JP2006175379A - Production method of hydrogen separation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production method of a hydrogen separation film enabling high hydrogen permeability and high purity of produced hydrogen and made of a little amount of a Pd alloy material. <P>SOLUTION: The production method of the hydrogen separation film comprises the steps of: obtaining ingot by dissolving Pd alloy in a floating type cold crucible dissolution method, removing inclusion accumulated parts of the ingot, and forging and rolling the ingot whose inclusion accumulated parts are removed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a hydrogen separation membrane. In particular, the present invention relates to a method for producing a hydrogen separation membrane having a Pd alloy as a main component, a sufficiently thin film thickness, and high hydrogen permeability.

  Conventionally, hydrogen separation membranes using Pd alloy membranes have been used for high-purity gas purification in semiconductor manufacturing plants. On the other hand, construction of a hydrogen station has been started to supply hydrogen to fuel cell vehicles that are being developed in recent years. As a hydrogen production method, an on-site type hydrogen production apparatus for producing hydrogen by reforming city gas or the like in a hydrogen station is being studied along with a method of delivering hydrogen produced in a factory by a tank truck or the like. As a hydrogen production apparatus, a membrane reformer type hydrogen production apparatus that is superior in production efficiency to the PSA method using an absorbent is being studied. The membrane reformer-type hydrogen production apparatus is designed to improve hydrogen production efficiency by installing a hydrogen separation membrane in a reactor that performs a reforming reaction of city gas or the like and drawing out hydrogen.

  As such a hydrogen separation membrane, for example, a palladium (Pd) -based metal membrane exhibiting extremely high hydrogen selective permeability is used. The hydrogen selective permeation phenomenon exhibited by Pd and its alloy film is that hydrogen molecules in the hydrogen mixed gas are adsorbed on the Pd film to be in an atomic state, further ionized, diffused to the opposite side of the film, and recombined. It is supposed to happen to become gas.

  As a method for producing the hydrogen separation membrane, there is a method in which Pd or a metal alloy of the alloy membrane is rolled after being melted by arc or melted at high frequency. As a result, the Pd alloy film can be thinned to about 20 μm. However, in this method, when the Pd alloy film is further thinned by a rolling method, a pinhole contained in the material and having an inclusion equivalent to the film thickness with a particle size of the order of 10 μm is generated. There's a problem. The presence of pinholes not only deteriorates the product yield, but also causes leakage and a decrease in the purity of produced hydrogen, and may adversely affect durability.

In the examination so far, the Pd alloy is melted by using high-frequency power as a heat source in a ceramic crucible such as alumina installed in a chamber in which a normal atmosphere is controlled, and cast into a mold such as high-purity carbon. In the case of forming a thin film by processing and rolling to form a hydrogen separation membrane, a decrease in yield due to the generation of pinholes was not a problem up to a film thickness of 20 μm and was applicable. On the other hand, when trying to further reduce the film thickness, it was possible to reduce the film thickness to about 5 μm by rolling, but the frequency of pinholes increased, and pinholes with an area of 1 cm ² or more which is practically required were increased. It was difficult to produce a film without this.

  Patent Document 1 describes a method for producing a hydrogen separation membrane in which a Pd alloy material obtained by melting in an arc in a water-cooled copper hearth or by high-frequency melting using a calcia crucible is rolled.

  In order to improve the performance of the hydrogen separation membrane, it is conceivable to reduce the thickness of the hydrogen separation membrane to increase the hydrogen permeation amount. Patent Document 2 describes a method for producing a hydrogen-selective palladium-supported metal sheet film by chemically etching or electrochemically dissolving at least one film surface of a cold-rolled palladium-supported film. However, since this method is performed after rolling, there are problems that the number of processes is increased and that Pd used for the production of the film is still large.

Further, Patent Documents 3 and 4 disclose a method for producing a hydrogen separation membrane in which a Pd alloy thin film is formed by plating, vapor deposition, or the like on a porous substrate that gives gas permeability to the substrate. In this method, the film thickness can be reduced to about 5 μm to 10 μm. However, in such a thin film forming method, since the pores on the porous substrate must be blocked, the film thickness inevitably increases. When trying to reduce the film thickness, it becomes impossible to completely close the pores on the porous substrate, it is difficult to eliminate film defects such as pinholes, it is difficult to become gas tight, and the production hydrogen purity is low. There is a problem.
JP 2003-10659 A Special table 2003-530488 Japanese Patent Laid-Open No. 62-121616 JP-A-5-123548

  An object of the present invention is to provide a method for producing a hydrogen separation membrane, which has a high hydrogen permeability, a high purity of the produced hydrogen, and can be produced with a small amount of Pd alloy material.

  As a result of investigating the cause of pinholes in the hydrogen separation membrane produced by the prior art by the present inventors, inclusion particles such as oxides having a diameter of 5 μm or more, which is the same as the film thickness, exist in the material and penetrate the membrane. It became clear that there are many. In addition, as a result of investigating the inclusion route of such inclusions, there is a possibility of mixing during melting casting and rolling, but the crucible material was eroded by the molten metal during the melting process, and part of the molten alloy was peeled off in the molten alloy. It is clear that some of them are separated by floating up to the upper surface due to the difference in density during melting, but most of them are mixed again in the alloy and solidified during casting. It was. Therefore, it was considered effective to reduce inclusions by preventing the crucible material that had been peeled from mixing into the molten alloy during melting of the alloy or by not peeling the crucible material.

  That is, the present invention is a method for manufacturing a hydrogen separation membrane, comprising: dissolving a Pd alloy by a floating cold crucible melting method to obtain an ingot; removing an inclusion accumulation portion of the ingot; and the inclusion Forging and rolling the ingot from which the accumulation portion has been removed.

  The present invention is also a method for producing a hydrogen separation membrane, comprising: dissolving a Pd alloy by a floating cold crucible melting method to obtain an ingot; removing an inclusion accumulation portion of the ingot; A step of melting the ingot from which the material accumulation portion has been removed again by a floating cold crucible melting method, a step of casting the melted Pd alloy into a mold, and a step of forming and rolling the cast Pd alloy .

  In the levitation type cold crucible melting, the melting atmosphere is preferably an argon atmosphere or an argon-based hydrogen mixed atmosphere. The argon-based hydrogen mixed atmosphere refers to an atmosphere containing argon as a main component and may contain 0.1 to 20% by volume of hydrogen.

  In the step of rolling the ingot from which the inclusion accumulation portion has been removed, the ingot is preferably rolled to 10 μm or less.

  In the above hydrogen separation membrane manufacturing method, the floating cold crucible melting method does not necessarily require the molten metal to be completely lifted from the crucible, and the molten metal and the crucible are in partial contact with each other. May be.

  According to another aspect, the present invention is a hydrogen separation membrane manufactured by the method described above.

  According to the method for producing a hydrogen separation membrane of the present invention, the hydrogen separation membrane can be reduced to 1/2 of the conventional thickness, specifically, to a thickness of 20 μm or less. Obtainable. In addition, since the hydrogen permeation performance is inversely proportional to the film thickness, by setting the film thickness to 1/2 that of the conventional film, it is possible to obtain hydrogen permeation performance more than twice that of the conventional one, and to halve the Pd alloy material used. The amount of hydrogen production / membrane cost can be increased four times or more compared to the case of the prior art.

  Hereinafter, the present invention will be described in detail with reference to embodiments. The following description does not limit the invention.

  A method for producing a hydrogen separation membrane according to an embodiment of the present invention includes a step of melting a Pd alloy by a floating cold crucible melting method to obtain an ingot, a step of removing an inclusion accumulation portion of the ingot, and an inclusion Rolling the ingot from which the accumulation portion has been removed.

  In the manufacturing method according to the present embodiment, as a Pd alloy used as a raw material, a Pd—Ag alloy, a Pd—Au alloy, a Pd—Cu alloy, a Pd—rare earth alloy, or the like can be used, but is not limited thereto. Such a Pd alloy may contain a metal other than the main component. Moreover, normally, the raw material itself put into the melting apparatus contains impurities having a particle diameter of 1 to 20 μm, for example, metal oxides such as alumina and silica.

  Such a Pd alloy raw material is melted by a floating cold crucible melting method. The levitation type cold crucible melting method is a method in which a conductive metal is placed in a water-cooled copper crucible that is divided into multiple or slits in the circumferential direction, an electromagnetic coil is installed around the crucible, and high-frequency power is applied to the coil. Eddy current is induced on the surface of the metal material, and the metal is melted by the Joule heat, and an electromagnetic reaction force acts between the eddy current acting on the metal surface and the eddy current generated on the crucible surface, so that the current conditions are appropriate. In this method, molten metal can be held in the air in a non-contact manner, and various metal materials are dissolved in a non-contact state with the crucible. However, in reality, it is difficult for the molten metal crucible to be completely in a non-contact state, and in some cases, the molten metal crucible may be in a contact state.

  In any case, there is almost no contact between the crucible and the molten metal, and since the crucible is a metal, there is no contamination inclusion due to ceramic crucibles such as alumina and silica during melting. Furthermore, in the floated molten metal, an outward flow is generated by a combination of electromagnetic force and buoyancy, so inclusions such as oxides with low density accumulate on the outer periphery of the molten metal. In particular, an oxide having a large particle size has a larger density difference from the molten metal, and therefore reliably accumulates on the outer periphery. By melting the molten metal in the crucible as it is and removing the outer peripheral portion by machining, a high-purity ingot with few inclusions such as oxides can be obtained. The high purity ingot is formed by forging or the like and rolled to obtain a hydrogen separation membrane with few inclusions and a low pinhole frequency even when rolled to a thickness of 10 μm or less.

  In the above-mentioned levitation type cold crucible melting, the crucible is usually installed in a container whose atmosphere can be controlled. Before melting the metal, it is preferable to evacuate the container with a vacuum pump and then replace the interior with Ar gas several times to perform the melting with the oxygen and nitrogen partial pressures in the container lowered as much as possible. However, since oxidation and nitridation of the molten metal may still be unavoidable, a mixed gas of Ar and hydrogen is used as a replacement gas to prevent this. As such a mixed gas, a gas mainly containing Ar gas and containing 0.1 to 20% by volume of hydrogen can be used. As a result, oxides and nitrides produced by oxidation and nitridation during metal dissolution can be reduced, and inclusions are limited by the synergistic effect with inclusion discharge effect due to the above-mentioned original floating-type cold crucible dissolution. Can be reduced. Thereby, even if it is rolled to a thickness of 10 μm or less, the probability of pinholes is reduced and the production yield of the hydrogen separation membrane can be increased.

  On the other hand, similarly, the floating type cold crucible melting is performed, and after removing the outer periphery of the solidified ingot, the floating type cold crucible melting is performed once again, and it can be cast into a mold as it is. In this method, by making the mold shape into a flat plate shape, subsequent forging can be omitted, simple post-rolling can be performed, and the manufacturing process can be shortened.

  The floating type cold crucible melting of the Pd alloy raw material can be carried out by using a commercially available cold crucible melting apparatus. Here, the cold-crucible dissolution apparatus and the principle of levitation dissolution using the apparatus will be briefly described.

  FIG. 1 shows an example of a commercially available cold crucible dissolving apparatus. The cold crucible melting apparatus 1 includes a crucible 2 and induction coils 3 and 4. The crucible 2 is usually a copper-bottomed, substantially cylindrical container that is water-coolable, and has slits that are divided into, for example, 16 parts in the circumferential direction. The shape varies depending on the dissolution capacity, but is usually 50 to 300 mm in inner diameter and 50 to 400 mm in depth. After melting, a tap 21 may be provided at the bottom of the crucible 2 for the purpose of casting in a separately installed mold. The upper induction coil 3 is a high-frequency coil (for example, 200 kW · 30 kHz) that is mounted on the side surface of the crucible 2. The lower induction coil 4 is mounted on the side surface of the tap 21 and is a low frequency coil (for example, 100 kW · 3 kHz) as compared with the upper induction coil 3. Each induction coil 3, 4 includes a power source 31, 41.

  In such a cold crucible melting apparatus 1, when the power sources 31 and 41 of the induction coils 3 and 4 mounted on the crucible 2 are turned on and a high-frequency current is passed, an alternating magnetic field is generated in the crucible 2. As a result, an eddy current opposite to the coil current is generated in the metal 5 in the crucible 2, an electromagnetic repulsive force acts between the two currents, and Joule heat is generated in the metal, so that the metal 5 is levitated, It is known to heat and dissolve. According to such a cold crucible melting apparatus 1, an outward flow can be generated in the metal 5, and inclusions such as metal oxide can be discharged to the surface of the metal 5, and stable melting can be achieved. Is advantageous.

  In the present embodiment, it is preferable to melt 0.1 to 10 kg of Pd alloy at a time by a batch type levitation type cold crucible melting method. This is because it is not preferable to dissolve a large amount of metal at a time in order to generate an outward flow in the Pd alloy and efficiently discharge inclusions such as metal oxides to the surface of the molten metal. . The current condition at this time is 10 to 400 kW, and the dissolution time is preferably 10 to 60 minutes. This is because it takes 5 minutes or more for the metal to be in a stable state after melting, to form an outward flow, and for inclusions such as oxides to be discharged to the surface. However, these conditions can be changed according to the size of the cold crucible dissolving apparatus, and such conditions can be appropriately determined by those skilled in the art.

  Next, the power supply is stopped and the metal 5 is cooled as it is in the crucible 2 and solidified to obtain a Pd alloy ingot. At this time, the cooling rate is preferably 200 to 500 ° C./min. This is because inclusions such as oxides discharged on the surface are easily fixed as they are by rapid cooling. The obtained Pd alloy ingot usually has a defect and inclusion accumulation portion at the outer peripheral portion by flotation type cold crucible melting. Here, the inclusion mainly refers to metal oxides such as aluminum oxide, silicon oxide, calcium oxide, and magnesium oxide.

Subsequently, after the Pd alloy ingot is cooled to room temperature, defects and inclusion accumulation portions of the Pd alloy ingot are removed by cutting. The defect and inclusion accumulation portion of the Pd alloy ingot refers to a portion where the frequency of inclusions having a particle size of 2 μm or more is 1 or more per 1 mm ² in cross-sectional area when the cross section of the ingot is observed. Such frequency observation of inclusions can be determined by polishing a sampled ingot section, observing with an optical microscope or an electron microscope, and measuring the size and number of inclusions.

  The removal of the inclusion accumulation part can be carried out by peripheral cutting using a commercially available lathe. The cutting tool is made of high speed tool steel, cemented carbide or the like. The facets discharged at the time of cutting can be recovered, dissolved and purified, and reused as pure Pd.

  Next, the Pd alloy obtained by the above operation and having a significantly reduced frequency of inclusions having a particle size of 2 μm or more is forged and rolled. Forging is performed, for example, by heating a Pd alloy to 500 ° C. in an electric furnace and pressing it with a forging machine (hydraulic press) to form a shape that is close to a rectangular parallelepiped that is easy to roll. Normally, the shape is close to a rectangular parallelepiped with a plate thickness of 50 mm or less.

  Rolling is repeated until the sheet thickness reaches a predetermined thickness, for example, using a two-stage or four-stage small roll mill until the sheet thickness is about 0.5 mm. If the reduction becomes difficult, annealing is performed halfway. Annealing can be performed in an electric furnace at, for example, 500 ° C. for 1 hour. When the plate thickness is 0.5 mm or less, for example, a 20-stage small roll mill is used to roll to a final film thickness of 20 μm or less. Since the length of the rolled material becomes longer than 1 m, it is wound around a roll and continuously supplied. Intermediate annealing is performed similarly. It is preferable to roll until the final film thickness is 20 μm or less, preferably 10 μm or less. This is because the thinner the film thickness, the higher the hydrogen permeation performance, and the amount of expensive Pd alloy used can be reduced per predetermined hydrogen separation membrane. Then, a hydrogen separation membrane can be obtained by adjusting to an appropriate size as necessary.

The hydrogen separation membrane made of the Pd alloy thus obtained has a film thickness of 20 μm or less, preferably 10 μm or less, and has no pinhole in an area unit of 0.01 m ² , for example, and can be obtained with a yield of 70% or more. The hydrogen permeation performance of the hydrogen separation membrane obtained by the present invention is such that the hydrogen permeation flow rate per unit area and unit pressure difference is 5 × 10 ⁻³ mol / m ² / s / Pa ^1/2 or more, and the hydrogen purity is It is 6N or more, and is a sufficient characteristic to be applied to a hydrogen production apparatus for a fuel cell system or a semiconductor factory.

  According to the levitated cold crucible melting method according to the present embodiment, in particular, since the Pd alloy can be levitated and melted, it is avoided that impurities derived from a melting container such as a crucible that has occurred in the prior art are mixed into the Pd alloy. be able to. Also, by melting the Pd alloy and solidifying it as it is without casting it, the inclusions discharged to the outer periphery of the molten metal in the floating type cold crucible melting are moved again inside the metal or biased. And the inclusions can be accumulated on the outer periphery of the metal and effectively removed. And the high purity of Pd alloy can be achieved by rolling such a Pd alloy ingot. Furthermore, according to the floating type cold crucible melting method, the crucible used for melting can be repeatedly used without being disposable.

  On the other hand, as another embodiment, the floating type cold crucible melting is similarly performed, and after removing the outer periphery of the solidified ingot as it is, the floating type cold crucible melting is performed once again and cast into a mold as it is. At this time, the second flotation type cold crucible dissolution can be performed under the same dissolution conditions. In this method, since the mold shape is a flat plate shape, subsequent forging can be omitted, simple post-rolling can be performed, and the process can be shortened. Also in this case, inclusions such as oxides are removed by the first floating-type cold crucible melting and deletion of the outer periphery of the ingot, and a hydrogen separation membrane having a large hydrogen separation membrane and no pinholes is obtained by rolling to 20 μm or less. Can do.

Example 1 of the present invention is shown below.
As raw materials, 2 to 10 mm massive pure Pd (purity 99.9%) was prepared in 760 g, and 2 to 10 mm massive pure Ag (purity 99.9%) in 240 g.
Dissolution was performed using a commercially available cold crucible dissolution apparatus shown in FIG. The cold crucible melting apparatus 1 includes a crucible 2, an upper induction coil 3 having 5 turns, a lower induction coil 4 having 3 turns, and a container 7 for controlling the atmosphere covering them. The crucible 2 is made of copper, has an inner diameter of 60 mm, a height of 80 mm, and has a structure in which the inside is water-cooled. The crucible 2 has a slit with a width of 0.1 mm so as to be divided into 16 pieces in the circumferential direction. The raw material was put into the crucible, and the inside of the container 7 was evacuated to 1 Pa or less with a vacuum pump. Then, pure argon gas having a purity of 99.99% was introduced, and the internal pressure of the container was set to 5 × 10 ⁴ Pa. This evacuation and argon gas replacement operation was repeated three times. Next, 90 kW of high frequency power with a frequency of 50 kHz was applied to the upper induction coil 3, and 40 kW of high frequency power with a frequency of 3 kHz was applied to the lower induction coil 4. The charged Pd—Ag alloy melted and floated. The melting time was 30 minutes, and then the input power was cut off and quenched. The molten metal solidified and became 500 ° C. or less in about 3 minutes.

Then, it cooled to room temperature and took out the Pd-Ag alloy ingot. The shape was almost a disk shape with a diameter of 60 mm and a thickness of 29 mm. Next, cutting defects such as sink marks and inclusion inclusions were removed by cutting. Based on the results of optical microscope and cross-sectional observation of a Pd-Ag ingot produced under the same conditions, the frequency of inclusions having a particle size of 2 μm or more per cross-sectional area of 1 mm ² is about 2 mm on the top surface of the ingot. Since the side and bottom surfaces were about 1 mm, the top surface was further removed by 3 mm from the bottom of the sink, and the side and bottom surfaces were removed by 2 mm. For the cutting process, a commercially available lathe and milling machine were used. The facets discharged at the time of cutting were recovered, dissolved and purified, and reused as pure Pd. The disk-shaped Pd—Ag alloy ingot having a diameter of about 56 mm and a thickness of about 19 mm, in which the frequency of inclusions having a particle diameter of 2 μm or more obtained by the above operation was significantly reduced, was then forged. Forging is repeated by heating the Pd alloy ingot at 600 ° C. in an electric furnace in which Ar gas is circulated at a flow rate of 10 L / min, taking out from the furnace and pressurizing with a forging machine (hydraulic press machine), The plate was approximately 50 mm long, approximately 47 mm long, and approximately 20 mm thick. This is for making it easy to roll in the subsequent process.

  Next, rolling was performed. The forged Pd—Ag alloy ingot was repeatedly rolled using a two-stage small roll mill (roll diameter: 150 mm) until the plate thickness of 20 mm before rolling reached 0.5 mm. In the middle, annealing was performed four times. For annealing, the Pd alloy ingot was heated at 600 ° C. for 1 hour in an electric furnace in which Ar gas was circulated at a flow rate of 10 L / min to cool the furnace. As a result, a Pd alloy plate having a width of about 50 mm, a length of about 1.8 m, and a plate thickness of 0.5 mm was obtained. Next, using a 20-stage small roll mill (rolling roll diameter: 12 mm), the film was rolled to a final film thickness of 5 μm. Since the rolled material has a length of 2 m or longer, the rolled material was rolled by rolling and passing through a rolling mill while continuously feeding the winding rolls. However. A stainless steel foil having a width of 50 m was added to the Pd alloy plate between the rolling mill and the take-up roll. Further, annealing was performed three times along the way. The annealing was performed by continuously supplying between the winding rolls and passing through an electric furnace installed between the winding rolls. At that time, an arbitrary portion of the Pd alloy plate was heated at 700 ° C. for 10 minutes or more.

A part of the Pd—Ag alloy hydrogen separation membrane having a width of 50 mm, a thickness of 5 μm, and a length of about 180 m obtained by the above steps was cut into a length of 200 mm.
Next, as shown in FIG. 2, a support plate 10 was manufactured. 2A is a front view of the support plate 10, and FIG. 2B is a side view. The support plate 10 is a stainless steel plate having a width of 50 mm, a length of 200 mm, and a thickness of 0.1 mm, and a large number of through-holes 101 are provided in the central portion leaving an edge width of 5 mm. Further, support plates having a width of 50 mm × a length of 200 mm and thicknesses of 0.3 mm and 0.5 mm were similarly manufactured. These three sheets and the Pd alloy hydrogen separation membrane were superposed and joined by diffusion bonding to obtain a joined body 12. Diffusion bonding was performed by applying a surface pressure of ² kg / mm ² in a vacuum furnace heated to 500 ° C. and maintaining for 1 hour.

  Next, a base plate 11 having a width of 54 mm, a thickness of 10 mm, and a length of 210 mm shown in FIG. 3 (a step of 6 mm in depth is performed at a portion having a width of 40 mm and a length of 180 mm excluding the edge on only one side). The stepped portion is connected to the outside by a pipe 111 at the end in the longitudinal direction by a pipe 111), and the joined body 12 is welded to the periphery thereof, and the structure of the hydrogen separation membrane shown in FIG. 13 was obtained.

  After confirming that there is no welding defect by PT test, as shown in FIG. 5, the membrane / support plate / base plate structure 13 is placed in a pressurized container 14 having an inner diameter of 70 mm and a length of 350 mm. Then, the inside of the container was pressurized to 2 MPa with nitrogen gas, and the amount of gas leaking from the base plate pipe 111 through the membrane / support plate was measured, thereby measuring the amount of leakage of the membrane. As the inspection determination threshold value, the leakage gas flow rate was set to 0.1 cc / min, and a specimen having a leakage amount less than this was regarded as acceptable. As a result of producing and evaluating 20 specimens by the above procedure, 15 specimens passed and a yield of 75% was obtained.

Next, as shown in FIG. 6, one of the structures 13 that passed the determination is placed in another container 14a having an inner diameter of 60 mm and a length of 250 mm, and the container is heated to 500 ° C. in a tubular furnace. A hydrogen gas flow of 0.2 MPa was charged, and the flow rate of hydrogen gas flowing out of the base plate pipe through the Pd alloy hydrogen separation membrane was measured. The pressure on the hydrogen take-out pipe side was set to 0.1 MPa. The hydrogen permeation flow rate per unit time, unit area, and unit pressure difference was calculated by dividing the amount of permeated hydrogen by the square root of time, membrane area, and hydrogen partial pressure difference. As a result, the hydrogen permeation flow rate is 5.3 × 10 ⁻³ mol / m ² / s / Pa ^1/2, which has sufficient characteristics to be applied to hydrogen production equipment for fuel cell systems or semiconductor factories. there were.

Example 2 of the present invention is shown below.
As a raw material, 4500 g of 2 to 10 mm lump pure Pd (purity 99.9%) and 500 g of 2 to 10 mm lump pure Ce (purity 99.9%) were prepared.
Dissolution was performed using a commercially available cold crucible dissolution apparatus shown in FIG. The crucible 2 was made of copper, had an inner diameter of 100 mm, a height of 100 mm, and had a structure in which the inside was water-cooled, and had a slit with a width of 0.1 mm so as to be divided into 24 in the circumferential direction. A hole with a diameter of 10 mm was formed at the center of the bottom of the crucible, and a water-cooled copper lid with a diameter of 9.8 mm was installed in the hole.

The raw material was put into the crucible, and the inside of the container 7 was evacuated to 1 Pa or less with a vacuum pump. Then, a 4N argon base 3% by volume hydrogen mixed gas was introduced, and the inside pressure of the container was set to 5 × 10 ⁴ Pa. This evacuation and argon-hydrogen mixed gas replacement operation was repeated three times. Next, high frequency power with a frequency of 50 kHz was applied to the upper induction coil 3 at 180 kW, and high frequency power at a frequency of 3 kHz was applied to the lower induction coil 4 at 70 kW. The charged Pd—Ce alloy melted and floated. The melting time was 30 minutes, and then the input power was cut off and quenched. The molten metal solidified and became 500 ° C. or less in about 3 minutes.

Subsequently, the Pd—Ce alloy was cooled to room temperature, and the Pd—Ce alloy ingot was taken out. The shape of the Pd—Ce alloy ingot was almost a disk shape having a diameter of 100 mm and a thickness of 52 mm. Next, casting defects such as sink marks and inclusion accumulation portions were removed by cutting. From the result of the optical microscope and cross-sectional observation of the Pd-Ag ingot produced under the same conditions in advance, the frequency of inclusions having a particle size of 2 μm or more per cross-sectional area of 1 mm ² is about 3 mm on the top surface of the ingot. Since the side and bottom surfaces were about 2 mm, the top surface was further removed by 4 mm from the bottom of the sink, and the side and bottom surfaces were removed by 3 mm cutting. For the cutting process, a commercially available lathe and milling machine were used.

The disc-shaped Pd—Ce alloy ingot obtained by the above operation and having a diameter of about 94 mm and a thickness of about 39 mm, in which the frequency of inclusions having a particle size of 2 μm or more was significantly reduced, was once again put into a cold-crucible melting apparatus. Next, after the inside of the container 7 was evacuated to 1 Pa or less with a vacuum pump, a 4N argon base 3% by volume hydrogen mixed gas was introduced, and the internal pressure of the container was set to 5 × 10 ⁴ Pa. This evacuation and argon-hydrogen mixed gas replacement operation was repeated three times. Next, high frequency power with a frequency of 50 kHz was applied to the upper induction coil 3 at 180 kW, and high frequency power at a frequency of 3 kHz was applied to the lower induction coil 4 at 70 kW. The charged Pd—Ce alloy melted again and floated. The melting time was 30 minutes, and then the operation of pulling out the lid at the bottom of the crucible was carried out with the input power kept unchanged. The molten Pd—Ce alloy was poured into a graphite mold placed thereunder and solidified in the mold. The inner dimensions of the mold were 120 mm in width, 20 mm in depth, and 200 mm in height, and the Pd—Ce alloy was a plate having a width of about 120 mm, a thickness of about 20 mm, and a length of about 110 mm.

  Next, the front and back surfaces of the plate-like Pd—Ce alloy plate are 2 mm deep, the width direction is 5 mm deep at both ends, and the both longitudinal ends are removed by milling and end milling, the width is 110 mm, and the thickness is 16 mm. The plate was 70 mm long.

  Next, the Pd—Ce alloy sheet was rolled. First, using a two-stage small roll mill (roll diameter: 150 mm), repeated rolling was performed until the plate thickness of 16 mm before rolling became 0.5 mm. In the middle, annealing was performed four times. In the annealing, the Pd—Ce alloy ingot was heated at 600 ° C. for 1 hour in an electric furnace in which Ar gas was circulated at a flow rate of 10 L / min to cool the furnace. As a result, a Pd alloy plate having a width of about 110 mm, a length of about 2.2 m, and a plate thickness of 0.5 mm was obtained. Next, using a 20-stage small roll mill (rolling roll diameter: 12 mm), the film was rolled to a final film thickness of 5 μm. Since the rolled material has a length of 2 m or longer, the rolled material was rolled by rolling and passing through a rolling mill while continuously feeding the winding rolls. However, a stainless steel foil having a width of 50 m was added to the Pd alloy plate between the rolling mill and the take-up roll. Further, annealing was performed three times along the way. The annealing was performed by continuously supplying between the winding rolls and passing through an electric furnace installed between the winding rolls. At that time, an arbitrary portion of the Pd alloy plate was heated at 700 ° C. for 10 minutes or more.

200 Pd—Ce alloy hydrogen separation membranes having a width of 50 mm and a length of 200 mm were cut out from a part of the Pd—Ag alloy hydrogen separation membrane having a width of 110 mm, a thickness of 5 μm, and a length of about 220 m obtained in the above steps.
Next, joining to the support plate 10 and welding to the base plate 11 were performed in the same manner as in Example 1, 200 structural bodies 13 were produced, and all these leaks were measured. Passed. The pass rate was 80%, which exceeded Example 1. The reason for this is that by mixing hydrogen gas into the atmosphere during cold crucible dissolution, the oxygen potential in the atmosphere due to water vapor adsorbed on the vessel wall surface etc. is lowered, and inevitable impurities such as Ce, Al, and Si that are easily oxidized in the molten metal This is thought to be because the progress of the oxidation of the metal was suppressed, and the oxide inclusions remaining in the alloy could be further reduced by a synergistic effect with the oxide particle discharge effect by the floating type cold crucible dissolution.

Next, the hydrogen gas flow rate was measured for four of the structures 13 that passed the determination in the same manner as in Example 1. As a result, the average hydrogen permeation flow rate of the four bodies is 1.2 × 10 ⁻² mol / m ² / s / Pa ^1/2, which is applicable to a hydrogen production apparatus for a fuel cell system or a semiconductor factory. It was sufficient characteristics.

Comparative Example 1

Comparative Example 1 of the present invention is shown below.
As materials, 760 g of 2 to 10 mm lump pure Pd (purity 99.9%) and 240 g of the same pure Ag (purity 99.9%) were prepared.
Dissolution was performed using a commercially available conventional high-frequency dissolution apparatus shown in FIG. The high-frequency melting apparatus 100 includes a crucible 102, a high-frequency coil 103 having 5 turns, a mold 106, and a container 107 for controlling the atmosphere covering them. The crucible 102 is made of alumina and has an inner diameter of 60 mm and a height of 80 mm. The crucible 102 has a structure that can be tilted 180 degrees in the vertical direction around the center. A graphite mold 106 was installed below the crucible 102. The inner dimension of the mold 106 was 55 mm in width, 20 mm in depth, and 200 mm in height. The Pd alloy material 105 was put into the crucible 102, and the inside of the container 107 was evacuated to 1 Pa or less with a vacuum pump. Thereafter, pure argon gas having a purity of 99.99% was introduced, and the internal pressure of the container 107 was set to 5 × 10 ⁴ Pa. This evacuation and argon gas replacement operation was repeated three times. Next, 60 kW of high frequency power having a frequency of 50 kHz was applied to the high frequency coil 103. The charged Pd—Ag alloy was dissolved. The melting time was 25 minutes, and then the input power was cut off, and the crucible 102 was tilted to flow the molten metal into the mold 106.

  It was cooled to room temperature as it was, and the Pd—Ag alloy ingot was taken out. The shape was a rectangular parallelepiped having a width of 55 mm, a depth of 20 mm, and a height of 75 mm. 2 mm from the surface in the width direction and depth direction of the rectangular parallelepiped ingot was cut and removed by end milling and milling, and the upper part 20 mm and the lower part 5 mm were cut in the height direction. As a result, a Pd—Ag alloy sheet having a width of 50 mm, a thickness of 16 mm, and a length of 50 mm was obtained.

  Next, the Pd—Ag alloy sheet was rolled. The Pd—Ag alloy sheet was repeatedly rolled using a two-stage small roll mill (roll diameter: 150 mm) until the plate thickness of 16 mm before rolling reached 0.5 mm. In the middle, annealing was performed four times. For annealing, the Pd alloy ingot was heated at 600 ° C. for 1 hour in an electric furnace in which Ar gas was circulated at a flow rate of 10 L / min to cool the furnace. As a result, a Pd alloy plate having a width of about 50 mm, a length of about 1.6 m, and a plate thickness of 0.5 mm was obtained. Next, it rolled to 5 micrometers which is a final film thickness using the 20-stage type small roll mill (rolling roll diameter 12mm). Finally, the width was about 50 mm, the length was about 160 m, and the film thickness was 5 μm. Since the rolled material has a length of 2 m or longer, the rolled material was rolled by rolling and passing through a rolling mill while continuously feeding the winding rolls. However, a stainless steel foil having a width of 50 m was added to the Pd alloy plate between the rolling mill and the take-up roll. Further, annealing was performed three times along the way. The annealing was performed by continuously supplying between the winding rolls and passing through an electric furnace installed between the winding rolls. At that time, an arbitrary part of the Pd alloy plate was heated at 700 ° C. for 10 minutes or more.

  Thereafter, similarly to Example 1, the Pd—Ag alloy hydrogen separation membrane was cut out, joined to the support plate 10, welded to the base plate 11, and it was confirmed by the PT test that there was no welding defect. The amount of leak was measured. As a result, all 20 specimens showed leakage of 0.1 cc / min or more, and no acceptable product was obtained.

  As a result of conducting detailed observation and component analysis by specifying the leak portion, aluminum oxide, silicon oxide, and aluminum silicon composite oxide particles having a diameter of 5 μm to 20 μm exist in the film in a form penetrating the film. It was revealed that there was a leak from its surroundings. Oxide particles are considered to be mainly intruded through impurities in the input material and mixing of the melting crucible.

Comparative Example 2

Comparative Example 2 of the present invention is shown below.
As in Comparative Example 1, a Pd—Ag alloy plate material having a width of 50 mm, a thickness of 16 mm, and a length of 50 mm was obtained by high-frequency melting, casting, and processing.

  Next, rolling was performed in the same manner as in Comparative Example 1. However, in Comparative Example 2, the final plate thickness was 20 μm. As a result, the width was 50 mm, the thickness was 20 μm, and the length was about 40 m. Thereafter, similarly to Example 1, the Pd—Ag alloy was cut out, joined to the support plate 10, and welded to the base plate 11, and it was confirmed by the PT test that there was no welding defect. Twenty such structural bodies 13 were produced. As a result of measuring the amount of leakage of the film of these structural bodies 13, 16 specimens showed leakage of 0.1 cc / min or less, resulting in acceptable products.

As a result of measuring the hydrogen permeation amount of the passed specimen in the same manner as in Example 1, the hydrogen permeation flow rate per unit time, unit membrane area, and unit hydrogen partial pressure difference was 1.2 × 10 ⁻³ mol / m ² / s. / Pa ^1/2, which is a permeation flow rate equal to or less than ¼ of Example 1, and was insufficient.

  As an application example of the present invention, it can be applied to a hydrogen production apparatus included in a fuel cell system.

FIG. 1 is a schematic view showing an example of a cold crucible dissolving apparatus that can be used in the method of the present invention. FIG. 2 is a schematic view of the support plate. FIG. 3 is a schematic view of the base plate. FIG. 4 is a schematic view of a structure of a hydrogen separation membrane comprising a hydrogen separation membrane, a support plate, and a base plate. FIG. 5 is a schematic view showing a method for measuring the amount of gas leakage in the hydrogen separation membrane. FIG. 6 is a schematic view showing a method for measuring the hydrogen permeation flow rate in the hydrogen separation membrane. FIG. 7 is a schematic view showing an example of a conventional high-frequency melting apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cold crucible melter 2 Crucible 3 Upper induction coil 31 Power supply 4 Lower induction coil 41 Power supply 5 Metal 6 Mold 7 Container 10 Support plate 101 Through-hole processing part 11 Base plate 111 Pipe 12 Membrane / support plate assembly 13 Structure 14 , 14a Pressurized container 100 High-frequency melting apparatus 102 Crucible 103 High-frequency coil 104 High-frequency power source 105 Pd alloy material 106 Mold

Claims (5)

Melting a Pd alloy by a floating cold crucible melting method to obtain an ingot;
Removing inclusion inclusions of the ingot;
Forging and rolling the ingot from which the inclusion accumulation part has been removed. Melting a Pd alloy by a floating cold crucible melting method to obtain an ingot;
Removing inclusion inclusions of the ingot;
Dissolving the ingot from which the inclusion accumulation portion has been removed again by a floating-type cold crucible melting method;
Casting the molten Pd alloy into a mold;
Forming and rolling a cast Pd alloy. A method for producing a hydrogen separation membrane. 3. The method for producing a hydrogen separation membrane according to claim 1, wherein in the levitation type cold crucible melting, a melting atmosphere is an argon atmosphere or an argon-based hydrogen mixed atmosphere. The method according to claim 1, wherein in the step of rolling the ingot from which the inclusion accumulation portion has been removed, the ingot is rolled to 20 μm or less. A hydrogen separation membrane produced by the method according to claim 1.

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