Hydrogen separation filter and method for manufacturing hydrogen separation filter

Abstract

Provided are: a hydrogen separation filter which has a high hydrogen permeation rate and which prevents or reduces separation between layers; and a method for producing the hydrogen separation filter. The hydrogen separation filter includes a porous substrate and a palladium layer provided on the porous substrate. The grain boundary number density observed in a cross-sectional secondary electron image of the palladium layer is 1-5 grains / [mu] m. A method for manufacturing a hydrogen separation filter includes forming a palladium layer on a porous base material by a sputtering method while keeping the temperature of the porous base material at 300-600 DEG C.

Description

Technical Field

[0001] This disclosure relates to a hydrogen separation filter and a method for manufacturing a hydrogen separation filter. Background Technology

[0002] As a method for purifying hydrogen, membrane separation using metal membranes is known. Patent Document 1 describes a porous filter and a hydrogen separation membrane in which a palladium thin film or palladium alloy thin film is formed on one side of the porous filter. The porous filter is characterized in that only defects larger than the micropores opening on one side of the porous ceramic membrane are blocked by the metal, while the micropores in the porous ceramic membrane are not blocked by the metal.

[0003] Patent Document 1: Description of Japanese Patent No. 5891512.

[0004] Hydrogen separation filters preferably have a high hydrogen permeation rate. Furthermore, it is desirable to prevent delamination between the porous substrate and the metal layer of the hydrogen separation filter. Therefore, this disclosure provides a hydrogen separation filter with a high hydrogen permeation rate and a method for manufacturing the same, which prevents or mitigates interlayer delamination. Summary of the Invention

[0005] This disclosure is made in the following ways.

[0006] [Method 1]

[0007] A hydrogen separation filter comprises a porous substrate and a palladium layer disposed on the porous substrate, wherein the grain boundary number density observed in a cross-sectional secondary electron image of the palladium layer is 1 to 5 per μm.

[0008] [Method 2]

[0009] According to the hydrogen separation filter of method 1, the porous substrate has an average pore diameter of 5 to 20 nm, a porosity of 30% to 70%, and a surface roughness of 0.1 to 2 μm.

[0010] [Method 3]

[0011] According to the hydrogen separation filter of method 1 or 2, the palladium layer has a thickness of 50 to 200 nm.

[0012] [Method 4]

[0013] The hydrogen separation filter according to any one of methods 1 to 3, wherein it has 5 mmol·s -1 ·m -2 ·Pa -0.5 The above refers to the hydrogen permeation rate.

[0014] [Method 5]

[0015] The method for manufacturing the hydrogen separation filter according to any one of modes 1 to 4, comprising: forming a palladium layer on a porous substrate by a sputtering method with the temperature of the porous substrate being 300°C to 600°C.

[0016] The hydrogen separation filter manufactured by the hydrogen separation filter of the present disclosure and the manufacturing method of the present disclosure has a high hydrogen permeation rate and prevents or mitigates peeling between layers. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a schematic cross-sectional view of the hydrogen separation filter of the embodiment.

[0018] EXPLANATION OF REFERENCE NUMERALS

[0019] 1: hydrogen separation filter; 10: porous substrate; 12: first face; 14: second face; 60: palladium layer. DETAILED DESCRIPTION

[0020] Hereinafter, the embodiments will be described with appropriate reference to the drawings. In the drawings referred to in the following description, the dimensional ratios and shapes of the components are sometimes exaggerated for the sake of explanation, and are not necessarily the same as the actual dimensional ratios and shapes. In the present application, the numerical range indicated using the symbol "to" includes the numerical values indicated before and after the symbol "to" as the lower limit value and the upper limit value, respectively. The upper limit value and the lower limit value of the numerical range described in the present application can be combined individually or arbitrarily to define a preferred range.

[0021] (1) Hydrogen separation filter

[0022] Figure 1 The hydrogen separation filter 1 of the embodiment shown includes a porous substrate 10 and a palladium layer 60 provided on the porous substrate 10. The palladium layer 60 can be formed directly on the porous substrate 10.

[0023] The porous substrate 10 is composed of an oxide material such as a metal oxide, a semi-metal oxide, or a mixture thereof, and is preferably composed of an oxide material. In the present application, "composed of" means that additional components that do not substantially adversely affect the performance of the hydrogen separation filter 1 can be included in addition to the recited material. "Consisting of" means that only the recited material is included, but does not exclude the inclusion of unavoidable impurities. As examples of the oxide material, alumina, zirconia, titania, and mixtures thereof can be given.

[0024] The porous substrate 10 can be of any shape having a first face 12 and a second face 14, such as a plate shape, a sheet shape, a cylindrical shape, or the like. The porous substrate 10 has fine pores through which hydrogen can pass, connecting from the first face 12 to the second face 14. The fine pores are closed by the palladium layer 60.

[0025] The average diameter of the pores of the porous base material 10 (average pore diameter) is preferably 5 to 20 nm, more preferably 5 nm or more and less than 20 nm, and particularly preferably 5 to 15 nm. By making the average pore diameter within the above range, the porous base material 10 has sufficient hydrogen permeability, and it is possible to plug the pores with a palladium layer 60 having a thickness of 50 to 200 nm. In the present application, the average pore diameter of the porous base material 10 is determined based on the pore diameter distribution obtained by the mercury intrusion method in accordance with JIS R1655:2003. The mercury intrusion method is a method in which mercury is caused to intrude into open pores by applying pressure, the relationship between the volume of the mercury that has intruded into the open pores and the pressure value applied at that time is obtained, based on the result, the open pores are assumed to be cylindrical, and the diameter of the open pores is calculated according to the Washburn formula.

[0026] The porous base material 10 can have a porosity of 30% to 70%. By making the porosity within the above range, the porous base material 10 has sufficient hydrogen permeability, and it is possible to plug the pores with a palladium layer 60 having a thickness of 50 to 200 nm. In the present application, the porosity of the porous base material 10 is the open porosity obtained by the Archimedes method in accordance with JIS R1634:1998.

[0027] The first face 12 of the porous base material 10 can have a surface roughness of 0.1 to 2 μm. In the present application, the surface roughness refers to the arithmetic average roughness Ra obtained by the optical interference method in accordance with JIS B0601:2013.

[0028] The palladium layer 60 is formed on the first face 12 of the porous base material 10. The palladium layer 60 generally has a higher hydrogen permeation rate than a layer of a palladium alloy such as a palladium-silver alloy of the same thickness.

[0029] The palladium layer 60 can have a thickness of 50 to 200 nm. This is a smaller value than the thickness of a conventional palladium layer for hydrogen separation. When the thickness of the palladium layer 60 is small, the hydrogen permeation rate per unit area of the palladium layer 60 (mmol s -1 ·m -2 ·Pa -0.5 ) is improved, and thus it is possible to achieve a target hydrogen permeation rate (mmol s -1 ·m -2 ·Pa -0.5 ) with a smaller area than in the related art. Therefore, the hydrogen separation filter 1 of the embodiment can reduce the amount of palladium used, and can be manufactured at a low cost.

[0030] In the palladium layer 60, the number density of grain boundaries is 1 to 5 / μm. In the present application, the number density of grain boundaries (pieces / μm) is obtained by counting the number of grain boundaries observed in a range of 5 μm in a direction perpendicular to the thickness direction of the palladium layer 60 in a secondary electron image of a cross section of the palladium layer 60, and dividing the number by 5 μm.

[0031] As shown in the examples described later, by making the number density of grain boundaries of the palladium layer 60 5 pieces / μm or less, the hydrogen separation filter 1 can have a high hydrogen permeation rate. The reason for this is considered to be as follows. The grain boundaries of the palladium layer 60 trap hydrogen passing through the palladium layer 60, delaying the permeation of hydrogen. By making the number density of grain boundaries of the palladium layer 60 5 pieces / μm or less, hydrogen is not trapped by the grain boundaries and easily passes through the palladium layer 60, and thus a high hydrogen permeation rate can be obtained.

[0032] In addition, by making the number density of grain boundaries of the palladium layer 60 1 piece / μm or more, occurrence of peeling between the porous base material 10 and the palladium layer 60 can be prevented or mitigated. The reason for this is considered to be as follows. Since the surface of a palladium crystal grain is originally flat, the surface of the palladium crystal grain is formed in contact with the surface of the porous base material 10 having the above-described surface roughness, and thus stress is generated. In addition, stress is also generated due to the difference in thermal expansion rate between the porous base material 10 and the palladium layer 60. The grain boundaries in the palladium layer 60 can relieve these stresses. By making the number density of grain boundaries of the palladium layer 60 1 piece / μm or more, the above-described stresses are sufficiently relieved, and occurrence of peeling between the porous base material 10 and the palladium layer 60 can be prevented or mitigated.

[0033] (2) Method for manufacturing hydrogen separation filter

[0034] The method for manufacturing the hydrogen separation filter of the embodiment includes forming a palladium layer on a porous base material by a sputtering method, with the temperature of the porous base material being 300 to 600°C.

[0035] By forming the palladium layer with the temperature of the porous base material being 300°C or more, a palladium layer having a number density of grain boundaries of 5 pieces / μm or less can be formed, and thus the manufactured hydrogen separation filter can have a high hydrogen permeation rate. By forming the palladium layer with the temperature of the porous base material being 600°C or less, a palladium layer having a number density of grain boundaries of 1 piece / μm or more can be formed, and thus occurrence of peeling between the porous base material and the palladium layer can be prevented or mitigated. The film formation rate of the palladium layer can be appropriately adjusted so that the number density of grain boundaries becomes a desired value. Generally, if the film formation rate is reduced, the number density of grain boundaries decreases.

[0036] The above describes the embodiment of the present disclosure in detail, but the present disclosure is not limited to the above-described embodiment, and various design changes can be made within the scope of the technical range recited in the claims.

[0037] [Examples]

[0038] Hereinafter, the present disclosure will be specifically described by examples, but the present disclosure is not limited to these examples.

[0039] (1) Production of hydrogen separation filter

[0040] A porous alumina substrate ( "Precision filter MF0.1" manufactured by Nippon Sheet Glass Co., Ltd., average pore diameter 100 nm) was coated with aluminum particles to produce a porous substrate having an average pore diameter of 8 nm, a void fraction of 40%, and a surface roughness of 0.4 μm. The average pore diameter was determined based on the pore size distribution obtained by the mercury intrusion method according to JIS R1655:2003. The void fraction was the open porosity obtained by the Archimedes method according to JIS R1634:1998. The surface roughness was the arithmetic average roughness Ra according to JIS B0601:2013 obtained by the optical interference method.

[0041] The porous substrate was placed in the film formation chamber of a sputtering device provided with a pure Pd target so as to face the pure Pd target. The film formation chamber was set to a low vacuum state of Ar gas atmosphere, and the porous substrate was heated to the temperature described in Table 1, and a Pd layer having a thickness of 100 nm was formed on the porous substrate by the sputtering method at the film formation rate described in Table 1. Specifically, a high voltage was applied to the pure Pd target as a cathode to generate glow discharge, ionize Ar, and make Ar ions collide with the target, and Pd atoms were ejected from the target to adhere to the porous substrate. The thickness of the Pd layer was determined using a cross-sectional reflection electron image of the hydrogen separation filter produced.

[0042] In Comparative Examples 2 and 3, the Pd layer was peeled off from the porous substrate. In Comparative Example 1 and Examples 1 to 4, a hydrogen separation filter in which the porous substrate and the Pd layer were well adhered was obtained.

[0043] (2) Measurement of grain boundary number density

[0044] A cross-sectional secondary electron image of the Pd layer formed in each of the examples and comparative examples was obtained using a scanning electron microscope, and the number of grain boundaries present in a range of 5 μm in length in a direction perpendicular to the thickness direction of the Pd layer was counted. The number of grain boundaries was divided by 5 μm to obtain the grain boundary number density (number / μm). The results are shown in Table 1.

[0045] (3) Measurement of hydrogen permeation rate

[0046] The hydrogen permeation rate per unit area (unit: mmol s m2) of the hydrogen separation filters of Comparative Example 1 and Examples 1 to 4 at 400°C was measured by gas chromatography according to JIS K7126:2006 (Plastics - Membranes and sheets - Gas permeability test method - Part 1: Differential pressure method).-1 • m -2 • Pa -0.5 ). The results are shown in Table 1. In addition, in order to compare with the prior art, the hydrogen permeation rate of the hydrogen separation membrane of Example 3 of Patent Document 1 at 400°C is also shown in Table 1. The hydrogen separation filters of Examples 1 to 4 had a hydrogen permeation rate of 5 mmol-s / m2Pa at 400°C, which is higher than the hydrogen permeation rate of the hydrogen separation membrane of Patent Document 1 at 400°C. -1 • m -2 • Pa -0.5 The above high hydrogen permeation rate is higher than the hydrogen permeation rate of the hydrogen separation membrane of Patent Document 1 at 400°C.

[0047] From the above evaluation results, in Comparative Example 1 and Examples 1 to 4 in which the grain boundary number density of the Pd layer is 1 or more per μm, peeling does not occur between the porous substrate and the Pd layer, and the hydrogen separation filter can be favorably produced, and the hydrogen separation filters of Examples 1 to 4 in which the grain boundary number density of the Pd layer is 5 or less per μm have a high hydrogen permeation rate.

[0048] [Table 1]

[0049]

Claims

1. A hydrogen separation filter comprising a porous substrate and a palladium layer disposed on the porous substrate, wherein, The grain boundary number density observed in the cross-sectional secondary electron image of the palladium layer is 1 to 5 per μm.

2. The hydrogen separation filter according to claim 1, wherein, The porous substrate has an average pore diameter of 5–20 nm, a porosity of 30%–70%, and a surface roughness of 0.1–2 μm.

3. The hydrogen separation filter according to claim 1, wherein, The palladium layer has a thickness of 50–200 nm.

4. The hydrogen separation filter according to claim 1, wherein, With 5 mmol·s -1 ·m -2 ·Pa -0.5 The above refers to the hydrogen permeation rate.

5. A method for manufacturing a hydrogen separation filter, wherein the hydrogen separation filter is the hydrogen separation filter according to any one of claims 1 to 4, wherein, The method for manufacturing the hydrogen separation filter includes: setting the temperature of a porous substrate to 300°C to 600°C, and forming a palladium layer on the porous substrate by sputtering.

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