JP3882089B1 - Crystalline double phase hydrogen permeable alloy and hydrogen permeable alloy membrane - Google Patents

Abstract

An object of the present invention is to provide a crystalline multiphase hydrogen permeable alloy having hydrogen permeability and hydrogen embrittlement resistance and usable at 473 K or higher.
A structure comprising a composite phase, wherein the composite phase surrounds the TiNb phase in which a eutectic (CoTi + TiNb) of a CoTi phase in which Nb is dissolved and a TiNb phase in which Co is dissolved is formed as an initial crystal. In the Co-Ti-Nb ternary phase diagram, Co ₂₀ Ti ₃₀ Nb ₅₀ , Co ₂₀ Ti ₁₀ Nb ₇₀ , Co ₁₀ Ti ₁₀ Nb ₈₀ and Co ₁₀ Ti ₃₀ Nb ₆₀ (however, the alloy composition is all atoms) %)) And an alloy composition on a line connecting Co ₂₀ Ti ₃₀ Nb ₅₀ and Co ₂₀ Ti ₁₀ Nb ₇₀ (all alloy compositions are atomic%). It is a crystalline multiphase hydrogen permeable alloy.
[Selection] Figure 1

Description

  The present invention relates to a crystalline hydrogen permeable alloy and a hydrogen permeable alloy film.

  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 solar power generation as a power source has been studied, but practical application is difficult in terms of cost 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 a reaction system in which H ₂ O is added to CH ₄ , a large amount of hydrogen is generated according to the following reaction formulas (1) to (3).

    (Chemical formula 1)

CH ₄ + H ₂ O⇔CO + 3H ₂ [gasification reaction (endothermic reaction)] (1)

    (Chemical formula 2)

CO + H ₂ O⇔CO ₂ + H ₂ [shift reaction (exothermic reaction)] (2)

      (1) + (2) = (3)

    (Chemical formula 3)

CH ₄ + 2H ₂ O⇔CO ₂ + 4H ₂ [endothermic reaction] (3)

The reaction takes place according to formulas (1) and (2), and eventually the reaction of formula (3) occurs. The reaction system contains impurities such as CO, CO ₂ , H ₂ O, and CH ₄ in addition to a 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.

  Hydrogen purification methods include an absorption method, a cryogenic separation method, an adsorption method, and a membrane separation method. Among these, the membrane separation method has been put into practical use. The membrane separation method uses the difference in the speed of gas passing through the membrane, and a polymer membrane or a metal membrane is used as the membrane.

  In the membrane separation method using a polymer membrane, hydrogen is separated and purified from the difference in diffusion rate of gas molecules passing through pores. In this membrane separation method, high-purity hydrogen cannot be obtained, but the system can be enlarged.

On the other hand, in the metal film, there are no pores in the polymer film, and the hydrogen permeation mechanism is as follows. When there is a hydrogen pressure difference across the metal film, on the high pressure side, hydrogen molecules (H ₂ ) dissociate into atoms (H) on the metal surface, dissolve in the metal, and enter and diffuse. The hydrogen atoms permeate the metal film, recombine with H ₂ on the low pressure side surface, and jump out. As a result, the hydrogen is purified. Hydrogen purification using a metal membrane is characterized by extremely high separation and permeation coefficients. In the purification of hydrogen using a metal film, for example, about 99% of hydrogen can be purified to about 99.99999%. Therefore, it can be said that a membrane separation method using a metal membrane is suitable for purification of high purity hydrogen for fuel cells.

  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. If this is the 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 the development of a metal film material to replace it is urgent.

It is indispensable that the hydrogen permeable alloy has the property of “occluding hydrogen” in the same manner as the hydrogen storage alloy. However, the material properties required for each material are completely different as shown in Table 1, and cannot be realized based on the development guidelines for hydrogen storage alloys.

  A hydrogen storage alloy is an alloy that can easily store and release hydrogen repeatedly. The principle is that the hydrogen pressure remains constant even when the hydrogen storage amount increases, that is, a pressure plateau occurs. As explained by Gibbs' phase law, the pressure plateau occurs when hydrogen is in solid solution (hereinafter referred to as hydrogen solid solution) and hydride coexists. If a hydride is not generated, a pressure plateau is not generated, and therefore it cannot be used efficiently as a hydrogen storage alloy.

  Although hydrides are brittle without exception, it is not an obstacle to hydrogen storage alloys, but rather an advantage. For example, there is no problem even if the alloy before hydrogen storage is brittle. This is because the alloy is easily self-pulverized by hydrogen storage, and the hydrogen storage / release rate is increased by increasing the specific surface area that reacts with hydrogen, which is advantageous as a hydrogen storage alloy.

  Further, the hydrogen storage alloy is used in a powder form and is not used in a plate form or a film form. When the operating temperature rises or the hydrogen pressure decreases, hydride formation becomes difficult and the properties as a hydrogen storage alloy deteriorate. Therefore, it is required to use at temperatures from room temperature to 150 ° C and under hydrogen of 0.5 MPa or more. It has been.

On the other hand, the hydrogen permeable alloy is the same as the hydrogen occluding alloy until the hydrogen molecules (H ₂ ) dissociate into hydrogen atoms (H) on the metal surface and enter the metal to be occluded.

  However, in hydrogen-permeable alloys, hydrogen containing impurities is on the high-pressure side, hydrogen purified by permeation of the metal film is on the low-pressure side, and a pressure difference, that is, a hydrogen concentration gradient is generated on both sides of the alloy. Driving power. Since it is essential to make a pressure difference on both sides of the alloy, it cannot be used in a powder state and is used as a plate or a film.

  The material generally has a property of becoming brittle when hydrogen is occluded. The hydrogen solid solution does not become so brittle, but when hydride is formed, it becomes brittle and self-pulverization occurs. Therefore, the formation of hydride must be avoided in hydrogen permeable alloys. In addition, when the temperature is lowered or the hydrogen pressure is increased, hydride formation is facilitated. Therefore, the hydrogen permeable alloy is used at a temperature of 200 ° C. (473 K) or more and under 0.5 MPa of hydrogen.

  As described above, the concept of alloy design of both materials is 180 degrees different, and it is impossible to use a hydrogen storage alloy as a hydrogen permeable alloy, and vice versa. In hydrogen permeable alloys, hydrogen embrittlement must be suppressed, and for this purpose, ductility must be exhibited before hydrogen storage and hydrides should not be produced.

In general, the hydrogen permeable material is used in a region where a hydrogen solid solution is formed. In such a case, hydrogen amount J (molH ₂ m ⁻² s ⁻¹ ) and hydrogen permeating the alloy film per unit time and unit area are used. 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 (4)

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. Therefore, it is essential that the mechanical properties of the alloy film are excellent. This is because a material having a high hydrogen permeability coefficient cannot be realized as a hydrogen-permeable alloy film if it is destroyed by hydrogen embrittlement. The reason why pure Nb having a hydrogen permeability coefficient 100 times higher than that of pure Pd is not used as a hydrogen permeable alloy film is that Nb has low hydrogen embrittlement resistance. Currently, the biggest development issue for hydrogen permeable alloys is how to suppress hydrogen embrittlement.

  As the hydrogen permeable alloy film, it is known that, for example, an alloy of V, Nb, Ta and Ti, Zr, Ni, Co is suitable (see, for example, Patent Document 2). The alloy design guideline in this document is to make a hydrogen permeable alloy from Ti, Zr, Hf which has hydrogen storage ability in V, Nb, Ta excellent in hydrogen permeability and Ni, Co which has catalytic action. is there. However, this document does not describe hydrogen embrittlement as well as hydrogen permeability. Further, even if an alloy is produced based on such guidelines, the alloy is broken by hydrogen embrittlement and cannot be used as a hydrogen permeable alloy.

  A similar document (see Patent Document 3) also describes an Nb-based hydrogen permeable alloy, but its hydrogen permeability is lower than that of Pd. These alloys assume a single phase, but it is difficult for the single phase to have contradictory properties of hydrogen permeability and hydrogen embrittlement resistance. If it is going to suppress hydrogen embrittlement with these alloys, the amount of hydrogen solid solution must be reduced, which causes a decrease in hydrogen permeability.

  Furthermore, in order to suppress hydrogen embrittlement, it is known to make an alloy structure amorphous (see, for example, Patent Document 4). However, since the diffusion coefficient of hydrogen in an amorphous alloy is generally lower than that in a crystalline material, high hydrogen permeability cannot be obtained. Further, since the amorphous material is crystallized when the temperature is increased, the use temperature is restricted. In particular, since an amorphous alloy produced for hydrogen permeation contains an element having a high binding force with hydrogen, crystallization occurs in hydrogen at a lower temperature.

  In order to solve such a problem, it has been proposed that the alloy is effective in making a double phase (see Non-Patent Document 1). The material properties are strongly influenced by the structure of the alloy, but the structure is strongly dependent on the alloy composition. Therefore, when discussing the characteristics of the material, it is meaningless unless the relationship between the alloy composition, structure, and characteristics is clearly indicated. However, this document does not specify the alloy composition. Moreover, nothing is mentioned about the relationship between alloy composition, structure, and properties.

  In other words, a multiphase alloy that can be used as a hydrogen permeable alloy needs to satisfy various conditions as shown below. Therefore, if it is a multiphase, it does not become an excellent hydrogen permeable alloy.

  First, in the Co—Ti—Nb system, the phases other than the CoTi phase in which Nb is dissolved and the TiNb phase in which Co is dissolved make the alloy brittle in the cast state and / or are brittle due to occlusion of a large amount of hydrogen. Due to the action of generating hydride, if a third phase other than these two phases is generated, it will be destroyed at the stage of sample preparation or by hydrogen embrittlement during the hydrogen permeation test. Therefore, it is essential to select an alloy composition that does not produce the third phase as much as possible.

  Even if the alloy is composed of two phases of the CoTi phase and the TiNb phase, it is indispensable to control the type of the phase generated as the primary crystal and the volume ratio thereof. Since the hydrogen permeability and ductility of the CoTi phase are lower than those of the TiNb phase, an alloy in which the CoTi phase is formed as a primary crystal has low hydrogen permeability and is susceptible to embrittlement and hydrogen embrittlement. Therefore, even if hydrogen permeation is possible, excellent hydrogen permeation characteristics cannot be expected. An alloy composition in which the TiNb phase is formed as a primary crystal is essential.

  In addition, since the hydrogen permeability of the present multiphase hydrogen permeable alloy is mainly borne by the TiNb phase, an alloy composition that increases the volume ratio of the TiNb phase should be selected. However, an excessive TiNb phase causes hydrogen embrittlement.

Furthermore, it is considered that Nb is mainly responsible for the hydrogen permeability of the TiNb phase. Therefore, an alloy composition that increases the Nb concentration in the TiNb phase should be selected. Further, when the Ti concentration in the alloy is high, the Ti concentration in the TiNb phase increases, so that a hydride such as TiH ₂ is generated, and destruction occurs even in the case of multiple phases. Therefore, in order to prevent the Ti concentration in the primary crystal from becoming excessive, the Ti concentration in the alloy is desirably 25 atomic% or less.

  As described above, in order to obtain the maximum hydrogen permeation characteristics while suppressing hydrogen embrittlement, fine control of the alloy composition is indispensable.

  In the Ni—Ti—Nb system, it is known that a multiphase hydrogen permeable alloy can be produced by controlling the type of phase to be generated and its volume ratio (see Patent Document 5). However, since the phase equilibrium differs depending on the alloy system, the necessary conditions for the multiphase hydrogen permeable alloy differ depending on the alloy system. Therefore, the characteristics of the Co—Ti—Nb alloy cannot be simply predicted from the knowledge obtained with the Ni—Ti—Nb alloy from the similarity in the periodic table.

  It is known that even in the Co—Ti—Nb system, a multi-phase hydrogen permeable alloy can be produced by controlling the kind of phase to be generated and its volume ratio (see Patent Document 6).

However, in the technique described in Patent Document 6, the Co ₃₅ Ti ₃₅ Nb ₃₀ (atomic%) alloy exhibits the maximum hydrogen permeation coefficient, but the value is 2.64 × 10 ⁻⁸ (molH ₂ m ⁻¹ s). ⁻¹ Pa ^−0.5 ), there is room for further study and consideration from a practical point of view. In this alloy system, as the Nb concentration increases, the volume fraction of the primary TiNb phase increases and the hydrogen permeability coefficient is expected to increase, but in this document, the hydrogen permeability coefficient decreases as the Nb concentration increases. ing. This is because the alloy composition is poorly selected, a part of the eutectic structure collapses, and the CoTi phase and other phases are generated in granular form. These phases adversely affect hydrogen permeation. If an alloy composed of a structure in which the primary TiNb phase is surrounded by a eutectic (CoTi + TiNb) can be produced, an improvement in the hydrogen permeability coefficient can be expected by increasing the Nb content.
JP-A-8-215551 (paragraph 0006) Japanese Patent Laid-Open No. 11-276866 (paragraph 0014) 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 No. 3749995 (paragraph 0039) Kunihiko Hashi et al., “Hydrogen Permeation Properties of Co—Ti—Nb Alloy”, Outline of the Japan Institute of Metals, VOL133, P.A. 427

  For this reason, the relationship between the alloy composition, structure, and hydrogen permeability is clarified, the hydrogen permeability and hydrogen embrittlement resistance are assigned to different phases, and a high-performance crystalline composite that can be used at 473K or higher is used. Realization of a phase hydrogen permeable alloy is desired.

  Accordingly, an object of the present invention is to provide a crystalline multi-phase hydrogen permeable alloy and a crystalline multi-phase hydrogen permeable alloy film that have hydrogen permeability and hydrogen embrittlement resistance and can be used at 473 K or higher. To do.

  The above-mentioned problem is that the present inventors have made a Co-Ti-Nb alloy with a TiNb phase in which Co is dissolved (hereinafter referred to as TiNb phase) and a CoTi phase in which Nb is dissolved (hereinafter referred to as CoTi phase). In an alloy composed of eutectic (CoTi + TiNb), by limiting the alloy composition to the vicinity of the composition on the line connecting the primary crystal composition and the eutectic composition, the primary crystal TiNb phase becomes eutectic (CoTi + TiNb). This was solved by finding that an alloy having an enclosed structure could be produced and that hydrogen embrittlement resistance could be maintained even when the volume ratio of the primary TiNb phase was increased.

  The multiphase Co—Ti—Nb-based crystalline hydrogen permeable alloy of the present invention is characterized by comprising a composite phase of a phase responsible for hydrogen permeability and a phase responsible for hydrogen embrittlement resistance.

  The multiphase Co—Ti—Nb alloy has a structure in which a eutectic (CoTi + TiNb) surrounds the initial phase TiNb phase. Thereby, even if the volume ratio of the primary TiNb phase is increased, it becomes possible to produce a multi-phase hydrogen permeable alloy that maintains hydrogen embrittlement resistance, and hydrogen can permeate efficiently.

The Co-Ti-Nb based alloy, Co-Ti-Nb3 on the diagram yuan state, the point _{A (Co 20 Ti 30 Nb 50} ), point _{B (Co 20 Ti 10 Nb 70} ), point _{C (Co 10 Ti} 10 Nb ₈₀ ) and point D (Co ₁₀ Ti ₃₀ Nb ₆₀ ) (where the alloy composition is all atomic%), and the point P on the Co—Ti—Nb ternary phase diagram It is in a region including a line segment PQ connecting (Co ₃₅ Ti ₃₅ Nb ₃₀ ) and point Q (Co ₅ Ti ₈ Nb ₈₇ ) (wherein the alloy composition is all atomic%), and the primary crystal and eutectic crystal It is the alloy composition which consists of only. If the amount of Nb is larger than this range, hydrogen embrittlement is remarkable and it is not suitable as a hydrogen permeable alloy. If the amount of Nb is less than this range, the hydrogen permeation coefficient becomes extremely small, so that it is not suitable as a hydrogen permeation alloy that can solve the aforementioned problems. On the other hand, if the Ti content or Co content is out of this range, the primary TiNb phase and the eutectic (CoTi + TiNb) structure are destroyed, or a third phase other than the TiNb phase and the CoTi phase is generated, and the hydrogen permeability coefficient and hydrogen resistance Since the embrittlement property is lowered, it is not suitable as a hydrogen permeable alloy.

  The metal film produced from the alloy of the present invention 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.

  A Pd film or a Pd alloy film is further formed on both surfaces of the metal film (that is, a side where the raw material to be treated is supplied and a side where purified hydrogen is extracted), and the thickness of the Pd film or the Pd alloy film is 50 to 400 nm. Features. 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 this study, by using a Co—Ti—Nb-based multiphase alloy having a specific composition, it is possible to achieve both excellent hydrogen permeability and resistance to hydrogen embrittlement at 473 K or higher. There is an effect.

First, in the Co ₃₀ Ti ₃₀ Nb ₄₀ (atomic%) alloy composed of a eutectic (CoTi + TiNb) and a primary TiNb phase in a cast state, the inventors of the present invention have the composition of the primary TiNb phase and the composition of the eutectic (CoTi + TiNb). Respectively. Next, on the Co-Ti-Nb ternary phase diagram, an alloy having a composition near the line connecting the two compositions is composed of a primary TiNb phase and a eutectic (CoTi + TiNb). Since the hydrogen embrittlement resistance can be maintained even if it is increased, the possibility of being useful as a metal film for hydrogen permeation that can solve the above-mentioned problems was found and confirmed by hydrogen permeation experiments.

According to the embodiment of the present invention, a film made of a Co—Ti—Nb-based alloy is used as the hydrogen permeable metal film, and this metal film is made of a primary TiNb phase and a eutectic (CoTi + TiNb). That is, the composition of the Co—Ti—Nb alloy material is represented by point A (Co ₂₀ Ti ₃₀ Nb ₅₀ ), point B (Co ₂₀ Ti ₁₀ Nb ₇₀ ), point C (Co ₁₀ Ti ₁₀ Nb ₈₀ ) and point D (Co ₁₀ Ti ₃₀ Nb ₆₀ ) (wherein the alloy composition is all atomic%), and on the Co—Ti—Nb ternary phase diagram , In a region including a line segment PQ connecting point P (Co ₃₅ Ti ₃₅ Nb ₃₀ ) and point Q (Co ₅ Ti ₈ Nb ₈₇ ) (wherein the alloy composition is all atomic%), and the primary crystal And an alloy composition consisting only of eutectic can provide a multiphase alloy material having a structure in which the primary crystal TiNb phase is surrounded by eutectic (CoTi + TiNb). Cast alloy material to gold A metal membrane can be provided. This multiphase alloy material is excellent in both properties of hydrogen permeability and hydrogen embrittlement resistance, and is suitable for forming a metal film for hydrogen permeation. Although the hydrogen permeability coefficient of this multiphase alloy varies depending on the composition, it shows a hydrogen permeability far exceeding that of a Pd alloy film currently in practical use as a metal film for hydrogen purification.

  The metal film made of the multi-phase alloy of the present invention is low in cost because it can be produced at a cost of 1/4 to 1/8 of that of the Pd alloy film. It can be said that it is a material that can be applied as an alternative.

  The method for producing the alloy material of the present invention is not particularly limited, but after blending the raw metal so as to have a predetermined composition, arc melting in an inert gas atmosphere such as Ar, or in an inert gas atmosphere such as Ar or in vacuum These are prepared by melting methods such as high-frequency induction heating melting, melting in an inert gas atmosphere such as Ar or in an electric furnace in vacuum, electron beam melting in vacuum, or laser heating melting.

  Or, after pulverizing the alloy prepared by the above melting method, alloy powder subjected to mechanical grinding in an inert gas atmosphere such as Ar, or after blending each raw metal powder to have a predetermined composition, Ar or the like It is produced by a powder metallurgy method for solidifying and molding a powder subjected to mechanical alloying in an inert gas atmosphere.

  From the experimental results for a number of compositions, the one in the broken line surrounded by points A, B, C and D shown in FIG. 1 (hydrogen permeable alloy according to the present invention) is particularly useful. In FIG. 1, the ■ mark indicates embrittlement in the cast state, the ♦ mark indicates that it becomes brittle during hydrogen permeation measurement, and the Δ mark outside the broken line area has excellent ductility but a small hydrogen permeation coefficient. These are all not suitable for hydrogen permeable alloy membranes. The ○ mark can be used as a hydrogen permeable alloy, but its hydrogen permeability coefficient is not so high. The ◎ marks are included in the hydrogen permeable alloy within the broken line surrounded by the points A, B, C and D described above.

  The thinner the metal membrane for hydrogen permeation, the greater the hydrogen permeation flux (amount) and the better the hydrogen permeation efficiency. However, as the thickness of the metal film is reduced, the mechanical strength is reduced. Therefore, in the case of these alloy systems, the thickness of the alloy film is preferably 0.01 to 3 mm.

  In order to use these alloy materials as metal membranes for hydrogen permeation, the source gas side (upstream, high-pressure hydrogen side) and the refined hydrogen side (downstream, low-pressure hydrogen side) sandwiching the alloy material on both sides of the alloy material In addition, it is necessary to further form a Pd film or a Pd alloy film for hydrogen dissociation and recombination, respectively. The thickness is generally 50 to 400 nm, preferably 100 to 200 nm.

  The method for forming Pd or Pd alloy film on both sides of the alloy film for hydrogen dissociation and recombination is not particularly limited. For example, vacuum deposition, spuck ring, ion plating, electrolytic plating, electroless plating, etc. Any of these may be used.

  Hereinafter, examples and comparative examples of the present study will be described.

  Example 1

Co (purity 99.9%), Ti (purity 99.5%) so that the composition of the Co _x Ti _y Nb _(100-xy) alloy material is x = 30 atomic% and y = 30 atomic%. A predetermined amount of Nb (99.9%) was blended. 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, 360 mmHg argon gas was introduced to perform arc melting. 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. A disk having a diameter of 12 mm and a thickness of 0.6 mm was cut out from the ingot thus obtained by electric discharge machining to obtain a measurement sample.

  After polishing both sides of the sample with a paper file, buff, and then α-alumina with a diameter of 0.5 μm, microstructure observation using a scanning electron microscope (SEM) and an energy dispersive X-ray analyzer (EDS) were used. Chemical analysis was performed.

FIG. 2 shows an SEM photograph of the Co ₃₀ Ti ₃₀ Nb ₄₀ alloy material. This alloy material has only a structure in which the white primary crystal TiNb phase is surrounded by eutectic (CoTi + TiNb). As a result of chemical analysis, the compositions of the eutectic (CoTi + TiNb) phase and the primary crystal TiNb phase were Co ₃₅ Ti ₃₅ Nb ₃₀ (atomic%) and Co ₅ Ti ₈ Nb ₈₇ (atomic%), respectively. These compositions are indicated by points P and Q on FIG.

  Next, a plurality of Co—Ti—Nb alloys having a composition near the line connecting the P point and the Q point were produced, and a hydrogen permeation test was performed.

Co (purity 99.9%), Ti (purity 99.5%) so that the composition of the Co _x Ti _y Nb _(100-xy) alloy material is x = 17 atomic% and y = 19 atomic%. A predetermined amount of Nb (99.9%) was blended, and a disk sample was prepared by the above method.

  Both sides of the sample were polished with a paper file, a buff, and then α-alumina having a diameter of 0.5 μm, and a scanning electron microscope (SEM) was used to observe the microstructure of the sample. The volume occupancy of the phase was calculated with a Macintosh computer using the public domain NIH image program.

An SEM photograph of the Co ₁₇ Ti ₁₉ Nb ₆₄ alloy material thus obtained is shown in FIG. It can be seen that it is composed only of primary TiNb and eutectic (CoTi + TiNb). The primary phase TiNb which is a white phase is surrounded by eutectic, and the volume ratio thereof is 65% by volume.

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 adhering 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. Then, 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 0.97 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 (4), the hydrogen permeation coefficient Φ is determined from the slope of the J × L vs. (Pu ^0.5 −Pd ^0.5 ) plot.

The hydrogen permeability coefficient at 673 K of the Co ₁₇ Ti ₁₉ Nb ₆₄ alloy material is 4.55 × 10 ⁻⁸ (molH ₂ m ⁻¹ s ⁻¹ Pa ^−0.5 ), which is 3.5 of that of pure Pd. It was twice.

  As described above, it has been found that the multiphase alloy composed of eutectic exhibits a particularly excellent hydrogen permeation coefficient, that is, hydrogen permeation characteristics, and can be used as a metal film for hydrogen permeation.

  (Example 2)

The production of the Co—Ti—Nb alloy was carried out in the same manner as in Example 1. However, the composition was such that x = 19 atomic% and y = 21 atomic%. The SEM photograph of the obtained Co ₁₉ Ti ₂₁ Nb ₆₀ alloy material in the cast state is shown in FIG. It can be seen that this alloy material is composed only of primary TiNb and eutectic (CoTi + TiNb). The primary phase TiNb, which is a white phase, was surrounded by eutectic, and the volume ratio was 61% by volume. This alloy material had a hydrogen permeation coefficient at 673 K of 4.19 × 10 ⁻⁸ (molH ₂ m ⁻¹ s ⁻¹ Pa ^−0.5 ), and could be used as a hydrogen permeable metal film.

  (Comparative Example 1)

  The method for producing the Co—Ti—Nb alloy was the same as in Example 1. The composition was such that x = 21 atomic% and y = 23 atomic%.

The obtained Co ₂₁ Ti ₂₃ Nb ₅₆ alloy material has a composition outside of the hydrogen-permeable multiphase Co—Ti—Nb alloy formation region according to the present invention (enclosed by points A, B, C, and D in FIG. 1). Although it was out of the area, it was a sample capable of measuring hydrogen permeation. This alloy material was composed only of primary crystal TiNb and eutectic (CoTi + TiNb), and the volume ratio of the primary crystal TiNb phase was 53% by volume. Hydrogen permeation coefficient at 673K of this alloy was _{^{3.31 × 10 -8 (molH 2 m}} -1 s -1 Pa -0.5).

  (Comparative Example 2)

  The method for producing the Co—Ti—Nb alloy was the same as in Example 1. The composition was such that x = 25.5 atomic% and y = 26.5 atomic%.

The obtained Co _25.5 Ti _26.5 Nb ₄₈ alloy material has a composition outside the hydrogen-permeable multiphase Co—Ti—Nb alloy formation region (points A, B, C and D) according to the present invention in FIG. It was a sample capable of measuring hydrogen permeation. This alloy material was composed only of primary TiNb and eutectic (CoTi + TiNb), and the volume ratio of the primary TiNb phase was 39% by volume. The hydrogen permeation coefficient of this alloy material at 673 K was 2.72 × 10 ⁻⁸ (molH ₂ m ⁻¹ s ⁻¹ Pa ^−0.5 ).

  (Comparative Example 3)

  The method for producing the Co—Ti—Nb alloy was the same as in Example 1. The composition was such that x = 30 atomic% and y = 30 atomic%.

The resulting _Co 30 _Ti 30 _{Nb 40} alloy material, surrounded by the composition of the hydrogen permeable for multi-phase Co-Ti-Nb alloy forming-area according to the present invention in FIG. 1 (point A, B, C and D Although it was out of the area, it was a sample capable of measuring hydrogen permeation. This alloy material was composed only of primary TiNb and eutectic (CoTi + TiNb), and the volume ratio of the primary TiNb phase was 24% by volume. Hydrogen permeation coefficient at 673K of this alloy was _{^{2.45 × 10 -8 (molH 2 m}} -1 s -1 Pa -0.5).

  (Comparative Example 4)

  The method for producing the Co—Ti—Nb alloy was the same as in Example 1. The composition was such that x = 35 atomic% and y = 35 atomic%.

The obtained Co ₃₅ Ti ₃₅ Nb ₃₀ alloy material has the same composition as the eutectic (CoTi + TiNb) phase. In FIG. 1, the composition was outside the hydrogen-permeable multiphase Co—Ti—Nb alloy formation region (outside the region surrounded by points A, B, C, and D) according to the present invention, but hydrogen permeation measurement is possible. Sample. This alloy material is composed only of eutectic (CoTi + TiNb), and no primary crystal TiNb phase is generated. The hydrogen permeation coefficient of this alloy material at 673 K was 2.32 × 10 ⁻⁸ (molH ₂ m ⁻¹ s ⁻¹ Pa ^−0.5 ).

  (Comparative Example 5)

  The method for producing the Co—Ti—Nb alloy was the same as in Example 1. The composition was such that x = 5 atomic% and y = 8 atomic%.

The obtained Co ₅ Ti ₈ Nb ₈₇ alloy material is an alloy having the same composition as the primary crystal TiNb phase. In FIG. 1, the composition is outside the hydrogen-permeable multiphase Co—Ti—Nb alloy formation region (outside the region surrounded by points A, B, C, and D) according to the present invention. This alloy material was a primary TiNb single phase alloy (volume ratio of TiNb phase was 100%). This alloy could not be used as a hydrogen permeable alloy because it became brittle due to hydrogen storage.

  (Comparative Example 6)

  The method for producing the Co—Ti—Nb alloy was the same as in Example 1. The composition was such that x = 10 atomic% and y = 10 atomic%.

The obtained Co ₁₀ Ti ₁₀ Nb ₈₀ alloy material has a composition surrounded by points A, B, C, and D outside the formation region of the hydrogen-permeable multiphase Co—Ti—Nb alloy according to the present invention in FIG. Out of area). This alloy material was composed only of primary TiNb and eutectic (CoTi + TiNb), and the volume ratio of the primary TiNb phase was 83% by volume. This alloy could not be used as a hydrogen permeable alloy because it became brittle due to hydrogen storage.

  From the above, it can be seen that all the alloys on the line connecting the P point and the Q point are composed only of primary TiNb and eutectic (CoTi + TiNb). FIG. 5 shows the relationship between the volume ratio of primary crystals of these alloys and the hydrogen permeability coefficient. When the Nb concentration of the alloy is small, the volume ratio of the primary TiNb phase is small and the hydrogen permeability coefficient is small (Comparative Examples 1 to 4). Therefore, in order to obtain a high-performance dual-phase hydrogen permeable alloy that can solve the above-described problems, it is necessary to increase the volume ratio of the primary TiNb phase. On the other hand, if the volume ratio of the primary TiNb phase is too large, it becomes embrittled during hydrogen storage and cannot be used as a hydrogen permeable alloy (Comparative Examples 5 and 6). Therefore, there is an upper limit for the Nb concentration. The upper limit is considered to be 58 to 75% by volume. By selecting an alloy composition in a range surrounded by A, B, C, and D in FIG. 1, an alloy having a particularly high hydrogen permeability coefficient can be obtained without being destroyed during hydrogen storage.

  (Comparative Example 7)

  The method for producing the Co—Ti—Nb alloy was the same as in Example 1. The composition was such that x = 30 atomic% and y = 20 atomic%.

The obtained Co ₃₀ Ti ₂₀ Nb ₅₀ alloy had a composition outside the hydrogen-permeable multiphase Co—Ti—Nb alloy formation region (outside the region surrounded by points A, B, C and D) in FIG. However, it was a sample capable of measuring hydrogen permeation. This alloy material was composed of primary TiNb, eutectic (CoTi + TiNb) and a small amount of CoTi phase, and the volume ratio of primary TiNb phase was 28% by volume. The hydrogen permeation coefficient at 673 K of this alloy material was 1.54 × 10 ⁻⁸ (molH ₂ m ⁻¹ s ⁻¹ Pa ^−0.5 ).

  (Comparative Example 8)

  The method for producing the Co—Ti—Nb alloy was the same as in Example 1. The composition was such that x = 20 atomic% and y = 20 atomic%.

The obtained Co ₂₀ Ti ₂₀ Nb ₆₀ alloy has a composition outside the hydrogen-permeable multiphase Co—Ti—Nb alloy forming region in FIG. 1 (outside the region surrounded by points A, B, C and D). Primary TiNb, eutectic (CoTi + TiNb) and a small amount of CoTi phase. The volume ratio of the primary TiNb phase was 45% by volume. This alloy could not be used as a hydrogen permeable alloy because it became brittle due to hydrogen storage.

From the results of Examples 1 and 2 and Comparative Example 8, the following is considered. Co ₁₇ Ti ₁₉ Nb ₆₄ alloy (Example 1) and Co ₁₉ Ti ₂₁ Nb ₆₀ alloy (Example 2) having an alloy composition on the PQ line and composed only of primary crystal TiNb and eutectic (CoTi + TiNb) The volume ratios of the primary TiNb phases were 65% by volume and 61% by volume, respectively, and despite the high volume ratios of the primary TiNb phases, they were not broken by hydrogen storage and exhibited extremely high hydrogen permeability coefficients. On the other hand, the Co ₂₀ Ti ₂₀ Nb ₆₀ alloy (Comparative Example 8) having an alloy composition deviated from the PQ line and generating a CoTi phase in addition to primary TiNb and eutectic (CoTi + TiNb) has a primary TiNb phase. Although the volume ratio was as low as 45%, it was broken by hydrogen embrittlement. From the above, it is considered that an alloy composed only of primary crystal TiNb and eutectic (CoTi + TiNb) and having no other phases is excellent in hydrogen embrittlement resistance.

  By limiting the alloy composition to the vicinity of the PQ line, an alloy composed of primary TiNb and eutectic (CoTi + TiNb) can be produced. Since the alloy having this structure is excellent in hydrogen embrittlement resistance, it does not break even when the volume ratio of the primary TiNb phase is increased, and an alloy having extremely high hydrogen permeability can be obtained.

  (Comparative Example 9)

  The method for producing the Co—Ti—Nb alloy was the same as in Example 1. The composition was such that x = 20 atomic% and y = 10 atomic%.

The obtained Co ₂₀ Ti ₁₀ Nb ₇₀ alloy has a composition outside the hydrogen-permeable multiphase Co—Ti—Nb alloy forming region in FIG. 1 (outside the region surrounded by points A, B, C and D). It was composed of primary crystal TiNb, eutectic (CoTi + TiNb) and a brittle CoNb intermetallic compound phase. This alloy could not be used as a hydrogen permeable alloy because it became brittle due to hydrogen storage.

  (Comparative Example 10)

  The method for producing the Co—Ti—Nb alloy was the same as in Example 1. The composition was such that x = 10 atomic% and y = 30 atomic%.

_Co 10 _Ti 30 _{Nb 60} alloy obtained, its composition be for hydrogen permeation diploid Co-Ti-Nb alloy forming-area (point A, B, outside the area surrounded by the C and D) in FIG. 1 The primary crystal TiNb and the eutectic (CoTi + TiNb) alone. The volume ratio of the primary TiNb phase was 80% by volume. This alloy could not be used as a hydrogen permeable alloy because it became brittle due to hydrogen storage.

  (Comparative Example 11)

  The method for producing the Co—Ti—Nb alloy was the same as in Example 1. The composition was such that x = 10 atomic% and y = 20 atomic%.

The obtained Co ₁₀ Ti ₂₀ Nb ₇₀ alloy has a composition outside the hydrogen-permeable multiphase Co—Ti—Nb alloy formation region (outside the region surrounded by points A, B, C and D) in FIG. The primary crystal TiNb and the eutectic (CoTi + TiNb) alone. This alloy could not be used as a hydrogen permeable alloy because it became brittle due to hydrogen storage.

  When the amount of Ti is smaller than that of the PQ line, a brittle CoTi intermetallic compound phase is generated, and thus cannot be used as a hydrogen permeable alloy. On the other hand, when Ti is excessive from the PQ line, even if the alloy is composed only of primary TiNb and eutectic (CoTi + TiNb), the Ti concentration of the primary crystal becomes high, and embrittlement occurs during hydrogen storage. Cause. Therefore, the alloy composition that can be used as the hydrogen permeable alloy is limited to the vicinity of the PQ line.

  According to the present invention, by using a Co—Ti—Nb crystalline 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, Furthermore, both hydrogen permeability and hydrogen embrittlement resistance 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.

FIG. 3 is a ternary phase diagram showing a composition region for producing a hydrogen-permeable multiphase Co—Ti—Nb-based alloy of the present invention, and the numerical values shown below the circles indicate the hydrogen permeation coefficient at 673K. The broken line region surrounded by points A, B, C, and D is an alloy composition in which the multiphase hydrogen permeable alloy according to the present invention is obtained in Examples 1 and 2. It is a SEM photograph of _Co 30 _Ti 30 _{Nb 40} alloy used to determine the eutectic composition (P point of Fig. 1) and the primary crystal composition of (Q point of Fig. 1). 2 is a SEM photograph of Co ₁₇ Ti ₁₉ Nb ₆₄ alloy in Example 1. 4 is a SEM photograph of Co ₁₉ Ti ₂₁ Nb ₆₀ alloy in Example 2. It is a graph which shows the relationship between the volume ratio of the primary crystal of the alloy (Example 1, 2 and Comparative Examples 1-4) on a PQ line | wire, and the hydrogen permeability coefficient in 673K.

Claims (3)

Comprising a composite phase, the composite phase surrounding the TiNb phase formed as a primary crystal of a co-crystal (CoTi + TiNb) of a CoTi phase in which Nb is dissolved and a TiNb phase in which Co is dissolved,
Co-Ti-Nb3 on the diagram yuan state, the point _{A (Co 20 Ti 30 Nb 50} ), point _{B (Co 20 Ti 10 Nb 70} ), point _{C (Co 10 Ti 10 Nb 80} ) and the point _{D (Co} 10 Ti ₃₀ Nb ₆₀ ) (wherein the alloy composition is all atomic%), and the alloy composition in the region surrounded by
In the Co-Ti-Nb ternary phase diagram, a line segment PQ connecting point P (Co ₃₅ Ti ₃₅ Nb ₃₀ ) and point Q (Co ₅ Ti ₈ Nb ₈₇ ) (however, the alloy composition is all atomic%) is included. The alloy composition consisting of only primary crystals and eutectic crystals.
A double phase Co—Ti—Nb-based crystalline double phase hydrogen permeable alloy characterized in that   A hydrogen permeable alloy film produced by blending each of the constituent elements of the crystalline hydrogen permeable alloy according to claim 1, wherein the thickness of the multiphase alloy is 0.01 to 3 mm.   A hydrogen permeable alloy characterized in that a Pd film or a Pd alloy film is formed on both sides of the hydrogen permeable alloy film according to claim 2, and the thickness of the Pd film or Pd alloy film is in the range of 50 to 400 nm. film.

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