JP4742269B2 - Method for producing double-phase hydrogen permeable alloy and double-phase hydrogen permeable alloy - Google Patents

Description

  The present invention relates to a method for producing a multiphase hydrogen permeable alloy and a multiphase hydrogen permeable alloy.

  High-purity hydrogen is used in the manufacture of semiconductors, optical fibers, chemicals, etc., and the amount of use is increasing year by year. Recently, hydrogen has attracted attention as a fuel for fuel cells, and if fuel cells are to be used in earnest in the future, a large amount of high-purity hydrogen is required. Therefore, development of a method capable of producing high-purity hydrogen in large quantities at low cost is desired.

  As a method for mass production of hydrogen, there are (1) a method by electrolysis of water using non-fossil resources and (2) a method by reforming hydrocarbons using fossil resources. In the electrolysis method (1), water electrolysis using electricity obtained by photovoltaic power generation as a power source has been studied, but practical application is difficult at the current technical level. Therefore, for the time being, it is realistic to produce hydrogen by (2) steam reforming of hydrocarbons.

As described above, hydrocarbon reforming is suitable for mass production of hydrogen. For example, in the reaction system _{H 2} O was added to _{CH 4, CO, CO 2,} H 2 O, the impurity gas such as CH ₄ are generated in addition to the large amount of hydrogen. In order to use hydrogen as a fuel cell feedstock, it must be separated and purified from these impurities. Further, unless the CO content in the purified hydrogen is 10 ppm or less, the Pt electrode of the fuel cell is damaged. In other words, in order to use hydrogen in a fuel cell, it is necessary to purify and purify it.

  There are various methods for purifying hydrogen. To obtain high-purity hydrogen for fuel cells, a membrane separation method using a metal membrane is suitable. The purification of hydrogen using a metal membrane is characterized by extremely large influences of the separation coefficient and permeation coefficient. In the purification of hydrogen using a metal film, for example, about 99% of hydrogen can be purified to about 99.99999%.

  As a hydrogen permeable metal film used for the hydrogen permeable film, an alloy mainly composed of Pd, such as a Pd—Ag alloy, a Pd—Ti alloy, or the like is known (for example, see Patent Document 1).

  By the way, a Pd—Ag alloy film has been put to practical use as a hydrogen permeable metal film. However, if the use of fuel cells becomes full-scale and a large amount of hydrogen is required, the demand for Pd—Ag alloys as hydrogen permeable metal films will increase accordingly. In such a case, Pd, which is expensive and less resource-intensive, is considered to be a limitation, and it is assumed that the Pd—Ag alloy film cannot cope with it, and material development of a metal film to replace it is urgently required.

  Attempts have been made to develop alloys based on Group 5A elements such as V, Nb, and Ta that have higher hydrogen permeability than Pd (see, for example, Patent Document 2), but these alloys become brittle when hydrogen is dissolved. Therefore, it is a problem to break down during use. Therefore, attempts have been made to make these alloys amorphous. However, the diffusion of hydrogen in the amorphous is slow, and it is easily crystallized in hydrogen and transformed into a brittle equilibrium phase, so that it cannot be used practically (see, for example, Patent Document 3). Therefore, a material that has high hydrogen permeability and is stable and resistant to hydrogen embrittlement has been desired.

  As a material for solving the above problems, a multiphase hydrogen permeable alloy has been proposed. This achieves both hydrogen permeability and hydrogen embrittlement resistance by making the phase responsible for hydrogen permeability and the phase responsible for hydrogen embrittlement multi-phase. For example, in the Ni-Ti-Nb system, a hydrogen permeable alloy having excellent hydrogen permeation resistance and equivalent to or better than pure Pd is obtained by forming a bcc structure NiTi phase responsible for hydrogen permeability and a B2 structure NiTi phase. It is known that it can be produced (see Patent Document 4).

In general, a hydrogen permeable alloy is used in a region where a hydrogen solid solution is formed. In such a case, a hydrogen amount J (molH ₂ m ⁻² s ⁻¹ ) and hydrogen permeating the alloy film per unit time and unit area. There is a relationship represented by the following equation with the transmission coefficient Φ (molH ₂ m ⁻¹ s ⁻¹ Pa ^−0.5 ).

J = Φ (P _u ^0.5 −P _d ^0.5 ) / L (1)

In the above formula, P _u and P _d (Pa) are the hydrogen pressure on the upstream side and the downstream side, respectively, and L is the thickness (m) of the hydrogen permeable alloy film.

  In order to increase the hydrogen permeation amount J, it is required to use a thin membrane with a higher pressure difference in addition to using an alloy having a large hydrogen permeation coefficient Φ. For efficient hydrogen production, hydrogen permeable alloys are used in membrane form. When a Ni—Ti—Nb alloy having excellent hydrogen permeation characteristics and hydrogen embrittlement resistance is used as a hydrogen permeation alloy film, it is essential to establish a manufacturing process up to thinning.

  For example, when producing a Ni-Ti-Nb-based multiphase hydrogen permeable alloy, an alloy composition is selected so that two-phase coexistence of a NiTi phase in which Nb is dissolved and a TiNb phase in which Ni is dissolved in an equilibrium state is obtained. There is a need. Usually, a melting / solidifying method is generally used as a method for producing an alloy, but in the case of this alloy, it is difficult to produce the alloy for the following reasons.

  First, the melting point of Nb is as high as 2469 ° C. Since the melting points of Ni and Ti are 1455 ° C. and 1670 ° C., respectively, when a mixture of these elements is heated, Ni and Ti are melted before Nb. Then, the Ni liquid, the Ti liquid, or the NiTi liquid generated by the reaction thereof surrounds Nb, making it difficult to heat to a temperature at which Nb melts, and Nb may remain undissolved. In order to prevent Nb from remaining undissolved, there are restrictions on the arrangement method and melting procedure of the raw metal, which has been a problem.

  Even when all of the raw metal can be dissolved, a difference in cooling rate occurs between the peripheral portion and the central portion of the alloy during solidification, and a uniform alloy structure is often not obtained. As a result, a difference in hydrogen permeability occurs depending on the alloy site, which is a practical problem.

  Since the hydrogen permeation amount is inversely proportional to the film thickness, it is necessary to reduce the thickness of the obtained alloy ingot. Therefore, it is assumed that a hydrogen permeable alloy thin film is produced by processing such as rolling. However, the Ni—Ti—Nb NiTi + TiNb two-phase alloy can be rolled at several tens of percent at room temperature, but is considerably lower than a general steel material. For this reason, rolling to an appropriate thickness as a hydrogen permeable alloy requires repeated rolling and annealing, which causes an increase in manufacturing costs.

When manufacturing a material containing a high melting point element or an element having a high vapor pressure, a powder process may be used. Such a technique is known, for example, as a method for producing a rare earth permanent magnet (Patent Document 5). An alloy produced using a melting / solidifying method is pulverized and compacted, and then subjected to a sintering treatment to produce a uniform permanent magnet having high holding power. Even in this multiphase hydrogen permeable alloy, it is considered that a uniform material can be produced using this method, but the alloy ingot produced by the melting / solidification method exhibits very high ductility and cannot be pulverized. .
JP-A-8-215551 (paragraph 0006) JP 2000-159503 A (paragraph 0006) Japanese Patent Laying-Open No. 2004-042017 (paragraphs 0005 and 0009) Japanese Patent Laying-Open No. 2005-232491 (paragraph 0029) Japanese Patent Laying-Open No. 2005-076045 (paragraphs 0017 and 0018)

  For this reason, it is possible to obtain a multi-phase hydrogen permeable alloy composed of a phase responsible for hydrogen permeability and a phase responsible for hydrogen embrittlement without using the melting / solidifying method, or the melting / solidifying method. It is desired to reduce the composition / tissue non-uniformity that occurs in

  Then, this invention aims at providing the technique which produces the double phase hydrogen permeable alloy comprised from the phase which bears hydrogen permeability, and the phase which bears hydrogen embrittlement resistance using a powder metallurgy process. .

  The above problem is that the present inventors pressurize a pure metal powder constituting a multiphase hydrogen permeable alloy or a powder obtained by dehydrogenation of an alloy hydride prepared by hydrogenation of the alloy at room temperature. It has been found that the problem can be solved by preparing a powder and subjecting the green compact to heat treatment in vacuum.

That is, the method for producing a multiphase hydrogen permeable alloy according to the first aspect of the present invention is a method for producing a multiphase hydrogen permeable alloy comprising a phase responsible for hydrogen permeability and a phase responsible for hydrogen embrittlement resistance. A first step of selecting a plurality of types of powder raw materials and mixing them together; a second step of pressing the powder raw material in a vacuum to produce a green compact; and the green compact in a third step of performing heat treatment, the in the first step, the plurality of types of the at least one powder raw material, the multi-phase hydrogen permeation alloy and hydrogen is produced by melting and solidification method The reaction product is selected to form a phase responsible for hydrogen permeability and a phase responsible for hydrogen embrittlement resistance.

  Here, the term “phase responsible for hydrogen permeability” in the present specification does not mean a phase that exclusively performs hydrogen permeation, but may have an aspect of hydrogen embrittlement resistance, but a function mainly responsible for hydrogen permeation. This means a phase having excellent hydrogen permeability. Similarly, the “phase responsible for hydrogen embrittlement resistance” also does not mean a phase that performs hydrogen embrittlement resistance exclusively, but may have an aspect of hydrogen permeability, but functions mainly responsible for hydrogen embrittlement resistance This means a phase having excellent hydrogen embrittlement resistance.

Thus, in the third step of performing the heat treatment through the second step of producing the green compact, it is possible to react in the solid phase and efficiently produce the multiphase hydrogen permeable alloy. In addition, if a powder raw material is used, it is possible to prevent unmelted refractory metal, solidification segregation, alloy composition and unevenness of the structure, which are problems in the melting / solidification method. Furthermore, if a powder raw material is used, a green compact having a shape close to the final shape, such as a thin film, can be easily produced, so that the thinning process after the alloy production can be simplified.

  For example, when a Ni—Ti—Nb hydrogen permeable alloy capable of hydrogen permeation is melted and solidified by a normal method, a two-phase structure of NiTi phase and TiNb phase is formed. When this alloy is reacted with hydrogen at room temperature, the NiTi phase and the TiNb phase occlude hydrogen and transform into hydrides to be easily pulverized. When this powder is compacted and heat-treated, hydrogen in the alloy is first released, and then the adhesion between the alloy particles proceeds. It is possible to produce a multiphase hydrogen alloy through such a process. Even if the composition and the structure are uneven during melting and casting, the composition and the structure are removed by powdering and mixing.

  The alloy system is not limited to the Ni—Ti—Nb system. The alloy system that is a multiphase hydrogen permeable alloy is an ABC system (where A is a group consisting of Fe, Co, Ni, B is a group consisting of Ti, Zr, Hf, and C is V, Nb and Ta). The ABC-based alloy can be used as a hydrogen permeable alloy when a two-phase region of an AB phase in which C is dissolved and a BC phase in which A is dissolved is formed. Even in these systems, since the enthalpy of formation between A and B and between A and C is large, it is possible to produce an alloy by combustion synthesis as in the case of Ni—Ti—Nb alloys. Moreover, the AB + BC two-phase alloy produced by the melting / solidifying method also reacts with hydrogen to form a hydride.

  In addition, for this reason, the powder raw materials to be selected are not limited to two or three types, but may be a plurality of types, and may be four or more types.

  Further, for this reason, in the first step, all of the selected powder raw materials may be pure metal powder or the above reaction product, but some are pure metal powder or the above reaction product. May be. That is, at least one of the plurality of selected powder raw materials may be pure metal powder or the reaction product.

  After the first step of selecting and mixing the powder raw material, a second step of applying pressure to the powder to produce a green compact is performed. Since the hydrogen permeable alloy membrane is used with a hydrogen pressure difference before and after the membrane, it must be a bulk material. Also, if there are large defects in the alloy, gases other than hydrogen permeate through the alloy, so it must be dense. Therefore, this process becomes indispensable. In addition, since the powder particles are densely packed by this step, an alloy material with few defects can be obtained by the progress of the combustion synthesis reaction.

The invention according to claim 2 is characterized in that, in the invention according to claim 1 , the temperature of the heat treatment is higher than 1000 ° C. in the third step. After the second step of producing the green compact, a third step of performing heat treatment is performed. If the heat treatment is not performed, the reaction of the powder particles does not occur and an appropriate phase as a hydrogen permeable alloy cannot be obtained. Heat treatment at a high temperature is required in order to generate these phases and to avoid leaving gaps between the powder raw materials. The heat treatment temperature is desirably higher than 1000 ° C.

A multi-phase hydrogen permeable alloy according to a third aspect of the present invention is produced by the method for producing a multi-phase hydrogen permeable alloy according to the first or second aspect, and has a thickness of 0.01 to 3 mm. . When the thickness exceeds 3 mm, the hydrogen permeation flux (amount) becomes small, and the hydrogen permeation efficiency is deteriorated. On the other hand, if the thickness is less than 0.01 mm, the mechanical strength becomes weak and impractical.

According to a fourth aspect of the present invention, in the third aspect of the invention, a Pd film or a Pd alloy film is formed on a surface that takes in hydrogen and a surface that takes out hydrogen, and the thickness of the Pd film or Pd alloy film is Is in the range of 50 to 400 nm. If a Pd film or a Pd alloy film having a predetermined thickness is formed on both sides of the raw material gas side (upstream, high-pressure side) and the purified hydrogen side (downstream, low-pressure hydrogen side) with the alloy material sandwiched in this way In addition, oxidation, nitridation, and the like of the alloy film can be prevented, and hydrogen can be easily dissociated and recombined. Outside this range, the Pd film or Pd alloy film peels off when it is thin, and becomes uneconomical when it is thick.

  According to the present invention, it is possible to produce a multiphase hydrogen permeable alloy composed of a phase responsible for hydrogen permeability and a phase responsible for hydrogen embrittlement resistance using a powder metallurgy process.

  Thereby, it is possible to suppress unmelted refractory metal, solidification segregation, alloy composition, and structure unevenness, which are problems in the melting / solidification method.

  Hereinafter, the best mode for carrying out the present invention will be described more specifically with reference to the drawings. Duplicate explanations are omitted. In addition, since description here is the best form by which this invention is implemented, this invention is not limited to the said form.

  As a result of various studies on a method for producing a multi-phase hydrogen permeable alloy comprising a phase responsible for hydrogen permeability and a phase responsible for hydrogen embrittlement resistance, the present inventors have determined from a pure metal powder raw material constituting the multi-phase hydrogen permeable alloy. It was found that it can be produced. It was also found that a multiphase hydrogen-permeable alloy can be produced even when a raw material is a powder of a reaction product of hydrogen and a multiphase hydrogen-permeable alloy produced by a dissolution / solidification method.

  An embodiment of the present invention is a method for producing a multiphase hydrogen permeable alloy composed of a phase responsible for hydrogen permeability and a phase responsible for hydrogen embrittlement resistance. It consists of a first step of mixing with each other, a second step of pressing the powder raw material to produce a green compact, and a third step of subjecting the green compact to a heat treatment.

  In the first step of selecting and mixing the powder raw material, a pure metal powder of an element constituting the multiphase hydrogen permeable alloy is selected as the powder raw material. The particle size of the powder raw material is not particularly limited, but in this production method, since alloying is performed by solid phase diffusion, the diffusion distance of atoms is shorter than that of a normal dissolution / solidification method. Therefore, powder with small grains is necessary. Preferably it is 100 mesh or less.

  Alternatively, in the first step of selecting and mixing the powder raw material, a reactive organism of hydrogen with a multiphase hydrogen permeable alloy prepared by a dissolution / solidification method is selected as the powder raw material. For the reasons described above, the particle size of the powder raw material is desirably 100 mesh or less.

  The means for mixing the powder raw material is not particularly limited, and may be any of dry mixing, wet mixing, or mechanical mixing using ball milling or the like.

  After the first step, a second step is performed in which powder raw materials are mixed and compacted into a shape close to the final shape. This step is an indispensable step for producing a dense alloy that does not transmit gas other than hydrogen and for producing an alloy having a strength that can withstand a hydrogen pressure difference.

  After loading the powder material, evacuation is performed. At the stage of loading the powder, a large amount of air exists between the powder particles, so when pressurized without vacuuming, the mixed air finally becomes a void and remains in the alloy. Since these voids cause a decrease in membrane strength and a decrease in hydrogen separation performance, it is essential to remove the air by evacuation. When the powder is pressed from above and below after evacuation, the powder particles are plastically deformed and broken, and the voids between the particles are gradually reduced, so that a green compact in which the particles are intertwined in a complicated manner can be produced.

  Since the green compact produced by the above method is not composed of a phase responsible for hydrogen permeation and a phase responsible for hydrogen embrittlement resistance, hydrogen separation ability cannot be obtained. Therefore, after the second step of compacting, the target phase is generated by heat treatment (for example, NiTi phase and TiNb phase in Ni—Ti—Nb system), and the third heat treatment is performed to improve the adhesion between particles. The process is performed.

  When the pure metal powder raw material is selected and mixed in the first step, the pure metal powder is alloyed during the heat treatment to form a NiTi phase and a TiNb phase. At the same time, it is possible to produce a dense alloy in which the produced alloy particles are firmly bonded to each other and do not transmit a gas other than hydrogen.

  On the other hand, when the powder raw material of the reaction product of the multiphase hydrogen permeable alloy and hydrogen produced by the dissolution / solidification method in the first step is selected and mixed, hydrogen is first released from the alloy hydride by heat treatment. Is done. Thereafter, the produced NiTi phase and TiNb phase are firmly bonded to each other, and a dense alloy that does not transmit gas other than hydrogen can be produced.

  The metal film made of the multi-phase hydrogen permeable alloy of the present invention can be manufactured at a cost of 1/4 to 1/8 of the Pd alloy film, and is low in cost. It can be said that it is a material that can be applied as a substitute for the occasion.

  Further, since the alloy can be obtained in a shape close to the final shape without being affected by undissolved residue at the time of melting and segregation at the time of solidification, the alloy manufacturing process can be simplified.

  As the thickness of the metal membrane for hydrogen permeation produced in this way is smaller, the hydrogen permeation flux (amount) increases and the hydrogen permeation efficiency is improved. However, as the metal film becomes thinner, the mechanical strength becomes weaker. Therefore, in the case of these alloy systems, the thickness is preferably 0.01 to 3 mm.

  In order to use these alloy materials as metal membranes for hydrogen permeation, the surface of the source gas side (upstream, high-pressure hydrogen side) and the purified hydrogen side (downstream, low-pressure hydrogen) are sandwiched between the alloy materials. It is necessary to further form a Pd film or a Pd alloy film for dissociation and recombination of hydrogen on both the hydrogen (side) and the surface on the extraction side. The thickness is generally 50 to 400 nm, preferably 100 to 200 nm.

  The method of forming Pd or Pd alloy film on both sides of these alloy films for hydrogen dissociation and recombination is not particularly limited. For example, vacuum deposition, sputtering, ion plating, electrolytic plating, electroless plating, etc. Either may be performed.

  Examples of the present invention and comparative examples will be described below.

  (Example 1)

Ni powder (purity 99.9 wt%, 100 mesh or less), Ti powder (purity 99.9 wt%, 100 mesh or less), and so that the composition of the alloy material is Ni ₂₁ Ti ₂₃ Nb ₅₆ (atomic%) Nb powder (purity 99.9% by weight, 100 mesh or less) was blended. Ethanol was added to the blended mixed powder to form a mud, and these were mixed with each other in an agate mortar.

The mixed mud powder mixture was loaded into a 10 mm diameter cylinder of a tablet press. Thereafter, the cylinder was evacuated for 15 minutes with an oil rotary pump to remove the atmosphere in the cylinder and volatilize ethanol. Thereafter, a pressure of 200 kg / cm ² was applied to the powder in the cylinder by a hydraulic press while evacuating using an oil rotary pump, and the pressure was maintained for 10 minutes. After reducing the pressure, a sample was taken out to obtain a green compact having a diameter of 10 mm and a thickness of 1 mm.

  An SEM photograph of the green compact is shown in FIG. 1, and an X-ray diffraction pattern immediately after the green compact is produced is shown in FIG. 2 (a). From the SEM photograph (FIG. 1), it can be seen that the powder particles are plastically deformed by compaction, and the particles are intertwined in a complicated manner. Further, from the X-ray diffraction pattern (FIG. 2), it can be seen that the green compact is composed of Ni having an fcc structure, Ti having an hcp structure, and Nb having a bcc structure.

Next, heat treatment was performed to obtain an appropriate phase as a hydrogen permeable alloy. The produced green compact was loaded into a transparent quartz tube, and the quartz tube was evacuated. The evacuation was performed to 5 × 10 ⁻³ Pa or less using an oil rotary pump and an oil diffusion pump. After the evacuation was completed, the quartz tube was sealed and then heat treatment was performed. The heat treatment temperature and time are 1100 ° C. and 1 hour. After completion of the heat treatment, the quartz tube was taken out and cooled to room temperature by air cooling.

Both sides of the sample after the heat treatment were polished with a paper file, a buff, and then α-alumina having a diameter of 0.5 μm to form a mirror surface. The X-ray diffraction pattern of this sample is shown in FIG. It can be seen that after the heat treatment, the phase changes to a two-phase structure of a phase having a B2 structure and a phase having a bcc structure. A scanning electron microscope (SEM) photograph of this alloy is shown in FIG. From FIG. 3, it was observed that there were two phases, a gray phase and a white phase. As a result of energy dispersive X-ray analysis (EDS), the composition of the gray phase is Ni _47.3 Ti _42.3 Nb _10.4 (atomic%), and the white phase is Ni _2.7 Ti _6.2 Nb _{91. 1} (atomic%). From the above results, it can be said that the gray phase is a B2 structure NiTi phase and the white phase is a bcc structure TiNb phase. In addition, no evidence of dissolution of the sample during the heat treatment was observed, and it can be said that the alloy was produced by solid phase reaction.

In FIG. 3, voids of about several μm are observed in the TiNb phase, but they are sufficiently small compared to the film thickness, so that the voids do not penetrate the film and gases other than hydrogen do not permeate. Moreover, although a black NiTi ₂ phase is observed, the amount produced is very small, and it can be said that it is mainly a two-phase alloy of a NiTi phase and a TiNb phase. From the above, it can be said that alloying and densification occur simultaneously in the heat treatment step.

  Next, a hydrogen permeation test of this sample was performed according to the following procedure.

The sample polished with α-alumina was washed with acetone and then set in a high-frequency magnetron sputtering apparatus. Using an oil rotary pump and a cryopump, vacuuming was performed up to 3 × 10 ⁻⁵ Torr. Thereafter, reverse sputtering was performed for 10 minutes using an RF power source in order to remove the oxide film and the like attached to the sample surface. Next, the sample was heated to 350 ° C. in the sputtering apparatus, and Pd sputtering was performed using a DC power source for 5 minutes. The thickness of the Pd film coated under these conditions is 190 nm.

Hydrogen permeation measurement was carried out by the following flow rate method. First, the disk sample on which the Pd film was formed was sealed with a Cu gasket. Next, both sides of the disk were evacuated with an oil diffusion pump to a pressure of 3 × 10 ⁻³ Pa or less, and then the disk was heated to 673 K and held as it was. Before introducing hydrogen gas, a permeation test with argon gas was performed. If permeation of argon gas is confirmed, there is a risk of fracture of the alloy or poor adhesion between particles, and it cannot be used as a hydrogen permeable alloy. Argon gas was introduced at 0.1 and 0.2 MPa to the downstream side and upstream side of the alloy, respectively, and the permeation of the argon gas was examined. As a result, the permeation of argon gas was not observed, and it was confirmed that the alloy sample was healthy.

After the argon gas permeation test, both sides of the alloy were again evacuated with an oil rotary pump. Thereafter, hydrogen gas (purity: 99.99999%) was introduced into the downstream side and the upstream side, respectively, at 0.1 and 0.2 MPa, and then hydrogen permeation measurement was performed. The upstream hydrogen pressure was increased from 0.2 MPa to 0.8 MPa, and the temperature was decreased stepwise from 673 K to 523 K at 50 K intervals. After maintaining at a constant temperature for 30 minutes, the hydrogen permeation test was started. The hydrogen permeation flux J (molH ₂ m ⁻² s ⁻¹ ) was measured using a mass flow meter.

As shown in Equation (1), the hydrogen permeation coefficient Φ is obtained from the slope of the J × L vs. (Pu ^0.5 −Pd ^0.5 ) plot.

FIG. 4 shows the temperature dependence of the hydrogen permeability coefficient Φ calculated from the slope of the J × L vs. (Pu ^0.5 −Pd ^0.5 ) plot for the alloy material obtained as described above in the form of an Arrhenius plot. . For comparison, FIG. 4 also shows the results of pure Pd and alloys of the same composition produced by melting and casting.

The hydrogen permeability coefficient of the alloy produced from this pure metal powder is 4.61 × 10 ⁻⁸ (molH ₂ m ⁻¹ s ⁻¹ Pa ^−0.5 ) at 673 K, and the hydrogen permeability coefficient decreases as the temperature decreases. did. Moreover, it turns out that it is higher than the hydrogen permeability coefficient of the alloy material produced by pure Pd or the melt | dissolution and casting method. Furthermore, the alloy produced from the pure metal powder does not break even at 523K, and has good hydrogen embrittlement resistance. As mentioned above, the alloy produced by this process has high hydrogen permeability compared with the melted / solidified material (1.8 × 10 ⁻⁸ (molH ₂ m ⁻¹ s ⁻¹ Pa ^−0.5 )). It could be used as a hydrogen permeable alloy.

  The reason why the alloy material made of the pure metal powder as a raw material has higher hydrogen permeability than the dissolved / solidified material is considered to be a difference in Nb concentration in the TiNb phase. This multiphase alloy is composed of two phases, a NiTi phase and a TiNb phase, and the TiNb phase is responsible for the hydrogen permeability of the alloy. When Ni, Ti, and Nb constituting this alloy are compared, Nb has the highest hydrogen permeability coefficient. Therefore, it is considered that Nb in the TiNb phase is responsible for the hydrogen permeability of the alloy. When the Nb concentration in the TiNb phase of the alloy produced from the powder and the melted / cast alloy was compared, the former was about 91 atomic% and the latter was about 83 atomic%. In other words, Nb having a high hydrogen permeability coefficient is concentrated in the TiNb phase of the alloy produced from the powder. This suggests that an alloy made from powder has a high hydrogen permeability coefficient.

  (Example 2)

  An alloy sample was prepared by the same composition and method as in Example 1. However, the heat treatment temperature and time are 1100 ° C. and 30 minutes. As a result of X-ray diffraction, SEM observation, and EDS analysis, this sample also mainly exhibited a two-phase structure of NiTi phase and TiNb phase.

The hydrogen permeability of this alloy sample was measured by the same method as in Example 1. This alloy sample has a hydrogen permeation coefficient of 4.65 × 10 ⁻⁸ (molH ₂ m ⁻¹ s ⁻¹ Pa ^−0.5 ) at 673K, and has a high hydrogen permeability compared to the dissolved / solidified material. It could be used as a hydrogen permeable alloy.

  Example 3

  An alloy sample was prepared by the same composition and method as in Example 1. However, the heat treatment temperature and time are 1050 ° C. and 6 hours. As a result of X-ray diffraction, SEM observation, and EDS analysis, this sample also mainly exhibited a two-phase structure of a NiTi phase and a TiNb phase.

The hydrogen permeability of this alloy sample was measured by the same method as in Example 1. This alloy sample has a hydrogen permeation coefficient of 4.41 × 10 ⁻⁸ (molH ₂ m ⁻¹ s ⁻¹ Pa ^−0.5 ) at 673 K, and has a high hydrogen permeability compared to the dissolved / solidified material. It could be used as a hydrogen permeable alloy.

  Example 4

  An alloy sample was prepared by the same composition and method as in Example 1. However, the heat treatment temperature and time are 1050 ° C. and 1 hour. As a result of X-ray diffraction, SEM observation, and EDS analysis, this sample also mainly exhibited a two-phase structure of NiTi phase and TiNb phase.

The hydrogen permeability of this alloy sample was measured by the same method as in Example 1. The hydrogen permeation coefficient of this alloy sample is 4.28 × 10 ⁻⁸ (molH ₂ m ⁻¹ s ⁻¹ Pa ^−0.5 ) at 673 K, and has high hydrogen permeability compared to the melted / solidified material. It could be used as a hydrogen permeable alloy.

  (Example 5)

An alloy sample was prepared in the same manner as in Example 1. However, the alloy composition was made to be Ni ₃₀ Ti ₃₀ Nb ₄₀ (atomic%). The heat treatment temperature and time are 1100 ° C. and 1 hour. As a result of X-ray diffraction, SEM observation, and EDS analysis, this sample also mainly exhibited a two-phase structure of NiTi phase and TiNb phase.

The hydrogen permeability of this alloy sample was measured by the same method as in Example 1. The hydrogen permeation coefficient of this alloy sample is 2.45 × 10 ⁻⁸ (molH ₂ m ⁻¹ s ⁻¹ Pa ^−0.5 ) at 673K, which is higher than the permeation coefficient of the dissolved / solidified material. And could be used as a hydrogen permeable alloy.

  From the above results, using a mixed powder of Ni powder, Ti powder and Nb powder as a raw material, and performing a heat treatment after producing a green compact, the powder raw material reacts during the heat treatment to produce a NiTi phase and a TiNb phase, It can be seen that this reactive organism binds tightly. Therefore, this method can be said to be effective as a method for producing a multiphase hydrogen permeable alloy having a high hydrogen permeability coefficient.

  (Example 6)

An alloy sample was prepared in the same manner as in Example 1. However, pure Co powder, pure Ti powder, and pure Nb powder were mixed so that the alloy composition would be Co ₂₁ Ti ₂₃ Nb ₅₆ (atomic%). The heat treatment temperature and time are 1210 ° C. and 1 hour. As a result of X-ray diffraction, SEM observation, and EDS analysis, this sample mainly exhibited a two-phase structure of a CoTi phase in which Nb was dissolved and a TiNb phase in which Co was dissolved.

The hydrogen permeability of this alloy sample was measured by the same method as in Example 1. The hydrogen permeation coefficient of this alloy sample is 3.80 × 10 ⁻⁸ (molH ₂ m ⁻¹ s ⁻¹ Pa ^−0.5 ) at 673 K, and the hydrogen permeation coefficient (3.31) of the dissolved / solidified material having the same composition. Compared to × 10 ⁻⁸ (molH ₂ m ⁻¹ s ⁻¹ Pa ^−0.5 )), it has high hydrogen permeability and can be used as a hydrogen permeable alloy.

  From the above results, it can be seen that the present method for producing a multiphase hydrogen permeable alloy is applicable not only to the Ni—Ti—Nb system but also to the Co—Ti—Nb system. An alloy system that can be used as a multiphase hydrogen permeable alloy is an ABC system (where A is a group consisting of Fe, Co, Ni, B is a group consisting of Ti, Zr, Hf, and C is V , Nb, and Ta). The ABC-based alloy can be used as a hydrogen permeable alloy when a two-phase region of an AB phase in which C is dissolved and a BC phase in which A is dissolved is formed. Even in these systems, the production enthalpy between A and B and between A and C is large, so it is considered that the present manufacturing method can be applied to alloy systems other than Ni—Ti—Nb and Co—Ti—Nb.

  (Example 7)

Predetermined amounts of Ni (purity 99.9%), Ti (purity 99.5%), and Nb (99.9%) were blended so that the alloy composition would be Ni ₂₁ Ti ₂₃ Nb ₅₆ (atomic%). This blend was loaded into an arc melting furnace and evacuated. The evacuation was performed to 1.3 × 10 ⁻³ Pa or less using an oil rotary pump and an oil diffusion pump. After completion of evacuation, arc melting was performed by introducing 36 mmHg argon gas. In order to produce a uniform alloy, the ingot after melting was inverted and remelted. The inversion-remelting of the ingot was performed 6 times. The ingot thus obtained was rolled at room temperature to obtain a plate-like sample having a width of 15 mm and a thickness of 1 mm.

The plate-like sample was washed with acetone, then loaded into a stainless pressure-resistant reaction vessel, and fixed to a Siebelz type hydrogen storage device. Next, the inside of the reaction vessel was evacuated to 1.3 × 10 ⁻³ Pa or less using an oil rotary pump and an oil diffusion pump. Thereafter, the reaction vessel was heated to 400 ° C. using an electric furnace and held for 1 hour while evacuating. This treatment is called activation treatment, and has the effect of removing the oxide film formed on the alloy surface and increasing the hydrogen storage rate. After the activation was completed, 5 MPa of hydrogen was introduced while maintaining the temperature and reacted with hydrogen for 1 hour. In this state, the reaction vessel was cooled to room temperature and held for 12 hours. Thereafter, hydrogen in the reaction vessel was released, and a hydrogenated sample was taken out.

  The sample taken out was very brittle due to occlusion of hydrogen. This sample was pulverized to 100 mesh or less in a mortar. Thereafter, a green compact was produced in the same manner as in Example 1. However, since a cylinder with a diameter of 20 mm was used in the compacting, the diameter of the obtained green compact was 20 mm.

  The hydrogen storage amount and hydrogen release curve of the sample after hydrogenation were examined using a hydrogen analyzer. After loading the sample into the graphite crucible, the released hydrogen was measured by heating the crucible at 2 K / sec. As a result, the hydrogen concentration in the sample was 1.7% by weight, and it was found that it was necessary to heat to 700 ° C. or higher in order to release all hydrogen.

  The green compact was loaded in the quartz space and evacuated as in Example 1. Thereafter, the quartz tube was heated to 1100 ° C. using an electric furnace while being evacuated and held for 6 hours. Thereafter, the quartz tube was air-cooled to room temperature, and an alloy sample was taken out.

  FIG. 5 shows an X-ray diffraction pattern ((a)) of a cast alloy sample prepared by arc melting, an X-ray diffraction pattern ((b)) of a green compact sample prepared after hydrogenation, and a sample after heat treatment. An X-ray diffraction pattern ((c)) is shown. In addition, SEM photographs of samples corresponding to the above (a) to (c) are shown in FIGS.

  A sample prepared by arc melting is composed of a B2 type NiTi phase and a bcc type TiNb phase which are necessary as a multiphase hydrogen permeable alloy. Further, the TiNb phase is generated as a primary crystal and has a structure surrounded by eutectic (NiTi + TiNb). This alloy can be permeated with hydrogen as it is, but the structure varies depending on the location, resulting in variations in hydrogen permeation characteristics.

The green compact samples after hydrogenation consisted of four kinds of hydrides of TiNbH phase (tetragonal), TiNbH ₂ phase (cubic), NiTiH phase (tetragonal) and NiTi ₂ H _0.5 phase (cubic). Was composed. The NiTi phase and TiNb phase that existed in the cast state are decomposed into four types of hydrides by hydrogen storage. In the SEM photograph of the green compact, it can be seen that the filling of the powder particles is incomplete compared to the case where the pure metal is compacted. This is probably because the hydride powder is hard and does not plastically deform.

As a result of hydrogen analysis of the sample after the heat treatment, the hydrogen content was almost zero. It can be seen that hydrogen is completely released by heat treatment at 1100 ° C. × 6 hours. From the X-ray diffraction pattern of this alloy, it can be seen that a part of NiTi ₂ phase is generated, but a B2 type NiTi phase and a bcc type TiNb phase are generated. Therefore, it can be said that when hydrogen is released from the hydride, the original phase structure is restored.

The hydrogen permeability of this alloy sample was measured by the same method as in Example 1. Prior to the measurement of hydrogen permeability, an Ar gas permeation test was performed, but no Ar gas permeation was observed. The hydrogen permeation coefficient of this alloy sample is 4.66 × 10 ⁻⁸ (molH ₂ m ⁻¹ s ⁻¹ Pa ^−0.5 ) at 673K, which is higher than the permeation coefficient of the dissolved / solidified material. And could be used as a hydrogen permeable alloy.

  As described above, a dense alloy having the original structure (NiTi + TiNb) can be produced by reacting an alloy produced by melting and solidification with hydrogen to form a hydride powder, and compacting and heat treatment.

  (Comparative Example 1)

An alloy sample was prepared by the same composition and method as in Example 1. However, the heat treatment temperature and time are 1000 ° C. and 6 hours. As a result of X-ray diffraction and EDS analysis, this alloy material mainly consists of a NiTi phase and a TiNb phase, but a relatively large amount of NiTi ₂ phase and NiNb phase, which are brittle intermetallic compounds, were generated. Many voids were also observed.

  When an Ar gas permeation test of this alloy was performed in the same manner as in Example 1, the Ar gas permeation was observed. It is considered that the alloy is not sufficiently densified. This alloy could not be used as a hydrogen permeable alloy.

  (Comparative Example 2)

  An alloy sample was prepared by the same composition and method as in Example 1. However, the heat treatment temperature and time are 800 ° C. and 6 hours. As a result of X-ray diffraction and EDS analysis, although a small amount of NiTi phase and TiNb phase were formed in this alloy material, a large amount of pure Ni, pure Ti and pure Nb phases were observed, and alloying did not proceed sufficiently I understood. Further, when an Ar gas permeation test of this alloy was performed in the same manner as in Example 1, the permeation of Ar gas was observed. It is considered that the alloy is not sufficiently densified. This alloy could not be used as a hydrogen permeable alloy.

  (Comparative Example 3)

  An alloy sample was prepared by the same composition and method as in Example 1. However, the heat treatment temperature and time are 1150 ° C. and 1 hour. As a result of SEM observation, it was observed that the crystal grains were spheroidized and the alloy was dissolved. In addition, many voids having a diameter exceeding 200 μm existed. Therefore, this alloy material could not be used as a hydrogen permeable alloy.

  From the above results, it is considered that a temperature higher than 800 ° C. is necessary for the alloying of the pure metal powder to proceed. Furthermore, a dense alloy cannot be obtained even if heat treatment is performed at a temperature of 1000 ° C. or lower. Therefore, in order to obtain an alloy material that can be used as a hydrogen permeable alloy, heat treatment at a temperature exceeding 1000 ° C. is essential. Further, when the alloy is dissolved, the advantage of the powder method, for example, the effect that Nb exists at a high concentration in the TiNb phase cannot be obtained, so that the heat treatment temperature is limited to the melting point or less of the alloy material.

  (Comparative Example 4)

  An alloy sample was prepared by the same composition and method as in Example 7. However, the heat treatment temperature and time are 1000 ° C. and 6 hours. The sample after the heat treatment had a NiTi + TiNb two-phase structure. When an Ar gas permeation test of this alloy was performed in the same manner as in Example 1, the Ar gas permeation was observed. It is considered that the alloy is not sufficiently densified. This alloy could not be used as a hydrogen permeable alloy. From the above, it can be said that a temperature exceeding 1000 ° C. is necessary to produce a dense alloy even in a production method via hydride.

  According to the present invention, a double-phase alloy having a specific composition, which is a composite alloy of a phase responsible for hydrogen permeability and a phase responsible for hydrogen embrittlement resistance, is obtained by hydrogenating a pure metal powder raw material and a cast material. It can be made from hydride powder. Through these compacting and heat treatment, both excellent hydrogen permeability and resistance to hydrogen embrittlement can be achieved. Therefore, since hydrogen can be permeated with extremely high efficiency, the obtained high-purity hydrogen can be applied to the manufacturing field of fuel for fuel cells, semiconductors, optical fibers, chemicals, and the like.

Ni powder in Example 1, is a SEM photograph of the powder compact after the preparation of the mixed powder so that the Ti powder and Nb powder _Ni 21 _Ti 23 _{Nb 56} (atomic%). It is the X-ray diffraction pattern after (a) green compact preparation in Example 1 and (b) heat processing. 2 is a SEM photograph of a sample after heat treatment in Example 1. 4 is a graph showing temperature dependence of a hydrogen permeation coefficient of an alloy material in Example 1. It is an X-ray diffraction pattern of (a) the alloy sample produced by arc melting in Example 7, (b) the sample after green compact production, and (c) the sample after heat processing. It is a SEM photograph of (a) the alloy sample produced by arc melting in Example 7, (b) the sample after green compact production, and (c) the sample after heat processing.

Claims (4)

A method for producing a multiphase hydrogen permeable alloy composed of a phase responsible for hydrogen permeability and a phase responsible for hydrogen embrittlement resistance,
A first step of selecting a plurality of types of powder raw materials and mixing them together;
A second step of pressing the powder raw material in a vacuum to produce a green compact;
And a third step of performing heat treatment to the green compact,
In the first step, as at least one of the plurality of types of powder raw materials, a reaction product of the multiphase hydrogen permeable alloy and hydrogen produced by a melting / solidification method is selected,
A method for producing a multi-phase hydrogen permeable alloy, comprising forming a phase responsible for hydrogen permeability and a phase responsible for hydrogen embrittlement resistance. The method for producing a multiphase hydrogen permeable alloy according to claim 1 , wherein, in the third step, the temperature of the heat treatment is higher than 1000 ° C. A multiphase hydrogen permeable alloy produced by the method for producing a multiphase hydrogen permeable alloy according to claim 1 or 2 and having a thickness of 0.01 to 3 mm. A Pd film or a Pd alloy film is formed on the surface that takes in hydrogen and the surface that takes out hydrogen,
4. The multiphase hydrogen permeable alloy according to claim 3, wherein the Pd film or the Pd alloy film has a thickness in the range of 50 to 400 nm.