Hydrogen separation filter and method for manufacturing hydrogen separation filter

Abstract

To provide a hydrogen separation filter which has a high hydrogen permeation rate and in which delamination is prevented or reduced, and to provide a method for producing the same.SOLUTION: The hydrogen separation filter includes a porous substrate and a palladium layer disposed on the porous substrate. The number density of crystal grain boundaries observed in a cross-sectional secondary electron image of the palladium layer is 1 to 5 / μm. The method for producing a hydrogen separation filter includes forming a palladium layer on a porous substrate by sputtering at a porous substrate temperature of 300 °C to 600 °C.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a hydrogen separation filter and a method for manufacturing a hydrogen separation filter. [Background technology]

[0002] A membrane separation method using a metal membrane is known as a method for purifying hydrogen. Patent Document 1 describes a porous filter characterized in that only defects larger than the micropores that open on one side of a porous ceramic membrane having micropores are blocked with metal, and the micropores in the porous ceramic membrane are not blocked with metal, and a hydrogen separation membrane in which a thin palladium or palladium alloy thin film is formed on one side of the porous filter. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5891512 specification Summary of the Invention [Problem to be solved by the invention]

[0004] It is desirable for a hydrogen separation filter to have a high hydrogen permeation rate. It is also desirable for delamination to not occur between the porous substrate and the metal layer of the hydrogen separation filter. Therefore, the present disclosure provides a hydrogen separation filter that has a high hydrogen permeation rate and prevents or reduces delamination between layers, and a method for manufacturing the same. [Means for solving the problem]

[0005] Aspects of the present disclosure include the following. [Aspect 1] A porous substrate; a palladium layer provided on the porous substrate; A hydrogen separation filter comprising: A hydrogen separation filter, wherein the number density of crystal grain boundaries observed in a cross-sectional secondary electron image of the palladium layer is 1 to 5 grains / μm. [Aspect 2] 2. The hydrogen separation filter according to aspect 1, wherein the porous substrate has an average pore size of 5 to 20 nm, a porosity of 30% to 70%, and a surface roughness of 0.1 to 2 μm. [Aspect 3] 3. The hydrogen separation filter according to aspect 1 or 2, wherein the palladium layer has a thickness of 50 to 200 nm. [Aspect 4] 5 mmol·s -1 m -2 Pa -0.5 A hydrogen separation filter according to any one of aspects 1 to 3, having a hydrogen permeation rate equal to or higher than this. [Aspect 5] A method for producing a hydrogen separation filter according to any one of aspects 1 to 4, comprising: A method comprising forming a palladium layer on a porous substrate by a sputtering method at a temperature of the porous substrate of 300°C to 600°C. [Effects of the Invention]

[0006] The hydrogen separation filter of the present disclosure and the hydrogen separation filter produced by the production method of the present disclosure have a high hydrogen permeation rate, and delamination between layers is prevented or reduced. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic cross-sectional view of a hydrogen separation filter according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments will be described with reference to the drawings as appropriate. In the drawings referred to in the following description, the dimensional ratios and shapes of each component are exaggerated for the sake of convenience and may differ from the actual dimensional ratios and shapes. Furthermore, in this application, a numerical range expressed using the symbol "to" includes the numerical values ​​before and after the symbol "to" as the lower and upper limits, respectively. The upper and lower limits of the numerical ranges described in this application can be used alone or in any combination to define a preferred range.

[0009] (1) Hydrogen separation filter 1 includes a porous substrate 10 and a palladium layer 60 provided on the porous substrate 10. The palladium layer 60 may be formed directly on the porous substrate 10.

[0010] The porous substrate 10 is composed of an oxide material such as a metal oxide, a semi-metal oxide, or a mixture thereof, and preferably consists of an oxide material. In this application, "composed of" means that in addition to the materials listed, additional components that do not substantially adversely affect the performance of the hydrogen separation filter 1 may be included. "Consisting of" means including only the materials listed, but does not exclude the inclusion of unavoidable impurities. Examples of oxide materials include aluminum oxide, zirconium oxide, titanium oxide, and mixtures thereof.

[0011] The porous substrate 10 may have any shape, such as a plate, sheet, or cylinder, and has a first surface 12 and a second surface 14. The porous substrate 10 has pores that connect the first surface 12 to the second surface 14 and allow hydrogen to pass through. The pores are blocked by a palladium layer 60.

[0012] The average diameter of the pores in the porous substrate 10 (average pore size) is preferably 5 to 20 nm, more preferably 5 nm or more but less than 20 nm, and particularly preferably 5 to 15 nm. Having an average pore size within the above range ensures that the porous substrate 10 has sufficient hydrogen permeability, and the pores can be blocked with a palladium layer 60 having a thickness of 50 to 200 nm. In the present application, the average pore size of the porous substrate 10 is determined based on a pore size distribution determined by mercury intrusion porosimetry in accordance with JIS R 1655:2003. Mercury intrusion porosimetry involves applying pressure to cause mercury to penetrate open pores, determining the relationship between the volume of mercury infiltrated into the open pores and the pressure value applied at that time, and then calculating the diameter of the open pores based on the result using the Washburn equation, assuming that the open pores are cylindrical.

[0013] The porous substrate 10 may have a porosity of 30% to 70%. When the porosity is within the above range, the porous substrate 10 has sufficient hydrogen permeability, and the pores can be blocked with the palladium layer 60 having a thickness of 50 to 200 nm. In the present application, the porosity of the porous substrate 10 is the open porosity determined by the Archimedes method in accordance with JIS R 1634:1998.

[0014] The first surface 12 of the porous substrate 10 may have a surface roughness of 0.1 to 2 μm. In the present application, the surface roughness refers to the arithmetic mean roughness Ra in accordance with JIS B 0601:2013, and is determined by optical interferometry.

[0015] A palladium layer 60 is formed on the first surface 12 of the porous substrate 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.

[0016] The palladium layer 60 may 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 (mmol s) per unit area of ​​the palladium layer 60 decreases. -1 m -2 Pa -0.5) is improved, the target hydrogen permeation rate (mmol s) can be achieved with a smaller area than with conventional technology. -1 Pa -0.5 ) can be achieved. Therefore, the hydrogen separation filter 1 according to this embodiment can reduce the amount of palladium used and can be produced at low cost.

[0017] The number density of the crystal grain boundaries is 1 to 5 grains / μm in the palladium layer 60. In the present application, the number density (grain boundaries / μm) is determined by counting the number of crystal grain boundaries observed within a 5 μm long range in a direction perpendicular to the thickness direction of the palladium layer 60 in a cross-sectional secondary electron image of the palladium layer 60, and dividing this number by 5 μm.

[0018] As will be shown in the examples described later, when the number density of the grain boundaries in the palladium layer 60 is 5 / μm or less, the hydrogen separation filter 1 can have a high hydrogen permeation rate. The inventors believe that the reason for this is as follows: The grain boundaries in the palladium layer 60 trap hydrogen passing through the palladium layer 60, slowing down the permeation of hydrogen. When the number density of the grain boundaries in the palladium layer 60 is 5 / μm or less, hydrogen can easily pass through the palladium layer 60 without being trapped by the grain boundaries, resulting in a high hydrogen permeation rate.

[0019] Furthermore, by having a number density of grain boundaries in the palladium layer 60 of 1 grain / μm or more, peeling between the porous substrate 10 and the palladium layer 60 is prevented or reduced. The inventors believe the reason for this is as follows: Because the surfaces of palladium crystal grains are essentially flat, stress is generated when the surfaces of the palladium crystal grains are formed so as to contact the surface of the porous substrate 10 having the above-mentioned surface roughness. Stress is also generated due to the difference in the thermal expansion coefficients of the porous substrate 10 and the palladium layer 60. The grain boundaries in the palladium layer 60 can relieve these stresses. By having a number density of grain boundaries in the palladium layer 60 of 1 grain / μm or more, the above-mentioned stress is sufficiently relieved, and peeling between the porous substrate 10 and the palladium layer 60 is prevented or reduced.

[0020] (2) Manufacturing method of hydrogen separation filter A method for producing a hydrogen separation filter according to an embodiment includes forming a palladium layer on a porous substrate by sputtering while setting the temperature of the porous substrate to 300 to 600°C.

[0021] By forming a palladium layer at a temperature of 300°C or higher, a palladium layer with a grain boundary number density of 5 / μm or less can be formed, thereby enabling the manufactured hydrogen separation filter to have a high hydrogen permeation rate. By forming a palladium layer at a temperature of 600°C or lower, a palladium layer with a grain boundary number density of 1 / μm or more can be formed, thereby preventing or reducing peeling between the porous substrate and the palladium layer. The deposition rate of the palladium layer may be appropriately adjusted so that the grain boundary number density is the desired value. In general, lowering the deposition rate decreases the grain boundary number density.

[0022] Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the above embodiments, and various design modifications can be made without departing from the technical scope described in the claims. [Example]

[0023] The present disclosure will be specifically described below using examples, but the present disclosure is not limited to these examples.

[0024] (1) Preparation of hydrogen separation filter A porous aluminum oxide substrate (NGK Insulators, Ltd. "Microfiltration Membrane MF0.1", average pore size 100 nm) was coated with aluminum particles to produce a porous substrate with an average pore size of 8 nm, a porosity of 40%, and a surface roughness of 0.4 μm. The average pore size was determined based on the pore size distribution measured by mercury intrusion in accordance with JIS R 1655:2003. The porosity was the open porosity measured by the Archimedes method in accordance with JIS R 1634:1998. The surface roughness was the arithmetic mean roughness Ra measured by optical interferometry in accordance with JIS B 0601:2013.

[0025] A porous substrate was placed facing the pure Pd target in a film-forming chamber of a sputtering apparatus equipped with a pure Pd target. The film-forming chamber was evacuated to a low vacuum of Ar gas, and the porous substrate was heated to the temperature listed in Table 1. A 100 nm-thick Pd layer was formed on the porous substrate by sputtering at the film-forming rate listed in Table 1. Specifically, a high voltage was applied using the pure Pd target as the cathode, generating a glow discharge to cationize Ar. The Ar cations collided with the target, ejecting Pd atoms from the target and depositing them on the porous substrate. The thickness of the Pd layer was measured using a cross-sectional backscattered electron image of the fabricated hydrogen separation filter.

[0026] The Pd layer peeled off from the porous substrate in Comparative Examples 2 and 3. In Comparative Example 1 and Examples 1 to 4, hydrogen separation filters were obtained in which the Pd layer was well attached to the porous substrate.

[0027] (2) Measurement of the number density of grain boundaries A scanning electron microscope was used to obtain cross-sectional secondary electron images of the Pd layers formed in each example and comparative example, and the number of grain boundaries present within a 5 μm length in the direction perpendicular to the thickness direction of the Pd layer was counted. The number of grain boundaries was divided by 5 μm to determine the number density (numbers / μm). The results are shown in Table 1.

[0028] (3) Measurement of hydrogen permeation rate The hydrogen permeation rates per unit area (unit: mmol s ) of the hydrogen separation filters of Comparative Example 1 and Examples 1 to 4 at 400°C were measured by gas chromatography in accordance with JIS K7126:2006 (Plastics - Films and sheets - Gas permeability test methods - Part 1: differential pressure method). -1 m -2 Pa -0.5 ) was measured. The results are shown in Table 1. For comparison with the prior art, the hydrogen permeation rate at 400°C of the hydrogen separation membrane of Example 3 of Patent Document 1 is also shown in Table 1. The hydrogen separation filters of Examples 1 to 4 had a hydrogen permeation rate of 5 mmol s -1 m -2 Pa -0.5 This was higher than the hydrogen permeation rate at 400°C of the hydrogen separation membrane of Patent Document 1.

[0029] The above evaluation results show that in Comparative Example 1 and Examples 1 to 4, in which the number density of the crystal grain boundaries in the Pd layer was 1 / μm or more, hydrogen separation filters could be successfully produced without delamination occurring between the porous substrate and the Pd layer, and that the hydrogen separation filters of Examples 1 to 4, in which the number density of the crystal grain boundaries in the Pd layer was 5 / μm or less, had a high hydrogen permeation rate.

[0030] [Table 1] [Explanation of symbols]

[0031] 1: hydrogen separation filter, 10: porous substrate, 12: first surface, 14: second surface, 60: palladium layer

Claims

1. A porous substrate; a palladium layer provided on the porous substrate; A hydrogen separation filter comprising: A hydrogen separation filter, wherein the number density of crystal grain boundaries observed in a cross-sectional secondary electron image of the palladium layer is 1 to 5 grains / μm.

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

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

4. 5 mmol·s －１ ・m －２ ・Pa －０．５ 2. The hydrogen separation filter according to claim 1, having a hydrogen permeation rate of at least 1000 ppm.

5. A method for producing the hydrogen separation filter according to any one of claims 1 to 4, comprising: A method comprising forming a palladium layer on a porous substrate by a sputtering method at a temperature of the porous substrate of 300°C to 600°C.

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