Hydrogen-permeable membrane composed of pdcu-based alloy

Abstract

A hydrogen-permeable membrane according to the present invention is composed of a PdCu-based alloy. The PdCu-based alloy is composed of 47.0-49.0 atom% of Pd, 0.001-0.15 atom% of an interstitial element EI, and 0.01-1.0 atom% of a substitutional element ES, where the balance is Cu and unavoidable impurities. The PdCu-based alloy contains, as the interstitial element EI, at least one element from among B, C, and N, and contains, as the substitutional element ES, a metal element necessarily including at least one of Ag, Au, and Al. The hydrogen-permeable membrane according to the present invention has improved hydrogen permeability in a low-temperature region of 200℃ or lower. Specifically, in the hydrogen-permeable membrane, the ratio (φ100 / φ300) between the hydrogen permeation coefficient φ100 at 100°C and the hydrogen permeation coefficient φ300 at 300°C is 0.4 or greater.

Description

Hydrogen-permeable membrane made of PdCu alloy

[0001] The present invention relates to a hydrogen-permeable membrane that selectively allows hydrogen to permeate from a hydrogen-containing gas, and in particular to a hydrogen-permeable membrane that has improved hydrogen permeability in the low temperature range.

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

[0003] Hydrogen-permeable membranes are materials used in devices for handling hydrogen, which are utilized in the various fields mentioned above. For example, the use of hydrogen in the fuel field requires high-purity hydrogen gas, and hydrogen purification devices using hydrogen-permeable membranes have been developed. Hydrogen sensors are also needed to measure the hydrogen concentration inside the power source and in the exhaust gas of fuel cell vehicles and the like. Hydrogen sensors are also necessary in the medical field for accurate and precise measurement of the hydrogen concentration of therapeutic gases. 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] The hydrogen-permeable membrane is made of a metal alloy that can selectively absorb and release hydrogen while diffusing it within. Among such metal alloy membranes, Pd alloy membranes (e.g., PdAg alloy and PdCu alloy) are well known, taking advantage of the selective hydrogen permeability of Pd (palladium). Hydrogen-permeable membranes made of PdCu alloys in particular have been put to practical use and are being mass-produced because they have fewer problems with hydrogen embrittlement and corrosion resistance (Patent Documents 1 and 2, Non-Patent Document 1).

[0005] JP 2001-262252 A JP 2008-12495 A

[0006] JamesRaphael Warren, “The Effect of Hydrogen on Palladium-Copper Based Membranes for Hydrogen Purification”, THE UNIVERSITY OF BIRMINGHAM, P22-29, 37-80.

[0007] The hydrogen permeation phenomenon in a hydrogen-permeable membrane made of a PdCu alloy membrane is due to atomic diffusion, and the hydrogen permeability coefficient at this time is temperature-dependent and is said to follow the so-called Arrhenius equation (Arrhenius plot). In the Arrhenius plot, the logarithm of the hydrogen permeability coefficient decreases linearly and inversely proportional to the reciprocal of temperature (1 / T). Therefore, if the hydrogen permeability coefficient at high temperatures is measured, the hydrogen permeability coefficient at low temperatures can be predicted.

[0008] However, according to the studies of the present inventors, it is difficult to predict the hydrogen permeability coefficient based on the Arrhenius plot described above for conventional hydrogen-permeable membranes made of PdCu alloys. Specifically, even if an Arrhenius plot is created based on the hydrogen permeability coefficient measured at high temperatures, the actual measured hydrogen permeability coefficient at low temperatures will be low and deviate from the Arrhenius plot. This means that hydrogen-permeable membranes made of PdCu alloys have lower than expected hydrogen permeability at low temperatures. While the temperature dependency of the hydrogen permeability coefficient itself cannot be avoided, it is undesirable for the hydrogen permeability coefficient to be lower than expected at low temperatures.

[0009] Previous studies on hydrogen-permeable membranes have mainly focused on increasing the hydrogen permeability coefficient, with not many studies on improving the temperature dependency of hydrogen-permeable membranes. This is because it is recognized that the hydrogen permeability coefficient is the most clear indicator of a hydrogen-permeable membrane's function, and that its level is important. Another factor behind this is that hydrogen-permeable membranes have traditionally been used in many applications, such as hydrogen purification equipment, which is permitted to operate at high temperatures.

[0010] However, some devices that use hydrogen-permeable membranes must operate at low temperatures. For example, hydrogen sensors for fuel cell vehicles and medical applications are designed for use at room temperature. These applications of hydrogen-permeable membranes have only recently attracted attention, but hydrogen-permeable membranes used in these new fields are required to exhibit higher hydrogen permeability at low temperatures.

[0011] The present invention has been made in light of the above background, and provides a hydrogen-permeable membrane made of a PdCu-based alloy, which has improved hydrogen permeability in the low-temperature range, which in the present invention is defined as the temperature range from room temperature (25°C) to 200°C.

[0012] To solve the above problems, the inventors investigated the causes of the decrease in hydrogen permeability of PdCu alloy membranes at low temperatures and countermeasures for this. The hydrogen permeability of PdCu alloys is exhibited in the β-phase, which has a B2 structure based on a body-centered cubic (bcc) lattice. Hydrogen exhibits hydrogen permeability by dissolving in the crystal lattice gaps of the PdCu alloy membrane in the β-phase and then moving and diffusing. Therefore, the hydrogen permeability of a PdCu alloy can be expressed as the product of the hydrogen solubility and the hydrogen mobility (ease of movement).

[0013] The present inventors have hypothesized that the reduction in hydrogen permeability of PdCu alloy membranes is due to the generation of vacancies caused by structural defects (lattice defects) in the PdCu alloy crystal. Based on computational chemistry and experimental / empirical findings, the present inventors have concluded the following regarding the relationship between structural defects in PdCu alloy crystals and the reduction in hydrogen permeability. (i) Possible structural defects in PdCu alloy crystals include Pd atom vacancies at Pd sites, Cu atom vacancies at Cu sites, and Cu vacancy-like double defects caused by the diffusion of Cu atoms into vacancies generated at Pd sites. Although the occurrence frequency of these defects differs, regardless of their occurrence, sites that trap hydrogen atoms are located near the defects, and binding energy that immobilizes hydrogen is generated at these sites. This binding energy affects hydrogen mobility. (ii) For hydrogen permeation to occur, the trapped hydrogen must move, which requires the application of energy exceeding the binding energy. (iii) The reason why the hydrogen permeability of PdCu alloys decreases at low temperatures is thought to be due to the binding energy near the defects mentioned above. When the PdCu alloy is in a high temperature range, the binding energy is relaxed by thermal energy, allowing hydrogen to migrate. However, this is difficult at low temperatures, preventing hydrogen from migrating, resulting in a decrease in hydrogen permeability.

[0014] As described above, the present inventors have considered that the decrease in hydrogen permeability at low temperatures is due to a decrease in hydrogen mobility caused by structural defects. Therefore, the present inventors have conceived the idea of ​​adding an interstitial element such as B to a PdCu alloy as a means of alleviating the binding energy and causing hydrogen migration even at low temperatures. In this regard, the results of subsequent computational chemistry studies by the present inventors have confirmed that the interstitial element introduced into a PdCu alloy enters the lattice near the structural defects, thereby alleviating the above-mentioned binding energy. Therefore, this approach can be said to contribute to improving hydrogen mobility.

[0015] However, according to the study of the present inventors, further investigation is required for the above-mentioned means. Light elements such as B and N, known as interstitial elements, are easily desorbed because they experience low binding energy within the crystal lattice of a PdCu alloy. To make a PdCu-based alloy into a hydrogen-permeable film, several processes are required, such as a melting process for producing an alloy ingot, annealing for processing, and heat treatment for converting the crystal structure to the β phase. The interstitial elements may be desorbed during such processing. If the interstitial elements are desorbed, the above-mentioned effect of relaxing the hydrogen binding energy will be lost.

[0016] Therefore, the present inventors decided to apply substitutional elements as further additive elements in order to stabilize the interstitial elements introduced into the PdCu alloy. The substitutional elements are placed in the vacancies, which are the structural defects described above. At this time, the substitutional elements generate repulsive or attractive forces due to interactions such as interatomic attractive forces with the surrounding Pd and Cu atoms, causing distortion in the crystal lattice. According to calculations by the present inventors, it is believed that this lattice distortion can restrain and stabilize the interstitial elements between the lattice.

[0017] Based on the results of the above-mentioned multi-stage investigation, the present inventors have conceived the idea of ​​simultaneously adding an interstitial element and a substitutional element to a PdCu alloy as a means of improving the hydrogen permeability of a PdCu alloy hydrogen-permeable membrane at low temperatures. They then conducted detailed studies on the range of elements suitable as substitutional and interstitial elements, and the conditions for obtaining the B2 structure (β phase) that is essentially required for functioning as a hydrogen-permeable membrane, and have conceived the present invention.

[0018] That is, the present invention solves the above-mentioned problems by providing a hydrogen-permeable film made of a PdCu-based alloy, the PdCu-based alloy containing 47.0 atomic % or more and 49.0 atomic % or less of Pd and 0.001 atomic % or more and 0.15 atomic % or less of an interstitial element E. Ｉ and a substitutional element E of 0.01 atomic % or more and 1.0 atomic % or less. Ｓ and the balance being Cu and unavoidable impurities, and the interstitial element E Ｉ is at least one element selected from B, C, and N, and the substitutional element E Ｓis a hydrogen-permeable film characterized in that it essentially contains at least one of Ag, Au, and Al as a metal element.

[0019] The structure and hydrogen permeability of the hydrogen-permeable membrane according to the present invention are described below, as well as its manufacturing method and applications. In this specification, ternary or higher alloys consisting of Pd, Cu, and other elements are referred to as PdCu-based alloys, and binary alloys consisting of Pd and Cu are referred to as PdCu alloys.

[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 contains Pd, Cu, and an interstitial element (E Ｉ ) and substitutional elements (E Ｓ PdCu alloy (PdCuE) containing I E S The functions and composition ranges of each of these constituent elements are as follows:

[0021] (A-1-1) Pd and Cu Because the hydrogen-permeable membrane according to the present invention is composed of a PdCu-based 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 a hydrogen-permeable membrane made of a PdCu-based alloy. The hydrogen permeability of a PdCu-based alloy is exhibited when its crystal system is in the β-phase, which is 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 a PdCu-based alloy and maintaining the phase structure necessary for exhibiting hydrogen permeability. Furthermore, Cu also has the effect of suppressing the decrease in strength of the PdCu-based alloy membrane due to hydrogen embrittlement.

[0022] In the PdCu-based alloy constituting the hydrogen-permeable membrane according to the present invention, the Pd concentration is set to 47.0 atomic % or more and 49.0 atomic % or less. If the Pd concentration exceeds 49.0 atomic %, it becomes difficult to develop the β phase, and it becomes difficult to obtain a sufficient amount of β phase even after heat treatment in the manufacturing process. On the other hand, since Pd is an essential element for exhibiting hydrogen permeability, a decrease in the Pd concentration leads to a decrease in the hydrogen permeability of the hydrogen-permeable membrane. Furthermore, if the Pd concentration is less than 47.0 atomic %, it becomes difficult to obtain sufficient hydrogen permeability even in high temperature regions. The Pd concentration is preferably set to 47.25 atomic % or more and 48.8 atomic % or less, and particularly preferably set to 47.75 atomic % or more and 48.5 atomic % or less. The Cu concentration is determined based on the Pd concentration and the E value described below. Ｉ Concentration and E Ｓ The remainder is the concentration of unavoidable impurities.

[0023] (A-1-2) Interstitial element (E Ｉ As described above, in the present invention, when lattice defects occur in a PdCu alloy, the interstitial element E is added as an additive element to relax the binding energy of hydrogen trapped near the defects. Ｉ This interstitial element E Ｉ is at least one of B (boron), C (carbon), and N (nitrogen).

[0024] Interstitial element E of the PdCu-based alloy constituting the hydrogen-permeable membrane according to the present invention Ｉ The concentration of is 0.001 atomic % or more and 0.15 atomic % or less. If it is less than 0.001 atomic %, the above effect is difficult to be exhibited, and no improvement in hydrogen permeability of the PdCu-based alloy at low temperatures is observed. In addition, interstitial elements such as B are elements that significantly inhibit the PdCu-based alloy from becoming β-phase. Therefore, if an excessive amount of PdCu-based alloy is added in excess of 0.15 atomic %, it becomes difficult to make it into a β-phase state. In this case, the hydrogen-permeable film will have poor hydrogen permeability not only at low temperatures but also at high temperatures. Interstitial element E Ｉ The concentration of the interstitial element E is more preferably 0.01 atomic % or more and 0.15 atomic % or less. ＩAt least one of B, C, and N is added as the element, and one of these elements may be added, or two or more elements may be added.

[0025] (A-1-3) Substitutional element (E Ｓ ) Substitutional element E Ｓ is the energy of the interstitial element (E) added to relax the binding energy of hydrogen trapped near the defect. Ｉ ) is an additive element that improves the stability of the substituted element E. Ｓ The hydrogen atoms substitute for Pd or Cu atoms in the PdCu alloy and interact with the surrounding Pd and Cu atoms to generate lattice distortion. This lattice distortion constrains the interstitial elements and promotes their solid solution. This improves the stability of the interstitial elements around the vacancies and maintains the hydrogen binding energy relaxation effect.

[0026] According to the study by the present inventors, among the metal elements that can be substitutional elements, Ag (silver), Au (gold), and Al (aluminum) are capable of exerting the above-mentioned effects. Ｓ is a metal element that essentially contains at least one of Ag, Au, and Al.

[0027] Substitutional element E of the PdCu alloy constituting the hydrogen-permeable membrane according to the present invention Ｓ The concentration of the substitutional element E is set to 0.01 atomic % or more and 1.0 atomic % or less. If it is less than 0.01 atomic %, it is difficult to achieve the above-mentioned effect. Ｓ The action of the interstitial element E Ｉ The purpose of the addition of substitutional elements is to stabilize the alloy, and it does not directly improve the hydrogen permeability. Rather, the addition of excessive substitutional elements leads to a decrease in the Cu concentration or Pd concentration in the alloy, which may hinder the formation of the β phase and cause a decrease in the hydrogen permeability in the entire temperature range, including the high temperature range. Therefore, the addition of substitutional elements E Ｓ The upper limit of the concentration of substitutional element E is 1.0 atomic %. Ｓ The concentration of is more preferably 0.1 atomic % or more and 0.5 atomic % or less.

[0028] As described above, the substitutional element E ＳIt is sufficient that at least one of Ag, Au, and Al is contained, and only one element may be added, or two or more elements may be added.

[0029] Furthermore, substitutional element E Ｓ is a metal element containing at least one of Ag, Au, and Al. Ｓ may contain metal elements other than Ag, Au, and Al. The substitutional element E is an element other than nonmetallic elements (hydrogen, halogen elements, and Group 18 elements), semimetallic elements (Si, Ge, As, Sb, Te, Se, Po, and At), and essential metal elements (Ag, Au, and Al). Specific examples of the substitutional element E include Mn, Cr, Fe, Ti, V, Co, Ni, Pt, Rh, Ru, Ir, Pt, Nb, Ta, Y, Ho, Hf, and Gd. While these other metal elements do not have the effects of Ag, Au, and Al, they have little effect on the hydrogen properties of the hydrogen-permeable film. Furthermore, Mn can be a useful additive element because it promotes β-phase formation. However, the substitutional element E Ｓ Even if the other metal element is included as the substitutional element E Ｓ The upper limit of the total concentration is 1.0 atomic %. Ｓ If the concentration of Pd or Cu becomes too high, the concentration of Pd or Cu becomes too low, which may result in a decrease in hydrogen permeability. Ｓ It is necessary that the content of is 0.01 atomic % or more.

[0030] (A-1-4) Inevitable Impurities The PdCu alloy film of the present invention contains Pd, Cu, and an interstitial element (E Ｉ ) and substitutional elements (E Ｓ However, the inclusion of unavoidable impurities is permitted. Examples of unavoidable impurities include the metalloid elements described above. The total amount of these unavoidable impurities is preferably 500 ppm or less.

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

[0032] The term "arbitrary cross section" means that the above conditions are satisfied in any cross section selected arbitrarily regardless of the direction of the PdCu-based alloy film. The area ratio should be calculated by observing the cross section of the PdCu-based alloy film in an area where both sides (both front and back ends) can be seen, and calculating the area of ​​the β phase relative to the total area of ​​the observation area. The observation area is preferably set to include both front and back ends of the PdCu-based alloy film and a width 10 times or more longer than the film thickness. The area ratio of the β phase in this arbitrary cross section is more preferably 98% or more, and the upper limit of the area ratio of the β phase is preferably 100%.

[0033] As a method for detecting the β phase in an arbitrary cross section of a PdCu-based alloy film, analysis by electron backscattered diffraction (EBSD) is effective. EBSD can obtain information on each crystal grain in the cross section of the alloy film, and this allows the distribution and area ratio of the β phase in the cross section of the alloy film to be measured and calculated.

[0034] The thickness of the PdCu-based alloy film constituting the hydrogen-permeable film 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. If the thickness exceeds 250 μm, the amount of hydrogen permeated is reduced, resulting in a decrease in purification efficiency. There are no particular restrictions on the shape of the PdCu-based film according to the present invention.

[0035] (A-3) Hydrogen Permeability of PdCu-Based Alloy Membrane According to the Present Invention The hydrogen-permeable membrane made of the PdCu-based alloy according to the present invention has excellent hydrogen permeability, particularly in the low-temperature range of 200°C or less. As described above, the hydrogen permeability coefficient of the PdCu-based alloy membrane deviates from the Arrhenius plot based on the high-temperature range in the low-temperature range, and the measured value is lower than the predicted value. In the present invention, such deviation of the hydrogen permeability coefficient in the low-temperature range is reduced.

[0036] A preferred specific embodiment of the hydrogen-permeable film according to the present invention is one having a hydrogen permeability coefficient φ at 100°C. １００ and hydrogen permeability coefficient φ at 300°C ３００ Since a decrease in the hydrogen permeability coefficient due to a decrease in temperature is inevitable, the ratio φ １００ / φ ３００ is less than 1. The hydrogen-permeable film according to the present invention suppresses the drop in hydrogen permeability coefficient in the low temperature range, thereby １００ / φ ３００ can be set to 0.4 or more. The reason why the hydrogen permeability coefficients at 100°C and 300°C are used as the characteristic evaluation standard for hydrogen-permeable films is that the hydrogen permeability coefficient tends to drop significantly around 100°C. The hydrogen permeability coefficient of PdCu-based alloy films is maximum in the range of 300°C to 400°C, and it is convenient to apply the measured value at 300°C. The hydrogen permeability coefficient φ (mol / m s Pa １ / ２ ) is calculated using the following formula:

[0037]

[0038] The ratio of the above hydrogen permeability coefficients φ １００ / φ ３００The measurement range for measuring (a) is not particularly limited as long as it is a range that includes 100°C and 300°C. The measurement range is preferably 25°C or higher and 400°C or lower. This is because the hydrogen permeability coefficient rarely reaches its maximum at temperatures above 400°C, and a decrease in the hydrogen permeability coefficient due to decomposition of the β phase is observed at temperatures higher than this. Furthermore, measuring the hydrogen permeability coefficient at 25°C or lower (room temperature or lower) requires a measuring device equipped with a cooling means, making the measurement large-scale. However, there is nothing preventing the measurement of the hydrogen permeability coefficient over a wider temperature range than 25°C or higher and 400°C or lower.

[0039] The hydrogen permeability of a PdCu alloy membrane is affected by the combined effects of the Pd concentration, Cu concentration, and the area ratio of the β phase in the cross section, as described above. Even if a hydrogen-permeable membrane has a high hydrogen permeability coefficient in the high temperature range due to an optimized alloy composition, it may be impossible to avoid a decrease in hydrogen permeability in the low temperature range. Ｉ and substitutional element E Ｓ The addition of , in cooperation with the optimization of the alloy composition and the area ratio of the β phase, aims to optimize hydrogen permeability in a temperature range including the low temperature range.

[0040] (B) Method for manufacturing hydrogen-permeable membrane according to the present invention Next, a preferred method for manufacturing a 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 of the above-mentioned composition and thinning it through plastic working such as rolling. A preferred embodiment includes heat treatment to optimize the area ratio of the β phase in the cross section of the thin film. A preferred method for manufacturing a hydrogen-permeable membrane according to the present invention will be described below.

[0041] (B-1) Manufacturing Process of PdCu-Based Alloy Film The manufacturing method of the PdCu-based alloy film is not particularly limited and can be appropriately selected depending on the film thickness, dimensions, etc. The PdCu-based alloy film can be formed by various thin film formation processes such as sputtering, vacuum deposition, chemical vapor deposition, plating, etc. Furthermore, a plate-shaped or foil-shaped PdCu-based alloy film can be manufactured by rolling an alloy ingot, etc.

[0042] In the production of a PdCu-based alloy film by the rolling method, a PdCu-based alloy ingot having the above composition is produced by a melt casting method, and then processed by an appropriate combination of hot forging, hot rolling, cold rolling, etc. to form an alloy film of a predetermined thickness. There are no particular restrictions on the processing steps from the ingot to the alloy film. However, since the introduction of processing strain in a PdCu-based alloy can promote phase transformation to the β phase, it is preferable to perform cold processing at a processing rate of 65% to 85% as the final processing step.

[0043] (B-2) Heat Treatment Process of PdCu-Based Alloy Film (Promoting Phase Transformation to β Phase) The PdCu-based alloy film having the above composition, manufactured by various methods, undergoes a phase transformation to the β phase when heat-treated within a predetermined temperature range. The heat treatment temperature is 275°C or higher and 400°C or lower. The phase transformation temperature (α phase → β phase) of the PdCu-based alloy film of the present invention varies depending on the composition even within the above composition range, but is estimated to be within the range of approximately 300°C to 400°C. Heat treatment at temperatures 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 higher in the film cross section. On the other hand, the β phase of PdCu-based alloys is known to decompose into the α phase at high temperatures, and β phase decomposition tends to occur at temperatures above 400°C. Therefore, the heat treatment temperature range is preferably 275°C or higher and 400°C or lower.

[0044] The atmosphere for the heat treatment for the phase transformation to the β phase is preferably a pressurized hydrogen-containing atmosphere, more preferably an atmosphere with a hydrogen partial pressure of 0.05 MPaG or more and 1.0 MPaG or less.

[0045] The heat treatment time is adjusted depending on the film thickness of the PdCu-based alloy film. The generation of β-phase by heat treatment proceeds from both surfaces of the PdCu-based alloy film, and the phase transformation inside the film progresses with the treatment time. In the present invention, since it is necessary to increase the area ratio of β-phase in the cross section of the PdCu-based alloy film, a sufficient heat treatment time is ensured so that the phase transformation occurs to the inside while taking the film thickness into consideration. For PdCu-based alloy films with a film thickness within the above-mentioned preferred range, the treatment time is preferably 5 hours or more. Note that, since decomposition of the β-phase is unlikely to occur if the heat treatment is performed within the above-mentioned temperature range, there is no problem with extending the treatment time.

[0046] (C) Uses of the Hydrogen-Permeable Membrane of the Present Invention The hydrogen-permeable membrane of the present invention has suitable hydrogen permeability over a wide range of temperatures, from high to low. This allows the present invention to be used in a variety of applications, such as hydrogen sensors, in addition to hydrogen purification devices (hydrogen purification processes).

[0047] (C-1) Hydrogen Purification Process and Hydrogen Purification Apparatus The hydrogen-permeable membrane according to the present invention is capable of purifying hydrogen by selectively allowing hydrogen to permeate from a hydrogen-containing gas (feed).

[0048] In this hydrogen purification process, it is preferable to set the treatment temperature (usage temperature) using the hydrogen-permeable membrane appropriately. The hydrogen purification method using a PdCu-based alloy membrane of the present invention has a suitable treatment temperature of 25°C or higher and 400°C or lower. In this treatment temperature range, the PdCu-based alloy membrane of the present invention can exhibit suitable hydrogen permeability that is distinguishable from conventional techniques, particularly in the low-temperature range. However, at temperatures exceeding 400°C, even the PdCu-based alloy membrane of the present invention may experience decomposition of the β phase, resulting in a decrease in the hydrogen permeability coefficient. Therefore, the upper limit of the suitable treatment temperature is 400°C.

[0049] The treatment temperature here refers to the temperature at which the hydrogen-containing gas to be purified comes into contact with and permeates the hydrogen-permeable membrane. The treatment temperature is adjusted by adjusting at least one of the temperature of the hydrogen-containing gas, the temperature of the hydrogen-permeable membrane, and the ambient temperature within the hydrogen production (purification) device within the above temperature range.

[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, the pressure on the primary side is made higher than that on the other side (secondary side) of the hydrogen-permeable membrane, and purified hydrogen that has permeated the hydrogen-permeable membrane is extracted. There are no particular restrictions on the pressure difference at this time.

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

[0052] The above hydrogen purification method is carried out by a hydrogen purification device that employs the hydrogen-permeable membrane of the present invention. The main components of this hydrogen purification device, other than the hydrogen-permeable membrane, can be the same as those of known hydrogen purification devices. When installing the hydrogen-permeable membrane in the hydrogen-permeable device, a gas-permeable support may be combined with the hydrogen-permeable membrane to supplement its mechanical strength. Examples of the support that can be used include metal mesh and porous sintered materials. However, a support is not essential, as the thickness of the hydrogen-permeable membrane may be sufficient to ensure mechanical strength.

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

[0054] Hydrogen sensors that use hydrogen-permeable membranes include gas sensors that use rare earth metals such as Y and La or semiconductor metal oxides such as Ga2O3 and SrTiO3 as the hydrogen detection element. In hydrogen sensors, hydrogen-permeable membranes are used as protective membranes that selectively allow hydrogen to permeate and supply hydrogen to the hydrogen detection element. In recent years, the development of concentration-cell-type hydrogen sensors has been reported. In concentration-cell-type hydrogen sensors, hydrogen-permeable membranes are used as the reference electrode and 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 of the present invention exhibits excellent hydrogen selectivity over a wide temperature range and constitutes the sensitive portion of various hydrogen sensors.

[0055] As explained above, the hydrogen-permeable membrane made of the PdCu-based alloy according to the present invention has excellent hydrogen permeability at low temperatures. The hydrogen permeability coefficient of a hydrogen-permeable membrane is expected to have a temperature dependency that follows an Arrhenius plot, and the present invention has hydrogen permeability that follows this tendency even at low temperatures.

[0056] 1 is a diagram showing the configuration of a hydrogen permeability measurement device used in the first and second embodiments. 2 is an Arrhenius plot of the hydrogen permeability coefficients of the PdCu-based alloy membranes of Example 1, Reference Examples 1 and 2, and Conventional Example 1, which are manufactured in the first embodiment. 3 is a diagram showing the results of EBSD analysis of the cross sections of the PdCu-based alloy membranes of Example 2 (B concentration: 0.05 atomic %) and Comparative Example 1 (B concentration: 0.2 atomic %), which are manufactured in the second embodiment.

[0057] First embodiment: Hereinafter, an embodiment of the present invention will be described. In this embodiment, an interstitial element E Ｉ B as a substitutional element E Ｓ A PdCu alloy membrane containing Ag was manufactured as a catalyst, and its hydrogen permeability coefficient was measured from high temperature to low temperature.

[0058] In this embodiment, the PdCu alloy to which each additive element is added has a basic composition of 47.25 atomic % Pd-52.75 atomic % Cu (this is referred to as Conventional Example 1), to which both Ag and B are added, to produce a PdCu-based alloy film (Example 1), and a PdCu-based alloy film to which either Ag or B is added (Reference Examples 1 and 2). That is, with respect to the basic composition (Conventional Example 1), the Pd concentration is not changed, and the Cu concentration is adjusted to add Ag and B. The composition of the PdCu-based alloy was set in this manner because, since the hydrogen permeability of the PdCu-based alloy membrane is largely dependent on Pd, it was considered preferable to make the Pd concentration uniform when comparing each sample. The PdCu-based alloy membrane was produced as follows.

[0059] [Production of PdCu-based alloy film] A PdCu-based alloy ingot of the target composition was produced by melt casting, and the ingot surface was chamfered and cleaned. Then, the PdCu-based alloy ingot was subjected to repeated cold rolling processes to produce a thin film. The rolling process was repeated multiple times with intermediate annealing at 600 to 900°C, and the final rolling was performed at a processing rate of 70%. In this embodiment, a PdCu-based alloy film with a thickness of 30 μm was produced.

[0060] Next, the PdCu-based 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 adding or not adding B. The composition of the PdCu-based alloy film produced in this embodiment is summarized in Table 1.

[0061]

[0062] [Cross-section analysis of PdCu alloy film] For various PdCu alloy films manufactured in this embodiment, the cross section was analyzed by EBSD, and the area ratio of the β phase in the cross section in the observation area was measured. As a pretreatment for EBSD analysis, the sample cross section was polished to a diamond paste of 0.25 μm, and then the surface was milled using an ion milling device (IM4000 manufactured by Hitachi High-Tech Corporation). 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, argon gas flow rate 0.07 cm ３ The surface was milled for 20 minutes under the condition of 0.15 rpm / min.

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

[0064] [Measurement of Water Permeability Coefficient of PdCu-Based Alloy Membrane] Next, the hydrogen permeability coefficient was measured for the PdCu-based alloy membranes of Example 1, Reference Examples 1 and 2, and Conventional Example 1. The produced hydrogen-permeable membrane was cut into a circular shape with a diameter of 21.3 mm. This hydrogen-permeable membrane was sandwiched together with a stainless steel wire mesh (diameter 18.4 mm) between an ICF34 flange gasket to prepare a sample (effective area 2.08 cm). ２ This sample was set in a sample holder. The sample holder is a vacuum vessel that has a primary space (gas supply side) and a secondary space (permeation gas side) for the sample (hydrogen-permeable membrane), and is equipped with nozzles for gas supply and gas discharge.

[0065] FIG. 1 shows an outline of the hydrogen permeability coefficient measurement device. The sample holder constructed as described above was set in an electric furnace and connected to a vacuum pump and the piping of various gas flow meters. Prior to measurement, the primary and secondary sides of the sample holder were evacuated and then replaced with hydrogen. Next, the furnace was heated to a predetermined measurement temperature, and hydrogen at a predetermined pressure was introduced into the primary side of the hydrogen-permeable membrane. The flow rate of hydrogen that had permeated to the secondary side was then measured. The permeability coefficient was calculated from the measured flow rate of the permeable 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°C (293K) to 400°C (673K) Supply gas: hydrogen (hydrogen concentration 99.99%) Primary-side pressure: 0.3 MPa·G Secondary-side pressure: 0 MPa·G Test time: 2.5 hours

[0066] [Evaluation Results] The Arrhenius plot showing the temperature dependence of the hydrogen permeability coefficient of the PdCu-based alloy membrane produced in this embodiment is shown in Figure 2. In addition, regarding the hydrogen permeability of the PdCu-based alloy membrane in this embodiment, the hydrogen permeability coefficient φ at 100°C was １００ and hydrogen permeability coefficient φ at 300°C ３００ , and the ratio of these (φ １００ / φ ３００ ) are summarized in Table 2.

[0067]

[0068] Referring to the measurement results of the hydrogen permeability coefficients of the PdCu alloy membranes of 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 coefficient in the high temperature range (300°C). However, the PdCu alloy membrane of Conventional Example 1 (47.25 atomic % Pd-52.75 atomic % Cu) shows a drop in the hydrogen permeability coefficient from around 200°C (1 / T = 0.0021), and shows the lowest value compared to the other PdCu alloy membranes at 100°C and 25°C. In contrast, B (interstitial element E Ｉ ) and Ag (substitutional element E ＳThe hydrogen permeability coefficient of the PdCu alloy membrane of Example 1 (47.25 atomic % Pd-52.1 atomic % Cu-0.5 atomic % Ag-0.15 atomic % B) to which ZnO was added showed little drop in the low temperature range as in Conventional Example 1, and showed a change that was close to a linear decreasing trend in the high temperature range. The improvement in the hydrogen permeability coefficient at low temperatures in Example 1 was due to the increase in the ratio of hydrogen permeability coefficients φ １００ / φ ３００ That is, the φ of Conventional Example 1 is １００ / φ ３００ is 0.28, while φ in Example 1 １００ / φ ３００ is 0.5, and it can be said that the PdCu-based alloy membrane of Example 1 effectively maintains the hydrogen permeability coefficient in the low temperature range.

[0069] In addition, B (interstitial element E Ｉ ) or Ag (substitutional element E Ｓ % Cu-0.5 atomic % Ag), which are PdCu-based alloy films containing only one of the two, have a hydrogen permeability coefficient ratio φ １００ / φ ３００ However, these are also larger than φ １００ / φ ３００ is less than 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 (substitutional element E Ｓ It is confirmed that the addition of both

[0070] Second embodiment: In this embodiment, similarly to the first embodiment, an interstitial element E Ｉ B as a substitutional element E Ｓ While Ag is used as the base element, a substitutional element E is added to a PdCu alloy having a basic composition (47.25 atomic % Pd-52.75 atomic % Cu). ｓ As a result, PdCu alloy membranes were produced by varying the concentration of Ag added, and the hydrogen permeability was evaluated.

[0071] The manufacturing process of the PdCu-based alloy film was the same as that of the first embodiment. Various PdCu-based alloy ingots were manufactured by melt casting, and then subjected to intermediate annealing and repeated cold rolling processes to form thin films. Then, heat treatment (400°C, 24 to 100 hours) was performed to transform the PdCu-based alloy into the β phase. The compositions of the PdCu-based alloy films manufactured in this embodiment are summarized in Table 3.

[0072]

[0073] The cross sections of various PdCu-based alloy films produced in this embodiment were also 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 to 6 and Comparative Example 2 (with a B content of 0.15 atomic % or less) all had an area ratio of the β phase in the cross section of 95% or more (100%). However, the area ratio of the β phase in the cross section of the PdCu-based alloy film of Comparative Example 1, in which the B content exceeded 0.15 atomic %, was 86%, less than 95%. The results of the EBSD analysis of the cross sections of the PdCu-based alloy films of Example 2 and Comparative Example 1 are shown in Figure 3. As shown in Figure 3, the PdCu-based alloy film of Example 2 was converted to the β phase throughout the entire cross section, while the PdCu-based alloy film of Comparative Example 1 had a region (α phase) that was not converted to the β phase in the central part of the cross section. This is presumably because B, which is added as an interstitial element, has the effect of inhibiting the formation of the β phase, and the formation of the β phase was incomplete in Comparative Example 1, in which B was added at a concentration exceeding 0.15 atomic %.

[0074] Next, the hydrogen permeability coefficients of the PdCu-based alloy membranes of Examples 2 to 6 and Comparative Example 2 were measured in the same manner as in the first embodiment. The measurements in this embodiment were performed using the same equipment and conditions as in the first embodiment. As for the PdCu-based alloy membrane of Comparative Example 1, since the central part of the membrane was not converted to the β phase as described above, it was determined that a sufficient hydrogen permeability coefficient could not be obtained even in the high temperature range, and therefore it was not measured.

[0075] The hydrogen permeability coefficient φ at 100°C for the PdCu alloy membrane manufactured in this embodiment １００ and hydrogen permeability coefficient φ at 300°C ３００ , and the ratio of these (φ １００ / φ ３００ ) are summarized in Table 4.

[0076]

[0077] From Table 4, the PdCu alloy films of Examples 2 to 6 (with Ag added at a concentration of 1.0 atomic % or less) have a φ １００ and φ ３００ Ratio to φ １００ / φ ３００ The φ of the PdCu alloy film of Conventional Example 1 of the first embodiment was 0.4 or more. １００ / φ ３００ In comparison with the value (0.20) of Example 1, it was confirmed that the PdCu-based alloy membranes of Examples 2 to 6 also had a significantly improved hydrogen permeability in the low temperature range.

[0078] On the other hand, in the PdCu-based alloy film of Comparative Example 2 in which the amount of Ag added was more than 1.0 atomic %, φ １００ / φ ３００ The value of was significantly reduced to less than 0.4. ｓ Therefore, from the results of the study in this embodiment, it is considered that the substitutional element E is necessary to function as a hydrogen permeable membrane and ensure hydrogen permeability in the low temperature range. Ｓ (Ag) and interstitial element E Ｉ It was confirmed that it is necessary to set an appropriate concentration of (B).

[0079] Third embodiment: In this embodiment, an interstitial element E Ｉ C as a substitutional element E Ｓ PdCu alloy film using Ag as an interstitial element E Ｉ B as a substitutional element E Ｓ PdCu-based alloy membranes were manufactured using Au and Al as the Pd-based metals, and their hydrogen permeability was evaluated. In this embodiment, PdCu-based alloy membranes were also manufactured using the above-mentioned basic composition (47.25 atomic % Pd-52.75 atomic % Cu) and a basic composition with a higher Pd concentration (48.3 atomic % Pd-51.7 atomic % Cu: Conventional Example 2) as comparative conventional PdCu alloys. Furthermore, one PdCu-based alloy membrane was manufactured with a composition (Pd concentration 47.8 atomic %) with an intermediate Pd concentration compared to these basic compositions.

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

[0081]

[0082] The cross sections of the various PdCu-based alloy films produced 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 area ratio of the β phase in the cross section of each of the PdCu-based alloy films produced in this embodiment was 95% or more.

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

[0084]

[0085] First, substitutional element E Ｓ Regarding the PdCu alloy films (Examples 7 and 8) using Al and Au as the conductors, both of them had a φ １００ and φ ３００ Ratio to φ １００ / φ ３００ Therefore, it can be said that these metal elements are also effective in suppressing the decrease in hydrogen permeability coefficient in the low temperature range. Ｓ The effects of metal elements other than Ag, Au, and Al, such as Cr, Fe, and Mn, were also investigated (Reference Examples 4 to 6). １００ / φ ３００ However, even in the case of a PdCu-based alloy membrane to which Cr, Fe, and Mn are added, if Ag, an essential metal element, is added at the same time, the value of φ １００ / φ ３００ The value of was 0.4 or more (Examples 11 to 13).Ｓ It was confirmed that the effect of suppressing the decrease in hydrogen permeability coefficient by adding Ag, Au, and Al was limited to Ag, Au, and Al. However, it was also confirmed that the effect was maintained even if other metal elements were added, as long as the above-mentioned essential metal elements were included.

[0086] In this embodiment, the interstitial element E Ｉ PdCu-based alloy films using C as the ion exchange film were also investigated (Examples 9 and 10). １００ / φ ３００ From the results, it can be seen that the interstitial element E Ｉ The effectiveness of C as a

[0087] In addition, in Reference Examples 3 and 7, the interstitial element E Ｉ or substitutional element E Ｓ As in the evaluation results of the first embodiment, the PdCu alloy membranes of Reference Examples 3 and 7 did not show any improvement in hydrogen permeability in the low temperature range. Ｉ and substitutional element E Ｓ It was also confirmed here that both are necessary.

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

Claims

1. A hydrogen-permeable film made of a PdCu-based alloy, wherein the PdCu-based alloy contains 47.0 atomic % or more and 49.0 atomic % or less of Pd and 0.001 atomic % or more and 0.15 atomic % or less of an interstitial element E. Ｉ and a substitutional element E of 0.01 atomic % or more and 1.0 atomic % or less. Ｓ and the balance being Cu and unavoidable impurities, Ｉ is at least one element selected from B, C, and N, and the substitutional element E Ｓ A hydrogen-permeable film characterized in that the metal element essentially contains at least one of Ag, Au, and Al.

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

3. Hydrogen permeability coefficient φ at 100℃ １００ and hydrogen permeability coefficient φ at 300°C ３００ Ratio to (φ １００ / φ ３００ 3. The hydrogen-permeable membrane according to claim 1, wherein the value of (a) is 0.4 or more.

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

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