HYDROGEN PERMEATION MEMBRANE MADE OF PdCu-BASED ALLOY

Abstract

To provide a hydrogen permeation membrane made of PdCu-based alloy, in which hydrogen permeability in low temperature region of 150°C or less is improved.SOLUTION: A hydrogen permeable membrane made of a PdCu-based alloy according to the present invention is characterized in that the PdCu alloy contains 47.0 atom% or more and 49.0 atom% or less of Pd, 0.01 atom% or more and 0.75 atom% or less of Ag, with the remainder being Cu and unavoidable impurities. In the hydrogen permeable membrane of the present invention, the ratio of the hydrogen permeability coefficient φ100 at 100°C to the hydrogen permeability coefficient φ300 at 300°C (φ100 / φ300) is 0.4 or more, and the decrease in the hydrogen permeability coefficient in the low temperature range is suppressed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[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 at low temperatures compared to conventional techniques. [Background technology]

[0002] Hydrogen is widely used in various fields, such as as a hydrogen source and 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 in fuel cells that power automobiles and heavy machinery, and in hydrogen engines. Furthermore, hydrogen is also attracting attention in the field of advanced medicine, and the effectiveness of hydrogen inhalation therapy for post-cardiac arrest syndrome has been reported.

[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] Hydrogen-permeable membranes are made of metal alloys that can selectively absorb and release hydrogen while diffusing it within. Among such metal alloy membranes, Pd alloy membranes (such as PdAg-based alloys and PdCu-based alloys) are well known, taking advantage of the selective hydrogen permeability of Pd (palladium). Hydrogen-permeable membranes made of PdCu-based alloys are becoming increasingly popular and are being mass-produced, as they are less susceptible to problems such as hydrogen embrittlement and poor corrosion resistance (Patent Documents 1 and 2, Non-Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-262252 [Patent Document 2] Japanese Patent Application Laid-Open 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. Summary of the Invention [Problem to be solved by the invention]

[0007] The phenomenon of hydrogen permeation through a hydrogen-permeable membrane made of a PdCu-based 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 an Arrhenius plot, the logarithm of the hydrogen permeability coefficient is negatively proportional to the reciprocal of temperature (1 / T), so by measuring the hydrogen permeability coefficient in a certain temperature range, it is possible to predict the hydrogen permeability coefficient in other temperature ranges.

[0008] However, according to the studies of the present inventors, the predictability of the hydrogen permeability coefficient based on the Arrhenius plot described above is not sufficient for hydrogen-permeable membranes made of PdCu-based alloys. Specifically, even if an Arrhenius plot is created based on hydrogen permeability coefficients measured at high temperatures, the measured hydrogen permeability coefficients at low temperatures deviate from the Arrhenius plot and are lower than the predicted values. In other words, hydrogen-permeable membranes made of PdCu-based alloys exhibit a greater-than-expected decrease in hydrogen permeability at low temperatures. While the temperature dependency of hydrogen permeability cannot be avoided, such a greater-than-expected decrease in hydrogen permeability coefficient is undesirable.

[0009] Previous studies on hydrogen-permeable membranes have focused mainly on increasing the hydrogen permeability coefficient, with not many studies on improving the temperature dependency of hydrogen-permeable membranes. This is because the hydrogen permeability coefficient is the clearest indicator of a hydrogen-permeable membrane's function. 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 intended for use at room temperature. These applications of hydrogen-permeable membranes have only recently attracted attention, but the hydrogen-permeable membranes used in these applications require 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 that has improved hydrogen permeability in the low-temperature range, which in the present invention refers to the temperature range from room temperature (25°C) to 150°C. [Means for solving the problem]

[0012] To solve the above problems, the inventors investigated the causes of the decrease in hydrogen permeability of PdCu-based alloy membranes at low temperatures and countermeasures for this. The hydrogen permeability of PdCu-based alloys is exhibited in the β phase of the B2 structure based on the bcc (body-centered cubic lattice). Hydrogen absorbed in a PdCu alloy membrane in this state diffuses through the gaps in the PdCu body-centered cubic lattice, thereby exhibiting hydrogen permeability.

[0013] According to the inventors' estimation, the cause of the decrease in hydrogen permeability of PdCu-based alloy membranes is thought to be the generation of vacancies due to lattice defects in the PdCu alloy crystal. Vacancies in PdCu alloys (body-centered cubic lattice) can occur at both Pd and Cu sites. When vacancies occur, hydrogen is trapped there and cannot be desorbed unless a certain amount of energy is applied. If the hydrogen-permeable membrane is at high temperatures, hydrogen can be desorbed by applying thermal energy. However, hydrogen desorption is difficult in low-temperature regions where thermal energy is scarce, and this is thought to cause a greater-than-expected decrease in hydrogen permeability.

[0014] If the decrease in hydrogen permeability at low temperatures is due to hydrogen trapping in vacancies, one possible solution is to add another element to the alloy system. When vacancies occur due to lattice defects, the added element replaces the vacancy, thereby continuing hydrogen diffusion and maintaining hydrogen permeability. Therefore, the inventors investigated additional elements that have such an effect and found that Ag is a particularly preferable additional element, leading to the invention.

[0015] That is, the present invention, which solves the above problems, is a hydrogen-permeable membrane made of a PdCu-based alloy, characterized in that the PdCu alloy contains 47.0 atomic % to 49.0 atomic % of Pd, 0.01 atomic % to 0.75 atomic % of Ag, and the balance being Cu and unavoidable impurities. Below, the structure and hydrogen permeability of the hydrogen-permeable membrane according to the present invention are explained, as well as its manufacturing method and applications.

[0016] (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 is made of a PdCu-based alloy (PdCuAg alloy) whose constituent elements are Pd, Cu, and Ag, excluding unavoidable impurities as described below. The functions and composition ranges of these constituent elements are as follows:

[0017] (A-1-1) Pd and Cu Since the hydrogen-permeable membrane according to the present invention is a PdCu-based alloy containing Ag, 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 bcc structure. Cu is an essential additive metal for promoting the phase transformation from the α phase to the β phase in the 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.

[0018] 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 during 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 at high temperatures. The Pd concentration is preferably set to 47.25 atomic % or more and 48.8 atomic % or less, and particularly preferably to 47.75 atomic % or more and 48.5 atomic % or less. The Cu concentration is the remainder of the Pd concentration, the Ag concentration (described below), and the concentration of unavoidable impurities.

[0019] (A-1-2)Ag Ag is an additive element that preferentially substitutes for vacancies when lattice defects occur in PdCu-based alloys, thereby suppressing hydrogen trapping and fixation and suppressing a decrease in hydrogen permeability at low temperatures. This vacancy filling effect and the suppression of a decrease in hydrogen permeability at low temperatures can also be achieved with metal elements other than Ag. However, according to the inventors' studies, Ag is particularly effective in improving hydrogen permeability at low temperatures. This is presumably due to Ag's high selectivity for vacancies. Therefore, in the present invention, Ag is specified as an additive element to the PdCu alloy membrane.

[0020] The Ag concentration in the PdCu-based alloy of the hydrogen-permeable membrane according to the present invention is set to 0.01 atomic % or more and 0.75 atomic % or less. If the Ag concentration is less than 0.01 atomic %, there is no effect of adding Ag. On the other hand, adding Ag in excess of 0.75 atomic % reduces the overall hydrogen permeability of the PdCu-based alloy membrane, worsening hydrogen permeability not only in the low temperature range but also in the high temperature range. The Ag concentration is preferably set to 0.1 atomic % or more and 0.5 atomic % or less, and particularly preferably to 0.15 atomic % or more and 0.38 atomic % or less.

[0021] (A-1-3) Inevitable impurities The PdCu-based alloy film of the present invention is composed of Pd, Cu, and Ag, and does not contain any other intentionally added elements. However, the inclusion of unavoidable impurities is permitted. Examples of unavoidable impurities include Fe and Si. The total amount of these unavoidable impurities is preferably 500 ppm or less.

[0022] (A-2) Crystal structure of PdCu alloy film Considering that hydrogen permeability in PdCu-based alloys is exhibited in the β-phase state, 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.

[0023] 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 alloy film. The area ratio should be calculated by observing the cross section of the PdCu alloy film in an area where both sides (both front and back ends) of the PdCu alloy film are visible, and calculating the area of the β phase relative to the total area of the observation region. The observation region is preferably set to include both front and back ends of the PdCu 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%.

[0024] Electron backscattered diffraction (EBSD) analysis is an effective method for detecting the β phase in any cross section of a PdCu alloy film. EBSD can obtain information on each crystal grain in the cross section of the alloy film, allowing the distribution and area ratio of the β phase in the cross section of the alloy film to be measured and calculated.

[0025] 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.

[0026] (A-3) Hydrogen permeability of the PdCu alloy membrane according to the present invention The hydrogen-permeable membrane made of a PdCu-based alloy according to the present invention has excellent hydrogen permeability, particularly in the low-temperature range of 150°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 at low temperatures, and measured values are lower than the predicted values. In the present invention, this deviation in the hydrogen permeability coefficient at low temperatures is reduced.

[0027] 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℃ 300 The ratio of φ to 0.4 is unavoidable. 100 / φ 300 is less than 1. The hydrogen-permeable film of the present invention suppresses the drop in hydrogen permeability coefficient in the low temperature range, thereby 100 / φ 300can be set to 0.4 or more. The reason why the hydrogen permeability coefficients at 100°C and 300°C are used as the performance evaluation standard for hydrogen-permeable membranes is that the hydrogen permeability coefficient tends to drop significantly around 100°C. The hydrogen permeability coefficient of PdCu-based alloy membranes is at its 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:

[0028]

number

[0029] The ratio of the above hydrogen permeability coefficients φ 100 / φ 300 The measurement range for the measurement of 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. Measurements below 25°C are not particularly meaningful. In addition, 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. However, there is nothing preventing the measurement of the hydrogen permeability coefficient from being measured over a wider range than 100°C or higher and 400°C or lower.

[0030] The hydrogen permeability of a PdCu-based alloy membrane is a function of the combined effects of the Pd concentration, Cu concentration, and the area fraction of the β phase in the cross section, as described above. Even if a hydrogen-permeable membrane has a high hydrogen permeability coefficient at high temperatures due to an optimized alloy composition, it may be impossible to avoid a decrease in hydrogen permeability at low temperatures. The addition of Ag to the PdCu alloy in the present invention, in cooperation with the optimization of the alloy composition and the area fraction of the β phase, optimizes hydrogen permeability across a wide temperature range, including low temperatures.

[0031] (B) Method for manufacturing a hydrogen-permeable membrane according to the present invention Next, a preferred method for producing a hydrogen-permeable membrane according to the present invention will be described. The hydrogen-permeable membrane according to the present invention can be produced by preparing a PdCu-based alloy of the above-described composition and reducing the thickness of the membrane through plastic working such as rolling. A preferred embodiment of the method includes heat treatment to optimize the area ratio of the β phase in the cross section of the membrane. A preferred method for producing a hydrogen-permeable membrane according to the present invention will be described below.

[0032] (B-1) Manufacturing process of PdCu alloy film The method for producing the PdCu alloy film is not particularly limited and can be appropriately selected depending on the film thickness, dimensions, etc. PdCu alloy films can be produced by various thin film formation processes such as sputtering, vacuum deposition, chemical vapor deposition, plating, etc. Furthermore, plate- or foil-shaped PdCu alloy films can be produced by rolling an alloy ingot, etc.

[0033] 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 melting and 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 the 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.

[0034] (B-2) Heat treatment process of PdCu alloy film (promoting phase transformation to β phase) Furthermore, PdCu-based alloy films having the above-described compositions, produced by various manufacturing methods, undergo a phase transformation to the β phase when heat-treated within a predetermined temperature range. The heat-treatment temperature is set to 275°C or higher and 400°C or lower. The phase transformation temperature (α phase to β phase) of the PdCu-based alloy film of the present invention varies depending on the composition even within the above-described 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 to 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 set to 275°C or higher and 400°C or lower.

[0035] 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.

[0036] The heat treatment time is adjusted depending on the film thickness of the PdCu-based alloy film. The generation of the β phase by heat treatment proceeds from both surfaces of the PdCu-based alloy film, and the phase transformation inside the film progresses as the treatment time increases. In the present invention, it is necessary to increase the area ratio of the β phase in the cross section of the PdCu-based alloy film, so 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, a treatment time of 5 hours or more is preferable. 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.

[0037] (C) Use of the hydrogen-permeable membrane according to the present invention The hydrogen-permeable membrane according to the present invention has suitable hydrogen permeability over a wide temperature range, from high to low, and can therefore be used in a variety of applications, including hydrogen sensors, in addition to hydrogen purification devices (hydrogen purification processes).

[0038] (C-1) Hydrogen purification process and hydrogen purification equipment 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).

[0039] In this hydrogen purification process, it is preferable to set the treatment temperature (usage temperature) using the hydrogen-permeable membrane appropriately. In the hydrogen purification method using a PdCu-based alloy membrane of the present invention, the treatment temperature is preferably 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 favorable hydrogen permeability that is differentiated 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.

[0040] 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 inside the hydrogen production (purification) device within the above temperature range.

[0041] In the purification of gases containing hydrogen, 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 the purified hydrogen that has permeated the hydrogen-permeable membrane is extracted. There are no particular restrictions on the pressure difference at this time.

[0042] 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.

[0043] 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.

[0044] (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 in hydrogen sensors.

[0045] 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. [Effects of the Invention]

[0046] The hydrogen permeability coefficient of a hydrogen-permeable membrane is expected to have a temperature dependency that conforms to an Arrhenius plot, and the present invention exhibits hydrogen permeability that conforms to this trend even at low temperatures. The hydrogen-permeable membrane made of a PdCu-based alloy according to the present invention exhibits hydrogen permeability that is better than that of conventional techniques, even at low temperatures of 150°C or less. [Brief explanation of the drawings]

[0047] [Figure 1] FIG. 2 is a diagram showing the configuration of a hydrogen permeability coefficient measuring device used in the present embodiment. [Figure 2] 1 is an Arrhenius plot showing the temperature dependence of the hydrogen permeability coefficient of a PdCu-based alloy membrane (basic composition: 48.3 atomic % Pd-51.7 atomic % Cu) of group A produced in this embodiment. [Figure 3] 1 is an Arrhenius plot showing the temperature dependence of the hydrogen permeability coefficient of a PdCu-based alloy membrane of group B (basic composition: 47.25 atomic % Pd-52.75 atomic % Cu) produced in this embodiment. [Figure 4] 1 is an Arrhenius plot showing the temperature dependence of the hydrogen permeability coefficient of a PdCu-based alloy membrane of group C (basic composition: 48.5 atomic % Pd-51.5 atomic % Cu) produced in this embodiment. [Figure 5] 1 is an example of an Arrhenius plot showing the temperature dependence of the hydrogen permeability coefficient of a PdCu-based alloy membrane (PdCuAl alloy membrane) manufactured as a reference example. [Figure 6] 1 is an example of an Arrhenius plot showing the temperature dependence of the hydrogen permeability coefficient of a PdCu-based alloy membrane (PdCuMn alloy membrane) produced as a reference example. DETAILED DESCRIPTION OF THE INVENTION

[0048] Hereinafter, an embodiment of the present invention will be described. In this embodiment, a hydrogen-permeable membrane made of a PdCu alloy and a hydrogen-permeable membrane made of a PdCuAg alloy in which Ag was added to a PdCu alloy were manufactured. Then, the hydrogen permeability coefficient of each hydrogen-permeable membrane was measured over a range from high to low temperatures. In this embodiment, PdCuAg alloy membranes were manufactured by using the PdCu alloys of the following three groups A to C as basic alloy compositions and adding 0.15 atomic % to 1.0 atomic % of Ag to these PdCu alloys. Group A: 48.3 atomic % Pd-51.7 atomic % Cu Group B: 47.25 atomic % Pd-52.75 atomic % Cu Group C: 48.5 atomic % Pd-51.5 atomic % Cu

[0049] In adjusting the composition of the PdCuAg alloys in the above three groups, the Pd concentration was left unchanged, but the Cu concentration was adjusted and Ag was added. This was done to replace the added Ag with Cu. The reason for setting the composition in this way was that the hydrogen permeability of the PdCu alloy membrane is largely dependent on Pd, and as mentioned above, Ag exerts its effect by substituting for vacancies in the PdCu alloy. The PdCu alloy membranes were manufactured as follows.

[0050] [Production of PdCu-based alloy film] A PdCu-based alloy ingot having a target composition was produced by melt casting, and the ingot surface was chamfered and cleaned. The PdCu-based alloy ingot was then 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 reduction ratio was 70%. In this embodiment, a PdCu-based alloy film having a thickness of 30 μm to 100 μm was produced. Next, the PdCu-based alloy film was heat-treated to promote the β-phase transformation. The heat treatment was performed in hydrogen at 0.30 MPaG at a heat treatment temperature of 300°C or 400°C for 24 hours. Table 1 summarizes the composition, film thickness, and heat treatment temperature of the PdCu-based alloy film produced in this embodiment.

[0051] [Table 1]

[0052] [Cross-sectional analysis of PdCu alloy film] The cross sections of the various PdCu alloy films produced were subjected to EBSD analysis, and the area ratio of the β phase in the cross section of the observation area was measured. As a pretreatment for EBSD analysis, the sample cross sections were polished to a fineness of 0.25 μm using diamond paste, 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. 3The surface was milled for 20 minutes under the conditions of 1 / min.

[0053] EBSD analysis was performed using an ultra-high-resolution analytical scanning electron microscope (SU-70, Hitachi High-Tech Corporation; NORDLYS-MAX3, Oxford Instruments). The analysis conditions were: pitch 0.2 μm, pinning mode 4x4, 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. The area fraction of the β phase (lattice constant 2.9662 Å) was measured using the image analysis software provided with the analyzer.

[0054] EBSD analysis confirmed that the PdCu-based alloy films (A-1 to A-5, B-1 to B-3, and C-1 to C-2) produced in this embodiment all had a β-phase area ratio of 95% or more in the cross section. In particular, the PdCu-based alloy films B-1 to B-3 had a β-phase area ratio of 100%. Furthermore, the β-phase area ratios of the PdCu-based alloy films A-1 to A-5 were in the range of 99.9% to 100%, and the β-phase area ratios of the PdCu-based alloy films C-1 to C-2 were 99.0% or more.

[0055] [Measurement of water permeability coefficient of PdCu alloy membrane] Next, the hydrogen permeability coefficient was measured for the hydrogen-permeable membranes (PdCu-based alloy membranes) produced by heat treatment at each temperature. The produced hydrogen-permeable membranes were cut into discs with a diameter of 21.3 mm. Samples were prepared by sandwiching this hydrogen-permeable membrane and a stainless steel wire mesh (diameter 18.4 mm) between ICF34 flange gaskets (effective area 2.08 cm). 2 This sample was set in a sample holder. The sample holder is a vacuum chamber that has a space on the primary side (gas supply side) and a space on the secondary side (permeation gas side) for the sample (hydrogen-permeable membrane), and is equipped with nozzles for gas supply and gas discharge.

[0056] Figure 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 the vacuum pump and 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 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) ~ 600℃ (873K) Supply gas: Hydrogen (hydrogen concentration 99.99%) Primary pressure: 0.3 MPa G Secondary pressure: 0MPa G Exam duration: 2.5 hours

[0057] [Evaluation results] 2 to 4 show Arrhenius plots showing the temperature dependence of the hydrogen permeability coefficient for the PdCu-based alloy membranes (PdCu alloy membrane and PdCuAg alloy membrane) of groups A to C produced in this embodiment. These figures show predicted lines of the hydrogen permeability coefficient estimated by linear approximation from measured values in the high-temperature range of 250°C to 400°C for PdCu alloy membranes without added Ag. However, for FIG. 4 (group C), the predicted line of the hydrogen permeability coefficient for the PdCuAg alloy membrane is also shown because there is a difference in the measured values with and without added Ag. As can be seen from FIGS. 2 to 4, the measured hydrogen permeability coefficient of the conventional PdCu alloy membrane without added Ag deviates from the predicted line near 150°C (1 / T = 0.0024), and the deviation becomes larger at lower temperatures. In contrast, for the Ag-added PdCuAg alloy membrane, although there is some deviation from the predicted line, the deviation is small, and it is clear that the decrease in hydrogen permeability coefficient at low temperatures is suppressed. Therefore, it was confirmed that the addition of Ag to the PdCu alloy membrane contributes to improving the hydrogen permeability coefficient at low temperatures.

[0058] However, the benefits of adding Ag to PdCuAg alloy membranes are limited to small amounts. In the PdCuAg alloy membranes with an Ag concentration of 1.0 atomic % shown in Figures 2 and 3, the reduction in the hydrogen permeability coefficient at low temperatures is not significant. Furthermore, these PdCuAg alloy membranes have low hydrogen permeability coefficients across the entire temperature range. Adding a large amount of Ag does not contribute to improving the properties of PdCu alloy membranes at all.

[0059] In this embodiment, in addition to the above sample, PdCuAg alloy membranes with Ag additions of 1.5 atomic %, 3 atomic %, and 6 atomic % were manufactured and their hydrogen permeability coefficients were measured. However, these membranes had extremely low hydrogen permeability coefficients across the entire temperature range, making them difficult to function as hydrogen-permeable membranes.

[0060] Regarding the hydrogen permeability of the PdCu alloy membrane and the PdCuAg alloy membrane in this embodiment, the hydrogen permeability coefficient φ at 100°C is 100 and hydrogen permeability coefficient φ at 300℃ 300 , and the ratio (φ 100 / φ 300 ) can be summarized as shown in Table 2 below.

[0061] [Table 2]

[0062] From Table 2, it can be seen that in the PdCuAg alloy membrane with appropriate Ag addition, the ratio of hydrogen permeability coefficients φ 100 / φ 300 It was confirmed that the hydrogen permeability coefficient was 0.4 or more, and that the hydrogen permeability coefficient was effectively maintained in the low temperature range.

[0063] Reference example (comparison with other metal additions) Here, in order to confirm that Ag is suitable as a metal element to be added to a PdCu alloy film, the inventors produced PdCu-based alloy films to which other metals were added and evaluated in the same manner as above. The manufacturing process of the PdCu-based alloy film was the same as above. In this reference example, PdCu-based alloy films (PdCuAl alloy films, PdCuMn alloy films) were also produced and evaluated using the PdCu alloys of Groups A to C as the basic composition and adding Al and Mn as additive metals. Note that Al and Mn were investigated in these reference examples because, like Ag, these elements are presumed to have the effect of stabilizing the phase transformation from an fcc structure (α phase) to a bcc structure (β phase).

[0064] As for the Arrhenius plots, which are the evaluation results of the PdCuAl alloy film and the PdCuMn alloy film as reference examples, the results for the PdCu-based alloy film of basic composition group A are shown in Figure 5 (PdCuAl alloy film) and Figure 6 (PdCuMn alloy film) as representative examples. When Al and Mn are added to the PdCu alloy film, the hydrogen permeability coefficient in the low temperature range improves slightly when the added concentration is about 0.5 atomic %. However, the improvement is extremely narrow, and the improvement effect is not as great as that of Ag. The ratio of the hydrogen permeability coefficient φ 100 / φ 300 The value of ρ was also less than 0.4. This tendency was similar for the PdCu-based alloy membranes of other basic compositions (Groups B and C). It was confirmed that Ag is the optimal metal to add to fill the vacancies that are the cause of the decrease in the hydrogen permeability coefficient of PdCu-based alloys. [Industrial Applicability]

[0065] The hydrogen-permeable membrane made of a PdCu-based alloy according to the present invention, by adding Ag, suppresses the decrease in hydrogen permeability coefficient at low temperatures observed in conventional hydrogen-permeable membranes made of PdCu alloys. This makes the present invention useful for the operation at low temperatures of various devices and equipment to which the hydrogen-permeable membrane is applied. The hydrogen-permeable membrane according to the present invention is expected to be applicable not only to hydrogen purification devices but also to hydrogen sensors for which operation at low temperatures is desirable.

Claims

1. In a hydrogen-permeable membrane made of a PdCu-based alloy, The PdCu alloy is a hydrogen-permeable film characterized in that it is composed of 47.0 atomic % or more and 49.0 atomic % or less of Pd, 0.01 atomic % or more and 0.75 atomic % or less of Ag, and the remainder being Cu and unavoidable impurities.

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

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