Metallic porous body, fuel cell, and method for manufacturing metallic porous body

Abstract

A metal porous body is provided, which includes a skeleton of a three-dimensional network structure, wherein the metal porous body has a sheet-like appearance, the skeleton is an alloy containing at least nickel and chromium, and the skeleton has iron dissolved therein, and the number of alumina powder adhering to the surface of the skeleton is 10 or less in the apparent area of 1 cm 2 of the metal porous body.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a metal porous body, a fuel cell, and a method of manufacturing a metal porous body. This application claims priority from Japanese Patent Application No. 2018-168091 filed on September 7, 2018, the entire disclosure of which is incorporated herein by reference. BACKGROUND

[0002] A conventionally known method of manufacturing a metal porous body having high porosity and a large surface area involves forming a metal layer on the surface of a resin porous body such as a resin foam. For example, a metal porous body can be manufactured by subjecting a resin molded body including a skeleton having a three-dimensional network structure to an electroconductive treatment to make the surface of the skeleton electroconductive, then performing electroplating to form a metal layer on the skeleton, and then, as necessary, burning off the resin molded body.

[0003] Metal porous bodies have a variety of applications, and some applications require the skeleton to have high corrosion resistance. As an example of a known metal porous body having high corrosion resistance, a metal porous body having a skeleton of a nickel-chromium alloy can be cited.

[0004] Japanese Patent Laid-Open No. 2012-149282 (Patent Document 1) teaches a method of manufacturing a metal porous body containing an alloy of nickel and chromium, in which the method involves preparing a metal porous body including a skeleton of nickel (hereinafter also referred to as “a nickel porous body”), then performing plating to form a layer of chromium on the surface of the skeleton, and subsequently performing heat treatment to diffuse the chromium.

[0005] Japanese Patent Laid-Open No. 08-013129 (Patent Document 2) teaches a method of manufacturing a metal porous body containing an alloy of nickel and chromium, which embeds a nickel porous body into a powder containing Al, Cr, and NH4Cl or a compound thereof, and then performs heat treatment in an atmosphere filled with Ar gas, H2 gas, and / or the like to induce diffusion penetration.

[0006] LIST OF CITATIONS

[0007] PATENT DOCUMENTS

[0008] Patent Document 1: Japanese Patent Laid-Open No. 2012-149282

[0009] Patent Document 2: Japanese Patent Laid-Open No. 08-013129 SUMMARY

[0010] A metal porous body according to one aspect of the present disclosure is

[0011] A metal porous body including a skeleton of a three-dimensional network structure,

[0012] wherein the metal porous body has a sheet-like appearance,

[0013] The skeleton is an alloy containing at least nickel (Ni) and chromium (Cr), and the skeleton has iron (Fe) solid-solved therein, and

[0014] The number of alumina (AI2O3) powders attached to the surface of the skeleton is 10 or less in the outer apparent area of the metal porous body of 1 cm 2

[0015] The fuel cell according to one aspect of the present disclosure is a fuel cell including a gas diffusion layer, wherein the gas diffusion layer is the above-described metal porous body.

[0016] The method of manufacturing a metal porous body according to one aspect of the present disclosure is a method of manufacturing the metal porous body according to the above-described aspect of the present disclosure, the method including:

[0017] preparing a porous body including a skeleton having a three-dimensional network structure and containing nickel as a main component;

[0018] alloying at least nickel and chromium by embedding the porous body in powders containing at least chromium (Cr), alumina (AI2O3) powders, and ammonium chloride (NH4CI), and performing heat treatment to induce diffusion penetration of chromium into the skeleton, thereby forming a metal porous body; and removing alumina powders attached to the surface of the skeleton of the metal porous body, so that the number of alumina powders attached to the surface of the skeleton of the metal porous body is 10 or less in the outer apparent area of the metal porous body of 1 cm 2 BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a schematic view showing an exemplary metal porous body according to an embodiment of the present disclosure;

[0020] Figure 2 is a photograph showing a cross section of an exemplary metal porous body according to an embodiment of the present disclosure;

[0021] Figure 3 is an enlarged view schematically showing a partial cross section of an exemplary metal porous body according to an embodiment of the present disclosure;

[0022] Figure 4 is a photograph of a polyurethane foamed resin as an exemplary resin-molded body including a skeleton having a three-dimensional network structure;

[0023] Figure 5 is a schematic view showing an exemplary state in which determination points A to I are defined on a metal porous body in a method of determining the number of alumina powders attached to the surface of the skeleton of the metal porous body; ​​

[0024] Figure 6 A photograph showing a cross section of the metal porous body No. 1 in the example;

[0025] Figure 7 A photograph showing a cross section of the metal porous body No. A in the comparative example.

[0026] Figure 8 A photograph showing a cross section of the metal porous body No. A in the comparative example. DETAILED DESCRIPTION

[0027] [Problems to be Solved by the Invention]

[0028] In recent years, various batteries such as fuel cells and power storage devices such as capacitors have been required to further improve power and capacity (downsizing).

[0029] As a gas diffusion layer of a fuel cell, a carbon structure or a stainless steel (SUS) structure is generally used. The carbon structure or the SUS structure is formed with grooves as gas passages. Each of the grooves has a continuous linear shape with a width of about 500 μm. The grooves occupy about half of the area of the boundary between the carbon structure or the SUS structure and an electrolyte, and thus the porosity of the gas diffusion layer is about 50%. Because the gas diffusion layer does not have a very high porosity and has a large pressure loss, a conventional fuel cell cannot have both a reduced size and an improved power.

[0030] To solve this problem, the present inventors have studied a metal porous body including a skeleton of a three-dimensional network structure instead of a carbon structure or a SUS structure as a gas diffusion layer of a fuel cell. By using a metal porous body having a high porosity as a gas diffusion layer, a fuel cell can have enhanced gas diffusion performance and higher gas utilization efficiency. For example, when the metal porous body is used as a gas diffusion layer in a polymer electrolyte fuel cell (PEFC), the metal porous body is exposed to strong acid generated by a membrane electrode assembly (MEA), and thus needs to have high corrosion resistance.

[0031] Because a metal porous body including a skeleton of a nickel-chromium alloy has high corrosion resistance, the metal porous body can be used as a gas diffusion layer of a fuel cell.

[0032] When a metal porous body is manufactured by using a plating method as described in the method of Patent Literature 1, it is necessary to use a trivalent chromium plating solution in consideration of the environment. However, when the trivalent chromium plating solution is used, the film formation rate is as low as about 0.3 μm / h, and thus it takes a long time to manufacture a metal porous body having a chromium alloy ratio of 20% or more. Therefore, there is room for improvement in terms of improving productivity.

[0033] To solve this problem, the present inventors have intensively studied the surface state of the skeleton in order to use a metal porous body manufactured by the diffusion penetration method of the method described in Patent Literature 2 as a gas diffusion layer of a fuel cell. As a result, it was found that a very small amount of Cr powder, alumina powder, silicon carbide powder, and the like did not diffuse but remained on the surface of the skeleton. If the powder remains on the surface of the skeleton, even a very small amount can cause a pressure loss of gas after the operation of the fuel cell.

[0034] In view of the above problem, an object of the present disclosure is to provide a metal porous body that is excellent in corrosion resistance and has a small number of fine particles attached to the surface of the skeleton at a low cost.

[0035] [Advantages of the Present Disclosure]

[0036] According to the present disclosure, a metal porous body that is excellent in corrosion resistance and has a small number of fine particles attached to the surface of the skeleton can be provided at a low cost.

[0037] [Description of Embodiments]

[0038] First, a description will be given of each aspect of the present disclosure.

[0039] (1) A metal porous body according to one aspect of the present disclosure is

[0040] a metal porous body including a skeleton of a three-dimensional network structure,

[0041] wherein the metal porous body has a tabular appearance,

[0042] the skeleton is an alloy containing at least nickel (Ni) and chromium (Cr), and the skeleton has iron (Fe) in solid solution, and

[0043] the number of alumina (AI2O3) powder attached to the surface of the skeleton is 10 or less in the outer apparent area of the metal porous body of 1 cm 2

[0044] According to the above aspect (1), a metal porous body that is excellent in corrosion resistance and has a small number of fine particles attached to the surface of the skeleton can be provided at a low cost.

[0045] (2) Preferably, in the metal porous body according to the above aspect (1), the skeleton includes a chromium oxide (Cr2O3) layer and a chromium carbide layer, the thickness of the chromium oxide layer is 0.1 μm or more and 3 μm or less, and the thickness of the chromium carbide layer is 1 μm or more and 20 μm or less.

[0046] According to the above aspect (2), a metal porous body having high hydrophobicity due to the presence of chromium oxide on the surface of the skeleton can be provided.

[0047] ​(3) Preferably, in the metal porous body according to the above aspect (1), the skeleton includes a chromium oxide (Cr203) layer as an outermost layer and includes a chromium carbide layer below the chromium oxide layer, the thickness of the chromium oxide layer is 0.1 pm or more and 3 pm or less, and the thickness of the chromium carbide layer is 0.1 pm or more and less than 1 pm.

[0048] According to the above aspect (3), it is possible to provide a metal porous body in which the skeleton has excellent toughness and high hydrophobicity.

[0049] (4) Preferably, the metal porous body according to any one of the above aspects (1) to (3) has a porosity of 60% or more and 98% or less.

[0050] According to the above aspect (4), it is possible to provide a metal porous body having a very high porosity.

[0051] (5) Preferably, the metal porous body according to any one of the above aspects (1) to (4) has an average pore diameter of 50 pm or more and 5000 pm or less.

[0052] According to the above aspect (5), it is possible to provide a metal porous body that, when used as a gas diffusion layer of a fuel cell, is capable of efficiently diffusing a gas and efficiently discharging water generated by power generation.

[0053] (6) A fuel cell according to an aspect of the present disclosure is a fuel cell including a gas diffusion layer, wherein the gas diffusion layer is a metal porous body according to any one of the above aspects (1) to (5).

[0054] According to the above aspect (6), it is possible to provide a small-sized fuel cell with a large power.

[0055] (7) A method of manufacturing a metal porous body according to an aspect of the present disclosure is a method of manufacturing a metal porous body according to any one of the above aspects (1) to (5). The method includes:

[0056] preparing a porous body including a skeleton having a three-dimensional network structure and containing nickel as a main component;

[0057] alloying at least the nickel and the chromium to form a metal porous body by embedding the porous body in a powder containing at least chromium (Cr), aluminum oxide (AI2O3) powder, and ammonium chloride (NH4CI), and performing heat treatment to induce diffusion penetration of the chromium into the skeleton; and

[0058] removing the aluminum oxide powder attached to the surface of the skeleton of the metal porous body so that the number of aluminum oxide powders attached to the surface of the skeleton of the metal porous body is 10 or less in an outer apparent area of 1 cm 2 of the metal porous body.

[0059] The method of manufacturing a metal porous body according to the above aspect (7) can inexpensively manufacture a metal porous body that is excellent in corrosion resistance and has fewer fine particles attached to the surface of the skeleton.

[0060] (8) Preferably, in the method of manufacturing a metal porous body according to the above aspect (7), the alumina powder attached to the surface of the skeleton of the metal porous body is removed by jetting high-pressure water to the metal porous body.

[0061] (9) Preferably, in the method of manufacturing a metal porous body according to the above aspect (7), the alumina powder attached to the surface of the skeleton of the metal porous body is removed by treating the metal porous body with an acid.

[0062] The method of manufacturing a metal porous body according to the above aspects (8) and (9) can easily manufacture a metal porous body that has fewer fine particles attached to the surface of the skeleton.

[0063] (10) Preferably, in the method of manufacturing a metal porous body according to any one of the above aspects (7) to (9),

[0064] The porous body is obtained by:

[0065] The surface of the skeleton of the resin molded body is subjected to an electroconductive treatment by applying carbon powder to the surface of the skeleton included in the resin molded body and having a three-dimensional network structure;

[0066] Nickel is plated on the surface of the skeleton of the resin molded body after the electroconductive treatment;

[0067] After the nickel plating, the resin molded body is removed by performing a heat treatment in an oxidizing atmosphere; and

[0068] After the resin molded body is removed, a heat treatment is performed in a reducing atmosphere containing water vapor (H2O) to reduce the amount of carbon remaining in the nickel.

[0069] According to the above aspect (10), it is possible to provide a metal porous body including a skeleton having a highly hydrophobic surface.

[0070] [Detailed Description of Embodiments]

[0071] Hereinafter, specific examples of the metal porous body, the fuel cell, and the method of manufacturing a metal porous body according to the embodiments of the present disclosure will be described in more detail. Note that the present disclosure is not limited by the examples given below, but is defined by the claims, and the present disclosure is intended to include all modifications and variations within the meaning and range of equivalency of the claims.

[0072] <METAL POROUS BODY>

[0073] Figure 1 A schematic view showing an example metal porous body according to an embodiment of the present disclosure is shown. As shown, a metal porous body 10 according to an embodiment of the present disclosure includes a skeleton 11 having a three-dimensional network structure and has a sheet-like appearance. Each hole defined by the skeleton 11 is a communicating hole connecting a surface of the metal porous body 10 to the inside of the metal porous body 10. Figure 1

[0074] Figure 2 A photograph showing a cross section of the skeleton 11 of the metal porous body 10 according to an embodiment of the present disclosure, which has a three-dimensional network structure, is shown. Figure 3 An enlarged view of the cross section of the metal porous body 10 shown is shown schematically. Figure 2 As shown generally, Figure 3 As shown generally, when the skeleton 11 has a three-dimensional network structure, the inside 13 of the skeleton 11 of the metal porous body 10 is hollow. The skeleton 11 is made of an alloy film 12. Further, the skeleton 11 forms a hole 14.

[0075] The skeleton 11 can be an alloy containing at least nickel (Ni) and chromium (Cr), and can be formed of a film in which iron (Fe) is solid-solved. Nickel is a component having the largest content ratio in the skeleton 11, and thus nickel is a main component. Chromium in the skeleton 11 can be alloyed with nickel and exist as Cr2Ni3, or can exist as chromium oxide (Cr2O3), and needless to say, it can be alloyed with other metal components. Iron can be solid-solved in the alloy components or metal components of the skeleton 11.

[0076] The chromium content of the skeleton 11 is preferably about 5 mass% or more and about 50 mass% or less. When the chromium content of the skeleton 11 is 5 mass% or more, a metal porous body having excellent corrosion resistance and not dissolving nickel in strong acid can be obtained. When the chromium content of the skeleton 11 is 50 mass% or less, a metal porous body having excellent tensile strength can be obtained at a lower manufacturing cost. From these viewpoints, the chromium content of the skeleton 11 is more preferably about 10 mass% or more and about 45 mass% or less, and further preferably about 20 mass% or more and about 40 mass% or less.

[0077] ​The iron content of the skeleton 11 is preferably from about 50 ppm to about 5000 ppm, more preferably from about 100 ppm to about 3000 ppm, and further preferably from about 200 ppm to about 2000 ppm. When the iron content of the skeleton 11 is 50 ppm or more, a spinel-type composite oxide FeCr2O4 can be formed below the FeO layer, and this spinel-type composite oxide FeCr2O4 can suppress the detachment of the above-mentioned chromium oxide from the surface of the skeleton 11. When the iron content of the skeleton 11 is 5000 ppm or less, an increase in the resistance of the porous metal body can be suppressed.

[0078] The skeleton 11 may intentionally or inevitably contain other components other than nickel, chromium or iron. Examples of these other components include manganese (Mn), silicon (Si), aluminum (Al) and zirconium (Zr). That is, the skeleton may further include at least one selected from the group consisting of manganese, silicon, aluminum and zirconium. In particular, when the skeleton 11 includes silicon in the form of SiO2, because SiO2 has the effect of inhibiting chromium oxide from detaching from the surface of the skeleton 11, the porous metal body has excellent hydrophobicity.

[0079] In the porous metal body 10 according to the embodiment of the present disclosure, at 1 cm 2 The amount (or number) of aluminum oxide (Al2O3) powder attached to the surface of the skeleton 11 in the apparent area of ​​the metal porous body 10 is less than 10. The lower limit of the number may be more than 0, or may be more than 1. In this embodiment, the above-mentioned "amount of aluminum oxide powder" can be understood as the number of aluminum oxide particles. When the metal porous body 10 is used, the aluminum oxide powder may be detached from the surface of the skeleton 11 and may be scattered around. Therefore, it is preferred that the amount of aluminum oxide powder attached to the surface of the skeleton 11 is as small as possible. Therefore, at 1 cm 2 The amount (number) of aluminum oxide (Al2O3) powder attached to the surface of the skeleton 11 is more preferably 5 or less, and further preferably 1 or less, per the apparent area of ​​the porous metal body 10. When the number of aluminum oxide powders attached to the surface of the skeleton is 10 or less and a porous metal body having such a skeleton is used as a gas diffusion layer in a fuel cell, the pressure loss of the gas during operation can be suppressed.

[0080] The amount of alumina powder attached to the surface of the skeleton 11 can be measured as follows.

[0081] like Figure 5 As shown, at 1cm 2The external apparent area of the flat plate-shaped metal porous body 10, along the long direction X and the short direction Y, in two end portions and a central portion, nine points are defined as measurement points A to I. Each of the two end portions refers to a portion inside the end edge and about 5 cm from the inside of the edge. Then, the measurement points A to I on the surface of the skeleton 11 are observed using a microscope with a magnification of 10 times. When the surface of the skeleton 11 is observed with the microscope, each measurement point A to I is observed in a field of view of 10 times, and the number of alumina powder observed in each field of view is counted. When observed with the microscope, it is observed from one surface of the metal porous body, and only the focused surface portion of the skeleton is observed. The average number of alumina powder in each field of view is defined as the number of alumina powder attached to the measurement point (for example, measurement point A). Similarly, the number of alumina powder attached to each other measurement point (measurement points B to I) is determined. The average value of the number of alumina powder attached to the measurement points A to I is defined as the number of alumina powder attached to 1 cm 2 the external apparent area of the metal porous body 10.

[0082] Preferably, the skeleton 11 includes a chromium oxide (Cr203) layer and a chromium carbide layer. Preferably, the outermost layer of the skeleton 11 is formed of the chromium oxide (Cr203) layer, and the chromium carbide layer is formed below the chromium oxide layer. Because the outermost layer of the skeleton 11 is formed of the chromium oxide layer, the metal porous body has excellent hydrophobicity. Furthermore, because the skeleton 11 includes the chromium carbide layer, the metal porous body has excellent hardness. When the chromium carbide layer is thick, the outermost layer of a part of the skeleton 11 can be formed of the chromium carbide layer, and the chromium oxide layer can be formed below the chromium carbide layer. The thickness of the chromium oxide layer and the thickness of the chromium carbide layer included in the skeleton 11 can be appropriately adjusted according to the different uses of the metal porous body.

[0083] The thickness of the chromium oxide layer as the outermost layer of the skeleton 11 is preferably 0.1 μm or more and 3 μm or less. When the thickness of the chromium oxide layer is 0.1 μm or more, the metal porous body can have stronger hydrophobicity. Because the surface of the skeleton 11 has high hydrophobicity, when the metal porous body is used as, for example, a gas diffusion layer of a fuel cell, water generated during power generation can be efficiently discharged. When the thickness of the chromium oxide layer is about 3 μm, the hydrophobicity effect of the chromium oxide layer reaches saturation, so the thickness of the chromium oxide layer can be set to 3 μm or less. Furthermore, by setting the thickness of the chromium oxide layer to 3 μm or less, an increase in the manufacturing cost of the metal porous body can be suppressed.

[0084] Because chromium carbide has high hardness, the presence of the chromium carbide layer in the skeleton 11 increases the hardness of the skeleton 11. However, too much chromium carbide can embrittle the skeleton 11. Chromium carbide in the chromium carbide layer can exist in two states: Cr7C3 and Cr 23C6. Chromium carbide can also be present on the grain boundaries between the chromium oxide crystals in the chromium oxide layer.

[0085] When the metal porous body is used in applications such as filters that require the skeleton to have high hardness, the thickness of the chromium carbide layer is preferably 1 pm or more and 20 pm or less.

[0086] When the thickness of the chromium carbide layer in the skeleton 11 is thin, the thickness of the outermost chromium oxide layer can be made thicker, and the chromium carbide layer can be formed below (on the inner side of the skeleton 11) the outermost chromium oxide layer. Therefore, when the metal porous body is used in applications such as gas diffusion layers for fuel cells that require the surface of the skeleton to have high hydrophobicity, the thickness of the chromium carbide layer is preferably 0.1 pm or more and 1 pm or less, more preferably 0.1 pm or more and 0.5 pm or less, and further preferably 0.1 pm or more and 0.3 pm or less.

[0087] The skeleton of the metal porous body can be analyzed by energy dispersive X-ray spectroscopy (EDX), X-ray fluorescence (XRF), and / or X-ray diffraction (XRD), thereby confirming the presence of the chromium oxide layer and the chromium carbide layer in the skeleton 11.

[0088] The porosity of the metal porous body 10 according to the embodiments of the present disclosure can be appropriately selected depending on the different uses of the metal porous body. The porosity of the metal porous body 10 is calculated by the following equation.

[0089] Porosity (%) = [1 - {Mp / (Vp x dp)}] x 100

[0090] Mp: mass of the metal porous body [g]

[0091] Vp: apparent volume of the metal porous body [cm 3 ]

[0092] dp: density of the metal or alloy constituting the metal porous body [g / cm 3 ]

[0093] For example, when the metal porous body 10 is used as a gas diffusion layer for a fuel cell, it is preferable that the gas diffusion performance be excellent and the pressure loss be small. Therefore, the porosity is preferably 60% or more and 98% or less, more preferably 70% or more and 98% or less, and further preferably 90% or more and 98% or less.

[0094] The average pore diameter of the metal porous body 10 according to the embodiments of the present disclosure can be appropriately selected depending on the different uses of the metal porous body. The average pore diameter of the metal porous body 10 is obtained by observing the surface of the metal porous body 10 in at least ten fields of view with a microscope or the like, counting the average number (nc) of pores per inch (= 25.4 mm = 25400 μm), and calculating the average pore diameter by the following equation.

[0095] Average pore diameter (μm) = 25400 μm / nc

[0096] For example, when the metal porous body 10 is used as a gas diffusion layer of a fuel cell, the average pore diameter of the metal porous body 10 can be selected in consideration of the diffusivity of gas passing through the pores 14 and pressure loss. More specifically, when the metal porous body is used as a gas diffusion layer of a fuel cell, the average pore diameter of the metal porous body is preferably 50 μm or more and 5000 μm or less, more preferably 100 μm or more and 1000 μm or less, and further preferably 200 μm or more and 700 μm or less.

[0097] The thickness of the metal porous body 10 according to the embodiments of the present disclosure is not particularly limited, and can be appropriately selected depending on the different uses of the metal porous body. The thickness of the metal porous body 10 can be measured by using, for example, a digital thickness gauge.

[0098] In many cases, when the thickness of the metal porous body is set to 0.1 mm or more and 3.0 mm or less, the metal porous body can be lightweight and have high strength. From these viewpoints, the thickness of the metal porous body 10 is more preferably 0.3 mm or more and 2.5 mm or less, and further preferably 0.4 mm or more and 2.0 mm or less.

[0099] < Fuel Cell >

[0100] As long as the fuel cell according to the embodiments of the present disclosure includes the above-described metal porous body according to the embodiments of the present disclosure as a gas diffusion layer, it can include the same other configurations as a conventional fuel cell. The type of the fuel cell is not particularly limited, and can be a solid polymer fuel cell or a solid oxide fuel cell. Furthermore, since the metal porous body 10 has electrical conductivity, the metal porous body 10 can be used as both a gas diffusion layer and a current collector in the fuel cell.

[0101] The fuel cell according to the embodiment of the present disclosure includes a gas diffusion layer having excellent gas diffusion performance, thereby having high gas utilization efficiency. Thus, miniaturization and power increase of the fuel cell are simultaneously achieved. Further, in the fuel cell according to the embodiment of the present disclosure, since the amount of alumina powder attached to the surface of the skeleton of the metal porous body is small, the alumina powder does not scatter when the fuel cell is used, and the pressure loss of the gas diffusion layer is small.

[0102] <Method for manufacturing metal porous body>

[0103] The method for manufacturing the metal porous body according to the embodiment of the present disclosure is a method for manufacturing the above-described metal porous body according to the embodiment of the present disclosure, and the method at least includes: a step of preparing a porous body containing nickel as a main component (preparation step); a step of alloying nickel and chromium of the porous body to obtain a metal porous body (alloying step); and a step of removing alumina attached to the surface of the skeleton of the metal porous body (removing step). The method can further include a step of reducing carbon remaining in the porous body (carbon removing step) as needed. Each step will be described in detail hereinafter.

[0104] (Preparation step)

[0105] The preparation step is a step of preparing a porous body including a skeleton having a three-dimensional network structure and containing nickel as a main component. The porous body as a whole has a sheet-like appearance. Since the metal porous body according to the embodiment of the present disclosure is obtained by alloying nickel and chromium of the porous body, the structure (e.g., porosity and average pore diameter) of the prepared porous body can be the same as the structure required for the metal porous body. As in the case of the metal porous body, the prepared porous body includes a skeleton generally having a hollow interior and a pore formed by the skeleton. The porosity and average pore diameter of the porous body are defined in the same manner as the porosity and average pore diameter of the metal porous body.

[0106] Note that the expression "skeleton containing nickel as a main component" means that nickel has the highest content in the skeleton of the porous body.

[0107] As the porous body including a skeleton having a three-dimensional network structure, for example, Celmet (metal porous body containing Ni as a main component. "Celmet" is a registered trademark) manufactured by Sumitomo Electric Industries, Ltd. can be preferably used. If the desired porous body is not commercially available, it can be manufactured by the following method.

[0108] -Conductivization treatment step-

[0109] First, a resin molded body (hereinafter, can be simply referred to as "resin molded body") which is in a sheet shape and includes a skeleton having a three-dimensional network structure is prepared. A polyurethane resin or a melamine resin can be used as the resin molded body. Figure 4 A photograph of a foamed polyurethane resin including a skeleton having a three-dimensional network structure is shown.

[0110] Next, the surface of the skeleton of the resin molded body is subjected to an electroconductive treatment by applying carbon powder onto the surface of the skeleton of the resin molded body. Examples of the carbon powder used in the electroconductive treatment include a powder of amorphous carbon such as carbon black and a powder of carbon such as graphite.

[0111] -Plating Step-

[0112] In the plating step, nickel plating is performed using the resin molded body whose surface has electroconductivity as a base material. Instead of plating, nickel sputtering and / or electroless plating can be employed to form a nickel film. However, from the viewpoint of productivity and cost, plating is preferable.

[0113] The nickel plating can be performed by a known technique. As a plating bath, a known or commercially available plating bath such as a Watts bath, a chloride bath or a sulfamate bath can be used. The nickel plating can be performed by immersing the resin molded body obtained by the electroconductive treatment in the plating bath, connecting the resin molded body to a cathode, connecting a nickel counter electrode plate to an anode, and passing a direct current or a pulse intermittent current.

[0114] -Resin Molded Body Removing Step-

[0115] After the plating step, the resin molded body on which the nickel plating film is formed on the surface of the skeleton is subjected to heat treatment in an oxidizing atmosphere, thereby removing the resin molded body used as a base material. For example, the removal of the resin molded body can be performed by heating the resin molded body to a temperature of about 600°C or higher and about 800°C or lower, preferably about 600°C or higher and 700°C or lower, in an oxidizing atmosphere such as air. Thus, the resin molded body used as a base material is burned out, and a porous body containing nickel as a main component is obtained.

[0116] -Carbon Removing Step-

[0117] Although the resin molded body removing step described above enables the resin molded body used as a base material to be removed, amorphous carbon powder or carbon powder used for the electroconductive treatment can remain inside (hollow portion) of the skeleton (nickel-plated film) of the porous body containing nickel as a main component. This carbon powder can become a source of chromium carbide in the alloying step of nickel and chromium described below. Therefore, when it is necessary to reduce the content of chromium carbide in the skeleton of the metal porous body according to the embodiments of the present disclosure, it is preferable to remove the carbon powder. When the amount of carbon remaining in the skeleton of the porous body containing nickel as a main component is 0.7 mass% or more, Cr7C3 will be generated in the alloying step (chromium diffusion treatment) described below. Furthermore, if a large amount of chromium is supplied, Cr 23 C6.

[0118] The carbon removing step can be performed by subjecting the porous body containing nickel as a main component to heat treatment in a reducing atmosphere containing water vapor (H2O). The heat treatment can be performed at 750°C or higher. The heat treatment temperature is preferably higher, but from the viewpoint of cost and the furnace material of the reduction furnace, the heat treatment temperature can be set to 1000°C or lower.

[0119] As the reducing gas, hydrogen, or a mixed gas of hydrogen and carbon dioxide or an inert gas can be used, or a combination of these gases can be used as necessary. In particular, from the viewpoint of improving the redox efficiency, it is preferable to add hydrogen to the reducing gas. By adding water vapor (H2O) to the reducing gas, carbon remaining inside the skeleton of the porous body containing nickel as a main component can be removed.

[0120] Furthermore, because this carbon removing step is performed in a reducing atmosphere, nickel oxidized in the resin molded body removing step can be reduced, thereby forming a dense metal film. When it is not necessary to remove carbon remaining inside the skeleton of the porous body containing nickel as a main component, heat treatment can be performed in a reducing gas without containing water vapor.

[0121] (Alloying step)

[0122] The alloying step is a step of diffusing and permeating chromium into the skeleton of the porous body containing nickel as a main component, thereby forming an alloy of nickel and chromium. Diffusion and permeation of chromium can be performed using any known technique. For example, a technique can be used which includes embedding the porous body containing nickel as a main component in a powder containing at least chromium, alumina, and ammonium chloride, and heating to a temperature of 800°C or higher and about 1100°C or lower in an atmosphere of an inert gas such as Ar gas or in an atmosphere of a gas having the same composition as the gas generated in the heat treatment.

[0123] Furthermore, when diffusion and permeation of chromium is performed in an iron furnace or a stainless steel furnace, iron or manganese can be solid-solved in the skeleton of the porous body.

[0124] (Powder Removal Step)

[0125] After the alloying step, a porous metal body including a skeleton is obtained, wherein the skeleton is an alloy containing at least nickel and chromium, and the skeleton has iron dissolved therein. However, after in-depth research, the inventors found that a small amount of aluminum oxide powder is attached to the surface of the skeleton. Therefore, in the method for manufacturing a porous metal body according to an embodiment of the present disclosure, a step of removing aluminum oxide powder (powder removal step) is performed after the alloying step. The powder removal step is performed so that at 1 cm 2 The number of alumina powders attached to the surface of the skeleton of the porous metal body is 10 or less per the external apparent area of ​​the porous metal body.

[0126] Examples of the method of removing the aluminum oxide powder from the surface of the skeleton include high-pressure cleaning, acid treatment, ultrasonic irradiation, and vibration.

[0127] High-pressure cleaning is performed by spraying high-pressure water onto the porous metal skeleton. For example, a high-pressure washer can be used to spray water onto the porous metal skeleton at a pressure of approximately 5 MPa to 10 MPa and a flow rate of approximately 5 L / min to 10 L / min. The higher the water temperature, the better the cleaning effect. Therefore, it is preferred to use water at a temperature of approximately 55°C to 70°C.

[0128] The acid treatment method can be performed by immersing the porous metal body in an acid that is difficult to dissolve Ni and / or Cr. As the acid, for example, nitric acid, hydrochloric acid, sulfuric acid, etc. can be used. The length of the immersion time can be appropriately adjusted according to the type and concentration of the acid used.

[0129] The ultrasonic irradiation method can be performed by immersing the porous metal body in water and irradiating it with ultrasonic waves.

[0130] The vibration method is a method of applying physical vibration to the porous metal body to separate the aluminum oxide powder from the skeleton. As an example, the porous metal body can be placed on a vibration plate and then the vibration plate can be vibrated.

[0131] After removing the aluminum oxide powder from the surface of the skeleton by any of the above methods, the porous metal body is drained and dried, and the amount of aluminum oxide powder attached to the surface of the skeleton is counted. This amount can be counted in the same manner as described in the description of the porous metal body according to the embodiment of the present disclosure.

[0132] If within 1cm 2The number of alumina powder adhered to the surface of the skeleton of the metal porous body is 11 or more in the apparent external surface area of the metal porous body, and the further cleaning is performed to remove the alumina powder so that the number is 10 or less.

[0133] <Notes>

[0134] The above description includes the features of the following notes.

[0135] (Note 1)

[0136] A sheet-shaped metal porous body including a skeleton of a three-dimensional network structure,

[0137] wherein the skeleton is an alloy containing at least nickel (Ni) and chromium (Cr), and the skeleton has iron (Fe) solid-solved therein,

[0138] the number of alumina (AI2O3) powder adhered to the surface of the skeleton is 10 or less in the apparent surface area of the metal porous body. 2

[0139] (Note 2)

[0140] The metal porous body according to Note 1, wherein

[0141] the skeleton includes a chromium oxide (Cr2O3) layer and a chromium carbide layer,

[0142] the thickness of the chromium oxide layer is 0.1 μm or more and 3 μm or less, and

[0143] the thickness of the chromium carbide layer is 1 μm or more and 20 μm or less.

[0144] (Note 3)

[0145] The metal porous body according to Note 1, wherein

[0146] the skeleton includes a chromium oxide (Cr2O3) layer as an outermost layer and includes a chromium carbide layer below the chromium oxide layer,

[0147] the thickness of the chromium oxide layer is 0.1 μm or more and 3 μm or less, and

[0148] the thickness of the chromium carbide layer is 0.1 μm or more and less than 1 μm.

[0149] (Note 4)

[0150] The metal porous body according to any one of Note 1 to Note 3, wherein the porosity of the metal porous body is 60% or more and 98% or less.

[0151] (Note 5)

[0152] ​The metal porous body according to any one of the Embodiments 1 to 4, wherein the average pore diameter of the metal porous body is 50 μm or more and 5000 μm or less.

[0153] (Embodiment 6)

[0154] A fuel cell including the metal porous body according to any one of the Embodiments 1 to 5 as a gas diffusion layer.

[0155] (Embodiment 7)

[0156] A method of manufacturing the metal porous body according to the Embodiment 1, the method comprising:

[0157] preparing a porous body including a skeleton having a three-dimensional network structure and containing nickel as a main component;

[0158] alloying at least the nickel and the chromium to form the metal porous body by embedding the porous body in a powder containing at least chromium (Cr), alumina powder (AI2O3), and ammonium chloride (NH4CI), and performing heat treatment to induce diffusion penetration of the chromium to the skeleton; and

[0159] removing the alumina powder adhering to the surface of the skeleton of the metal porous body so that the number of the alumina powder adhering to the surface of the skeleton of the metal porous body is 10 or less in 1 cm 2 of the outer apparent area of the metal porous body.

[0160] (Embodiment 8)

[0161] The method of manufacturing the metal porous body according to the Embodiment 7, wherein the alumina powder adhering to the surface of the skeleton of the metal porous body is removed by jetting high-pressure water to the metal porous body.

[0162] (Embodiment 9)

[0163] The method of manufacturing the metal porous body according to the Embodiment 7, wherein the alumina powder adhering to the surface of the skeleton of the metal porous body is removed by treating the metal porous body with an acid.

[0164] (Embodiment 10)

[0165] The method of manufacturing the metal porous body according to any one of the Embodiments 7 to 9, wherein

[0166] The porous body is obtained by:

[0167] The surface of the skeleton of the resin molded body is subjected to an electric conduction treatment by applying carbon powder to the surface of the skeleton included in the resin molded body and having a three-dimensional network structure.

[0168] After the electroconduction treatment, nickel is plated on the surface of the skeleton of the resin molded body;

[0169] After the nickel plating, the resin molded body is removed by heat treatment in an oxidizing atmosphere; and

[0170] After the resin molded body is removed, heat treatment is performed in a reducing atmosphere containing water vapor (H2O) to reduce the amount of carbon remaining in the nickel.

[0171] (Parenthetical Note 11)

[0172] The metal porous body according to Parenthetical Note 1, wherein the alloy containing at least nickel and chromium is Cr2Ni3.

[0173] (Parenthetical Note 12)

[0174] The metal porous body according to Parenthetical Note 1, wherein the chromium content in the skeleton is 5 mass% or more and 50 mass% or less.

[0175] (Parenthetical Note 13)

[0176] The metal porous body according to Parenthetical Note 1, wherein the iron content in the skeleton is 50 ppm or more and 5000 ppm or less.

[0177] (Parenthetical Note 14)

[0178] The metal porous body according to Parenthetical Note 1, wherein the skeleton further contains at least one selected from the group consisting of manganese, silicon, aluminum, and zirconium.

[0179] [Examples]

[0180] Hereinafter, the present application will be described in more detail in the form of examples. These examples are given for the purpose of illustration and the metal porous body and the like according to the present disclosure are not limited to those in these examples. The scope of the present application is defined by the claims and includes all modifications and variations within the meaning and range equivalent to the claims.

[0181] (Example 1)

[0182] <Preparation Step>

[0183] A porous body including a skeleton of a three-dimensional network structure was prepared in the following manner.

[0184] -Electroconduction Treatment Step-

[0185] A polyurethane sheet having a width of 1 m and a thickness of 1.0 mm was used as a resin molded body including a skeleton of a three-dimensional network structure. The porosity of the resin molded body was 96% and the average pore diameter was 450 μm.

[0186] 100 g of carbon black as amorphous carbon having a particle size of 0.01 μm or more and 0.20 μm or less was dispersed in 0.5 L of a 10% acrylate resin aqueous solution, whereby an adhesive coating was prepared at this ratio.

[0187] Next, the resin molded body was continuously immersed in the adhesive coating, pressed with a roller, and dried to form a conductive layer on the surface of the skeleton of the resin molded body. In this way, the resin molded body was subjected to a conductive treatment.

[0188] - plating step -

[0189] Nickel was deposited on the surface of the skeleton of the resin molded body subjected to the conductive treatment in an amount of 500 g / m 2 by electroplating, thereby producing a resin structure having a nickel plating film on the surface of the skeleton of the resin structure.

[0190] - resin molded body removing step -

[0191] Then, in order to remove the resin molded body from the resin structure thus obtained, the resin structure was heated to 700°C in the atmosphere (in an oxidizing atmosphere). Thus, the resin molded body was removed and a porous body containing nickel as a main component was obtained.

[0192] - reduction step -

[0193] Subsequently, in order to reduce the nickel in the porous body thus obtained, the porous body was heated to 1000°C in a reducing atmosphere containing a reducing gas which was a mixed gas of H2and N2(ammonia decomposition gas).

[0194] Thus, a porous body in which nickel was reduced and annealed was obtained.

[0195] < alloying step >

[0196] In a stainless steel furnace, a mixed powder was prepared by mixing 1 mass% of Al powder, 50 mass% of Cr powder, 0.5 mass% of NH4Cl, and the balance of Al2O3powder, and the porous body was embedded in the prepared mixed powder. Next, heat treatment was performed at 1000°C for 10 hours.

[0197] < powder removing step >

[0198] The metal porous body obtained after the alloying step was sprayed with water at a pressure of 8 MPa and a flow rate of 6 L / min using a high-pressure washer (Hobby 80 manufactured by Asada Co., Ltd.) to remove the powder remaining on the surface of the skeleton. The temperature of the sprayed water was 65°C. The distance between the metal porous body and the nozzle was 200 to 300 mm. After the surface was washed for about 60 seconds, the opposite surface was washed in the same manner. After washing with high-pressure water, the metal porous body was dried, thereby obtaining the metal porous body No. 1.

[0199] (Example 2)

[0200] The metal porous body No. 2 was obtained in the same manner as in Example 1, except that the powder removal step was performed as follows.

[0201] <Powder removal step>

[0202] The metal porous body obtained after the alloying step was immersed in 1 mol / L nitric acid and gently shaken for 1 hour. After the treatment with the nitric acid, the metal porous body was washed with water, thereby obtaining the metal porous body No. 2.

[0203] (Example 3)

[0204] The metal porous body No. 3 was obtained in the same manner as in Example 1, except that the reduction step in the preparation step of Example 1 was replaced with the following carbon removal step.

[0205] -Carbon removal step-

[0206] The heat treatment was performed in the same manner as in Example 1 except that a gas obtained by adding water vapor (H2O) to a mixed gas of H2 and N2 (a decomposition gas of ammonia) was used for the reduction step performed in Example 1, and thereby a porous body from which carbon was removed was obtained.

[0207] (Comparative Example 1)

[0208] The metal porous body No. A was obtained in the same manner as in Example 1, except that the powder removal step in Example 1 was not performed.

[0209] (Comparative Example 2)

[0210] The metal porous body No. B was obtained in the same manner as in Example 3, except that the powder removal step in Example 3 was not performed.

[0211] (Evaluation)

[0212] <Measurement of alumina powder attached to the surface of the skeleton>

[0213] The number of alumina powder adhered to the surface of the skeleton of each of the metal porous bodies No. 1 to No. 3 and the metal porous bodies No. A to No. B was measured in the above-described manner.

[0214] As a result, among the external apparent area of 1 cm 2 of the metal porous body, the number of the metal porous body No. 1 was 0, the number of the metal porous body No. 2 was 1, the number of the metal porous body No. 3 was 1, the number of the metal porous body No. A was 20, and the number of the metal porous body No. B was 25.

[0215] Thus, it was confirmed that the number of alumina powder adhered to the surface of the skeleton of the metal porous bodies No. 1 to No. 3 according to the embodiments of the present disclosure was very small, as compared with the conventional metal porous bodies No. A and No. B.

[0216] The measurement results are listed in Table 1.

[0217] <Enlarged photograph of the surface of the skeleton>

[0218] Figure 7 and Figure 8 Each of the photographs obtained by observing the surface of the skeleton of the metal porous body No. 1 and the metal porous body No. A with an optical microscope is shown. The magnification of the optical microscope was 40 times.

[0219] As shown in Figure 7 , almost no alumina powder was found on the surface of the skeleton of the metal porous body No. 1. In contrast, as shown in Figure 8 , alumina powder was found at several positions on the surface of the skeleton of the metal porous body No. B.

[0220] <Measurement of the composition of the skeleton>

[0221] The composition and alloy components of the skeleton of each of the metal porous bodies No. 1 to No. 3 and the metal porous bodies No. A to No. B were detected by EDX analysis and / or XRD analysis. The cross section of the skeleton of each metal porous body was observed by SEM. In addition, the surface of the skeleton of each metal porous body was etched with nitric acid, and the cross section of the skeleton was detected by SEM. In this way, the presence of a chromium carbide layer was confirmed.

[0222] The measurement results are listed in Table 1.

[0223] <Hydrophobicity>

[0224] Each metal porous body was left to stand, and 1 drop (about 0.03 to 0.05 ml) of pure water was added to the outer main face of each metal porous body using a dropper. The metal porous body was visually observed from the side face thereof, and the time until the water drop was not observed from the outer main face (until the water drop was immersed in the hole) was measured.

[0225] The results are summarized in Table 1.

[0226] <Pressure loss>

[0227] The pressure loss was measured by performing a flow-pressure loss test by flowing a gas in the long axis direction of the holes of each metal porous body. Specifically, as shown in the circuit diagram of Fig. 1, a gas was supplied from a pump 73 to a test sample (metal porous body) 70 at a flow rate of 0.5 L / min, and the pressure PI of the gas before passing through the test sample (metal porous body) 70 and the pressure P2 after passing through the test sample were measured using a pressure gauge 72. The pressure loss ΔP in each test sample (metal porous body) 70 was calculated as ΔP = PI - P2. The flow rate of the gas was measured by a flow meter 71. Figure 6

[0228] The results are summarized in Table 1.

[0229]

[0230] List of reference numerals

[0231] 10: metal porous body; 11: skeleton; 12: alloy film constituting the skeleton; 13: inside of the skeleton; 14: hole; A: gas flow direction; 70: test sample (metal porous body); 71: flow meter; 72: pressure gauge; 73: pump.​

Claims

1. A porous metal body comprising a skeleton of a three-dimensional network structure, wherein the porous metal body has a flake-like appearance, The skeleton is an alloy containing at least nickel and chromium, and iron is solid-solved in the skeleton, and the iron content of the skeleton is 50 ppm or more and 5000 ppm or less, and In 1cm 2 The number of alumina powders attached to the surface of the skeleton is 1 or less in the external apparent area of ​​the porous metal body. The skeleton includes a chromium oxide layer as an outermost layer and a chromium carbide layer below the chromium oxide layer, and The thickness of the chromium oxide layer is not less than 0.1 μm and not more than 3 μm. The thickness of the chromium carbide layer is greater than 0.1 μm and less than 1 μm, The chromium carbide layer includes Cr7C3.

2. A porous metal body comprising a skeleton of a three-dimensional network structure, wherein the porous metal body has a flake-like appearance, The skeleton is an alloy containing at least nickel and chromium, and iron is solid-solved in the skeleton, and In 1cm 2 The number of alumina powders attached to the surface of the skeleton is 1 or less in the external apparent area of ​​the porous metal body. The framework comprises silicon in the form of SiO2, The skeleton includes a chromium oxide layer as an outermost layer and a chromium carbide layer below the chromium oxide layer, and The thickness of the chromium oxide layer is not less than 0.1 μm and not more than 3 μm. The thickness of the chromium carbide layer is greater than 0.1 μm and less than 1 μm, The chromium carbide layer includes Cr7C3.

3. The porous metal body according to claim 1 or 2, wherein The porosity of the porous metal body is 60% to 98%.

4. The porous metal body according to claim 1 or 2, wherein The average pore diameter of the porous metal body is 50 μm or more and 5000 μm or less.

5. A fuel cell comprising a gas diffusion layer, The gas diffusion layer is a porous metal body according to any one of claims 1 to 4.

6. A method for producing the porous metal body according to claim 1 or 2, the method comprising: preparing a porous body including a skeleton having a three-dimensional network structure and containing nickel as a main component; forming a porous metal body by embedding the porous body in a powder containing at least chromium, aluminum oxide powder, and ammonium chloride, and performing a heat treatment to induce diffusion and penetration of the chromium into the skeleton, thereby alloying at least nickel and chromium; as well as The aluminum oxide powder attached to the surface of the skeleton of the porous metal body is removed by spraying high-pressure water on the porous metal body or treating the porous metal body with acid so that the aluminum oxide powder is removed within 1 cm 2 In the external apparent area of ​​the porous metal body, the number of the alumina powders attached to the surface of the skeleton of the porous metal body is 1 or less, wherein The porous body is obtained by: Conducting a surface of a skeleton of a resin molded body having a three-dimensional network structure by applying carbon powder to the surface of the skeleton; After the conductive treatment, nickel plating is performed on the surface of the skeleton of the resin molded body; After nickel plating, the resin molded body is removed by heat treatment in an oxidizing atmosphere; as well as After removing the resin molded body, heat treatment is performed in a reducing atmosphere containing water vapor to reduce the amount of carbon remaining in the nickel so that the amount of carbon remaining in the skeleton of the porous body containing nickel as a main component is 0.7% by mass or more.

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