JP2006088037A - Hydrogen-permeable film and its producing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that the work of sealing a pinhole of a porous substrate, for example, the work of electroplating the surface of a metal porous body (the porous substrate) with Ni and Pd and shot-peening (glass bead-blasting) the Ni/Pd-electroplated porous substrate to fill up a minute crack, is troublesome. <P>SOLUTION: A hydrogen-permeable film is deposited on the porous substrate through which hydrogen gas is made to pass easily. Impurity-containing reformed gas is brought into contact with one surface of the hydrogen-permeable film to permeate hydrogen in the reformed gas and the permeated hydrogen is emitted selectively from the other surface of the hydrogen-permeable film. The hydrogen-permeable film G is deposited on the surface of the porous substrate 7 flattened by rolling. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hydrogen permeable membrane and a method for producing the hydrogen permeable membrane.

  Conventionally, in a membrane reformer type fuel cell that uses city gas, natural gas, oil, etc. as primary energy, after the city gas is led to a membrane reformer that functions as a reformer and hydrogen purifier, the reformed gas is generated. The hydrogen is purified and extracted by utilizing the phenomenon that only the hydrogen gas contained in the reformed gas permeates the hydrogen permeable membrane.

  Such a hydrogen permeable membrane for a membrane reformer includes palladium (Pd) from the viewpoint of stability in a high temperature environment in the reformer or hydrogen permeation performance with respect to a reformed gas containing impurities such as CO and CO2. ) And Pd-based materials made of a Pd alloy are used.

  However, Pd is a rare metal that is rarer than gold (Au), and is very expensive and difficult to obtain. Membrane reformers that have been commercialized using such Pd-based materials have a simpler device configuration than conventional reformers that do not use hydrogen permeable membranes, but are not necessarily advantageous from a cost standpoint. It ’s not good. For this reason, as a new hydrogen permeable film material replacing the Pd-based material, a tantalum (Ta) -based material, niobium (Nb) -based material, vanadium (V) -based material having a hydrogen solid solution amount approximately one digit larger than Pd, or Many hydrogen-absorbing alloy (MH) materials have been proposed. These can be materials having hydrogen permeation performance comparable to or higher than that of Pd and Pd alloys as conventional materials.

  Here, as shown in FIG. 3, the hydrogen permeation mechanism by the hydrogen permeable membrane uses a pressure difference of hydrogen gas between the front and back sides of the permeable membrane G (concentration difference of hydrogen dissolved in the membrane) as a driving force, In the film G, hydrogen molecules H2 dissociate and dissolve in the form of atoms, diffuse to the low-pressure side, recombine, and are released again as hydrogen molecules H2.

  The reformed gas supplied to the high pressure side contains not only hydrogen but also impurity gases such as unreacted hydrocarbon gas (CH 4), CO, and CO 2, which are present in the hydrogen permeable membrane due to restrictions such as atomic size. Does not dissolve. For this reason, only hydrogen gas having a theoretical purity of 100% is released from the low pressure side of the hydrogen permeable membrane. Because of this mechanism, it can be said that the higher the hydrogen solubility and the hydrogen diffusion coefficient, the better the material for the hydrogen permeable membrane, and the lower the hydrogen permeable membrane thickness, the higher the hydrogen permeation rate. I understand that I can do it.

  As a method for producing such a hydrogen permeable membrane, foil formation by rolling or direct film formation on a porous support (substrate) is carried out. In particular, the thinner the hydrogen permeable film, the higher the hydrogen permeation rate can be realized. Therefore, it is advantageous to directly form a dense and thin film of several tens of μm on the support by the thin film method. Document 1), vacuum deposition (for example, Patent Document 2), ion plating (for example, Patent Document 3), sputtering (for example, Patent Document 4), low pressure plasma spraying (for example, Patent Document 5), CVD method (for example, Patent Document 6) Etc. have been tried.

  On the other hand, since the substrate used for the hydrogen permeable membrane needs to pass hydrogen that has passed through the hydrogen permeable membrane thereon, a porous substrate is used. As the porous substrate, an expensive ceramic substrate having a small hole is used, or a film is formed after applying fine particles to the surface of an inexpensive substrate having a large hole (for example, Patent Document 7). The film is melted and the surface is melted with a laser to fill the hole, and the film is further formed to prepare the surface (for example, Patent Document 8), or the film is formed and the surface is blasted with glass beads to fill the hole (for example, patent) Document 9), it has been proposed to perform a sealing treatment by a technique such as re-depositing a film afterwards only on the hole that is vacant after film formation (for example, Patent Document 10).

  Specifically, Patent Document 7 discloses a method in which pores on the surface of a nickel porous body (porous substrate) are covered with nickel particles, fired, and subjected to a sealing treatment for smoothing the surface, followed by Pd plating. Thus, a Pd film with few pinholes can be formed.

  In Patent Document 8, a Pd-based film is formed on the surface of a metal porous body (porous substrate) by a low pressure plasma spraying method, and then the film surface is instantaneously heated with a laser beam to eliminate pores.

  In Patent Document 9, electric Ni plating and electric Pd plating are performed on the surface of a metal porous body (porous substrate), and then the plated layer is shot peened (glass bead blasting). Thereafter, the metal porous body (porous) Electroless Pd plating is performed while vacuuming from the back surface of the substrate. This crushes countless fine cracks in the electric Pd plating and enables vacuum suction.

  In Patent Document 10, after a Pd-based film is formed on the surface of a porous body (porous substrate), a pinhole is probed, a metal is deposited on the probed pinhole portion, and the deposited metal is alloyed with Pd. The pinhole is closed by heat treatment at a temperature to be changed.

In general, it is known that when the film is thinned, a large internal stress remains in the film, and in the film manufactured by the plasma CVD method, the film is formed by alternately laminating films of tensile and compressive internal stress. Attempts have been made to cancel the internal stress of the film and prevent damage to the film such as peeling that occurs when the internal stress is reduced and the film is formed thick (for example, Patent Document 11).
Japanese Patent Laid-Open No. 5-137979 JP-A-10-297906 JP-A-11-267477 JP 2002-126477 A Japanese Patent Laid-Open No. 5-078810 JP 2003-135943 A JP 2000-11902 A JP H05-078810 A JP H05-123548 A JP 2002-119834 A JP-A-11-131240

  The aim of thinning the hydrogen permeable film is to make the hydrogen permeable film as thin as possible to increase the hydrogen permeation amount, and the point of the film forming technique is to eliminate pinholes in the film that cause the leak of impurity gas.

  However, most of the films produced by the above-mentioned thin film method are mainly related to Pd films or Pd alloy films that have been used conventionally, and an increase in hydrogen permeation amount cannot be expected. In many reports so far, pinholes remain in the film formed on the porous substrate. On the other hand, for materials such as Ta, Nb, V, etc., which show a transmission coefficient 5 times to 10 times that of Pd-based alloys, attempts have been made to reduce the thickness by vacuum deposition, ion plating, sputtering rigging, etc. However, most basic research has been conducted, and only a few examples have examined the hydrogen permeation performance and durability of membranes, and there are examples in which detailed considerations concerning internal stress and structure of membranes are particularly important. The current situation is not.

  Patent Document 7 that fills a pinhole is a method in which pores on the surface of a nickel porous body (porous substrate) are covered with nickel particles and fired, and a sealing process is performed to smooth the surface, followed by Pd plating. Yes, Patent Document 8 is to instantaneously heat the film surface with a laser beam to eliminate pores. Patent Document 10 searches for a pinhole, and deposits and deposits a metal on the searched pinhole part. The metal is heat-treated at a temperature at which it is alloyed with Pd to close the pinhole, and in any case, the sealing treatment for the porous substrate is complicated. In addition, Patent Document 9 performs shot peening treatment (glass bead blasting) on the plating layer, crushes countless fine cracks in electric Pd plating, and enables vacuum suction to create pinholes by mechanical treatment. It closes, enables vacuum suction and enables electroless Pd plating while vacuum suction. As a result, the hydrogen-permeable membrane is sealed, but not only is the blasting operation complicated, There is a technical problem that the plating layer is unavoidably caused by blasting, and the subsequent electroless Pd plating layer tends to be thick.

  In the present invention, first, a simple mechanical treatment is applied to the porous substrate to flatten the surface without extreme irregularities, and the non-permeable permeation membrane layer to be applied thereafter is thinned, and the hydrogen permeation amount Is to increase.

  Further, the present invention uses Ta, Nb, V or the like or its alloy thin film, particularly Ta or its alloy thin film as the main material of the hydrogen permeable film as an alternative material for the Pd-based material which is expensive and inferior in hydrogen permeability. Considering appropriately suppressing the amount and rate of hydrogen solid solution, while ensuring sufficient hydrogen permeation performance, excellent hydrogen permeation that can avoid problems caused by internal stress and film structure during film formation A method for manufacturing a film is proposed.

  Specifically, the structure of the porous substrate makes it difficult for pinholes to occur, and the internal stress of the film is reduced so that the film does not break down by controlling the pressure, temperature, or film formation speed during film formation. The film formation conditions are controlled so that a gas component other than hydrogen cannot pass through the crystal grain boundaries of the film as the film structure, and an optimal hydrogen permeable film is obtained.

According to the first aspect of the present invention, hydrogen is formed on a porous substrate through which hydrogen gas easily passes, and hydrogen in the reformed gas containing impurities in contact with one surface is permeated and selectively released from the other surface. In the permeable membrane,
The hydrogen permeable film is characterized in that a hydrogen permeable film G is formed on the surface of the porous substrate 7 whose surface is flattened by rolling.
The invention according to claim 2 is a hydrogen that is formed on a porous substrate through which hydrogen gas easily passes, allows hydrogen in the reformed gas containing impurities in contact with one surface to permeate, and selectively releases from the other surface. In the permeable membrane,
Having a single layer or multiple layers of hydrogen permeable film G formed on the surface of the porous substrate 7 by sputtering using Ta or Ta alloy as a material;
The range of internal stress of the layer of the hydrogen permeable membrane G is within ± 15 × 10 ⁴ N / cm ² from compressive stress to tensile stress, and is formed at a pressure of 1 × 10 ¹ Pa or less. The hydrogen permeable membrane is characterized in that the gap between the crystal grain boundaries is kept small so that only hydrogen can pass through the crystal grain boundaries.
According to a third aspect of the present invention, hydrogen is formed on a porous substrate through which hydrogen gas easily passes and allows hydrogen in the reformed gas containing impurities in contact with one surface to permeate and selectively release from the other surface. In the method for producing a permeable membrane,
A method for producing a hydrogen permeable membrane, characterized in that the surface of the porous substrate 7 is flattened by rolling, and the hydrogen permeable membrane G is formed on the surface of the porous substrate 7.
According to a fourth aspect of the present invention, hydrogen is formed on a porous substrate through which hydrogen gas easily passes, and hydrogen in the reformed gas containing impurities in contact with one surface is permeated and selectively released from the other surface. In the method for producing a permeable membrane,
Forming a hydrogen permeable film G on the surface of the porous substrate 7 by a sputtering method;
Deposition of the hydrogen permeable membrane G with an internal stress range of ± 15 × 10 ⁴ N / cm ² from compressive stress to tensile stress and a film forming pressure of 1 × 10 ¹ Pa or less during film formation. In the method of manufacturing a hydrogen permeable membrane, the gap is kept small so that only hydrogen can pass through the crystal grain boundary of the hydrogen permeable membrane G.
The invention according to claim 5 is the method for producing a hydrogen permeable membrane according to claim 4, further comprising the step of flattening the surface of the porous substrate 7 by rolling before the step of forming the film. .
The invention of claim 6 is the method of manufacturing a hydrogen permeable film according to claim 3, 4 or 5, wherein the hydrogen permeable film G is made of Ta or a Ta alloy.
In the invention of claim 7, the range of the internal stress is achieved by maintaining the film formation pressure when the hydrogen permeable film G is formed in the range of 5 × 10 ⁻¹ Pa to 1 × 10 ¹ Pa. The method for producing a hydrogen permeable membrane according to claim 4, 5 or 6.
In the invention of claim 8, the range of the internal stress is achieved by maintaining the temperature of the porous substrate 7 at the time of forming the hydrogen permeable film G in the range of -20 ° C to 800 ° C. The method for producing a hydrogen permeable membrane according to claim 4, 5, 6, or 7.
The range of the internal stress is achieved by maintaining the film formation rate when the hydrogen permeable film G is formed in the range of 0.0001 μm / second to 0.01 μm / second. 9. The method for producing a hydrogen permeable membrane according to claim 4, 5, 6, 7 or 8.
According to a tenth aspect of the present invention, the hydrogen permeable membrane G is composed of a plurality of layers G1 and G2, and in order to reduce the internal stress of the hydrogen permeable membrane G, the film formation conditions for compressive stress and the film formation conditions for tensile stress are alternately used. The layers G1 and G2 are formed, and the thicknesses of the layers G1 and G2 are set in the range of 0.1 μm to 2 μm. Alternatively, 9 is a method for producing a hydrogen permeable membrane.

  According to the independent claims 1 and 3, the porous substrate is previously rolled, and the extreme convex portions on the surface are crushed and flattened. Since the hydrogen permeable film is formed on the flattened substrate, it is possible to obtain a high quality hydrogen permeable film having no through holes such as pinholes and excellent hydrogen permeable performance by using the hydrogen permeable film as a thin film. .

According to claims 2 and 4, the range of the internal stress of the layer of the hydrogen permeable film formed on the surface of the porous substrate by the sputtering method is ± 15 × 10 ⁴ N / from compressive stress to tensile stress. within ² cm. As a result, the internal stress can be easily reduced to the predetermined range so that the hydrogen permeable membrane does not peel off by adjusting parameters such as the gas pressure and temperature during film formation, and the film formation rate. Peeling of the film from the substrate is favorably suppressed. In addition, a hydrogen permeable film is formed at a film formation pressure of 1 × 10 ¹ Pa or less during film formation so that only hydrogen can pass through the crystal grain boundary of the hydrogen permeable film, that is, an impurity gas other than hydrogen gas passes. The gap between the crystal grain boundaries is kept small so that there are no pinholes or gaps between the crystal grain boundaries.

  According to the fifth aspect, since there is a step of flattening the surface of the porous substrate by rolling before the film forming step, the same effects as the first and third aspects of the invention can be achieved. .

  According to claim 6, since the hydrogen permeable membrane is made of Ta or Ta alloy, the equilibrium dissociation pressure of hydrogen is high even in a high temperature region around 500 ° C. which is an assumed use temperature region when used for a membrane reformer, Under operating pressure, it is difficult to produce hydride and has excellent crack resistance.

According to claim 7, the range of the internal stress is achieved by maintaining the film formation pressure during the formation of the hydrogen permeable film in the range of 5 × 10 ⁻¹ Pa to 1 × 10 ¹ Pa. Therefore, as compared with claims 2 and 4, the gap between the crystal grain boundaries is kept small enough so that only hydrogen can pass through the crystal grain boundaries of the hydrogen permeable film.

According to the eighth aspect of the present invention, by maintaining the substrate temperature in the range of −20 ° C. to 800 ° C. during the formation of the hydrogen permeable film, the crystal is within the range of internal stress within ± 15 × 10 ⁴ N / cm ^2. A good state of a crystal structure in which the gap between the grain boundaries is kept small and there is no crack is easily achieved.

According to the ninth aspect, the amount of defects generated in the hydrogen permeable membrane can be reduced by maintaining the film formation rate during the formation of the hydrogen permeable membrane in the range of 0.0001 μm / second to 0.01 μm / second. The gap between the crystal grain boundaries is kept small within the range of the internal stress within ± 15 × 10 ⁴ N / cm ² , and a good state of the crystal structure without cracks is easily achieved.

  According to the tenth aspect, the hydrogen permeable film is composed of a plurality of layers, and the film is formed by alternately applying the film forming condition of the compressive stress and the film forming condition of the tensile stress in order to reduce the internal stress of the hydrogen permeable film. The thickness of each layer is set in the range of 0.1 μm to 2 μm. This makes it possible to satisfactorily offset the internal stress, with the upper limit being 2 μm, which is the maximum thickness capable of canceling the internal stress, and the thickness being less than 5 μm, while avoiding an increase in the number of laminations and the time required for film formation. it can.

  1 to 13 show an embodiment of a method for producing a hydrogen permeable membrane according to the present invention. As shown in FIG. 1, the hydrogen permeable membrane assembly M includes a porous substrate 7 as a strength member and a hydrogen permeable membrane G formed on one surface of the substrate 7. This hydrogen permeable membrane G is incorporated in a membrane reformer, allows hydrogen in the reformed gas containing impurities in contact with the one side surface to permeate, and selectively releases hydrogen from the other side surface.

  The hydrogen permeable membrane G may be Pd and a Pd alloy (Pd-based material), but preferably a metal element (non-Pd) other than Pd and a Pd alloy (Pd-based material) whose hydrogen solid solution amount per unit volume is larger than Pd. For example, a plate-like body having a uniform thickness. Specifically, the hydrogen permeable membrane G is preferably an alternative material to a Pd-based material such as tantalum (Ta), niobium (Nb), vanadium (V), hydrogen storage alloy (MH), and is particularly made of Ta or Ta alloy. Ta-based materials are preferred.

  The porous substrate 7 was previously rolled and flattened. By applying such a mechanical treatment, the extreme convex portions on the surface are crushed and flattened. If the substrate 7 is made of metal (for example, made of stainless steel), the convex portion on the surface is elastically deformed. If the substrate 7 is made of a brittle material such as ceramic, the convex portion on the surface is plastically deformed and flattened. The large holes of the come to close. The porous substrate 7 includes a thin film G previously formed.

  The reason why the porous substrate 7 is rolled and flattened will be described in detail in relation to sputtering. Porous substrates have large irregularities on the surface for manufacturing reasons, but it is found that these irregularities make the film atoms wrap around especially during sputtering, making it impossible to fill the pores. This is because when the surface is flattened as much as possible, it has been found that the degree of hole filling is extremely improved.

  Here, as a method for flattening the porous substrate 7, an expensive ceramic substrate having a small hole is used, a film is attached after applying fine particles to the surface of the inexpensive substrate 7 having a large hole, Holes that are formed and melted with a laser to fill the hole, and then further formed to prepare the surface, or a film is formed and the surface is blasted with glass beads to fill the hole. Although methods such as re-depositing the film later on only this part have been considered, all of these methods are expensive and time-consuming methods, leading to an increase in cost.

  Therefore, the inventors of the present invention focused on an inexpensive rolling method in which a gap between a pair of rolls is simply passed once, and as a result of repeated tests, the porous substrate 7 was easily flattened without impairing gas permeability. It was confirmed that the diameter of the pores of the porous substrate 7 was also reduced. However, depending on the amount of rolling, the pores may be crushed so that the gas permeability of the porous substrate 7 may be affected. Therefore, it is desirable to find optimum conditions depending on the material and structure of the porous substrate 7. .

  On one side surface of the substrate 7 subjected to the appropriate rolling, the hydrogen permeable film G was formed in a single layer or a plurality of layers so as to form a thin film by a film forming means comprising sputtering. One side surface of the hydrogen permeable membrane G is a surface that comes into contact with a high pressure side to which a reformed gas containing an impurity gas such as hydrocarbon gas (CH 4), CO, and CO 2 shown in FIG. 3 is supplied. Since one side surface of the substrate 7 is flattened, a hydrogen permeable film G without a pinhole that causes an impurity gas leak is easily formed, and the thin hydrogen permeable film G having a small internal stress is used. In order to allow only hydrogen to pass through the crystal grain boundary of the hydrogen permeable membrane G, the crystal grain boundary gap is maintained at a predetermined gap.

  When this hydrogen permeable membrane assembly M is incorporated into a membrane reformer and the reformed gas containing impurities such as CO and CO2 is introduced with the one side surface on which the hydrogen permeable membrane G is formed as the high pressure side, the hydrogen gas between both sides Only the hydrogen gas contained in the reformed gas permeates through the hydrogen permeable membrane G and the substrate 7, and the hydrogen can be purified and extracted.

  An outline of the sputtering method used as the film forming method will be described with reference to FIG. Generally, a sputtering apparatus has pumps 2 and 3 for evacuation, a power source 4 for generating plasma for sputtering, and a gas inlet 9 serving as a plasma source in a chamber 1, and further serves as a film raw material. A target 5 and a substrate 7 for forming a hydrogen permeable film G thereon are arranged. The substrate 7 is supported by the support 6. Further, in some cases, a mechanism 8 for heating the substrate 7 and a mechanism 10 for adjusting the rotation and vertical height of the substrate 7 are added. The temperature of the substrate 7 is adjusted by the amount of power supplied to the heating mechanism 8, and the film forming speed is adjusted by the amount of power supplied to the power source 4 and the distance between the target 5 and the substrate 7. The film forming direction with respect to the substrate 7 depends on the position of the substrate 7 and the target 5 in the apparatus, but can be adjusted in various directions such as up / down / left / right and oblique directions, and the film forming pressure (gas pressure) can be adjusted from the gas inlet 9. It can be adjusted by the flow rate of the gas and the degree of opening and closing of the valve disposed immediately before the vacuum pump 2.

  The reason for selecting the sputtering method as the film forming means is that basically any material can be easily formed into a thin film by the sputtering method. In addition, the target 5 is not only able to form a pure metal or alloy processed into a disk shape on three or four electrodes and mix even by complex sputtering while simultaneously sputtering to make various alloys. Alternatively, a powder may be used, or a film of a material to be formed on the target 5 may be disposed. That is, many possibilities can be tried. Further, the properties of the film to be formed can be easily changed by gas pressure and temperature at the time of film formation, film formation speed, distance between the substrate 7 and the target 5, rotation of the substrate 7, application of a bias voltage to the substrate 7, and the like. This is also an advantage of the sputtering method. However, as the film forming means, it is possible to adopt a film forming method that basically exhibits the same effect, instead of the sputtering method, and is not particularly limited to the sputtering method.

  The reason for selecting Ta and its alloy system from non-Pd materials as the alloy system is that Ta or Ta alloy is around 500 ° C, which is the assumed operating temperature range when used for membrane reformers compared to Nb and V-based materials This is because the equilibrium dissociation pressure of hydrogen is high even in the high temperature region, and it has the property that hydride is hardly generated under the working pressure. On the other hand, since the Nb system has a low equilibrium dissociation pressure, hydride is easily generated even at around 500 ° C. and is easily cracked. V has an equilibrium dissociation pressure higher than that of Ta and does not generate hydride up to 300 ° C or less. However, V has a drawback that diffusion with Pd or Pd alloy provided as a catalyst layer easily proceeds in the temperature range of around 500 ° C. is there. In addition, when Ta alloy is used, the material to be added to Ta has a region that forms a solid solution with Ta, and the reaction heat with hydrogen is positive and the action of raising the equilibrium dissociation pressure is increased. Fe, Cr, Ni, Mo, W 2, Au, Pt, or Ru is preferable because it works to suppress the above. However, even in the case of Nb, V or their alloys, there is a possibility that such disadvantages can be solved by the thin film production method, production conditions, component adjustment, change of use conditions, control of hydrogen dissolution amount, etc. Therefore, it is not particularly limited to Ta or Ta alloy.

  By the way, not only the said sputtering method but internal stress remains in a film | membrane when it thins. The main cause depends on the method and conditions of film formation, but it is said that internal defects that occur inside the film during film formation, the crystal growth orientation and growth mode of the film, and the difference in thermal expansion between the substrate and film material are involved. It has been broken. Thin films produced by sputtering are no exception, but sputtering can easily reduce internal stress so that the film does not peel off by adjusting parameters such as gas pressure, temperature, and deposition rate during deposition. there is a possibility.

  Therefore, in reducing the thickness of the hydrogen permeable membrane, attention was focused on internal stress that affects the hydrogen permeation performance and the durability of the membrane, and attempts were made to reduce it and search for stable film formation conditions. Here, the reason why the internal stress affects the hydrogen permeability is that the internal stress is caused by a defect inside the film or a strain caused by a difference in thermal expansion between the substrate and the film, and the defect acts as a trapping factor for hydrogen atoms. This is because the amount of movement of hydrogen is reduced, and the strain distorts the gaps between atoms for hydrogen diffusion and makes it difficult for hydrogen to pass. The reason why the internal stress affects the durability is that when the film has an internal stress, the film easily peels off from the substrate 7 due to the magnitude of the internal stress, but when the hydrogen is dissolved in the film G, the hydrogen permeable film This is because G itself undergoes volume expansion and a large stress is added. Therefore, if G originally has a large internal stress, it becomes easier to peel off and the durability is lost.

As a result of investigations by the present inventors, in the Ta and Ta-based alloy films, the range of the internal stress of the manufactured hydrogen permeable film G is 15 × 10 ⁴ N / cm in absolute value from compressive stress to tensile stress. It was found that if it was within ² , peeling from the substrate 7 did not occur. Even under film formation conditions where peeling does not occur, when the film formation pressure is high, the crystal grains of the film are greatly opened and pinholes are likely to occur, and impurity gases other than hydrogen gas are also generated. Because it will pass. The pressure condition for forming such a film that does not have pinholes or crystal grain boundary gaps through which large internal stresses that cause such delamination, impurity gases other than hydrogen gas pass, is ¹ to 5 × 10 ⁻¹ Pa. It was in the range of × 10 ¹ Pa. For this reason, the internal stress range of the hydrogen permeable membrane is within 15 × 10 ⁴ N / cm ² from compressive stress to tensile stress, and the gap is small so that only hydrogen can pass through the crystal grain boundary of the membrane. It must be maintained in a state.

Accordingly, the range of internal stress of the layer of the hydrogen permeable membrane G is within ± 15 × 10 ⁴ N / cm ² from compressive stress to tensile stress, and is formed at a pressure of 1 × 10 ¹ Pa or less. It is desirable that the gap be maintained at a small gap so that only hydrogen can pass through the crystal grain boundaries of the permeable membrane. Further, if the hydrogen permeable film is formed at a film formation pressure of 1 × 10 ¹ Pa or less, only hydrogen can pass through the crystal grain boundary of the hydrogen permeable film, that is, an impurity gas other than hydrogen gas. The gaps between the crystal grain boundaries are kept small so that there are no pinholes or gaps between the crystal grain boundaries that pass through. Further, by maintaining the film formation pressure during the formation of the hydrogen permeable film in the range of 5 × 10 ⁻¹ Pa to 1 × 10 ¹ Pa, it is possible to pass only hydrogen at the crystal grain boundary of the hydrogen permeable film. In addition, the gap between the crystal grain boundaries can be kept small.

This will be described with reference to the experimental results shown in FIG.
As shown in FIG. 8, the internal stress of the Ta film G formed at a film forming pressure in the range of 5 × 10 ⁻¹ Pa to 1 × 10 ¹ Pa is within ± 15 × 10 ⁴ N / cm ² , and the entire film As a result of observation, peeling of the film G was not observed.

This range of internal stress within ± 15 × 10 ⁴ N / cm ² is satisfactorily achieved by maintaining the substrate temperature in the range of −20 ° C. to 800 ° C. during the formation of the hydrogen permeable film. .

  In other words, if the film 7 is not controlled to be forcedly cooled using the substrate 7 having excellent heat conduction regardless of the film formation method, the temperature of the substrate 7 is increased to a predetermined temperature as time passes. However, the internal stress tends to be reduced when the substrate temperature at the time of film formation is increased. This is because the difference in thermal expansion due to the difference in thermal expansion coefficient between the film material and the substrate material is generally reduced as the substrate temperature rises. However, if the temperature is too high, the internal stress may be excessively increased due to the difference in the amount of thermal expansion. When the temperature is low, the Ta film becomes brittle and brittle.

  Therefore, there is an optimum value for the substrate temperature, and when the film material is Ta or Ta alloy, the temperature of the substrate 7 at the time of forming the hydrogen permeable film can be maintained in the range of -20 ° C to 800 ° C. Is optimal.

Further, the range of the internal stress within ± 15 × 10 ⁴ N / cm ² maintains the film formation rate during the formation of the hydrogen permeable film G within the range of 0.0001 μm / second to 0.01 μm / second. Can be achieved well.

  That is, the amount of defects generated in the film G varies depending on the growth rate of the thin film, and the internal stress changes accordingly. When the film formation rate is slow, the internal stress becomes small, but it cannot be industrially realized. Therefore, 0.0001 μm / second or more is necessary, and when the film formation rate is high, the internal stress increases and peeling occurs. Because of this, the upper limit was set to 0.01 μm / second. In other words, when the film formation rate is low, the number of atoms that collide with the film during film formation is small, and the thermal energy generated by the collision and the defect density per unit volume are small. When the film formation rate is high, the number of atoms that collide with the film during film formation increases, and the thermal energy generated by the collision and the defect density per unit volume increase. As the influence of the amount of defects increases, the internal stress increases and peeling occurs.

  On the other hand, when used as the hydrogen permeable film G, the volume expansion of the Ta film occurs due to the solid solution of hydrogen, and therefore, when the film G already has internal stress and a force is applied between the substrate 7 and the Ta film G. Since peeling easily occurs and sufficient durability may not be ensured, it is preferable that the internal stress of the film G is as small as possible.

  However, in the case of the Ta film G, an internal stress such as a tensile stress or a compressive stress is generated depending on the film forming conditions, and a large tensile stress with respect to the film forming pressure is suddenly changed to a large compressive stress at a certain pressure. For this reason, it is very difficult to form a film under the condition that the internal stress of the film G does not occur. The internal stress of a thin film is generally said to be smaller as the film thickness is thinner, with the exception of some substances that show a larger internal stress when it is thin. Since it is necessary to pass only the porous substrate 7, it is inevitably possible to fill the pores of the porous substrate 7 only by reducing the internal stress by thinning the film G. A thickness of μm or more is required. And if the film | membrane G is a single layer film | membrane, when a film | membrane will be several micrometers or more in thickness, internal stress will also become large.

  On the other hand, in the thin film, by repeatedly forming the internal stress of the tensile stress and the compressive stress alternately, the stress can be canceled and the internal stress can be reduced. However, the magnitude of the internal stress varies depending on the material of the film G, and when the internal stress is reduced by alternately laminating the films G1, G2 of the internal stress of the tensile stress and the compressive stress, The effect varies depending on the situation.

  In the investigation by the present inventors, in the case of a film G made of Ta-based material made of Ta or Ta alloy, a method of alternately forming films under a tensile stress film forming condition equivalent to a compressive stress film forming condition is used. It has been found that the effective thickness of each layer is 0.1 μm to 2 μm.

  The reason for this is that when the film thickness is thinner than 0.1 μm, the number of laminations increases, and it takes time to form the film, which is not industrially feasible. The thickness by which internal stress can be canceled by the lamination was up to 5 μm. When the film G is thicker than 5 μm, even if films having opposite stresses are stacked, peeling or the like occurs before canceling the film stress. Therefore, it is preferable to offset the stress by setting the upper limit of the film thickness to 2 μm or less, considering that the hydrogen permeable film should be as thin as possible and having multiple layers. However, if the film thickness must be increased, Film formation is possible up to 5 μm.

  Therefore, when the hydrogen permeable film G is composed of a plurality of layers G1 and G2, in order to reduce the internal stress of the hydrogen permeable film G, the film formation conditions for compressive stress and the film formation conditions for tensile stress are applied alternately. It is desirable that the thickness of each layer G1, G2 is set in the range of 0.1 μm to 2 μm while the film is formed.

  According to the present invention, in a hydrogen permeable film G of Ta and Ta-based alloy produced by sputtering, internal stress and crystal structure can be controlled by the pressure, temperature, and film formation speed during film formation. The hydrogen permeable membrane G with reduced internal stress by preventing the internal stress from breaking and generating pinholes and repeating the film formation under the stress condition opposite to the stress even under the film G having the internal stress. Can be created. Therefore, it is possible to provide a high-performance hydrogen permeable membrane G that replaces Pd and Pd-based alloys.

Example 1
On the one side surface of the rolled porous substrate 7 shown in FIG. 6 (microphotograph at 4 × magnification), the film forming pressure (gas pressure) is 5 × 10 ⁻¹ Pa at room temperature using the sputtering apparatus shown in FIG. The Ta film G was formed in the range of 1 × 10 ¹ Pa, and the peeling state of the film G and the surface state of the film G were investigated. FIG. 7 shows the result of observing the surface of the hydrogen permeable film G on the substrate 7 at a magnification of 2,000 with a scanning electron microscope (SEM). As can be seen from the figure, the surface of the film G formed within the range of the film forming conditions was dense, and no large gaps were observed in the holes and crystal grain boundaries. Further, as shown in FIG. 8, the internal stress of the Ta film formed in the film forming pressure range of 5 × 10 ⁻¹ Pa to 1 × 10 ¹ Pa is within ± 15 × 10 ⁴ N / cm ^2. No peeling was observed. FIG. 9 is an overall observation photograph of the hydrogen permeable membrane assembly M viewed from the hydrogen permeable membrane G side. On the other hand, as a result of observing the surface of the film at a magnification of 50,000 times with a scanning electron microscope (SEM), the surface of the film formed in the range of the above film forming conditions was dense as shown in FIG. It was not done. Furthermore, the He leak test of the film G is performed at room temperature using the leak test apparatus shown in FIG. 13, and it is confirmed that there is no He leak even when the membrane reformer is used. Therefore, it is possible to prevent the passage of impure gas when using the membrane reformer.

  In this leak test apparatus, a hydrogen permeable membrane G with a substrate 7 (hydrogen permeable membrane assembly M) is hermetically sandwiched between a pair of He introduction pipes 20 and 21 via O-rings 22 and 23, and the hydrogen permeable membrane G He gas is supplied at a predetermined pressure from the He introduction pipe 20 on the side, and the He gas passing and flowing out from the He introduction pipe 20 on the substrate 7 side is guided to the He leak detector 24 for detection.

(Comparative Example 1)
The film forming pressure is in the range of 5 × 10 ⁻¹ Pa to 1 × 10 ¹ Pa at room temperature using a sputtering apparatus on a porous substrate having an uneven surface that is not rolled as shown in FIG. Then, a Ta film was formed, and the peeling state of the film and the surface state of the film were investigated. When the surface of the film was observed at a magnification of 2,000 with a scanning electron microscope (SEM), as shown in FIG. 5, the surface had large irregularities, and many unfilled holes were observed in the film. Further, as a result of conducting a He leak test of the film at room temperature using the leak test apparatus shown in FIG. 13, it was confirmed that there was a leak.

(Comparative Example 2)
A Ta film was formed on the rolled porous substrate 7 of Example 1 at room temperature using a sputtering apparatus at a film forming pressure of 4 × 10 ⁻¹ Pa or less. And the surface condition of the membrane was investigated. The Ta film formed at a film forming pressure of 4 × 10 ⁻¹ Pa or less has a dense film surface and no large gap at the crystal grain boundary as shown in the observation result by SEM in FIG. However, as shown in FIG. 8, the internal stress (absolute value) exceeds about 15 × 10 ⁴ N / cm ² , and as a result of observation of the entire film similar to that shown in FIG. As a result, the He leak test could not be performed.

(Comparative Example 3)
A Ta film G was formed on the rolled porous substrate 7 of Example 1 at room temperature using a sputtering apparatus at a film formation pressure in the range of 1 × 10 ¹ Pa to 5 × 10 ¹ Pa. The stress, film peeling condition and film surface condition were investigated. As shown in FIG. 8, the Ta film G formed at a film forming pressure in the range of more than 1 × 10 ¹ Pa to 5 × 10 ¹ Pa has an internal stress (absolute value) of about 2 × 10 ⁴ N / cm ^2. A small and good value of about 0.3 × 10 ⁴ N / cm ² was observed, and no peeling was observed from the entire surface observation of the film G similar to that shown in FIG. However, as shown in FIG. 12, in SEM observation at a magnification of 50,000 times the surface of the film G, it was found that a large gap was observed at the crystal grain boundary, and gas other than hydrogen could pass through. Furthermore, as a result of conducting a He leak test of the film G at room temperature using the leak test apparatus shown in FIG. 13, a large leak was confirmed.

(Example 2)
A Ta film G is formed on the rolled porous substrate 7 of Example 1 using a sputtering apparatus, the temperature of the substrate 7 during film formation is set to 800 ° C., and the film formation pressure is set to 5 × 10 ⁻¹ Pa. The internal stress of G, the peeling state of the film G, and the surface state of the film were investigated. As a result, the internal stress of the film G was about −15 × 10 ⁴ N / cm ² , and no peeling of the film G was observed from the same overall observation photograph of the film G as shown in FIG. On the other hand, as a result of observing the surface of the film G by SEM at a magnification of 50,000 times, the surface of the film G was dense as shown in FIG. 11, and no large gap was observed at the crystal grain boundary. Moreover, as a result of conducting a He leak test of the film at room temperature using the leak test apparatus shown in FIG. 13, it was confirmed that there was no leak.

(Comparative Example 4)
A Ta film was formed on the rolled porous substrate 7 of Example 1 using a sputtering apparatus at a substrate temperature of 900 ° C. and a film forming pressure of 5 × 10 ⁻¹ Pa. The film peeling condition and the film surface condition were investigated. As a result, the internal stress of the film was about 13 × 10 ⁴ N / cm ² , and the film was not peeled from the entire observation photograph of the film similar to that shown in FIG. On the other hand, as a result of observing the surface of the film at 50,000 times with SEM, the surface of the film was dense as in FIG. 11, and no large gap was seen at the grain boundary, but cracks were partially generated. Further, as a result of conducting a He leak test of the film at room temperature using the leak test apparatus shown in FIG. 13, a He leak occurred.

(Comparative Example 5)
The Ta film G was formed on the rolled porous substrate of Example 1 using the sputtering apparatus, the substrate temperature during film formation was −40 ° C., the film formation pressure was 5 × 10 ⁻¹ Pa, and the film G The internal stress, the peeling state of the film G, and the surface state of the film G were investigated. As a result, the internal stress of the film was about 7 × 10 ⁴ N / cm ² , and the film was not peeled from the entire observation photograph of the film similar to that shown in FIG. On the other hand, as a result of observing the surface of the film G by SEM at a magnification of 50,000 times, the surface of the film G was dense as shown in FIG. 11 and no large gap was seen at the grain boundary, but a crack was partially generated. . The cause of the crack seems to be due to embrittlement of the Ta film G at a low temperature. Further, as a result of conducting a He leak test of the film G at room temperature using the leak test apparatus shown in FIG. 13, a leak of He occurred.

(Example 3)
A Ta film G was formed on the rolled porous substrate 7 of Example 1 at room temperature with a film forming pressure of 5 × 10 ⁻¹ Pa and a film forming rate of 0.01 μm / second. The internal stress, the peeling state of the film G, and the surface state of the film were investigated. As a result, the internal stress of the film G was about -14.5 × 10 ⁴ N / cm ² , and no peeling of the film G was observed from the whole film observation photograph similar to that shown in FIG. On the other hand, as a result of observing the surface of the film G by SEM at a magnification of 50,000 times, the surface of the film G was dense as shown in FIG. 11, and no large gap was observed at the crystal grain boundary. Moreover, as a result of conducting a He leak test of the film G at room temperature using the leak test apparatus shown in FIG. 13, it was confirmed that there was no leak.

(Comparative Example 6)
A Ta film was formed on the rolled porous substrate of Example 1 at room temperature at a film forming pressure of 5 × 10 ⁻¹ Pa and a film forming speed of 0.02 μm / sec. The film peeling condition and the film surface condition were investigated. As a result, the internal stress of the film was about 23 × 10 ⁴ N / cm ² , and the film was peeled from the entire observation of the film, and the He leak test could not be performed. FIG. 10 shows an overall observation photograph of the film.

Example 4
On the rolled porous substrate 7 of Example 1, using a sputtering apparatus, Ta films G were alternately formed at a room temperature of 2 × 10 ⁰ Pa and 3 × 10 ⁰ Pa at a thickness of 1 μm each. The internal stress of the film G, the peeling state of the film G, and the surface state of the film G were investigated with a total thickness of 20 μm. As a result, the internal stress of the film G was about 1.4 × 10 ⁴ N / cm ² on the tensile stress side, and no peeling of the film G was observed from the same overall observation photograph of the film as shown in FIG. . On the other hand, as a result of observing the surface of the film G by SEM at a magnification of 50,000 times, the surface of the film G was dense as shown in FIG. 11, and no large gap was observed at the crystal grain boundary. Moreover, as a result of conducting a He leak test of the film G at room temperature using the leak test apparatus shown in FIG. 13, it was confirmed that there was no leak.

(Reference example)
Using a sputtering apparatus on the rolled porous substrate of Example 1, Ta films G were alternately formed at a film forming pressure of 2 × 10 ⁰ Pa and 3 × 10 ⁰ Pa at a thickness of 5 μm at room temperature. Then, the internal stress of the film G, the peeling state of the film G, and the surface state of the film G were investigated with a total thickness of 20 μm. As a result, the internal stress of the film G was about 10 × 10 ⁴ N / cm ² on the tensile stress side, and peeling of the film G was not observed from the same overall observation photograph of the film as shown in FIG. On the other hand, as a result of observing the surface of the film G by SEM at a magnification of 50,000 times, the surface of the film G was dense as shown in FIG. 11, and no large gap was observed at the crystal grain boundary. Moreover, as a result of conducting a He leak test of the film G at room temperature using the leak test apparatus shown in FIG. 13, it was confirmed that there was no leak.

(Comparative Example 7)
Using a sputtering apparatus on the rolled porous substrate of Example 1, Ta films were alternately formed at a room temperature of 2 × 10 ⁰ Pa and 3 × 10 ⁰ Pa at a thickness of 10 μm, The internal stress of the film, the state of peeling of the film and the surface state of the film were investigated with a total thickness of 20 μm. As a result, the film formed as the second layer was partially peeled off.

Schematic showing the structure of the porous substrate and the hydrogen permeable membrane formed on it The figure which shows the outline of sputtering equipment Explanatory drawing of hydrogen permeation mechanism by hydrogen permeable membrane Photograph showing the irregularities of an untreated porous substrate Photomicrograph showing the state of a film formed on an untreated porous substrate with irregularities Photograph showing the irregularities of the porous substrate after rolling Photomicrograph showing the surface of a hydrogen permeable membrane formed on a rolled porous substrate Diagram showing the relationship between gas pressure during film formation and internal stress of Ta film Whole observation photograph of hydrogen permeable membrane showing no peeling after film formation Photo of the entire hydrogen permeable membrane showing peeling after film formation SEM photograph showing the surface of a hydrogen permeable membrane with no gaps in crystal grain boundaries SEM photograph showing the surface of a hydrogen permeable membrane with large gaps in the grain boundaries The figure which shows the outline of the apparatus for performing a He leak test

Explanation of symbols

  1: chamber, 7: porous substrate, G: hydrogen permeable membrane, G1, G2: layer, M: hydrogen permeable membrane assembly.

Claims (10)

In a hydrogen permeable membrane that is formed on a porous substrate through which hydrogen gas easily passes, allows hydrogen in the reformed gas containing impurities in contact with one surface, and selectively releases from the other surface,
A hydrogen permeable membrane (G) formed on the surface of a porous substrate (7) whose surface is flattened by rolling. In a hydrogen permeable membrane that is formed on a porous substrate through which hydrogen gas easily passes, allows hydrogen in the reformed gas containing impurities in contact with one surface, and selectively releases from the other surface,
Having a single layer or multiple layers of hydrogen permeable membrane (G) formed on the surface of the porous substrate (7) by sputtering using Ta or Ta alloy as a material;
The range of internal stress of the layer of the hydrogen permeable membrane (G) is within ± 15 × 10 ⁴ N / cm ² from compressive stress to tensile stress, and is formed at a pressure of 1 × 10 ¹ Pa or less, and hydrogen permeation A hydrogen permeable membrane characterized in that a gap between crystal grain boundaries is kept small so that only hydrogen can pass through the crystal grain boundaries of the film (G). In a method for producing a hydrogen permeable membrane that is formed on a porous substrate through which hydrogen gas easily passes and allows hydrogen in a reformed gas containing impurities in contact with one surface to permeate and selectively release from the other surface,
A method for producing a hydrogen permeable membrane, characterized in that the surface of the porous substrate (7) is flattened by rolling and a hydrogen permeable membrane (G) is formed on the surface of the porous substrate (7). In a method for producing a hydrogen permeable membrane that is formed on a porous substrate through which hydrogen gas easily passes and allows hydrogen in a reformed gas containing impurities in contact with one surface to permeate and selectively release from the other surface,
Forming a hydrogen permeable film (G) on the surface of the porous substrate (7) by sputtering;
The range of internal stress of the layer of the hydrogen permeable membrane (G) is within ± 15 × 10 ⁴ N / cm ² from compressive stress to tensile stress, and the film formation pressure during film formation is 1 × 10 ¹ Pa or less. A method for producing a hydrogen permeable membrane, characterized in that a gap between the crystal grain boundaries is kept small so that only hydrogen can pass through the crystal grain boundaries of the hydrogen permeable membrane (G). The method for producing a hydrogen permeable membrane according to claim 4, further comprising a step of flattening the surface of the porous substrate (7) by rolling before the step of forming the film. The method for producing a hydrogen permeable membrane according to claim 3, 4 or 5, wherein the hydrogen permeable membrane (G) is made of Ta or a Ta alloy. The range of the internal stress is achieved by maintaining the film formation pressure at the time of forming the hydrogen permeable film (G) in the range of 5 × 10 ⁻¹ Pa to 1 × 10 ¹ Pa. The method for producing a hydrogen permeable membrane according to claim 4, 5 or 6. The range of the internal stress is achieved by maintaining the temperature of the porous substrate (7) during the formation of the hydrogen permeable membrane (G) in the range of −20 ° C. to 800 ° C. The method for producing a hydrogen permeable membrane according to claim 4, 5, 6, or 7. The range of the internal stress is achieved by maintaining the film formation rate during the film formation of the hydrogen permeable membrane (G) in the range of 0.0001 μm / second to 0.01 μm / second. A method for producing a hydrogen permeable membrane according to claim 4, 5, 6, 7 or 8. The hydrogen permeable membrane (G) is composed of a plurality of layers (G1, G2), and a compressive stress film forming condition and a tensile stress film forming condition are alternately applied to reduce the internal stress of the hydrogen permeable film (G). The layers (G1, G2) are formed, and the thickness of each layer (G1, G2) is set in the range of 0.1 μm to 2 μm. A method for producing a 7, 8, or 9 hydrogen permeable membrane.

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