstrates this effect at high temperatures, resulting in blocking of hydrogen permeation flow.

[0111] Removal of the hydroxide layer

[0112] Subsequently, by replacing the mixed gas supply with "dry" hydrogen (without the presence of oxygen or water), the initial PRF value was restored. This indicates that the chromium hydroxide layer decomposed in the absence of oxygen or water. The decomposition of the barrier hydroxyl groups dissociates the hydrogen and allows the next stage of the infiltration process to proceed.

[0113] In summary, the barrier can be converted back to a highly permeable state as desired by exposing the barrier to dry hydrogen (such as pure hydrogen) at an elevated temperature of at least 300°C (such as about 400°C, or at least 400°C).

[0114] By using passive auto-catalytic recombiners (PARs), very similar catalytic reactions are applied on the catalyst surface to suppress the risk of self-explosion of hydrogen-oxygen mixtures in nuclear reactors and fusion reactors [Steffen et al. (2019)].

[0115] Additional experiments

[0116] Experimental validation of the observations was achieved by complementary spectroscopic and microscopic methods.

[0117] Figure 4 A FIB-SEM cross-section of a chromium film is shown, revealing the columnar internal structure and large grain size of the Eurofer underneath. After the permeation measurement, a protective layer was added on top of the Cr to improve image contrast and preserve the nanobarrier.

[0118] Figure 5 Shown in 10 -7 XPS depth analysis studies of the chromium oxide surface layer (in the absence of protective deposits) after heating at 400° C. for 18 hours in a vacuum at 500 Pa. The thickness of the chromium oxide formed on the surface before and during the vacuum treatment was found to be between 1 nm and 2 nm, as determined by studies using an Ar gun sputtering.

[0119] Figure 6 The deconvoluted high-resolution XPS spectrum after permeation cycles with hydrogen and 5% O2 is shown, indicating the presence of Cr(OH)3 (the shadow peak at 577.2 eV) in the Cr 2p3 / 2 The share in the nuclear grade distribution increases.

[0120] Figure 7 The results show that CrO x Figure 2. Time-resolved in situ DRIFT (Drift Reflectance Infrared Fourier Transform) spectra of Ar+H2 on the left, Ar+H2+5% O2 in the middle, and Ar+H2 on the right. The spectra show the formation and decomposition of two OH groups, one for water and the other for chromium hydroxide. The spectra confirm the catalytic nature of the gas-phase water formation and the appearance of an atomically thin hydroxide layer. The ratio of hydrogen to oxygen in the argon gas stream flowing through the analytical DRIFT cell corresponds to the ratio in the permeation experiment.

[0121] PRF and penetration considerations

[0122] One technique for in-situ evaluation of hydrogen permeation barriers (HPBs) is to measure the permeability of gaseous hydrogen through a coated membrane consisting of a thick metal substrate with a thin HPB deposited upstream, as performed in one set of examples described herein. The thickness of the substrate is much smaller than its diameter, which enables the data to be presented in one dimension, in the direction of hydrogen permeation. The permeability, j, at a specific temperature is expressed as the number of hydrogen molecules per unit area per unit time.

[0123] Substrate permeability P at a specific upstream hydrogen pressure and temperature s The permeation reduction factor (PRF) is defined as the permeation rate through the uncoated membrane j 未包覆 Relative to the permeability through the coated membrane j 包覆 The steady-state ratio is given by the following equation:

[0124]

[0125] While PRF represents a valuable engineering property of HPB, it does not reveal the mechanism of permeation. Permeability is the result of several processes that hydrogen undergoes on its path through the coated membrane.

[0126] The following assumptions allow the PRF values ​​of the coated membranes to be correlated with fundamental HPB properties. Two key parameters of a specific bulk material that control the hydrogen permeability, P, are the diffusion coefficient, D, and the solubility, K. The basic formula for hydrogen transport through the bulk applies to idealized pure metals with high solubility. In equilibrium, Sievert's law describes the number of hydrogen atoms that will dissolve at a specific external hydrogen pressure and temperature.

[0127] The diffusivities, solubility, and permeability in both layers are assumed to be known and are designated as D and D for the solid substrate, respectively. s , K s and P s , and for thin HPB films are designated as D f , K f and P f It is assumed that all processes are thermally activated and can be described by Arrhenius dependence. The diffusion coefficient D describes the diffusion process in any layer, and its exponential temperature dependence is given by the exponential term D0 and the diffusion activation energy E. D Similar relationships hold for K and P in all layers [Andrew et al. (1992)].

[0128] Depending on the upstream hydrogen pressure, two distinguishable permeation mechanisms are introduced for bare membranes related to the hydrogen transport scheme. The first is usually described as the diffusion-limited scheme (DLR), because bulk diffusion controls the kinetics. The second case is the surface-limited scheme (SLR), because surface reactions control the process [Shipilevsky et al. (1989)]. The SLR is valid under the assumption of the low pressures at which the HPB is applied, but experimental evaluation of its efficiency is rigorous or impossible. Therefore, the reported HPB data were recorded at high pressures and temperatures, where the DLR may not be valid in all the assumed details.

[0129] DLR can be applied to coated membranes, i.e., double-layer membranes, under the same assumptions as for bare membranes. The permeation of both layers is diffusion limited, and the effective permeability coefficient of such a double layer, P, is eff It is given by:

[0130]

[0131] where d s represents the substrate thickness, and d f Indicates the thickness of the HPB film. Figure 8 Depicted in Figure 8 Details of the membranes used to evaluate HPB efficiency are shown (where B is the diameter of the membrane).

[0132] PRF and P f are related, as shown in the following equation:

[0133] PRF=1+d f P s / (d s P f ).

[0134] For PRF>>1, P f and P s A simple correlation between can be written as:

[0135]

[0136] From an experimental point of view, determining low P on highly permeable substrates f It is easier to determine the PRF value than on low permeability substrates, since the measured permeabilities are usually close to the set detection limit. Many authors have had to increase the test temperature to well above the predetermined operating temperature to obtain a reliable PRF. It can only be assumed that extrapolation to lower temperatures is a tolerable operation, since P f The temperature dependence may be different from that of P s .

[0137] Because D f and K fAll are included in P f In the case of δ-H2O, they cannot be determined separately unless the time evolution of the permeability following a stepwise change in the driving hydrogen pressure is also recorded.

[0138] ***

[0139] The features disclosed in the preceding description or in the appended claims, expressed in their specific form or as a method or process for performing a disclosed function or for obtaining a disclosed result, may, where appropriate, be used alone or in any combination of these features to implement the invention in its different forms.

[0140] Although the present invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art upon giving this disclosure. Therefore, the exemplary embodiments of the present invention set forth above are intended to be illustrative rather than restrictive. Various changes may be made to the described embodiments without departing from the spirit and scope of the present invention.

[0141] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purpose of enhancing the reader's understanding. The inventors do not wish to be bound by any of these theoretical explanations.

[0142] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0143] Throughout this specification, including the appended claims, unless the context requires otherwise, the words "comprise" and "include" and variations such as "comprises," "comprising," and "including," will be understood to imply the inclusion of stated integers or steps or groups of integers or steps but not the exclusion of any other integers or steps or groups of integers or steps.

[0144] It must be noted that, as used in the specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from "about" one particular value and / or to "about" another particular value. When such a range is expressed, another embodiment includes from the from particular value and / or to the other particular value. Similarly, when a value is expressed as an approximation by use of the antecedent "about," it is understood that the particular value forms another embodiment. The term "about" in relation to a numerical value is optional and means, for example, + / - 10%.

[0145] References

[0146] A number of publications are cited above in order to more fully describe and disclose the present invention and the state of the art to which the present invention pertains. Full citations of these references are provided below. The entirety of each of these references is incorporated herein.

[0147] Jones et al., Materials for the Hydrogen Economy, CRC (2007).

[0148] Causey et al., Tritium Barriers and Tritium Diffusion in Fusion Reactors, in: Comprehensive Nuclear Materials, Vol. 4, RJ ​​Konings, Elsevier (2012), pp. 511-549.

[0149] Esteban et al., Hydrogen transport and trapping in Eurofer '97, J. Nucl. Mater. (2007), pp. 367-370.

[0150] US20130171442 A1.

[0151] et al., Impact of surface oxide on hydrogen permeability of chromium membranes, Int. J. Hydrog. Energy (2023), pp. 9723-9733.

[0152] V., Hydrogen permeation barriers: basic requirements, materials selection, deposition methods, and quality evaluation, Nucl.Mater.Energy(2019), Volume 19, Pages 451-457.

[0153] Henderson et al., The interaction of water with solid surfaces: fundamental aspects revisited, Surf. Sci. Rep. (2002), Vol. 46, pp. 1-308.

[0154] Andrew et al., Models for hydrogen permeation in metals, J. Appl. Phys. (1992), Vol. 72, pp. 2749-2757.

[0155] Shipilevsky et al., Competition of bulk and surface processes in the kinetic of hydrogen and nitrogen evolution from metals into vacuum, Surface Science (1989), Vol. 216, pp. 509-527.

[0156] Steffen et al., Prevention of hydrogen accumulation inside the vacuumvessel pressure suppression system of the ITER facility by means of passive auto-catalytic recombiners, Intl. J. Hydrog. Energy (2019), Volume 44, Pages 8971-8980.

Claims

1. A method for forming a hydrogen permeation barrier on a metal substrate, the method comprising the following steps: (i) heating the metal substrate to a temperature between 25° C. and 500° C.; (ii) exposing the heated metal substrate to a mixed gas supply comprising hydrogen and an oxygen-containing gas; as well as (iii) generating said hydrogen permeation barrier comprising one or more layers, wherein said one or more layers comprises a hydroxide layer. The method of claim 1 , wherein the metal substrate comprises chromium.

3. The method of claim 2, wherein the metal substrate comprises chromium and iron, optionally wherein the iron is contained in steel.

4. The method of claim 3, wherein the metal substrate comprises a chromium layer and an iron-containing layer, optionally wherein the iron-containing layer is an iron layer or a steel layer.

5. The method of claim 4, wherein the metal substrate comprises stainless steel, optionally martensitic stainless steel.

6. The method according to any one of claims 2 to 5, wherein the hydroxide layer is a chromium hydroxide layer.

7. The method according to any one of claims 1 to 6, wherein the hydroxide layer has a thickness of at most 1 nm and / or wherein the hydroxide layer is a monolayer.

8. The method according to any one of claims 1 to 7, wherein the one or more layers of the hydrogen permeation barrier further comprise an oxide layer, optionally a chromium oxide layer.

9. The process according to any one of claims 1 to 8, wherein the oxygen-containing gas is O2 or H2O and / or wherein the mixed gas supply comprises hydrogen and oxygen in an atomic ratio (H:O) between 95:5 and 99.7:0.

3.

10. The method according to any one of claims 1 to 9, wherein In step (i), the metal substrate is additionally placed under subatmospheric pressure, optionally under vacuum.

11. The method according to any one of claims 1 to 10, wherein In the heating of step (i), the metal substrate is heated to a temperature between 50°C and 500°C, or between 200°C and 450°C, or between 300°C and 400°C.

12. The method of any one of claims 1 to 11, wherein the hydrogen permeation barrier on the metal substrate provides a permeation reduction factor (PRF) of at least 1000.

13. The method of any one of claims 1 to 12, further comprising the step of removing the hydroxide layer by exposing the hydrogen permeation barrier to a supply of dry hydrogen at a temperature of at least 300°C or at least 400°C.

14. An article for storing or transporting hydrogen, wherein the article comprises a wall having an iron-containing layer, a chromium layer, a chromium oxide layer, and a chromium hydroxide layer; optionally, wherein the iron-containing layer is an iron layer or a steel layer.

15. Use of a sheet comprising an iron-containing layer, a chromium layer, a chromium oxide layer and a chromium hydroxide layer for storing or transporting hydrogen; optionally, wherein the iron-containing layer is an iron layer or a steel layer.

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