BEST MODE FOR CARRYING OUT THE INVENTION

[0027] A hydrogen-gas separating structure as one embodiment of a hydrogen permeable structure of the present invention is constructed by forming metallic thin films, containing Pd, within pores of a porous support or the surface of the porous support.

[0028] The porous support has no special limitation on materials thereof, and can be made of a metallic material such as SUS316L, or any of ceramics including various oxides, e.g., aluminum oxide, and various nitrides, e.g., silicon nitride. Among ceramics, a porous body of silicon nitride is particularly preferable. The pore size of the porous support is not limited to a particular value, but it is preferably not more than 1 μm and not less than 0.1 μm. If a porous support having the pore size over 1 μm is used, the thin films formed in pores and containing Pd would be too thick, thus resulting in being less economical and deterioration of hydrogen permeability. If the pore size is less than 0.1 μm, the thin films would be too thin, thus resulting in problems in terms of durability.

[0029] According to the manufacturing method of the present invention, a solution feed material containing Pd is supplied through one surface of the porous support, and a reducing feed material is supplied through the other surface thereof. Upon contact of the solution containing Pd and the reducing feed material, Pd is reduced and metallic Pd is deposited, whereby the thin film(s) containing Pd can be formed on the surface of the porous support or within the pores inside the porous support. Also, by adjusting the concentration and reaction conditions of either or both of the Pd containing solution and the reducing feed material, the thin films containing Pd can be formed only inside the porous support, i.e., in a region inward of the surface of the porous support. Since the thus obtained thin films are formed within the pores of the porous support, those thin films are surrounded by the skeleton (matrix) of the porous support and high durability can be obtained. Particularly, when the thin films are formed only inside the porous support, those thin films are entirely surrounded by the skeleton (matrix) of the porous support and hence higher durability can be obtained. Note that, if both the feed materials are supplied onto the same surface, the thin films containing Pd cannot be formed in the porous support because fine particles of metallic Pd start deposition immediately after the feed materials are in contact with each other.

[0030] The hydrogen permeability of the hydrogen permeable film is in reverse proportion to a film thickness. For example, the permeability of hydrogen through a 2 μm-thick film is 10 times the permeability through a 20 μm-thick film. With a 10-time increase in hydrogen permeability through the film, the film surface area required for obtaining the same amount of hydrogen permeable through the film is reduced to {fraction (1/10)}. Thus, when the thickness of the hydrogen permeable film is reduced to {fraction (1/10)}, the required weight of the film is reduced to {fraction (1/100)}. According to the present invention, therefore, since a dense hydrogen permeable film having good hydrogen permeability can be formed in thickness of not more than 2 μm, it is possible to provide a low-cost, high-performance and compact hydrogen permeable structure. Conversely, if the film thickness is less than 0.01μ, problems such as the deterioration of the hydrogen separation performance and a decrease of durability would occur.

[0031] In the solution containing Pd, any of a palladium complex, palladium chloride, palladium acetate, etc. is usable as a solute. Also, by adjusting a PH of the solution with acids or bases, such as hydrochloric acid and acetic acid, the maximum solubility of the solute can be adjusted and hence the reduction reaction velocity can also be adjusted. Further, by employing a solution in which a platinum compound, a silver compound, or the like is dissolved together with a Pd compound, thin films of a Pd—Pt alloy or a Pd—Ag alloy can be formed. A preferable example of the platinum compound is platinum chloride or a platinum organic complex, and a preferable example of the silver compound is silver chloride or a silver organic complex.

[0032] The reducing feed material may be in the form of a liquid or gas. In the case of a liquid, a solution containing a reductant is usable. When dimethylamine borane, NaBH ₄ , LiBH ₄ , KBH ₄ , or the like is used as the reductant, not only water but also alcohol can be used as a solvent. However, in the case of LiBH ₄ in particular, an alcoholic solution is preferably used since LiBH ₄ decomposes upon reaction with water, though it has maximum reducing power. Using an alcoholic solution is advantageous in that, by increasing the size of a hydrophobic radical in alcohol, affinity with an aqueous solution containing Pd ions can be reduced, and hence a more local and thinner Pd-containing film can be formed. Further, in the case where both of the Pd-containing solution and the reductant-containing solution are used, by spraying either or both of the solutions in a state of mist with a sprayer, for example, disturbance at the interface between the Pd-containing solution and the reductant-containing solution is reduced, and hence the pores can be sealed off with thinner films. Accordingly, the spraying method is able to reduce the amount of Pd used and is more economical.

[0033] In the case using gas, any reducing gas can be used, but a preferable example is hydrogen. Also, a gas mixture with another kind of gas may also be used to control the reaction velocity. Further, by filling the porous support beforehand with a material that is gas permeable and can be removed later, it is possible to control the position where the hydrogen permeable film is to be formed. One example of such a filling material is paraffin. Paraffin is hydrogen permeable. For example, if paraffin is filled to half the thickness of the porous support and the Pd-containing solution is supplied from the side that is not filled with paraffin and hydrogen is supplied from the side that is filled with paraffin, then, the supplied hydrogen passes through the paraffin and reaches the paraffin surface, whereupon reduction reaction occurs between the Pd-containing solution and hydrogen gas, and a hydrogen-permeable film containing Pd can be formed on the paraffin surface. By adjusting the amount of paraffin filled, the position where the film is to be formed can be controlled. After the hydrogen-permeable film containing Pd has been formed, the paraffin can be dissolved and removed using an organic solvent, e.g., dichloromethane.

[0034] When the solution containing Pd ions contacts the reducing feed material, Pd is reduced and a metal containing Pd is deposited. The metal is gradually deposited within the pores of the porous support such that eventually the metal fills the pores at a certain thickness and seals off the pores. The reduction reaction continues until the pores are completely sealed off. The thickness of the thin films containing Pd and the position where the thin films are formed inside the porous support can be controlled in accordance with, e.g., the pore size of the porous support, the concentration of the Pd-containing solution, the concentration of the reductant in the reducing feed material, and the reaction temperature, as well as the kind of solvent and a PH when the reducing feed material is a solution.

[0035] The porous support has no limitation in its shape. In the case of a flat plate, the Pd-containing solution and the reductant-containing solution may be supplied to the plate from opposite sides. In the case of a hollow cylinder, those solutions can be supplied through an inner peripheral surface and an outer peripheral surface of the cylinder.

[0036] In the method of manufacturing the hydrogen permeable structure according to the present invention, the reduction reaction continues until the pores are completely sealed off, as described above. This means that when defects such as pinholes are present in the formed hydrogen permeable film, the reduction reaction occurs first in those defects such as pinholes. In other words, defects such as pinholes caused in the hydrogen permeable structure can easily be repaired by applying the method according to the present invention since a metal containing Pd can be thereby deposited only in the defects such as pinholes. The method of the present invention is also, applicable to the case of regenerating a failed structure.

[0037] Further, a feature of the hydrogen permeable structure according to the present invention is that it has a layer formed by depositing a metal containing Pd in the porous support or porous powder so as to sealed off pores, and that the amount of nitrogen permeable through the structure is small: not more than 0.6 ml/min/cm ² under a differential pressure of 1 atmospheric pressure. Accordingly, hydrogen having a high purity can be obtained.

EXAMPLE 1

[0038] A disk having a diameter of 22 mm and a thickness of 1 mm was prepared by machining a porous sintered body of silicon nitride 1 with a pore size of 0.3 μm. The disk was glass-bonded, as shown in FIG. 1 , to one end surface of a cylindrical holder 2 made of a dense ceramic and having an outer diameter of 22 mm. After pouring, in the dense ceramic cylindrical holder, 20 ml of a solution that was prepared by dissolving 30 g of Pd(NO ₃ ) ₂ in 1 liter of 1N-nitric acid, the cylinder was immersed in a 1.0 g/l aqueous solution of dimethylamine borane 4 for 2 minutes within a thermostatic chamber 5 . The solution temperature was adjusted so as to be maintained at 25° C. using a heater and a cooler (not shown). After 2 minutes, the grass-bonded disk and cylindrical holder were removed from the thermostatic chamber, and a porous support disk was obtained by disconnecting the glass bonding. The surface of the porous support disk, which had been subjected to the aqueous solution of dimethylamine borane, had a black discoloration and exhibited electrical continuity. It was hence confirmed that a Pd metal was deposited.

[0039] The thus obtained disk was heat-treated at a temperature of 500° C. for 1 hour in hydrogen under 101.325 kPa (1 atmospheric pressure). After the heat treatment, the Pd structure was measured by X-ray diffraction and confirmed to be of face-centered cubic lattice. Then, the disk was cut and the cut section was observed with an electron microscope. As a result, it was confirmed that Pd was deposited in pores up to a depth of 0.5 μm from the surface having a black discoloration, and Pd thin films of 0.5 μm thickness were formed in the pores.

[0040] The hydrogen permeability of the hydrogen permeable structure obtained as described above was measured. More specifically, the permeation amount of hydrogen or nitrogen was measured by introducing a pure gas of hydrogen or nitrogen at a temperature of 400° C. through one surface of the hydrogen permeable structure under a pressure difference of 101.325 kPa (1 atmospheric pressure). As a result, it was confirmed that the permeation amount of hydrogen was 80 ml/min/cm ² and the permeation amount of nitrogen was 0.05 ml/min/cm ² , and hence that practically only hydrogen was allowed to selectively pass through the structure. Also, a heat cycle test of 500 cycles was conducted between temperature of 400° C. and room temperature in a hydrogen gas atmosphere of 101.325 kPa (1 atmospheric pressure). After the test, peeling-off and cracks of the films were inspected by visual observation and by using an electron microscope, respectively. As a result, no physical deterioration of the films, such as peeling-off and cracks, was observed.

EXAMPLE 2

[0041] A porous disk made of silicon nitride and a cylindrical holder made of a dense ceramic, similar to those used in EXAMPLE 1, were prepared. After pouring 20 ml of a solution that was prepared by dissolving 30 g of Pd(NO ₂ )(NH ₃ ) ₂ in 1 liter of 1N-nitric acid, into the dense ceramic cylindrical holder, the cylinder was immersed in a solution, which was prepared by dissolving 2.0 g of NaH ₂ PO ₂ in 1 liter of pure water, for 2 minutes within a thermostat. The solution temperature was adjusted so as to be maintained at 25° C. using a heater and a cooler (not shown). After 2 minutes, the grass-bonded disk and cylindrical holder were removed from the thermostatic chamber, and a porous support disk was obtained by disconnecting the glass bonding.

[0042] The thus obtained disk was measured for the hydrogen permeability in the same manner as in EXAMPLE 1. As a result, it was confirmed that the permeation amount of hydrogen was 60 ml/min/cm ² and the permeation amount of nitrogen was 0.03 ml/min/cm ² , and hence that practically only hydrogen was allowed to selectively pass through the disk.

EXAMPLE 3

[0043] A porous disk made of silicon nitride and a cylindrical holder made of a dense ceramic, similar to those used in EXAMPLE 1, were prepared. After pouring 20 ml of a solution that was prepared by dissolving 30 g of Pd(NO ₂ ) ₂ (NH ₃ ) ₂ in 1 liter of 1N-nitric acid, into the dense ceramic cylindrical holder, the cylinder was immersed in a solution, which was prepared by dissolving 3.0 g of hydrazine in 1 liter of pure water, for 2 minutes within a thermostat. The solution temperature was adjusted so as to be maintained at 25° C. using a heater and a cooler (not shown). After 2 minutes, the grass-bonded disk and cylindrical holder were removed from the thermostatic chamber, and a porous support disk was obtained by disconnecting the glass bonding.

[0044] The thus obtained disk was measured for the hydrogen permeability in the same manner as in EXAMPLE 1. As a result, it was confirmed that the permeation amount of hydrogen was 60 ml/min/cm ² and the permeation amount of nitrogen was 0.03 ml/min/cm ² , and hence that practically only hydrogen was allowed to selectively pass through the disk.

EXAMPLE 4

[0045] A porous disk made of silicon nitride 1 and a cylindrical holder made of a dense ceramic 2 , similar to those used in EXAMPLE 1, were prepared. After glass-bonding the disk to one end surface of the dense ceramic cylindrical holder as in EXAMPLE 1, a solution of Pd(NO ₃ ) ₂ 3 was poured into the cylindrical holder and, as shown in FIG. 2 , the cylindrical holder was placed in a thermostatic chamber 5 such that the surface of the Pd(NO ₃ ) ₂ was positioned outside the thermostat. Then, a hydrogen gas of 101.325 kPa (1 atmospheric pressure) was introduced into the thermostat. After introducing the hydrogen gas for 5 minutes, the porous disk made of silicon nitride was removed from the thermostatic chamber. The surface of the disk, which had been subjected to the hydrogen gas, had a black discoloration and exhibited electrical continuity. It was hence confirmed that a Pd metal was deposited. The thus obtained disk was cut and the cut section was observed with an electron microscope. As a result, it was confirmed that Pd was deposited in pores up to a depth of 0.8 μm from the surface having a black discoloration, and Pd thin films of 0.8 μm thickness were formed in the pores. Note that thin films containing Pd can also be formed by putting into the thermostatic chamber, as in FIG. 1 , the entirety of the container made of the porous silicon nitride disk and the dense ceramic cylindrical holder, in which the Pd(NO ₃ ) ₂ solution is filled. This method, however, is uneconomical because the reduction reaction occurs at the surface of the Pd-containing solution in the container as well and Pd is also deposited there.

[0046] The hydrogen permeability of the hydrogen permeable structure obtained as described above was measured in the same manner as in EXAMPLE 1. As a result, it was confirmed that the permeation amount of hydrogen was 60 ml/min/cm ² and the permeation amount of nitrogen was 0.03 ml/min/cm ² , and hence that practically only hydrogen was allowed to selectively pass through the structure. Also, a heat cycle test of 500 cycles was conducted between temperature of 400° C. and room temperature in a hydrogen gas atmosphere of 101.325 kPa (1 atmospheric pressure). After the test, peeling-off and cracks of thin films were inspected by visual observation and by using an electron microscope, respectively. As a result, no physical deterioration of the films, such as peeling-off and cracks, was observed.

EXAMPLE 5

[0047] A disk having a diameter of 22 mm and a thickness of 1 mm was prepared by machining a porous sintered body of silicon nitride having a pore size of 0.3 μm. Paraffin having the melting point of 70° C. was filled in the disk up to a depth of 0.5 mm. The disk was glass-bonded to one end surface of a cylindrical holder made of a dense ceramic and having an outer diameter of 22 mm such that the disk surface filled with the paraffin was faced outward. After pouring 20 ml of a solution that was prepared by dissolving 30 g of Pd(NO ₃ ) ₂ in 1 liter of 1N-nitric acid, into the dense ceramic cylindrical holder, the cylindrical holder was put into a thermostat. A hydrogen gas of 101.325 kPa (1 atmospheric pressure) was then, introduced into the thermostat and such a condition was held for 5 minutes, during which period the temperature in the thermostat was maintained at 25° C. After 5 minutes, the porous disk made of silicon nitride was removed from the thermostat. No change was observed in the external appearance of the disk. The disk was cut and the cut section was observed with an electron microscope. As a result, as schematically illustrated in FIG. 3 , it was confirmed that a Pd film 8 was deposited in pores with a thickness of 0.3 μm from the forefront surface of the filled paraffin 9 , and Pd thin films were formed in the pores, in thickness of 0.3 μm from the position of 0.5 mm in the direction of thickness of the porous disk made of silicon nitride.

[0048] The paraffin was dissolved and removed by three repetitions of immersing the hydrogen permeable structure obtained as described above in dichloromethane for 15 minutes, replacing the dichloromethane with new dichloromethane, at each 15-minute immersion. After drying the hydrogen permeable structure, it was heat-treated at a temperature of 500° C. for 1 hour in hydrogen under 101.325 kPa (1 atmospheric pressure). The hydrogen permeability of the thus obtained hydrogen permeable structure was measured in the same manner as in EXAMPLE 1. As a result, it was confirmed that the permeation amount of hydrogen was 90 ml/min/cm ² and the permeation amount of nitrogen was 0.05 ml/min/cm ² , and hence that practically only hydrogen was allowed to selectively pass through the structure. Also, a heat cycle test of 500 cycles was conducted between temperature of 400° C. and room temperature in a hydrogen gas atmosphere of 101.325 kPa (1 atmospheric pressure). After the test, peeling-off and cracks of the films were inspected by visual observation and by using an electron microscope, respectively. As a result, no physical deterioration of the films, such as peeling-off and cracks, was observed.

EXAMPLE 6

[0049] As in EXAMPLE 1, an assembly of a porous disk made of silicon nitride and a cylindrical holder made of a dense ceramic was prepared by glass-bonding them. A solution prepared by dissolving 27 g of Pd(NO ₃ ) ₂ and 3 g of Pt(NO ₂ ) ₂ (NH ₃ ) ₂ in 1 liter of 1N-nitric acid was poured into the dense ceramic cylindrical holder. Then, the cylinder was immersed in a 1.0 g/l aqueous solution of dimethylamine borane for 2 minutes within a thermostat. The solution temperature was adjusted so to be maintained at 25° C. After 2 minutes, the grass-bonded disk and cylindrical holder were removed from the thermostatic chamber, and a porous support disk was obtained by disconnecting the glass bonding. The thus obtained disk was heat-treated at a temperature of 500° C. for 1 hour in hydrogen under 101.325 kPa (1 atmospheric pressure). Then, the disk was cut and the cut section was observed with an electron microscope. As a result, it was confirmed that a metal was deposited in pores up to a depth of 0.5 μm, and metallic thin films of 0.5 μm thickness were formed in the pores. The composition of the metallic thin films was examined by fluorescent X-ray analysis, and it was found to be 89 wt % Pd and 11 wt % Pt.

[0050] The hydrogen permeability of the hydrogen permeable structure obtained as described above was measured in the same manner as in EXAMPLE 1. As a result, it was confirmed that the permeation amount of hydrogen was 90 ml/min/cm ² and the permeation amount of nitrogen was 0.05 ml/min/cm ² , and hence that practically only hydrogen was allowed to selectively pass through the structure. Also, a heat cycle test of 500 cycles was conducted between the temperature of 400° C. and room temperature in a hydrogen gas atmosphere of 101.325 kPa (1 atmospheric pressure). After the test, peeling-off and cracks of the films were inspected by visual observation and by using an electron microscope, respectively. As a result, no physical deterioration of the films, such as peeling-off and cracks, was observed.

EXAMPLE 7

[0051] A disk having a diameter of 22 mm and a thickness of 1 mm was prepared using porous SUS316L with a filtration size of 0.5 μm. The disk was silver-brazed to one end surface of a cylinder made of a dense SUS316L and having an outer diameter of 22 mm. After pouring the same solution as used in EXAMPLE 1 into the cylinder, the cylinder was immersed in a solution of a reductant (propanol) within a thermostat, the solution being the same as used in EXAMPLE 1. After 10 minutes, the porous disk made of porous SUS316L was removed from the thermostatic chamber.

[0052] The thus obtained disk was heat-treated at a temperature of 500° C. for 1 hour in hydrogen under 101.325 kPa (1 atmospheric pressure). After the heat treatment, the disk was cut and the cut section was observed with an electron microscope. As a result, it was confirmed that Pd was deposited in pores up to a depth of 1.5 μm, and Pd thin films of 1.5 μm thickness were formed in the pores.

[0053] The hydrogen permeability of the hydrogen permeable structure obtained as described above was measured in the same manner as in EXAMPLE 1. As a result, it was confirmed that the permeation amount of hydrogen was 30 ml/min/cm ² and the permeation amount of nitrogen was 0.01 ml/min/cm ² , and hence that practically only hydrogen was allowed to selectively pass through the structure. Also, a heat cycle test of 500 cycles was conducted between the temperature of 400° C. and room temperature in a hydrogen gas atmosphere of 101.325 kPa (1 atmospheric pressure). After the test, peeling-off and cracks of the films were inspected by visual observation and by using an electron microscope, respectively. As a result, no physical deterioration of the films, such as peeling-off and cracks, was observed.

EXAMPLE 8

[0054] A disk having a diameter of 22 mm and a thickness of 1 mm was prepared by machining a porous sintered body of silicon nitride having a pore size of 0.3 μm. One surface of the disk was polished with a polishing solution including γ-alumina powder of a 0.05-μm average particle size dispersed therein. Also, the γ-alumina powder was filled into holes of the disk surface to make it flat. Subsequently, the disk filled with the y-alumina powder was sintered in an atmosphere at 750° C. for 30 minutes. The thus sintered disk was glass-bonded, as shown in FIG. 1 , to one end surface of a cylindrical holder made of a dense ceramic and having an outer diameter of 22 mm, at which time, the disk surface flattened with the y-alumina powder was positioned to face outward of the cylinder (downward in FIG. 1 ). After pouring 20 ml of a solution prepared by dissolving 25 g of PdCl ₂ in 1 liter of 1N-hydrochloric acid, into the dense ceramic cylindrical holder, the holder was immersed in a 1.0 g/l aqueous solution of dimethylamine borane for 2 minutes within a thermostat. The solution temperature was adjusted so as to be maintained at 25° C. using a heater and a cooler (not shown). After 2 minutes, the grass-bonded disk and cylindrical holder were removed from the thermostatic chamber, and a porous support disk was obtained by disconnecting the glass bonding. The surface of the porous support disk, which had been subjected to the aqueous solution of dimethylamine borane, had metallic luster and exhibited electrical continuity. It was hence confirmed that a Pd metal was deposited.

[0055] The thus obtained disk was heat-treated at a temperature of 500° C. for 1 hour in hydrogen under 101.325 kPa (1 atmospheric pressure). After the heat treatment, the disk was cut and the cut section was observed with an electron microscope. FIG. 4 schematically shows the observed section. As a result of the observation, it was confirmed that the γ-alumina 10 was filled into pores of the porous silicon nitride up to a depth of 0.5 μm from the Pd-deposited disk surface and Pd 8 was deposited in gaps between particles of the γ-alumina powder. It was also confirmed that Pd 8 deposited on the disk surface was in the form of a thin film having a thickness of 0.1 μm. Further, as a result of observing the disk surface with a Scanned Electron Microscope (SEM), it was confirmed that nearly 100% area of the entire disk surface was covered with Pd.

[0056] The hydrogen permeability of the hydrogen permeable structure obtained as described above was measured in the same manner as in EXAMPLE 1. As a result, it was confirmed that the permeation amount of hydrogen was 120 ml/min/cm ² and the permeation amount of nitrogen was 0.05 ml/min/cm ² , and hence that practically only hydrogen was allowed to selectively pass through the structure. Also, a heat cycle test of 500 cycles was conducted between the temperature of 400° C. and room temperature in a hydrogen gas atmosphere of 101.325 kPa (1 atmospheric pressure). After the test, peeling-off and cracks of the film were inspected by visual observation and by using an electron microscope, respectively. As a result, no physical deterioration of the film, such as peeling-off and cracks, was observed.

EXAMPLE 9

[0057] A disk having a diameter of 22 mm and a thickness of 1 mm was prepared by machining a porous sintered body of silicon nitride having a pore size of 0.3 μm. One surface of the disk was polished with a polishing solution including γ-alumina powder of a 0.05-μm average particle size dispersed therein. Also, the γ-alumina powder was filled into holes in the disk surface to make it flat. The disk filled with the γ-alumina powder was glass-bonded to one end surface of a cylindrical holder made of a dense silicon nitride and having an outer diameter of 22 mm, at which time, the disk surface flattened with the γ-alumina powder was positioned to face outward of the cylinder. Then, 20 ml of a solution prepared by dissolving 25 g of PdCl ₂ in 1 liter of 1N-hydrochloric acid was poured into the dense silicon-nitride cylindrical holder. A 2-propanol solution containing 0.25 g/l of NaBH ₄ was filled into a sprayer, and mist of the solution was sprayed on the outer surface of the bonded disk. With the spray of the solution in the state of mist, drips falling from the disk were black in the initial period, thus showing the progress of reduction reaction. After continuing to spray for about 5 minutes, falling drips became transparent, whereupon it was determined that the reduction reaction was completed. Then, spraying of the solution was stopped, and a porous support disk was obtained by disconnecting the glass bonding. The surface of the porous support disk, which had been subjected to the spray of the solution, was black and exhibited electrical continuity. It was hence confirmed that a Pd metal was deposited.

[0058] The thus obtained disk was heat-treated at a temperature of 500° C. for 1 hour in hydrogen under 101.325 kPa (1 atmospheric pressure). After the heat treatment, the disk was cut and the cut section was observed with an electron microscope. FIG. 5 schematically shows the observed section. As a result of the observation, it was confirmed that the γ-alumina 10 was filled into pores of the porous silicon nitride up to a depth of 0.5 μm from the Pd-deposited disk surface and Pd 8 was deposited in gaps between particles of the γ-alumina powder. It was also confirmed that Pd was not deposited on the surface of the porous disk made of silicon-nitride.

[0059] The hydrogen permeability of the hydrogen permeable structure obtained as described above was measured in the same manner as in EXAMPLE 1 . As a result, it was confirmed that the permeation amount of hydrogen was 140 ml/min/cm ² and the permeation amount of nitrogen was 0.02 ml/min/cm ² , and hence that practically only hydrogen was allowed to selectively pass through the structure. Also, a heat cycle test of 1000 cycles was conducted between the temperature of 400° C. and room temperature in a hydrogen gas atmosphere of 101.325 kPa (1 atmospheric pressure). After the test, peeling-off and cracks of the film were inspected by visual observation and by using an electron microscope, respectively. As a result, no physical deterioration of the film, such as peeling-off and cracks, was observed. Thus, it was found that by forming Pd-containing thin films only inside the porous support the durability was greatly improved. Further, Pd deposited in the disk was dissolved in aqua regia and subjected to Inductively Coupled Plasma (ICP) emission spectroscopic analysis. As a result, the amount of Pd was 1.5 g/m ² . Accordingly, it was found that the amount of Pd was reduced to half by employing the spraying method because the amount of Pd deposited in the hydrogen permeable structure by the method of immersing the disk in the reductant-containing solution, as with EXAMPLE 8, was 3.0 g/m ² .

EXAMPLE 10

[0060] The surface of the disk-shaped hydrogen permeable structure obtained with EXAMPLE 8, on which a Pd film was formed, was artificially abraded and flawed 10 times using a No. 1200 polishing paper. The amount of nitrogen having passed through the flawed disk was measured in the same manner as in EXAMPLE 1. As a result, the measured amount was 15 ml/min/cm ² , which was considerably increased from 0.05 ml/min/cm ² , i.e., the amount measured prior to flawing of the disk. In other words, it was evident that the Pd thin film was partly broken.

[0061] A Pd film was formed on the flawed disk in the same manner and under the same conditions as those in EXAMPLE 8. The disk thus repaired was measured for permeability of hydrogen or nitrogen in the same manner as in EXAMPLE 1. As a result, it was confirmed that the permeation amount of hydrogen was 120 ml/min/cm ² and the permeation amount of nitrogen was 0.05 ml/min/cm ² . It was hence found that the flaws were repaired and the disk was restored to its original permeability.

Industrial Applicability

[0062] According to the present invention, as described above, physical deterioration of the hydrogen permeable film, such as peeling-off and cracks, can be greatly reduced and durability of the hydrogen permeable film can be increased. Also, the position where a thin film containing Pd is to be formed can be controlled as desired, and defects such as pinholes can easily be repaired.