Hydrogen permeation membrane made of PdCu alloy

Abstract

This invention relates to hydrogen permeation membranes composed of PdCu alloys. The PdCu alloys of this invention are characterized by comprising 47.0 atomic% or more and 49.0 atomic% or less Pd, 0.01 atomic% or more and 0.75 atomic% or less Ag, and the balance Cu and unavoidable impurities. The hydrogen permeation coefficient Φ of the hydrogen permeation membrane of this invention at 100°C is... 100 Hydrogen permeability coefficient Φ at 300℃ 300 The ratio (Φ) 100 / Φ 300 With a value of 0.4 or higher, the reduction in hydrogen permeability coefficient in the low-temperature region is suppressed. The hydrogen permeability of the hydrogen permeation membrane of the present invention is improved in the low-temperature region below 150°C.

Description

Technical Field

[0001] This invention relates to hydrogen permeation membranes that selectively allow hydrogen to permeate from hydrogen-containing gases. In particular, it relates to hydrogen permeation membranes with improved hydrogen permeability in low-temperature regions compared to existing technologies. Background Technology

[0002] Hydrogen is widely used in various fields, including as a hydrogen source and reducing agent in the synthesis of various compounds. In recent years, hydrogen has attracted attention as a renewable energy source, and its applications in fuel cells as a power source for automobiles / heavy machinery and as fuel gas for hydrogen engines are highly anticipated. In addition, hydrogen has also attracted attention in the field of cutting-edge medicine; for example, the effectiveness of hydrogen inhalation therapy for post-cardiopulmonary arrest syndrome has been reported.

[0003] Hydrogen permeation membranes are materials used in devices for the efficient utilization of hydrogen in the aforementioned fields. For example, the efficient utilization of hydrogen in the fuel sector requires high-purity hydrogen, thus hydrogen purification devices using hydrogen permeation membranes have been developed. Furthermore, hydrogen sensors are needed for measuring the hydrogen concentration inside the power source and in the exhaust gas of fuel cell vehicles, etc. Hydrogen sensors are also needed for the accurate and precise measurement of hydrogen concentration in therapeutic gases in the medical field. Hydrogen permeation membranes, which selectively allow only hydrogen to permeate from the target gas, can be suitable for use as hydrogen sensors in these applications.

[0004] Hydrogen permeation membranes are made of metal alloys capable of diffusing and releasing selectively adsorbed hydrogen internally. Among such metal alloy membranes, Pd alloy membranes (PdAg-based alloys, PdCu-based alloys, etc.) are known, particularly utilizing the selective hydrogen permeability of Pd (palladium). Hydrogen permeation membranes made of PdCu-based alloys, in particular, are progressing towards practical application and mass production due to fewer problems caused by hydrogen embrittlement and corrosion resistance (Patent Documents 1, 2, Non-Patent Document 1).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2001-262252

[0008] Patent Document 2: Japanese Patent Application Publication No. 2008-12495

[0009] Non-patent literature

[0010] Non-patent literature 1: James Raphael Warren, "The Effect of Hydrogen onPalladium-Copper Based Membranes for Hydrogen Purification", THE UNIVERSITY OFBIRMINGHAM, P22-29, 37-80. Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] Hydrogen permeation in hydrogen-permeable membranes composed of PdCu alloy films is caused by atomic diffusion. Therefore, the hydrogen permeation coefficient exhibits temperature dependence and is considered to follow the so-called Arrhenius equation (Arrhenius diagram). In the Arrhenius diagram, the logarithm of the hydrogen permeation coefficient is inversely proportional to the reciprocal of temperature (1 / T). Therefore, by measuring the hydrogen permeation coefficient in an appropriate temperature region, it is possible to predict the hydrogen permeation coefficient in other temperature regions.

[0013] However, according to the inventors' research, for hydrogen permeation membranes composed of PdCu alloys, the predictive power of the hydrogen permeability coefficient based on the Arrhenius diagram, as described above, is not sufficiently reliable. Specifically, even when an Arrhenius diagram is constructed based on the hydrogen permeability coefficient measured in the high-temperature region, the measured value of the hydrogen permeability coefficient in the low-temperature region deviates from the diagram and becomes a value lower than predicted. That is, the hydrogen permeability of the hydrogen permeation membrane composed of PdCu alloys decreases more than expected in the low-temperature region. While the temperature dependence of the hydrogen permeability coefficient is unavoidable, this unexpected decrease in the hydrogen permeability coefficient is not preferable.

[0014] To date, research on hydrogen permeation membranes has primarily focused on increasing the hydrogen permeability coefficient, with limited attention paid to improving the temperature dependence of these membranes. This is because the hydrogen permeability coefficient is the most explicit indicator of a hydrogen permeation membrane's function. Furthermore, the most effective applications of hydrogen permeation membranes have historically been in equipment such as hydrogen purification devices that allow operation in high-temperature environments, which also contributes to the aforementioned background.

[0015] However, some devices utilizing hydrogen permeation membranes require operation in low-temperature regions. For example, hydrogen sensors for fuel cell vehicles and medical applications are designed for use at room temperature. These applications of hydrogen permeation membranes have received considerable attention in recent years, but those used in these fields require higher hydrogen permeability at low temperatures.

[0016] This invention was made against the background described above, and provides a hydrogen permeation membrane composed of a PdCu alloy, whose hydrogen permeability in the low-temperature region is improved. It should be noted that, in this invention, the low-temperature region refers to the temperature range from room temperature (25°C) to 150°C.

[0017] Methods for solving problems

[0018] To address the aforementioned issues, the inventors investigated the reasons for the reduced hydrogen permeability of PdCu alloy films in the low-temperature region and proposed countermeasures. The hydrogen permeability of PdCu alloys is achieved in the β-phase state of the B2 structure based on a bcc (body-centered cubic) lattice. Hydrogen trapped in the PdCu alloy film in this state diffuses through the interstices of the PdCu body-centered cubic lattice, thereby contributing to hydrogen permeability.

[0019] According to the inventors' hypothesis, the reduced hydrogen permeability of PdCu alloy films is attributed to the generation of vacancies caused by lattice defects in the PdCu alloy crystal. These vacancies in the PdCu alloy (body-centered cubic lattice) can be generated at both Pd and Cu sites. Furthermore, if vacancies are generated, hydrogen is trapped there and cannot escape without a certain amount of energy. If the hydrogen permeation membrane is at a high temperature, hydrogen can be released by applying thermal energy. However, it has been observed that hydrogen release is difficult in low-temperature regions where thermal energy is lacking, leading to a more significant reduction in hydrogen permeability than expected.

[0020] If the reduced hydrogen permeability in the low-temperature region is due to hydrogen capture at vacancies, a possible countermeasure is to add other elements to the alloy system. When vacancies are generated due to lattice defects, the added element displaces the vacancies, thereby allowing hydrogen diffusion to continue and maintaining hydrogen permeability. Therefore, the inventors studied added elements with such an effect and found that Ag is a particularly preferred added element, thus completing the present invention.

[0021] That is, the present invention, which solves the above-mentioned problems, is a hydrogen permeation membrane composed of a PdCu alloy, characterized in that the PdCu alloy is composed of 47.0 atomic% or more and 49.0 atomic% or less of Pd, 0.01 atomic% or more and 0.75 atomic% or less of Ag, and the balance being Cu and unavoidable impurities. The structure and hydrogen permeability of the hydrogen permeation membrane of the present invention will be described below, along with its manufacturing method and application.

[0022] (A) The composition of the hydrogen permeation membrane of the present invention

[0023] (A-1) Alloy Composition

[0024] The hydrogen permeation membrane of the present invention, apart from the unavoidable impurities described later, is composed of a PdCu alloy (PdCuAg alloy) with Pd, Cu, and Ag as constituent elements. The functions and composition ranges of these constituent elements are as follows.

[0025] (A-1-1)Pd and Cu

[0026] The hydrogen permeation membrane of the present invention is a PdCu alloy containing Ag; therefore, Pd and Cu are essential and major constituent elements of the present invention. Furthermore, Pd is an essential metal for ensuring the hydrogen permeability of the hydrogen permeation membrane composed of the PdCu alloy. Additionally, the hydrogen permeability of the PdCu alloy is achieved when its crystal system is the β phase with a bcc structure. Cu is an essential additive metal for promoting the phase transformation from the α phase to the β phase in the PdCu alloy and maintaining the phase composition required for hydrogen permeability. Moreover, Cu also has the function of suppressing the reduction in strength of the PdCu alloy membrane caused by hydrogen embrittlement.

[0027] In the PdCu alloy constituting the hydrogen permeation membrane of the present invention, the Pd concentration is set to 47.0 atomic% or more and 49.0 atomic% or less. When the Pd concentration exceeds 49.0 atomic%, the formation of the β phase becomes difficult, and even after heat treatment during the manufacturing process, it is difficult to obtain a sufficient amount of β phase. On the other hand, Pd is an essential element for hydrogen permeation performance, so a decrease in the Pd concentration leads to a decrease in the hydrogen permeability of the hydrogen permeation membrane. Furthermore, when the Pd concentration is below 47.0 atomic%, it is difficult to obtain sufficient hydrogen permeability even in high-temperature regions. The Pd concentration is preferably 47.25 atomic% or more and 48.8 atomic% or less, and particularly preferably 47.75 atomic% or more and 48.5 atomic% or less. Furthermore, the Cu concentration is the balance of the Pd concentration, the Ag concentration (described later), and the unavoidable impurity concentration.

[0028] (A-1-2)Ag

[0029] Ag is an additive element used to preferentially displace lattice defects in PdCu alloys into vacancies, thereby suppressing hydrogen capture and fixation and inhibiting the decrease in hydrogen permeability in low-temperature regions. This vacancy-filling effect and the suppression of hydrogen permeability reduction in low-temperature regions can also occur with other metallic elements besides Ag. However, according to the inventors' research, Ag has a particularly high effect on improving hydrogen permeability in low-temperature regions. This is presumably because Ag has a high selectivity for vacancy. Therefore, the present invention specifies Ag as an additive element for PdCu alloy films.

[0030] In this invention, the Ag concentration in the PdCu alloy of the hydrogen permeation membrane is set to be 0.01 atomic% or more and 0.75 atomic% or less. Below 0.01 atomic%, there is no effect from adding Ag. On the other hand, adding more than 0.75 atomic% of Ag reduces the overall hydrogen permeability of the PdCu alloy membrane, worsening not only at low temperatures but also at high temperatures. This Ag concentration is preferably 0.1 atomic% or more and 0.5 atomic% or less, and particularly preferably 0.15 atomic% or more and 0.38 atomic% or less.

[0031] (A-1-3) Unavoidable impurities

[0032] The PdCu alloy film of the present invention is composed of Pd, Cu, and Ag, and does not contain any other intentionally added elements. However, the presence of unavoidable impurities is permitted. Examples of unavoidable impurities include Fe and Si. These unavoidable impurities are preferably set to a total of 500 ppm or less.

[0033] (A-2) Crystal structure of PdCu alloy films

[0034] Considering that the hydrogen permeability of PdCu alloys is achieved in the β-phase state, and that the expected function of a hydrogen permeation membrane is to allow hydrogen to permeate its cross-section, it is preferable that the hydrogen permeation membrane of the present invention has a high proportion of the β-phase in its cross-section. Specifically, the hydrogen permeation membrane of the present invention preferably has a β-phase area fraction of 95% or more in any cross-section.

[0035] "Arbitrary cross-section" means that any cross-section of the PdCu alloy film, regardless of its orientation, satisfies the above conditions. The area ratio should be calculated by observing the visible area on both sides (inner and outer ends) of the PdCu alloy film and based on the area of ​​the β phase relative to the total area of ​​the observation area. Regarding the observation area, it is preferable to define the area encompassing both sides of the PdCu alloy film and a width at least 10 times the film thickness as the observation area. It should be noted that the area ratio of the β phase in this arbitrary cross-section is more preferably 98% or higher, and the upper limit of the β phase area ratio is preferably 100%.

[0036] Electron backscattered diffraction (EBSD) is an effective method for detecting the β phase in any cross-section of a PdCu alloy film. EBSD provides information on each grain in the alloy film cross-section, allowing for the determination and calculation of the β phase distribution and area fraction.

[0037] It should be noted that the thickness of the PdCu alloy membrane constituting the hydrogen permeation membrane of the present invention is preferably 1 μm or more and 250 μm or less. When the thickness is less than 1 μm, the mechanical strength is insufficient, leading to difficulties in processability. Furthermore, when the membrane thickness exceeds 250 μm, the hydrogen permeation rate decreases, thus resulting in reduced purification efficiency. In addition, there are no particular limitations regarding the shape of the PdCu membrane of the present invention.

[0038] (A-3) Hydrogen permeability of the PdCu alloy membrane of the present invention

[0039] The hydrogen permeation membrane of the present invention, composed of a PdCu alloy, exhibits excellent hydrogen permeability, particularly in the low-temperature region below 150°C. As mentioned above, the hydrogen permeation coefficient of the PdCu alloy membrane deviates from the Arrhenius diagram based on the high-temperature region in the low-temperature region, resulting in a value lower than the predicted value. In the present invention, such deviation of the hydrogen permeation coefficient in the low-temperature region is reduced.

[0040] Regarding the hydrogen permeation membrane of the present invention, a preferred embodiment is one with a hydrogen permeation coefficient Φ at 100°C. 100 Hydrogen permeability coefficient Φ at 300℃ 300 The ratio is above 0.4. Since the decrease in hydrogen permeability coefficient with decreasing temperature is inevitable, the above ratio Φ... 100 / Φ 300 Less than 1. The hydrogen permeation membrane of the present invention, by suppressing the decrease in hydrogen permeability coefficient in the low-temperature region, enables Φ... 100 / Φ 300 The value is above 0.4. Furthermore, the hydrogen permeability coefficients at 100℃ and 300℃ are used as the evaluation criteria for hydrogen permeation membrane characteristics because there is a tendency for the hydrogen permeability coefficient to decrease significantly near 100℃. Also, the hydrogen permeability coefficient of PdCu alloy membranes reaches its maximum in the range above 300℃ and below 400℃, making the measurement value at 300℃ more convenient. It should be noted that the hydrogen permeability coefficient Φ (mol / m·s·Pa) 1 / 2 It can be calculated using the following formula.

[0041]

[0042] J: Permeability flow rate, Φ: Permeability coefficient

[0043] l: film thickness, P f Supply pressure, P p osmotic pressure

[0044] Regarding the ratio Φ used to determine the above hydrogen permeability coefficient 100 / Φ 300The measurement range is not particularly limited as long as it includes the range of 100℃ and 300℃. The preferred measurement range is above 25℃ and below 400℃. Measurements below 25℃ are not particularly meaningful. Furthermore, the hydrogen permeability coefficient rarely reaches its maximum at temperatures above 400℃, and a decrease in the hydrogen permeability coefficient due to the decomposition of the β phase is observed at higher temperatures. However, this does not preclude measuring the hydrogen permeability coefficient in a wider range than just above 100℃ and below 400℃.

[0045] The hydrogen permeability of PdCu alloy films is the result of the combined effects of Pd and Cu concentrations, β-phase area ratio, and other factors, as previously mentioned. Furthermore, even hydrogen permeable films with high hydrogen permeability coefficients in high-temperature regions achieved through alloy composition optimization sometimes cannot avoid a decrease in hydrogen permeability in low-temperature regions. In this invention, the addition of Ag to the PdCu alloy, combined with optimization of alloy composition and β-phase area ratio, aims to optimize hydrogen permeability across a temperature range including the low-temperature region.

[0046] (B) Method for manufacturing the hydrogen permeation membrane of the present invention

[0047] Next, a preferred method for manufacturing the hydrogen permeation membrane of the present invention will be described. The hydrogen permeation membrane of the present invention can be manufactured by preparing a PdCu alloy with the above-described composition and then performing plastic processing such as rolling to form a thin film. Furthermore, as a preferred embodiment, a heat treatment is included to optimize the area ratio of the β phase in the cross-section of the thin film. Hereinafter, a preferred method for manufacturing the hydrogen permeation membrane of the present invention will be described.

[0048] (B-1) Manufacturing process of PdCu alloy film

[0049] The manufacturing method for PdCu alloy films can be selected appropriately based on factors such as film thickness and size, without any particular limitation. PdCu alloy films can be formed using various thin film formation processes, including sputtering, vacuum evaporation, chemical vapor deposition, and plating. Furthermore, plate-shaped and foil-shaped PdCu alloy films can be manufactured by rolling alloy blocks (ingots).

[0050] Regarding the manufacture of PdCu alloy films using rolling, PdCu alloy ingots of the above composition are manufactured by melting and casting, and then processed by a suitable combination of hot forging, hot rolling, and cold rolling to produce alloy films of a specified thickness. There are no particular restrictions on the processing steps from ingot to alloy film. However, in PdCu alloys, the introduction of processing strain can promote the phase transformation to the β phase; therefore, a final processing step with a cold working rate of 65% to 85% is preferred.

[0051] (B-2) Heat treatment process for PdCu alloy films (to promote phase transformation to the β phase)

[0052] Then, the PdCu alloy films with the above-described composition, manufactured by various methods, exhibit a phase transition to the β phase by heat treatment within a specified temperature range. This heat treatment temperature is set to 275°C or higher and 400°C or lower. The phase transition temperature (α phase → β phase) of the PdCu alloy films of the present invention varies depending on the composition, even within the above-described composition range, but is presumably in the range of approximately 300°C to 400°C. Furthermore, heat treatment below 275°C does not result in a phase transition to the β phase, or it is difficult to achieve an area fraction of 95% or higher for the β phase in the film cross-section. On the other hand, it is known that the β phase of PdCu alloys decomposes into the α phase at high temperatures, and there is a tendency for β phase decomposition above 400°C. Therefore, the heat treatment temperature range is preferably set to 275°C or higher and 400°C or lower.

[0053] A pressurized hydrogen-containing atmosphere is preferred as the atmosphere for heat treatment to induce a β-phase transition. An atmosphere with a hydrogen partial pressure of 0.05 MPaG or higher and 1.0 MPaG or lower is more preferred.

[0054] The heat treatment time can be adjusted according to the film thickness of the PdCu alloy film. The formation of the β phase induced by heat treatment begins at both surfaces of the PdCu alloy film, and the phase transformation progresses within the film as the treatment time increases. In this invention, since it is necessary to increase the area ratio of the β phase in the cross-section of the PdCu alloy film, sufficient heat treatment time is ensured while considering the film thickness to allow the phase transformation to occur internally. For PdCu alloy films with a thickness within the above-mentioned preferred range, a treatment time of 5 hours or more is preferred. It should be noted that as long as the heat treatment is performed within the above-mentioned temperature range, the decomposition of the β phase is unlikely to occur; therefore, setting a long treatment time is not a problem.

[0055] (C) Utilization of the hydrogen permeation membrane of the present invention

[0056] The hydrogen permeation membrane of this invention exhibits suitable hydrogen permeability across a wide range of temperatures, from high to low. Therefore, in addition to hydrogen purification devices (hydrogen purification processes), this invention can also be used in various other applications, such as hydrogen sensors.

[0057] (C-1) Hydrogen purification process and hydrogen purification equipment

[0058] The hydrogen permeation membrane of the present invention can selectively permeate hydrogen from a hydrogen-containing gas (feed) to purify hydrogen.

[0059] In this hydrogen purification process, it is preferable to appropriately set the processing temperature (operating temperature) of the hydrogen permeation membrane. In the hydrogen purification method using the PdCu alloy membrane of the present invention, a processing temperature of 25°C or higher and 400°C or lower is considered suitable. Regarding this range of processing temperatures, the PdCu alloy membrane of the present invention exhibits suitable hydrogen permeability, particularly in the low-temperature region, which distinguishes it from existing technologies. However, at temperatures exceeding 400°C, even the PdCu alloy membrane of the present invention may experience β-phase decomposition, leading to a decrease in the hydrogen permeability coefficient. Therefore, as a suitable processing temperature, an upper limit of 400°C is set.

[0060] It should be noted that the processing temperature here refers to the temperature of the area where the hydrogen-containing gas, which is the object of purification, comes into contact with and permeates through the hydrogen permeation membrane. The processing temperature can be adjusted by setting at least one of the temperature of the hydrogen-containing gas, the temperature of the hydrogen permeation membrane, and the atmospheric temperature within the hydrogen production (purification) apparatus to the aforementioned temperature range.

[0061] In the purification of hydrogen-containing gas, the gas to be processed is supplied to one side (primary side) of a hydrogen permeation membrane. Then, by increasing the pressure on the primary side relative to the other side (secondary side) of the membrane, purified hydrogen permeates from the membrane. There are no particular limitations regarding the pressure difference at this point.

[0062] It should be noted that in the hydrogen purification process using the PdCu alloy membrane of the present invention, the heat-treated PdCu alloy membrane used to form the β phase as described above can be used, but the heat treatment can also be performed just before the hydrogen purification process begins. That is, an untreated PdCu alloy membrane can be prepared and heat-treated in a hydrogen atmosphere at a temperature of 275°C or higher and 400°C or lower to form a hydrogen permeation membrane, and then the treatment temperature can be set to 25°C or higher and 400°C or lower to allow the target gas to permeate through the hydrogen permeation membrane.

[0063] The above hydrogen purification method can be implemented using a hydrogen purification apparatus employing the hydrogen permeation membrane of the present invention. The main components of this hydrogen purification apparatus, except for the hydrogen permeation membrane, are the same as those of known hydrogen purification apparatuses. It should be noted that when the hydrogen permeation membrane is placed in the hydrogen permeation apparatus, a gas-permeable support can be combined with the hydrogen permeation membrane to compensate for mechanical strength. As the support, metal mesh, porous sintered materials, etc., can be used. However, since mechanical strength can sometimes be ensured by the thickness of the hydrogen permeation membrane, a support is not always necessary.

[0064] (C-2) Hydrogen sensor

[0065] As mentioned at the beginning, highly sensitive hydrogen sensors are needed to address emerging applications of hydrogen, such as fuel cells and medical technologies. The hydrogen permeation membrane of this invention can also be suitable for use in hydrogen sensors.

[0066] Hydrogen sensors utilizing hydrogen permeation membranes include gas sensors that use rare earth metals such as Y and La, and semiconductor metal oxides such as Ga2O3 and SrTiO3 as hydrogen detection elements. In these sensors, the hydrogen permeation membrane serves as a protective membrane that selectively allows hydrogen to permeate and supplies hydrogen to the detection element. Furthermore, in recent years, the development of concentration cell-type hydrogen sensors has been reported. In these sensors, the hydrogen permeation membrane is used as both the standard electrode and the sample electrode. The membrane imparts selective hydrogen permeability to both electrodes and supplies the permeated hydrogen to the electrolyte. The hydrogen permeation membrane of this invention exhibits excellent hydrogen selectivity over a wide temperature range and can be used as the sensing element in various hydrogen sensors.

[0067] Invention Effects

[0068] The hydrogen permeability coefficient of hydrogen permeation membranes is predicted to tend to follow a temperature dependence according to the Arrhenius diagram, and the present invention exhibits hydrogen permeability following this tendency even in low-temperature regions. Furthermore, the hydrogen permeation membrane of the present invention, composed of a PdCu alloy, demonstrates superior hydrogen permeability compared to existing technologies even in low-temperature regions below 150°C. Attached Figure Description

[0069] Figure 1 This is a diagram showing the configuration of the hydrogen permeability measuring device used in this embodiment.

[0070] Figure 2 This is an Arrhenius plot showing the temperature dependence of the hydrogen permeation coefficient of the PdCu alloy film (basic composition: 48.3 atomic% Pd - 51.7 atomic% Cu) of Group A manufactured in this embodiment.

[0071] Figure 3 This is an Arrhenius plot showing the temperature dependence of the hydrogen permeation coefficient of the PdCu alloy film (basic composition: 47.25 atomic% Pd - 52.75 atomic% Cu) of Group B manufactured in this embodiment.

[0072] Figure 4 This is an Arrhenius plot showing the temperature dependence of the hydrogen permeation coefficient of the PdCu alloy film (basic composition: 48.5 atomic% Pd - 51.5 atomic% Cu) of group C manufactured in this embodiment.

[0073] Figure 5 This is an example of an Arrhenius plot showing the temperature dependence of the hydrogen permeation coefficient of a PdCu alloy film (PdCuAl alloy film) manufactured as a reference example.

[0074] Figure 6This is an example of an Arrhenius plot showing the temperature dependence of the hydrogen permeation coefficient of a PdCu alloy film (PdCuMn alloy film) manufactured as a reference example. Detailed Implementation

[0075] The embodiments of the present invention will be described below. In this embodiment, a hydrogen permeation membrane made of a PdCu alloy and a hydrogen permeation membrane made of a PdCuAg alloy in which Ag is added are manufactured. Then, for each hydrogen permeation membrane, the hydrogen permeation coefficient is measured from the high temperature region to the low temperature region. In this embodiment, the following three groups of PdCu alloys A to C are used as the basic alloy composition, and PdCuAg alloy membranes in which 0.15 atomic% to 1.0 atomic% Ag is added to these PdCu alloys are manufactured.

[0076] Group A: 48.3 atoms % Pd - 51.7 atoms % Cu

[0077] Group B: 47.25 atoms % Pd - 52.75 atoms % Cu

[0078] Group C: 48.5 atoms % Pd - 51.5 atoms % Cu

[0079] Regarding the composition adjustments of the PdCuAg alloys in the above three groups, the Pd concentration is not changed; instead, the Cu concentration is adjusted to add Ag. This is to allow the added Ag to replace Cu. This composition setting takes into account that the hydrogen permeability of the PdCu alloy film largely depends on Pd, and as mentioned above, Ag exerts its effect by being replaced into the cavities of the PdCu alloy. The manufacturing of the PdCu alloy film is as follows.

[0080] [Manufacturing of PdCu-based alloy films]

[0081] A PdCu alloy ingot with the target composition is manufactured by melting and casting, and the surface of the ingot is cleaned by surface cutting. Then, the PdCu alloy ingot is repeatedly subjected to cold rolling processes to produce a thin film. During the rolling process, intermediate annealing at 600–900°C is performed more than twice, and the final rolling yield is set to 70%. In this embodiment, a PdCu alloy film with a thickness of 30 μm to 100 μm is manufactured. Next, the PdCu alloy film is heat-treated to induce a β-phase transformation. The heat treatment is performed in 0.30 MPaG of hydrogen at a temperature of 300°C or 400°C for 24 hours. The composition, film thickness, and heat treatment temperature of the PdCu alloy film manufactured in this embodiment are summarized in Table 1.

[0082] [Table 1]

[0083] [Cross-sectional analysis of PdCu alloy films]

[0084] For various PdCu alloy films manufactured, EBSD analysis was performed on the cross-sections to determine the area fraction of the β phase in the observed region. As a pretreatment for EBSD analysis, the sample cross-sections were finely ground using 0.25 μm diamond polishing paste, followed by surface milling using an ion milling apparatus (Hitachi Advanced Technology Corporation IM4000). The ion milling conditions were: stage control F2, acceleration 0.1 kV, discharge 1.5 kV, ion beam irradiation angle 70 degrees, eccentricity 4 mm, and argon flow rate 0.07 cm³. 3 Mill the surface for 20 minutes at a rate of / minute.

[0085] EBSD analysis was performed using an ultra-high resolution analytical scanning electron microscope (Hitachi Advanced Technology Co., Ltd. SU-70, and Oxford Instruments Co., Ltd. NORDLYS-MAX3). Analysis conditions were: step size 0.2 μm, pixel binning mode 4×4, gain 0, automatic exposure time, EBSD solver settings, strip number 12, and Hough resolution 60. The analysis was performed using reflector 44 for the FCC phase (lattice constant 3.7653 Å) and reflector 43 for the B2 phase. The area fraction of the β phase (lattice constant 2.9662 Å) was then measured using the image analysis software provided with the analytical apparatus.

[0086] The EBSD analysis confirmed that the β-phase area fraction in the cross-sections of the PdCu alloy films (A-1 to A-5, B-1 to B-3, C-1 to C-2) manufactured in this embodiment was all above 95%. In particular, the β-phase area fraction of the PdCu alloy films B-1 to B-3 was 100%. Furthermore, the β-phase area fraction of the PdCu alloy films A-1 to A-5 was in the range of 99.9% to 100%, and the β-phase area fraction of the PdCu alloy films C-1 to C-2 was above 99.0%.

[0087] [Determination of hydrogen permeability coefficient of PdCu alloy membranes]

[0088] Next, the hydrogen permeation coefficient was measured for the hydrogen permeation membranes (PdCu alloy membranes) manufactured by heat treatment at various temperatures. A circle with a diameter of 21.3 mm was cut from the manufactured hydrogen permeation membrane. This hydrogen permeation membrane was then clamped together with a stainless steel mesh (18.4 mm in diameter) using an ICF34 flange gasket to prepare a sample (effective area 2.08 cm²). 2The sample is mounted in a sample holder. The sample holder is a vacuum container with a primary side (gas supply side) and a secondary side (permeable gas side) relative to the sample (hydrogen permeation membrane), and is equipped with nozzles for gas supply and gas discharge.

[0089] Figure 1 The diagram shows an outline of the hydrogen permeability coefficient measuring apparatus. A sample holder constructed as described above is installed in an electric furnace and connected to piping for a vacuum pump and various gas flow meters. Before measurement, the primary and secondary sides of the sample holder are evacuated and then purged with hydrogen. Next, the furnace is heated to the specified measurement temperature, and hydrogen gas at a specified pressure is introduced into the primary side of the hydrogen permeation membrane. Then, the flow rate of hydrogen permeating to the secondary side is measured. The permeability coefficient is calculated from the measured flow rate of the permeate gas (hydrogen), the supply-side pressure, the permeate-side pressure, and the membrane thickness of the hydrogen permeation membrane. The measurement conditions in this embodiment are as follows.

[0090] • Measurement temperature: 20℃ (293K)~600℃ (873K)

[0091] • Supply gas: Hydrogen (99.99% hydrogen concentration)

[0092] Primary side pressure: 0.3 MPa·G

[0093] Secondary lateral pressure: 0 MPa·G

[0094] • Test duration: 2.5 hours

[0095] [Evaluation Results]

[0096] For the PdCu alloy films (PdCu alloy films and PdCuAg alloy films) of groups A to C manufactured in this embodiment, the curves based on the Arrhenius plot representing the temperature dependence of the hydrogen permeability coefficient are plotted in the figure below. Figures 2-4 These figures show predicted lines for the hydrogen permeability coefficient, derived linearly from measurements of PdCu alloy films without Ag in the high-temperature region of 250°C–400°C. However, regarding… Figure 4 (Group C) Due to the difference in measured values ​​with and without Ag, a predicted line for the hydrogen permeability coefficient of the PdCuAg alloy film is also shown. According to... Figures 2-4 The hydrogen permeability coefficient of the existing PdCu alloy film without added Ag deviates from the predicted line starting around 150℃ (1 / T = 0.0024), and the deviation increases in the low-temperature region below this temperature. In contrast, for the PdCuAg alloy film with added Ag, although the deviation from the predicted line is slight, the magnitude is smaller, indicating that the decrease in hydrogen permeability coefficient in the low-temperature region is suppressed. Therefore, it is confirmed that adding Ag to the PdCu alloy film helps improve the hydrogen permeability coefficient in the low-temperature region.

[0097] However, the advantages of adding Ag to PdCuAg alloy films are limited to cases where the amount added is small. Regarding... Figure 2 and Figure 3 The PdCuAg alloy film with an Ag concentration of 1.0 atomic% did not show a significant improvement in the reduction of hydrogen permeability in the low-temperature region. Furthermore, the hydrogen permeability of these PdCuAg alloy films remained low across the entire temperature range. It can be said that adding a large amount of Ag contributed nothing to improving the properties of the PdCu alloy film.

[0098] It should be noted that, in this embodiment, in addition to the samples mentioned above, PdCuAg alloy films with Ag addition amounts of 1.5 atomic%, 3 atomic%, and 6 atomic% were also manufactured, and their hydrogen permeability coefficients were measured. However, these alloy films exhibited significantly low hydrogen permeability coefficients across the entire temperature range, making them unsuitable as hydrogen permeation membranes.

[0099] Regarding the hydrogen permeability of the PdCu alloy film and PdCuAg alloy film in this embodiment, the hydrogen permeability coefficient Φ at 100°C is used. 100 and hydrogen permeability coefficient Φ at 300℃ 300 and their ratio (Φ) 100 / Φ 300 The results are summarized in Table 2 below.

[0100] [Table 2]

[0101] Table 2 confirms that the ratio Φ of the hydrogen permeability coefficient of the PdCuAg alloy film with appropriate Ag addition is... 100 / Φ 300 The hydrogen permeability coefficient, which is above 0.4, was effectively maintained in the low-temperature region.

[0102] Reference example (comparison with the addition of other metals)

[0103] Here, in order to confirm that Ag is the preferred metal element to be added to the PdCu alloy film, the inventors manufactured PdCu alloy films with other metals added and evaluated them in the same manner as described above. The manufacturing process of the PdCu alloy films was the same as described above. In addition, this reference example also uses the above-described PdCu alloys from groups A to C as the basic composition, and manufactures and evaluates PdCu alloy films (PdCuAl alloy film, PdCuMn alloy film) with Al and Mn added as additive metals. It should be noted that Al and Mn were studied as reference examples because it is speculated that these elements, like Ag, have the effect of stabilizing the phase transition from the fcc structure (α phase) to the bcc structure (β phase).

[0104] The Arrhenius diagram for evaluating PdCuAl alloy films and PdCuMn alloy films, used as reference examples, shows the results for PdCu alloy films of basic composition group A as a representative example. Figure 5 (PdCuAl alloy film) Figure 6 (PdCuMn alloy film). When Al and Mn are used as additive elements in the PdCu alloy film, the hydrogen permeability coefficient in the low-temperature region is slightly improved at an addition concentration of approximately 0.5 atomic%. However, the improvement is minimal and does not show the same effect as Ag. The ratio of hydrogen permeability coefficients Φ 100 / Φ 300 It is also less than 0.4. This tendency is the same for PdCu alloy films with other basic compositions (groups B and C). Ag was identified as the preferred metal for adding cavities that contribute to the reduction of hydrogen permeability in PdCu alloys.

[0105] Industrial availability

[0106] The hydrogen permeation membrane of this invention, constructed from a PdCu alloy, suppresses the decrease in hydrogen permeability coefficient observed in existing PdCu alloy hydrogen permeation membranes at low temperatures by adding Ag. Therefore, this invention is significant for the operation of various devices and apparatuses using hydrogen permeation membranes in low-temperature regions. In addition to applications in hydrogen purification devices, the hydrogen permeation membrane of this invention is also expected to be used in hydrogen sensors that require operation in low-temperature regions.

Claims

1. A hydrogen permeation membrane, which is a hydrogen permeation membrane composed of a PdCu-based alloy, characterized in that, The PdCu alloy consists of 47.0 atomic% or more and 49.0 atomic% or less of Pd, 0.01 atomic% or more and 0.75 atomic% or less of Ag, and the balance of Cu and unavoidable impurities.

2. The hydrogen permeation membrane according to claim 1, wherein the area fraction of the β phase in any cross section is 95% or more.

3. The hydrogen permeation membrane according to claim 1 or 2, wherein the hydrogen permeation coefficient Φ at 100°C 100 Hydrogen permeability coefficient Φ at 300℃ 300 The ratio (Φ) 100 / Φ 300 The value is above 0.

4.

4. The hydrogen permeation membrane according to claim 1 or 2, wherein the thickness is 1 μm or more and 250 μm or less.

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