Hydrogen permeable membrane made of PdCu alloy

Abstract

To provide a hydrogen permeable membrane made of a PdCu-based alloy having improved hydrogen permeability in a low temperature region of 200°C or less.SOLUTION: A hydrogen-permeable membrane made of a PdCu-based alloy comprises: 47.0 atom% or more and 49.0 atom% or less of Pd; 0.001 atom% or more and 0.15 atom% or less of an interstitial element EI; 0.01 atom% or more and 1.0 atom% or less of a substitutional element ES; and the balance of Cu and inevitable impurities. The interstitial element EI contains at least one of B, C, and N, and the substitutional element ES contains a metal element essentially containing at least one of Ag, Au, and Al. In the hydrogen-permeable membrane according to the present invention, a ratio (φ100 / φ300) of a hydrogen permeability coefficient φ100 at 100°C to a hydrogen permeability coefficient φ300 at 300°C is 0.4 or more, and a decrease in the hydrogen permeability coefficient in a low temperature range of 200°C or less is suppressed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This invention relates to a hydrogen permeable membrane that selectively permeates hydrogen from a hydrogen-containing gas. In particular, it relates to a hydrogen permeable membrane with improved hydrogen permeability in the low-temperature range. [Background technology]

[0002] Hydrogen is widely used in various fields, such as as a hydrogen source and reducing agent in the synthesis processes of various compounds. In recent years, hydrogen has attracted attention as a renewable energy source, and its use as a fuel gas for fuel cells and hydrogen engines that power automobiles and heavy machinery is also expected. Furthermore, hydrogen is attracting attention in the field of advanced medicine, and for example, the effectiveness of hydrogen inhalation therapy for post-cardiac arrest syndrome has been reported.

[0003] Hydrogen permeable membranes are materials used in equipment for handling hydrogen in the various fields mentioned above. For example, in the fuel sector, high-purity hydrogen gas is required, so hydrogen purification equipment using hydrogen permeable membranes has been developed. Hydrogen sensors are also necessary to measure the hydrogen concentration inside the power supply and in the exhaust gas of fuel cell vehicles, etc. Hydrogen sensors are also necessary for the accurate and precise measurement of the hydrogen concentration of therapeutic gases in the medical field. Hydrogen permeable membranes, which selectively allow only hydrogen to permeate from the gas to be measured, can be suitably used as hydrogen sensors in these applications.

[0004] Hydrogen permeable membranes are composed of metal alloys that selectively absorb hydrogen and release it while diffusing it internally. Among such metal alloy membranes, Pd (palladium) alloy membranes (such as PdAg alloys and PdCu alloys) that utilize the selective hydrogen permeability of Pd are particularly well known. In particular, hydrogen permeable membranes made of PdCu alloys are being put into practical use and mass-produced because they have fewer problems related to hydrogen embrittlement and corrosion resistance (Patent Documents 1, 2, Non-Patent Document 1). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2001-262252 [Patent Document 2] Japanese Patent Publication No. 2008-12495 [Non-patent literature]

[0006] [Non-Patent Document 1] JamesRaphael Warren, “The Effect of Hydrogen on Palladium-Copper Based Membranes for Hydrogen Purification”, THE UNIVERSITY OF BIRMINGHAM, P22-29, 37-80. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The hydrogen permeation phenomenon in a hydrogen permeable film made of PdCu alloy is due to atomic diffusion, and therefore the hydrogen permeation coefficient is temperature-dependent and follows the so-called Arrhenius equation (Arrhenius plot). In the Arrhenius plot, the logarithm of the hydrogen permeation coefficient decreases linearly in negative proportion to the reciprocal of the temperature (1 / T), so by measuring the hydrogen permeation coefficient in the high-temperature range, it is possible to predict the hydrogen permeation coefficient in the low-temperature range.

[0008] However, according to the inventors' studies, the predictability of the hydrogen permeability coefficient based on the Arrhenius plot described above is difficult to achieve for conventional hydrogen permeable films made of PdCu alloy. Specifically, even if an Arrhenius plot is created based on the hydrogen permeability coefficient measured in the high-temperature range, the measured value of the hydrogen permeability coefficient in the low-temperature range deviates from the Arrhenius plot and becomes a low value. This means that the hydrogen permeability of hydrogen permeable films made of PdCu alloy is lower than expected in the low-temperature range. While it is unavoidable that the hydrogen permeability coefficient is temperature-dependent, it is undesirable for the hydrogen permeability coefficient to be lower than expected in the low-temperature range.

[0009] Previous studies on hydrogen permeable membranes have primarily focused on increasing the hydrogen permeability coefficient, with relatively few studies addressing the improvement of the temperature dependence of these membranes. This is because the hydrogen permeability coefficient is considered the most important indicator of a hydrogen permeable membrane's function, and its level is considered crucial. Furthermore, the fact that hydrogen permeable membranes have traditionally been used in equipment such as hydrogen purification systems that are permitted to operate at high temperatures is another contributing factor to this situation.

[0010] However, some devices that utilize hydrogen permeable membranes require operation in low-temperature ranges. For example, hydrogen sensors for fuel cell vehicles and hydrogen sensors for medical applications are designed for use at room temperature. While these fields of application for hydrogen permeable membranes have only recently attracted attention, these new applications require membranes that can exhibit higher hydrogen permeability at low temperatures.

[0011] The present invention was made against the background described above, and provides a hydrogen permeable film made of a PdCu alloy with improved hydrogen permeability in the low-temperature range. In this invention, the low-temperature range is defined as the temperature range from room temperature (25°C) to 200°C. [Means for solving the problem]

[0012] To address the above issues, the inventors investigated the factors causing a decrease in hydrogen permeability in PdCu alloy films at low temperatures and countermeasures for doing so. The hydrogen permeability of PdCu alloys is exhibited in the β phase state, which has a B2 structure based on a body-centered cubic (bcc) lattice. Hydrogen exhibits hydrogen permeability by solid dissolving in the gaps of the crystal lattice of the PdCu alloy film in the β phase state, as well as by moving and diffusing. Therefore, the hydrogen permeability in PdCu alloys can be expressed as the product of the solid solubility of hydrogen and the mobility (ease of movement) of hydrogen.

[0013] The inventors considered that the decrease in hydrogen permeability of PdCu alloy films is due to the generation of vacancies caused by structural defects (lattice defects) in the PdCu alloy crystal. Therefore, the inventors obtained the following considerations regarding the relationship between structural defects in PdCu alloy crystals and the decrease in hydrogen permeability through computational chemistry and experimental / empirical knowledge. (i) Structural defects in PdCu alloy crystals can include vacancies of Pd atoms at Pd sites, vacancies of Cu atoms at Cu sites, and Cu vacancy-like double defects resulting from the diffusion of Cu atoms into vacancies at Pd sites. Although the frequency of occurrence differs, in any case, there is a site near the defect that traps hydrogen atoms, and binding energy is generated at this site that immobilizes the hydrogen. This binding energy affects the mobility of hydrogen. (ii) For hydrogen to permeate, the trapped hydrogen must move, and for this to happen, it is necessary to impart energy that exceeds the binding energy mentioned above. (iii) The reason why the hydrogen permeability of PdCu alloys decreases in the low-temperature range is thought to be due to the binding energy near the defects described above. When PdCu alloys are in the high-temperature range, hydrogen can move due to the relaxation of the binding energy by thermal energy. In the low-temperature range, this is difficult, so hydrogen cannot move, and as a result, the hydrogen permeability decreases.

[0014] As described above, the inventors considered that the decrease in hydrogen permeability at low temperatures is due to a decrease in hydrogen mobility caused by structural defects. Therefore, the inventors conceived of adding interstitial elements such as B to PdCu alloys as a means to relax the binding energy and induce hydrogen movement even at low temperatures. In this regard, computational chemistry studies conducted by the inventors have confirmed that interstitial elements introduced into PdCu alloys penetrate the lattice near structural defects, thereby causing the relaxation of the binding energy described above. Therefore, this means can be said to contribute to improving the mobility of hydrogen.

[0015] However, according to the inventors' research, further investigation is needed regarding the above-mentioned means. Light elements such as B and N, known as interstitial elements, have low binding energy within the crystal lattice of PdCu alloys and are easily desorbed. To make a PdCu alloy into a hydrogen permeable film, several processes are necessary, including a melting process for alloy ingot production, annealing for processing, and heat treatment for β-phase formation of the crystal structure. Interstitial elements may desorb during these processing steps. If desorption of interstitial elements occurs, the hydrogen binding energy relaxation effect described above will be lost.

[0016] Therefore, the inventors decided to try applying substitutional elements as further additives to stabilize interstitial elements introduced into PdCu alloys. Substitutional elements are placed in vacancies, which are structural defects as described above. In this case, the substitutional elements generate repulsive or attractive forces due to interactions such as interatomic attractive forces with the surrounding Pd and Cu atoms, thereby forming strain in the crystal lattice. According to the inventors' calculations, it is believed that this lattice strain can constrain and stabilize the interstitial elements between the lattices.

[0017] Based on the results of the multi-stage considerations described above, the inventors conceived of simultaneously adding interstitial and substitutional elements to a PdCu alloy as a means of improving hydrogen permeability in the low-temperature range of a hydrogen permeable membrane made of PdCu alloy. They then conducted a detailed study on the range of suitable elements as substitutional and interstitial elements, and the conditions for obtaining the B2 structure (β phase) inherently required for the function of a hydrogen permeable membrane, leading to the present invention.

[0018] In other words, the present invention, which solves the above problems, is a hydrogen permeable membrane made of a PdCu-based alloy, wherein the PdCu-based alloy contains 47.0 atomic% to 49.0 atomic% of Pd and 0.001 atomic% to 0.15 atomic% of interstitial element E I And substitutional element E, which is between 0.01 atomic% and 1.0 atomic%. S The remainder consists of Cu and unavoidable impurities, and the interstitial element E I is at least one of the elements B, C, and N, and the substitutional element E SThis is a hydrogen permeable membrane characterized by being a metallic element that essentially contains at least one of Ag, Au, or Al.

[0019] The following describes the structure and hydrogen permeability of the hydrogen permeable membrane according to the present invention, as well as its manufacturing method and applications. In this specification, a ternary or higher alloy consisting of Pd, Cu, and other elements is referred to as a PdCu alloy, and a binary alloy consisting of Pd and Cu is referred to as a PdCu alloy.

[0020] (A) Structure of the hydrogen permeable membrane according to the present invention (A-1) Alloy composition The hydrogen permeable membrane according to the present invention, excluding unavoidable impurities described later, consists of Pd and Cu, and interstitial elements (E I ) and substitutional elements (E S PdCu-based alloys (PdCuE) have ) as an essential constituent element. I E S It consists of alloys. The function and composition range of each of these constituent elements are as follows:

[0021] (A-1-1) Pd and Cu Since the hydrogen permeable membrane according to the present invention is composed of a PdCu alloy, Pd and Cu are essential and major constituent elements of the present invention. Pd is an essential metal for ensuring the hydrogen permeability of the hydrogen permeable membrane made of the PdCu alloy. Furthermore, the hydrogen permeability of the PdCu alloy is exhibited when its crystal system is in the β phase, which has a B2 structure. Cu is an essential additive metal for promoting the phase transformation from the α phase (face-centered cubic lattice (fcc)) to the β phase in the PdCu alloy and for maintaining the phase configuration necessary for exhibiting hydrogen permeability. In addition, Cu also has the effect of suppressing the decrease in strength of the PdCu alloy film due to hydrogen embrittlement.

[0022] In the PdCu-based alloy constituting the hydrogen permeable membrane according to the present invention, the Pd concentration is 47.0 atomic % or more and 49.0 atomic % or less. When the Pd concentration exceeds 49.0 atomic %, it becomes difficult to express the β phase, and it becomes difficult to obtain a sufficient amount of the β phase even after heat treatment in the manufacturing process. On the other hand, since Pd is an essential element for exhibiting hydrogen permeation performance, a decrease in the Pd concentration leads to a decrease in the hydrogen permeability of the hydrogen permeable membrane. And when the Pd concentration becomes less than 47.0 atomic %, it becomes difficult to obtain sufficient hydrogen permeability even in the high temperature range. 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. And the Cu concentration is the remainder of the Pd concentration, the E I concentration and the E S concentration, and the inevitable impurity concentration.

[0023] (A-1-2) Intrusion type element (E I ) As described above, in the present invention, when lattice defects occur in the PdCu alloy, the intrusion type element E I is applied as an additive element for relaxing the binding energy of hydrogen trapped near the defect. This intrusion type element E I is at least one of B (boron), C (carbon), and N (nitrogen).

[0024] The concentration of the intrusion type element E I in the PdCu-based alloy constituting the hydrogen permeable membrane according to the present invention is 0.001 atomic % or more and 0.15 atomic % or less. If it is less than 0.001 atomic %, it is difficult to exhibit the above effect, and an improvement in the hydrogen permeability of the PdCu-based alloy in the low temperature range is not observed. In addition, intrusion type elements such as B are elements that greatly inhibit the β-phase transformation of the PdCu-based alloy. Therefore, when the PdCu-based alloy is added in excess exceeding 0.15 atomic %, it becomes difficult to make it in the β-phase state. In this case, not only in the low temperature range but also in the high temperature range, a hydrogen permeable membrane with poor hydrogen permeability is obtained. The concentration of the intrusion type element E I is more preferably 0.01 atomic % or more and 0.15 atomic % or less. Further, the PdCu-based alloy of the present invention has an intrusion type element E IAt least one of B, C, or N is added, and it is acceptable to add only one of these elements, or two or more elements.

[0025] (A-1-3) Substitutional element (E S ) Substitutional element E S This is an interstitial element (E) added to relieve the binding energy of hydrogen trapped near the defect. I It is an additive element that improves the stability of ). To explain this effect in more detail, substitutional element E S This involves substituting Pd or Cu atoms in a PdCu alloy, generating lattice strain through interaction with surrounding Pd and Cu atoms. This lattice strain constrains interstitial elements and promotes their solid solution. As a result, the stability of interstitial elements around vacancies is improved, and the hydrogen binding energy relaxation effect is maintained.

[0026] Furthermore, according to the inventors' studies, among the metallic elements that can act as substitutional elements, only Ag (silver), Au (gold), and Al (aluminum) can exhibit the effects described above. Therefore, substitutional element E in the present invention S This refers to metallic elements that must contain at least one of Ag, Au, or Al.

[0027] Substitutional element E of the PdCu-based alloy constituting the hydrogen permeable membrane according to the present invention S The concentration of [element name] should be between 0.01 atomic% and 1.0 atomic%. Below 0.01 atomic%, the above-mentioned effects are difficult to achieve. On the other hand, substitutional element E S The action of interstitial element E near the vacancy I Its purpose is stabilization, and it does not directly improve hydrogen permeability. Rather, the addition of excess substitutional elements can lead to a decrease in the Cu or Pd concentration in the alloy, potentially hindering β-phase formation and causing a decrease in overall hydrogen permeability across a wide temperature range, including high temperatures. Therefore, substitutional element E S The concentration of [substitutional element] shall be capped at 1.0 atomic percent. S The concentration of [the substance] is more preferably between 0.1 atomic% and 0.5 atomic%.

[0028] Furthermore, as mentioned above, substitutional element E S It is sufficient that it contains at least one of Ag, Au, or Al, and it may contain only one element or two or more elements.

[0029] Furthermore, substitutional element E S It is a metallic element containing at least one of Ag, Au, or Al. In other words, substitutional element E S It may contain other metallic elements besides Ag, Au, and Al. Substitutive metallic elements are nonmetallic elements (hydrogen, halogens, Group 18 elements), metalloid elements (Si, Ge, As, Sb, Te, Se, Po, At), and elements other than essential metallic elements (Ag, Au, Al). Specifically, examples of other metallic elements include Mn, Cr, Fe, Ti, V, Co, Ni, Pt, Rh, Ru, Ir, Pt, Nb, Ta, Y, Ho, Hf, Gd, etc. While these other metallic elements do not exhibit the effects of Ag, Au, and Al as described above, they have little impact on the hydrogen properties of the hydrogen permeable membrane. Furthermore, Mn can be a useful additive element because it promotes β-phase formation. However, substitutional element E S Even if other metal elements are included as such, substitutional element E S The upper limit of the overall concentration is 1.0 atomic percent. As mentioned above, substitutional element E S If the concentration of becomes excessively high, the Pd or Cu concentration will decrease, which can reduce hydrogen permeability. Also, even if other metal elements are present, substitutional elements of Ag, Au, and Al E S It must contain at least 0.01 atomic percent.

[0030] (A-1-4) Inevitable impurities The PdCu-based alloy film of the present invention comprises Pd, Cu, and an interstitial element (E I ) and substitutional elements (E S It is composed of the above. However, the inclusion of unavoidable impurities is permissible. Examples of unavoidable impurities include the metalloid elements mentioned above. It is preferable that the total amount of these unavoidable impurities be 500 ppm or less.

[0031] (A-2) Crystal structure of PdCu alloy film Considering that hydrogen permeability in PdCu alloys is exhibited in the β phase state, which has a B2 structure, and that the hydrogen permeable film is expected to permeate hydrogen through its cross-section, it is preferable that the hydrogen permeable film according to the present invention has a high proportion of the β phase in its cross-section. Specifically, it is preferable that the hydrogen permeable film according to the present invention has a β phase area ratio of 95% or more in any cross-section.

[0032] An arbitrary cross-section means that the above conditions are met in any cross-section arbitrarily selected from the PdCu alloy film, regardless of direction. The area ratio should be calculated by performing cross-sectional observation in an area where both sides (both front and back) of the PdCu alloy film are visible, and then calculating the area of ​​the β phase relative to the total area of ​​the observation area. Preferably, the observation area should include both front and back ends of the PdCu alloy film and have a width that is 10 times or more the length of the film thickness. Furthermore, it is more preferable that the area ratio of the β phase in this arbitrary cross-section be 98% or more, and preferably that the upper limit of the area ratio of the β phase be 100%.

[0033] For detecting the β phase in any cross-section of a PdCu alloy film, electron backscattered diffraction (EBSD) analysis is an effective method. EBSD makes it possible to obtain information on each crystal grain in the cross-section of the alloy film, thereby measuring and calculating the distribution and area fraction of the β phase in the cross-section of the alloy film.

[0034] Furthermore, the thickness of the PdCu-based alloy film constituting the hydrogen permeable membrane according to the present invention is preferably 1 μm or more and 250 μm or less. If the thickness is less than 1 μm, the mechanical strength is insufficient and handling is difficult. Also, if the thickness exceeds 250 μm, the amount of hydrogen permeation decreases, resulting in a decrease in purification efficiency. Furthermore, there are no particular restrictions on the shape of the PdCu-based film according to the present invention.

[0035] (A-3) Hydrogen permeability of the PdCu-based alloy film according to the present invention The hydrogen permeable film made of the PdCu-based alloy according to the present invention exhibits excellent hydrogen permeability, particularly in the low-temperature range of 200°C or below. As described above, the hydrogen permeability coefficient of the PdCu-based alloy film deviates in the low-temperature range from the Arrhenius plot based on the high-temperature range, and a lower value is measured than the predicted value. In the present invention, the aforementioned deviation of the hydrogen permeability coefficient in the low-temperature range is reduced.

[0036] A preferred specific embodiment of the hydrogen permeable membrane according to the present invention is one in which the hydrogen permeability coefficient φ at 100°C is 100 and the hydrogen permeability coefficient φ at 300°C 300 The ratio to is 0.4 or greater. Since a decrease in the hydrogen permeability coefficient due to a decrease in temperature is unavoidable, the ratio φ 100 / φ 300 The value becomes less than 1. The hydrogen permeable membrane according to the present invention suppresses the drop in the hydrogen permeability coefficient in the low temperature range, thereby reducing φ 100 / φ 300 This can be set to 0.4 or higher. Furthermore, the reason for applying the hydrogen permeability coefficients at 100°C and 300°C to the characterization criteria for hydrogen permeable films is that the hydrogen permeability coefficient tends to drop significantly around 100°C. Also, the hydrogen permeability coefficient of PdCu-based alloy films is highest in the range of 300°C to 400°C, and it is convenient to apply the measurement value at 300°C. Note: Hydrogen permeability coefficient φ(mol / m·s·Pa) 1 / 2 ) is calculated using the following formula.

[0037]

number

[0038] The ratio of the hydrogen permeation coefficients φ mentioned above 100 / φ 300There are no particular restrictions on the measurement range for measuring hydrogen permeability, as long as it includes 100°C and 300°C. Preferably, the measurement range is between 25°C and 400°C. This is because the hydrogen permeability coefficient is rarely at its maximum above 400°C, and a decrease in the hydrogen permeability coefficient due to the decomposition of the β-phase is observed at higher temperatures. Furthermore, measuring the hydrogen permeability coefficient below 25°C (below room temperature) requires a measuring device equipped with a cooling mechanism, making the measurement process more complex. However, there is no reason to prevent measuring the hydrogen permeability coefficient over a wider temperature range than between 25°C and 400°C.

[0039] The hydrogen permeability of PdCu alloy films is influenced by a combination of factors, including the Pd and Cu concentrations and the area ratio of the β phase in the cross-section, as described above. Furthermore, even if a hydrogen permeable film has a high hydrogen permeability coefficient at high temperatures due to optimization of the alloy composition, it may not be possible to avoid a decrease in hydrogen permeability at low temperatures. Interstitial element E in the PdCu alloy in this invention I and substitutional element E S The addition of this compound works in conjunction with optimizing the alloy composition and the area fraction of the β phase to optimize hydrogen permeability over a wide temperature range, including low temperatures.

[0040] (B) Method for producing a hydrogen permeable membrane according to the present invention Next, a preferred method for manufacturing the hydrogen permeable membrane according to the present invention will be described. The hydrogen permeable membrane according to the present invention can be manufactured by preparing a PdCu-based alloy with the above-described composition and forming it into a thin film through plastic processing such as rolling. In a preferred embodiment, this includes a heat treatment to optimize the area ratio of the β phase in the cross-section of the thin film. The preferred method for manufacturing the hydrogen permeable membrane according to the present invention will be described below.

[0041] (B-1) Manufacturing process for PdCu-based alloy films The manufacturing method for PdCu alloy films can be appropriately selected according to the film thickness, dimensions, etc., and is not particularly limited. PdCu alloy films can be manufactured using various thin-film formation processes such as sputtering, vacuum deposition, chemical deposition, and plating. Plate-shaped and foil-shaped PdCu alloy films can also be manufactured by rolling or other processes on alloy ingots.

[0042] The production of PdCu alloy films by the rolling method involves manufacturing a PdCu alloy ingot of the above composition by a melting and casting method, and then processing it by appropriately combining hot forging, hot rolling, cold rolling, etc., to produce an alloy film of a predetermined thickness. There are no particular restrictions on the processing steps from ingot to alloy film. However, in the case of PdCu alloys, since the introduction of processing strain can promote the phase transformation to the β phase, it is preferable to perform cold processing with a processing rate of 65% to 85% as the final processing step.

[0043] (B-2) Heat treatment process for PdCu alloy films (accelerating phase transformation to β phase) The PdCu alloy films with the above compositions, manufactured using various methods, exhibit a phase transformation to the β phase upon heat treatment within a predetermined temperature range. This heat treatment temperature is set to be between 275°C and 400°C. The phase transformation temperature (α phase → β phase) of the PdCu alloy film of the present invention varies depending on the composition even within the above composition range, but is estimated to be approximately within the range of 300°C to 400°C. Heat treatment below 275°C either does not result in a phase transformation to the β phase, or makes it difficult to achieve a β phase area ratio of 95% or more in the film cross-section. On the other hand, the β phase of PdCu alloys is known to decompose into the α phase at high temperatures, and decomposition of the β phase tends to occur above 400°C. Therefore, it is preferable to set the heat treatment temperature range to between 275°C and 400°C.

[0044] A pressurized hydrogen-containing atmosphere is preferred for the heat treatment atmosphere for the phase transformation to the β phase. More preferably, the atmosphere should have a hydrogen partial pressure of 0.05 MPaG or more and 1.0 MPaG or less.

[0045] The heat treatment time is adjusted according to the thickness of the PdCu alloy film. The formation of the β phase by heat treatment proceeds from both surfaces of the PdCu alloy film, and the phase transformation progresses within the film as the treatment time increases. In this invention, it is necessary to increase the area ratio of the β phase in the cross-section of the PdCu alloy film, so a sufficient heat treatment time is ensured so that the phase transformation occurs even to the interior, while taking the film thickness into consideration. For PdCu alloy films with the above-mentioned preferred film thickness range, a treatment time of 5 hours or more is preferable. Furthermore, if the heat treatment is performed within the above temperature range, decomposition of the β phase is unlikely to occur, so there is no problem with making the treatment time longer.

[0046] (C) Forms of use of hydrogen permeable membrane according to the present invention The hydrogen permeable membrane according to the present invention has suitable hydrogen permeability from high temperature ranges to low temperature ranges. Therefore, the present invention can be used in various forms, including hydrogen sensors, in addition to hydrogen purification equipment (hydrogen purification processes).

[0047] (C-1) Hydrogen purification process and hydrogen purification equipment The hydrogen permeable membrane according to the present invention can selectively permeate hydrogen from a hydrogen-containing gas (feed) to purify hydrogen.

[0048] In this hydrogen purification process, it is preferable to appropriately control the processing temperature (operating temperature) of the hydrogen permeable membrane. In the hydrogen purification method using a PdCu-based alloy membrane in the present invention, a suitable processing temperature is 25°C to 400°C. Within this processing temperature range, the PdCu-based alloy membrane of the present invention can exhibit superior hydrogen permeability that differentiates it from conventional technologies, especially in the low-temperature range. However, at temperatures exceeding 400°C, even with the PdCu-based alloy membrane of the present invention, decomposition of the β phase may occur, potentially reducing the hydrogen permeability coefficient; therefore, 400°C is set as the upper limit for the suitable processing temperature.

[0049] The processing temperature here refers to the temperature in the region where the hydrogen-containing gas to be purified contacts and permeates the hydrogen permeable membrane. The processing temperature is adjusted by keeping at least one of the following temperatures within the specified range: the temperature of the hydrogen-containing gas, the temperature of the hydrogen permeable membrane, or the ambient temperature inside the hydrogen production (purification) apparatus.

[0050] In the purification of hydrogen-containing gases, the gas to be treated is supplied to one side (primary side) of a hydrogen permeable membrane. At this time, by increasing the pressure on the primary side relative to the other side (secondary side) of the hydrogen permeable membrane, purified hydrogen that has permeated through the membrane is extracted. There are no particular restrictions on the pressure difference at this time.

[0051] Furthermore, in the hydrogen purification process using a PdCu-based alloy film according to the present invention, a PdCu-based alloy film that has undergone heat treatment for β-phase formation as described above may be used, but the heat treatment may also be performed immediately before the hydrogen purification process. That is, an untreated PdCu-based alloy film may be prepared and heat-treated in a hydrogen atmosphere at a temperature of 275°C to 400°C to form a hydrogen permeable film, and then the treatment temperature may be set to 25°C to 400°C to allow the gas to be treated to permeate through the hydrogen permeable film.

[0052] The above hydrogen purification method is carried out using a hydrogen purification apparatus to which the hydrogen permeable membrane according to the present invention is applied. The main components of this hydrogen purification apparatus, other than the hydrogen permeable membrane, can be the same as those of known hydrogen purification apparatuses. When installing the hydrogen permeable membrane in the hydrogen permeation apparatus, a gas-permeable support may be combined with the hydrogen permeable membrane to supplement its mechanical strength. Metal mesh, porous sintered material, etc., can be used as the support. However, a support is not essential, as mechanical strength may be ensured by the thickness of the hydrogen permeable membrane.

[0053] (C-2) Hydrogen sensor As mentioned at the beginning, highly sensitive hydrogen sensors are needed to address new applications of hydrogen, such as fuel cells and medical technologies. The hydrogen permeable membrane according to the present invention can be suitably used as a hydrogen sensor.

[0054] Hydrogen sensors to which hydrogen permeable membranes are applied include gas sensors that use rare earth metals such as Y and La, or semiconductor metal oxides such as Ga2O3 and SrTiO3, as hydrogen sensing elements. In hydrogen sensors, the hydrogen permeable membrane is used as a protective film that selectively permeates hydrogen and supplies hydrogen to the hydrogen sensing element. In recent years, the development of concentration cell type hydrogen sensors has also been reported. In concentration cell type hydrogen sensors, the hydrogen permeable membrane is used as the standard electrode and the sample electrode. The hydrogen permeable membrane imparts selective hydrogen permeability to both electrodes and supplies the permeated hydrogen to the electrolyte. The hydrogen permeable membrane according to the present invention exhibits excellent hydrogen selectivity over a wide temperature range and constitutes the sensing part of various hydrogen sensors. [Effects of the Invention]

[0055] As described above, the hydrogen permeable film made of the PdCu alloy according to the invention exhibits excellent hydrogen permeability in the low-temperature range. The hydrogen permeability coefficient of the hydrogen permeable film is expected to have a temperature dependence in accordance with the Arrhenius plot, and the present invention exhibits hydrogen permeability in accordance with this tendency even in the low-temperature range. [Brief explanation of the drawing]

[0056] [Figure 1] A diagram showing the configuration of the hydrogen permeation coefficient measuring device used in the first and second embodiments. [Figure 2] Arrhenius plots of hydrogen permeability coefficients for PdCu-based alloy films manufactured in Example 1, Reference Examples 1 and 2, and Conventional Example 1 according to the first embodiment. [Figure 3] This figure shows the results of EBSD analysis of cross-sections of PdCu-based alloy films produced in Example 2 (B concentration: 0.05 atomic%) and Comparative Example 1 (B concentration: 0.2 atomic%) according to the second embodiment. [Modes for carrying out the invention]

[0057] First Embodiment The embodiments of the present invention will be described below. In this embodiment, interstitial element E I B is a substitutional element, and E is a substitutional element. SA PdCu alloy film with added Ag was fabricated, and its hydrogen permeability coefficient was measured from high to low temperatures.

[0058] In this embodiment, a basic composition of 47.25 atoms % Pd - 52.75 atoms % Cu was used as the PdCu alloy to which each additive element was added (referred to as Conventional Example 1). A PdCu alloy film with both Ag and B added (Example 1) and a PdCu alloy film with either Ag or B added (Reference Example 1, Reference Example 2) were manufactured. That is, compared to the basic composition (Conventional Example 1), the Cu concentration was adjusted without changing the Pd concentration to add Ag and B. The reason for setting the composition of the PdCu alloy in this way is that the hydrogen permeability of the PdCu alloy film largely depends on Pd, so it was considered preferable to standardize the Pd concentration when comparing each sample. The PdCu alloy film was manufactured as follows.

[0059] [Manufacturing of PdCu-based alloy films] A PdCu alloy ingot of the desired composition was manufactured by a melt casting method, and the ingot surface was cleaned by surface grinding. Then, a thin film was manufactured by repeatedly performing a cold rolling process on the PdCu alloy ingot. In the rolling process, multiple processes were carried out with intermediate annealing at 600 to 900°C, and the final rolling reduction rate was 70%. In this embodiment, a PdCu alloy film with a thickness of 30 μm was manufactured.

[0060] Next, the PdCu alloy film was heat-treated to promote the β phase transformation. This heat treatment was carried out in hydrogen at 0.3 MPaG at a heat treatment temperature of 400°C for a treatment time of 24 to 100 hours. The heat treatment time was adjusted by whether or not B was added. Table 1 summarizes the composition of the PdCu alloy film produced in this embodiment.

[0061] [Table 1]

[0062] [Cross-sectional analysis of PdCu alloy films] For the various PdCu-based alloy films manufactured in this embodiment, the cross-section was subjected to EBSD analysis, and the area ratio of the β phase in the cross-section within the observation region was measured. As a pretreatment for EBSD analysis, the sample cross-section was polished to a thickness of 0.25 μm using diamond paste, and then the surface was milled using an ion milling apparatus (Hitachi High-Tech 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 gas flow rate 0.07 cm². 3 The surface was milled for 20 minutes under the condition of / min.

[0063] EBSD analysis was performed using an ultra-high-resolution scanning electron microscope (SU-70, Hitachi High-Tech Corporation; NORDLYS-MAX3, Oxford Instruments Ltd.). The analysis conditions were: pitch 0.2umm, pinning mode 4x4, gain 0, exposure time auto, EBSD solver setting, number of bands 12, and Huff 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 (lattice constant 2.9662 Å). The area ratio of the β phase (B2 phase) was measured using image analysis software provided in the analyzer. As a result of this EBSD analysis, the PdCu-based alloy films of Example 1, Reference Examples 1 and 2, and Conventional Example 1, all manufactured in this embodiment, had a β phase area ratio of 100% in their cross-sections.

[0064] [Measurement of water permeability coefficient of PdCu alloy film] Next, the hydrogen permeability coefficient was measured for the PdCu-based alloy films of Example 1, Reference Examples 1 and 2, and Conventional Example 1. The fabricated hydrogen permeable film was cut into a circle with a diameter of 21.3 mm. A sample was prepared by sandwiching this hydrogen permeable film together with a stainless steel wire mesh (diameter 18.4 mm) in an ICF34 flange gasket (effective area 2.08 cm²). 2 This sample was placed in the sample holder. The sample holder is a vacuum container that has a primary side (gas supply side) space and a secondary side (permeate gas side) space relative to the sample (hydrogen permeable membrane), and is equipped with nozzles for gas supply and gas discharge.

[0065] Figure 1 shows a schematic diagram of the hydrogen permeability coefficient measurement apparatus. The sample holder configured as described above was set in an electric furnace and connected to the piping of a vacuum pump and various gas flow meters. Before measurement, the primary and secondary sides of the sample holder were evacuated and then replaced with hydrogen. Next, after raising the furnace temperature to a predetermined measurement temperature, hydrogen at a predetermined pressure was introduced to the primary side of the hydrogen permeable membrane. Then, the hydrogen flow rate that permeated to the secondary side was measured. The permeability coefficient was calculated from the measured flow rate of the permeated gas (hydrogen), the supply side pressure, the permeation side pressure, and the thickness of the hydrogen permeable membrane. The measurement conditions in this embodiment were as follows. ·Measurement temperature: 20℃ (293K) ~ 400℃ (673K) • Supply gas: Hydrogen (hydrogen concentration 99.99%) Primary pressure: 0.3 MPa·G Secondary pressure: 0 MPa·G • Exam duration: 2.5 hours

[0066] [Evaluation Results] Figure 2 shows the Arrhenius plot illustrating the temperature dependence of the hydrogen permeability coefficient for the PdCu-based alloy film manufactured in this embodiment. Furthermore, the hydrogen permeability of the PdCu-based alloy film in this embodiment is shown, specifically the hydrogen permeability coefficient φ at 100°C. 100 and the hydrogen permeability coefficient φ at 300°C 300 , and their ratio (φ 100 / φ 300 Table 2 summarizes the following:

[0067] [Table 2]

[0068] Referring to the measurement results of the hydrogen permeability coefficients of the PdCu alloy films in Example 1, Reference Examples 1 and 2, and Conventional Example 1 shown in Figure 2 and Table 2, it can be said that there is almost no difference in the hydrogen permeability coefficients in the high temperature range (300°C). However, the PdCu alloy film of Conventional Example 1 (47.25 atoms %Pd - 52.75 atoms %Cu) shows a drop in hydrogen permeability coefficient from around 200°C (1 / T = 0.0021), and shows the lowest values ​​at 100°C and 25°C compared to the other PdCu alloy films. In contrast, B (interstitial element E) I ) and Ag (substitutable element E S The hydrogen permeability coefficient of the PdCu-based alloy film (47.25 atoms %Pd - 52.1 atoms %Cu - 0.5 atoms %Ag - 0.15 atoms %B) in Example 1, to which ) was added, showed less of a drop in the low-temperature range as in Conventional Example 1, and exhibited a change closer to a linear decrease in the high-temperature range. The improvement in the hydrogen permeability coefficient at low temperatures in Example 1 is due to the ratio of the hydrogen permeability coefficients φ 100 / φ 300 This will become clear if you refer to the following. That is, the φ of conventional example 1 100 / φ 300 While 0.28 is the φ of Example 1, 100 / φ 300 The value is 0.5, which indicates that the hydrogen permeability coefficient of the PdCu-based alloy film in Example 1 is effectively maintained in the low-temperature range.

[0069] Also, B (interstitial element E I ) or Ag (substitutable element E S Reference Example 1 (47.25 atoms %Pd - 52.6 atoms %Cu - 0.15 atoms %B) and Reference Example 2 (47.25 atoms %Pd - 52.25 atoms %Cu - 0.5 atoms %Ag), which are PdCu-based alloy films with only one of the above added, show a ratio of hydrogen permeability coefficient φ compared to Conventional Example 1. 100 / φ 300 It is getting bigger. However, these are also φ 100 / φ 300 It is below 0.4. In other words, in order to improve the hydrogen permeability coefficient in the low temperature range, B (interstitial element E) I ) and Ag (substitutable element E S It is confirmed that both of the following must be added.

[0070] Second Embodiment In this embodiment, similar to the first embodiment, interstitial element E I B is a substitutional element, and E is a substitutional element. S While applying Ag as a substitute element, substitutional element E is added to a PdCu alloy with a basic composition of (47.25 atoms % Pd - 52.75 atoms % Cu). s We fabricated PdCu-based alloy films by varying the concentration of Ag added, and evaluated their hydrogen permeability.

[0071] The manufacturing process for the PdCu alloy film was the same as in the first embodiment. Various PdCu alloy ingots were manufactured by melt casting, and the cold rolling process was repeated while performing intermediate annealing to produce a thin film. Then, a heat treatment (400°C, 24 to 100 hours) was performed for phase transformation to the β phase. Table 3 summarizes the composition of the PdCu alloy film manufactured in this embodiment.

[0072] [Table 3]

[0073] In this embodiment as well, the cross-sections of various PdCu-based alloy films manufactured were subjected to EBSD analysis to measure the area ratio of the β phase in the cross-section. As a result, it was confirmed that the PdCu-based alloy films of Examples 2-6 and Comparative Example 2 (with a B content of 0.15 atomic% or less) all had an area ratio of 95% or more (100%) of the β phase in the cross-section. However, the β phase area ratio in the cross-section of the PdCu-based alloy film of Comparative Example 1, which had a B content exceeding 0.15 atomic%, was 86% and less than 95%. Figure 3 shows the results of the EBSD analysis of the cross-sections of the PdCu-based alloy films of Example 2 and Comparative Example 1. As shown in Figure 3, the PdCu-based alloy film of Example 2 was β-phase-ified throughout the entire cross-section, but in the PdCu-based alloy film of Comparative Example 1, a region that was not β-phase-ified (α phase) remained in the central part of the cross-section. This is presumed to be because B, added as an interstitial element, inhibits β-phase formation, and therefore β-phase formation was incomplete in Comparative Example 1, where B was added at a concentration exceeding 0.15 atomic percent.

[0074] Next, the hydrogen permeability coefficients of the PdCu-based alloy films of Examples 2-6 and Comparative Example 2 were measured in the same manner as in the first embodiment. The same apparatus and conditions as in the first embodiment were used for the measurements in this embodiment. As mentioned above, the PdCu-based alloy film of Comparative Example 1 was not β-phase-formed in the central part of the film, so it was determined that a sufficient hydrogen permeability coefficient could not be obtained even at high temperatures, and it was therefore excluded from the measurement.

[0075] The hydrogen permeability coefficient φ at 100°C for the PdCu-based alloy film manufactured in this embodiment is as follows: 100 and the hydrogen permeability coefficient φ at 300°C 300 , and their ratio (φ 100 / φ 300 Table 4 summarizes the data.

[0076] [Table 4]

[0077] From Table 4, the PdCu-based alloy films of Examples 2 to 6 (Ag addition concentration of 1.0 atomic% or less) are φ 100 and φ 300 Ratio φ 100 / φ 300 All of these values ​​were 0.4 or higher. The φ of the PdCu alloy film in Conventional Example 1 of the First Embodiment 100 / φ 300 In comparison with the value (0.20), it was confirmed that the hydrogen permeability in the low-temperature range was greatly improved in the PdCu-based alloy films of Examples 2 to 6.

[0078] On the other hand, in the PdCu-based alloy film of Comparative Example 2, where the amount of Ag added exceeds 1.0 atomic%, φ 100 / φ 300 The value of the substitution element E decreased significantly, falling below 0.4. s This is presumed to be due to the excessive addition of E. S (Ag) and interstitial element E I It was confirmed that it is necessary to set an appropriate concentration for (B).

[0079] Third Embodiment : In this embodiment, C is used as the interstitial element E I and Ag is used as the substitutional element E S to produce PdCu-based alloy films, and B is used as the interstitial element E I and Au and Al are used as the substitutional element E S to produce PdCu-based alloy films, and their hydrogen permeabilities were evaluated. Also, in this embodiment, as the conventional PdCu alloy for comparison, PdCu-based alloy films applying the above basic composition (47.25 atomic% Pd - 52.75 atomic% Cu) and the basic composition with a higher Pd concentration than this (48.3 atomic% Pd - 51.7 atomic% Cu: Comparative Example 2) were also produced. Further, for these basic compositions, one kind of PdCu-based alloy film with an intermediate Pd concentration (Pd concentration 47.8 atomic%) was produced.

[0080] The manufacturing process of the PdCu-based alloy film was the same as that of the first and second embodiments. Table 5 shows the summary of the compositions of the PdCu-based alloy films manufactured in this embodiment.

[0081]

Table 5

[0082] The cross-sections of the various PdCu-based alloy films produced were analyzed by EBSD to measure the area ratio of the β-phase on the cross-section. As a result, it was confirmed that for all the PdCu-based alloy films manufactured in this embodiment, the area ratio of the β-phase on the cross-section was 95% or more.

[0083] Then, for the PdCu-based alloy films of Examples 7 to 13, Reference Examples 3 to 7, and Comparative Example 2, the hydrogen permeability coefficients were measured in the same manner as in the first and second embodiments. For the PdCu-based alloy films manufactured in this embodiment, the hydrogen permeability coefficient φ 100 at 100 °C and the hydrogen permeability coefficient φ 300 at 300 °C, and the ratio of these (φ 100 / φ 300 ) are shown in Table 6 as the summary of the results.

[0084]

Table 6

[0085] First, regarding the PdCu-based alloy films (Examples 7 and 8) to which Al and Au were applied as the substitutional element E S in both cases, the ratio φ 100 to φ 300 was 0.4 or more. Therefore, it can be said that these metal elements are also effective in suppressing the decrease in the hydrogen permeation coefficient in the low-temperature range. On the other hand, in the present embodiment, the effects of Cr, Fe, and Mn, which are other metal elements than Ag, Au, and Al, as the substitutional element E S have also been investigated (Reference Examples 4 to 6). The PdCu-based alloy films of these reference examples had a value of φ 100 / φ 300 less than 0.4, and a decrease in the hydrogen permeation coefficient in the low-temperature range was observed. However, even in the PdCu-based alloy films added with Cr, Fe, and Mn, if they were alloy films added with Ag, which is an essential metal element, at the same time, the value of φ 100 / φ 300 became 0.4 or more (Examples 11 to 13). From these results, it was confirmed that the effect of suppressing the decrease in the hydrogen permeation coefficient by the addition of the substitutional element E S is limited to Ag, Au, and Al. However, it was also confirmed that if the above essential metal elements are included, the effect is maintained even if other metal elements are added.

[0086] Also, in the present embodiment, the PdCu-based alloy films to which C was applied as the interstitial element E I were also investigated (Examples 9 and 10). In these PdCu-based alloy films, φ 100 / φ 300 was 0.4 or more. From this result, the effectiveness of C as the interstitial element E I was confirmed.

[0087] In addition, Reference Examples 3 and 7 are for the interstitial element E I or the substitutional element E S ​​​​This is a PdCu-based alloy film to which only one of the two elements is added. Similar to the evaluation results in the first embodiment, no improvement in hydrogen permeability in the low-temperature range was observed in the PdCu-based alloy films of Reference Examples 3 and 7. To improve hydrogen permeability in the low-temperature range, interstitial element E I and substitutional element E S This also confirmed that both are necessary. [Industrial applicability]

[0088] The hydrogen permeable membrane according to the present invention is a PdCu alloy with interstitial element E I and substitutional element E S The present invention consists of a PdCu-based alloy thin film with added elements. Due to the action of these added elements, the decrease in hydrogen permeability coefficient at low temperatures, which is observed in conventional hydrogen permeable membranes made of PdCu alloy films, is suppressed in this invention. This invention is significant for the operation of various equipment and devices to which hydrogen permeable membranes are applied at low temperatures. The hydrogen permeable membrane according to the present invention is expected to be applicable not only to hydrogen purification equipment but also to hydrogen sensors where operation at low temperatures is desirable.

Claims

1. In a hydrogen permeable membrane made of a PdCu alloy, The aforementioned PdCu-based alloy is Pd in ​​an amount of 47.0 atomic% or more and 49.0 atomic% or less, Interstitial element E: 0.001 atomic% to 0.15 atomic% Ｉ and, Substitutional element E: 0.01 atomic% to 1.0 atomic% Ｓ and, The remainder consists of Cu and unavoidable impurities. The aforementioned interstitial element E Ｉ is at least one of elements B and C, The aforementioned substitution element E Ｓ It is a metallic element that essentially contains at least 0.01 atomic percent or more of Ag, Au, or Al. A hydrogen permeable membrane characterized by having a β-phase area ratio of 95% or more in any cross-section.

2. Hydrogen permeability coefficient φ at 100°C １００ and the hydrogen permeation coefficient φ at 300°C ３００ Ratio to (φ １００ / φ ３００ A hydrogen permeable membrane according to claim 1, wherein the ratio is 0.4 or more.

3. A hydrogen permeable membrane according to claim 1 or claim 2, having a thickness of 1 μm or more and 250 μm or less.

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