Nickel-chromium porous body and method for producing nickel-chromium porous body

Abstract

A nickel-chromium porous body having a skeleton that has a three-dimensional mesh structure, wherein: the skeleton has a hollow interior, and has a main metal layer and surface oxide layers formed on both surface sides of the main metal layer; the surface oxide layers have a thickness of 0.5 μm or greater and have chromium oxide as a main component; the main metal layer is made of nickel-chromium having a chromium content of 10 mass% or greater overall; ranges of the main metal layer measuring at least 3 μm from the interfaces in contact with the surface oxide layers have a chromium content of 20 mass% or greater; and the surface oxide layers and the main metal layer are in intimate contact without any gaps present therebetween.

Description

[Technical Field]

[0001] This disclosure relates to a nickel-chromium porous body and a method for producing the same. This application claims priority to Japanese Patent Application No. 2020-156399 filed on September 17, 2020, Japanese Patent Application No. 2020-163246 filed on September 29, 2020, and Japanese Patent Application No. 2020-169661 filed on October 7, 2020, and incorporates the entire contents of these Japanese applications by reference. [Background technology]

[0002] Sheet-like porous metal bodies with a three-dimensional mesh-like structure skeleton are used in a variety of applications, including filters, catalyst carriers, metal composites, and battery electrode plates. Celmet (registered trademark, manufactured by Sumitomo Electric Industries, Ltd.), a porous metal body made of nickel, is widely used in various industrial fields, for example, as electrodes for alkaline storage batteries such as nickel-metal hydride batteries, and as supports for industrial deodorizing catalysts.

[0003] The porous metal body may be required to have corrosion resistance depending on the intended use. Nickel-chromium porous bodies, whose skeletons are formed from nickel-chromium alloys, are known as porous metal bodies having high corrosion resistance. Methods for manufacturing nickel-chromium porous bodies are known, including those described in Japanese Patent Laid-Open No. 2012-149282 (Patent Document 1) and Japanese Patent Laid-Open No. 08-013129 (Patent Document 2).

[0004] Patent Document 1 describes a method for producing a nickel-chromium porous body by plating a chromium layer on the surface of a nickel-based porous body, and then diffusing the chromium by heat treatment. Patent Document 2 describes a method for producing a nickel-chromium porous body by a diffusion infiltration method in which a nickel porous body is embedded in Cr and NH4Cl powder and then heat treated in an Ar or H2 gas atmosphere.

[0005] Japanese Patent Laid-Open Publication No. 2017-054797 (Patent Document 3) describes that the corrosion resistance of a porous metal body can be further improved by forming an oxide film on the surface of the skeleton of the porous metal body. Furthermore, methods for forming an oxide film on the surface of the skeleton of a porous metal body include heat treatment in an oxidizing atmosphere and treatment with an acidic solution followed by heat treatment. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-149282 [Patent Document 2] Japanese Patent Application Publication No. 08-013129 [Patent Document 3] Japanese Patent Application Publication No. 2017-054797 Summary of the Invention

[0007] The nickel-chromium porous body according to one embodiment of the present disclosure comprises: A nickel-chromium porous body having a skeleton with a three-dimensional network structure, the skeleton is hollow and has a main metal layer and surface oxide layers formed on both sides of the main metal layer; The surface oxide layer has a thickness of 0.5 μm or more. 1.0μm or less and the main component is chromium oxide, the main metal layer is nickel chromium with a chromium content of 10% by mass or more as a whole, and the chromium content in the range of at least 3 μm from the interface in contact with the surface oxide layer is 20% by mass or more; the surface oxide layer and the main metal layer are in close contact with each other without any gaps; Nickel chromium porous body.

[0008] A method for producing a nickel-chromium porous body according to one embodiment of the present disclosure includes the steps of: A method for producing a nickel-chromium porous body according to one aspect of the present disclosure, comprising: preparing a nickel porous body having a skeleton with a three-dimensional network structure; a step of chromizing the nickel porous body by a diffusion penetration method to obtain a nickel-chromium porous body; a step of forming a surface oxide layer on the surface of the skeleton by heat treating the nickel-chromium porous body after the chromizing treatment; and In the step of obtaining a nickel-chromium porous body by chromizing, the temperature of the heat treatment is 900°C or higher and 1200°C or lower, The heat treatment is carried out in hydrogen gas containing at least water vapor. A method for producing a nickel-chromium porous body. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram of a nickel-chromium porous body according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a cross-sectional photograph of a nickel-chromium porous body according to an embodiment of the present disclosure. [Figure 3] FIG. 3 is an enlarged schematic view of a partial cross section of a nickel-chromium porous body according to an embodiment of the present disclosure. [Figure 4] FIG. 4 is a schematic diagram of the cross section of the skeleton of the nickel-chromium porous body shown in FIG. 3 taken along line AA. [Figure 5] FIG. 5 is an enlarged view of the area surrounded by the dashed line in FIG. [Figure 6] FIG. 6 is a schematic diagram of a processed nickel-chromium porous body according to an embodiment of the present disclosure. [Figure 7] FIG. 7 is a schematic diagram of a processed nickel-chromium porous body according to an embodiment of the present disclosure. [Figure 8] FIG. 8 is a photograph of the cross section of the skeleton of the nickel-chromium porous body No. 1 produced in the example, observed with an electron microscope. [Figure 9] FIG. 9 is a photograph of a cross section of the skeleton of nickel chromium porous body No. A produced in the comparative example, observed with an electron microscope. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Problem to be solved by this disclosure] Porous metal bodies are often subjected to processes such as rolling, cutting, groove forming, and bending depending on the intended use. The present inventors conducted a detailed study to determine what changes occur in the skeleton of a porous metal body having an oxide film on the skeleton surface when the body is subjected to the above-mentioned processes (particularly cutting processes that involve the application of large forces). As a result, it was confirmed that when a conventional porous metal body having an oxide film on the skeleton surface is cut, the oxide film peels off from the skeleton surface near the cut surface or cracks are formed in the oxide film. The reason for this is that, in general, an oxide film does not have high adhesion to the metal that constitutes the skeleton, and therefore, when force is applied, gaps are likely to form at the interface between the oxide film and the metal. In some cases, gaps may already exist at the interface between the oxide film and the metal when the oxide film is formed.

[0011] Therefore, an object of the present disclosure is to provide a nickel-chromium porous body in which the oxide film on the skeleton surface is less likely to peel off even when processed, such as by cutting. [Effects of this disclosure]

[0012] According to the present disclosure, it is possible to provide a nickel-chromium porous body in which the oxide film on the skeleton surface is hardly peeled off even when processed, such as by cutting.

[0013] [Description of the embodiments of the present disclosure] The nickel-chromium porous body according to one embodiment of the present disclosure comprises: A nickel-chromium porous body having a skeleton with a three-dimensional network structure, the skeleton is hollow and has a main metal layer and surface oxide layers formed on both sides of the main metal layer; the surface oxide layer has a thickness of 0.5 μm or more and is mainly composed of chromium oxide; the main metal layer is nickel chromium with a chromium content of 10% by mass or more as a whole, and the chromium content in the range of at least 3 μm from the interface in contact with the surface oxide layer is 20% by mass or more; the surface oxide layer and the main metal layer are in close contact with each other without any gaps; By adopting such a configuration, it is possible to provide a nickel-chromium porous body in which the oxide film on the skeleton surface is less likely to peel off even when subjected to processing such as cutting.

[0014] The nickel-chromium porous body is When cut in the thickness direction, the surface oxide layer may be in close contact with the main metal layer over 80% or more of the skeleton of the fracture surface. By adopting such a configuration, it is possible to provide a nickel-chromium porous body in which the surface oxide layer is unlikely to peel off from the surface of the skeleton even when the nickel-chromium porous body is cut.

[0015] The nickel-chromium porous body is The thickness may be 0.5 mm or more and 5.0 mm or less. By adopting such a configuration, it is possible to provide a lightweight and strong nickel chromium porous body.

[0016] The nickel-chromium porous body is The porosity may be 60% or more and 98% or less. By adopting such a configuration, it is possible to provide a nickel chromium porous body with a high porosity.

[0017] The nickel-chromium porous body is The bottom surface is polygonal and curved from the bottom surface to the top surface, The bottom surface has a side length of 2 mm or more and 10 mm or less, The height from the bottom surface to the top may be 0.5 mm or more and 5 mm or less. By adopting such a configuration, it is possible to provide a nickel porous body having a shape suitable for use as a filter or a catalyst support.

[0018] The nickel-chromium porous body is The bottom surface is circular and the top surface is hemispherical, The bottom surface has a diameter of 2 mm or more and 10 mm or less, The height from the bottom surface to the top may be 0.5 mm or more and 5 mm or less. By adopting such a configuration, it is possible to provide a nickel porous body having a shape suitable for use as a filter or a catalyst support.

[0019] A method for producing a nickel-chromium porous body according to one embodiment of the present disclosure includes the steps of: preparing a nickel porous body having a skeleton with a three-dimensional network structure; a step of chromizing the nickel porous body by a diffusion penetration method to obtain a nickel-chromium porous body; a step of forming a surface oxide layer on the surface of the skeleton by heat treating the nickel-chromium porous body after the chromizing treatment; and The heat treatment is carried out in hydrogen gas containing at least water vapor. By adopting such a configuration, it is possible to provide a method for producing a nickel-chromium porous body in which the oxide film on the skeleton surface is less likely to peel off even when processing such as cutting is performed.

[0020] In the method for producing the nickel-chromium porous body, in the step of obtaining the nickel-chromium porous body by chromizing, The temperature for the heat treatment may be 900° C. or higher and 1200° C. or lower. By adopting such a configuration, it is possible to provide a method for producing a nickel-chromium porous body in which the oxide film on the skeleton surface is less likely to peel off even when processing such as cutting is performed.

[0021] [Details of the embodiments of the present disclosure] Specific examples of nickel-chromium porous bodies and methods for manufacturing nickel-chromium porous bodies according to embodiments of the present disclosure will be described in more detail. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0022] <Nickel-chromium porous body> An example of a nickel-chromium porous body 10 according to an embodiment of the present disclosure is outlined in Fig. 1. An enlarged photograph of the skeleton 11 of the three-dimensional network structure of the nickel-chromium porous body 10 shown in Fig. 1 is shown in Fig. 2, and an enlarged schematic diagram of a cross section of the nickel-chromium porous body 10 shown in Fig. 2 is shown in Fig. 3.

[0023] As shown in FIG. 1, the nickel chromium porous body 10 has a skeleton 11 with a three-dimensional network structure, and in many cases has a flat plate-like appearance as a whole.

[0024] As shown in FIG. 3, the skeleton 11 of the nickel-chromium porous body 10 is composed of a main metal layer 12 and a surface oxide layer 13, and the interior 14 of the skeleton is hollow. The pores 15 formed by the skeleton 11 are interconnected pores formed by cells modeled as a regular dodecahedron that are connected from the surface to the interior of the nickel-chromium porous body 10. A schematic diagram of the AA cross section of the skeleton 11 is shown in FIG. 4. The cross-sectional shape of the skeleton 11 can be modeled as a triangle with a hollow center (the interior 14 of the skeleton). The skeleton 11 is composed of the main metal layer 12 and surface oxide layers 13 formed on both sides of the main metal layer 12. Each surface oxide layer 13 faces the interior 14 of the skeleton and the pores 15 of the nickel-chromium porous body 10.

[0025] FIG. 5 shows an enlarged view of the skeleton 11 in the portion surrounded by the dashed line in FIG. 4. Each surface oxide layer 13 formed on both sides of the main metal layer 12 has a thickness of 0.5 μm or more and contains chromium oxide as a main component. The main component refers to the component that is contained in the largest amount in the surface oxide layer 13. In addition to chromium oxide, the surface oxide layer 13 may also contain nickel, nickel oxide, Fe, etc.

[0026] The upper limit of the thickness of the surface oxide layer 13 is not particularly limited, but may be approximately 1.0 μm or less, taking into consideration the cost required to form the surface oxide layer 13. If the surface oxide layer 13 is too thick, it will be prone to peeling off from the surface of the main metal layer 12. Furthermore, since the surface oxide layer 13 increases the surface resistance of the nickel-chromium porous body 10, the thickness of the surface oxide layer 13 may be thin when the nickel-chromium porous body 10 is used for applications requiring electrical conductivity. From these viewpoints, the upper limit of the thickness of the surface oxide layer 13 may be 2.0 μm or less, or may be 1.0 μm or less.

[0027] The main metal layer 12 is composed entirely of nickel chromium with a chromium content of 10% by mass or more. The higher the chromium content, the more excellent the corrosion resistance of the main metal layer 12. Therefore, the upper limit of the chromium content of the main metal layer 12 is not particularly limited, but considering the cost required for alloying, it may be approximately 50% by mass or less. From these perspectives, the chromium content of the main metal layer 12 as a whole may be 15% by mass or more and 50% by mass or less, or 20% by mass or more and 40% by mass or less. In addition to nickel chromium, the main metal layer 12 may intentionally or unavoidably contain other components such as nickel and chromium oxide.

[0028] The main metal layer 12 has a chromium content of 10% by mass or more overall, but the chromium concentration is 20% by mass or more in a range R extending from the interface with the surface oxide layer 13 to at least 3 μm. As will be described later, in the process of producing the nickel-chromium porous body 10 according to the embodiment of the present disclosure, by adjusting the chromium content in the range R extending from the interface with the surface oxide layer 13 to at least 3 μm to 20% by mass, a nickel-chromium porous body 10 in which the main metal layer 12 and the surface oxide layer 13 are tightly adhered to each other without any gaps can be obtained. The chromium content in the range R may be 30% by mass or more and 80% by mass or less, or 40% by mass or more and 60% by mass or less.

[0029] In the skeleton 11 constituting the nickel-chromium porous body 10 according to the embodiment of the present disclosure, the main metal layer 12 and the surface oxide layer 13 are tightly adhered to each other with no gaps between them. Therefore, even if a strong force is applied to the skeleton 11 by bending or cutting, the nickel-chromium porous body 10 is unlikely to have the surface oxide layer 13 peel off, and is therefore able to maintain high corrosion resistance.

[0030] For example, when the nickel-chromium porous body 10 is cut in the thickness direction Z, the surface oxide layer 13 may be in close contact with the main metal layer 12 over 80% or more of the skeleton 11 on the fracture surface. The proportion of the surface oxide layer 13 in close contact with the main metal layer 12 on the fracture surface of the nickel-chromium porous body 10 is determined as follows: First, the nickel-chromium porous body 10 is embedded in resin and then cut in the thickness direction, and the fracture surface is observed under an electron microscope. The entire thickness direction × 20 mm width is observed, and the length of the portion of the surface oxide layer 13 in close contact with the main metal layer 12 is measured for all skeletons observed on the fracture surface. If it is immediately apparent from the electron microscope photograph of the fracture surface that the surface oxide layer 13 is only slightly peeled from the main metal layer 12, the length of the peeled portion may be measured, and the length of the closely contacted portion may be calculated as "(total perimeter of the skeleton × 2) - (length of the peeled portion)." The reason for doubling the total perimeter of the skeleton in this case will be described later. The ratio of the portion of the surface oxide layer 13 that is in close contact with the main metal layer 12 in the skeleton of the fracture surface is calculated by the following formula [A]. expression [A] Percentage of contact area (%) = (length of contact area) / (total circumference of skeleton × 2) × 100

[0031] Because the surface oxide layer 13 is also formed on the interior 14 side of the skeleton, the "length of the adhesion portion" in the above formula [A] refers to the length of the portion where the surface oxide layer 13 adheres to both the pore 15 side and the interior 14 side of the main metal layer 12 constituting the skeleton 11. Similarly, the above "length of the peeled portion" refers to the length of the portion where the surface oxide layer 13 peels off from both the pore 15 side and the interior 14 side of the main metal layer 12 constituting the skeleton 11. Note that, to determine the "length of the adhesion portion" as described above, the above formula [A], which calculates the "proportion of the adhesion portion" in the skeleton of the fracture surface, divides the "length of the adhesion portion" by twice the "total perimeter of the skeleton." Similarly, when calculating the "length of the adhesion portion" from the "length of the peeled portion," it is necessary to subtract the length of the peeled portion from twice the total perimeter of the skeleton. Furthermore, because the cross section of the skeleton 11 is modeled as a roughly triangular shape as described above, the "total perimeter of the skeleton" in the above formula [A] can be calculated using the following formula [B]. Formula [B] Skeleton circumference total length = (number of skeletons x total length of three sides) In formula [B], "number of skeletons" means the number of skeletons present on the observed fracture surface, and "total length of three sides" means the sum of the lengths of the three sides of skeleton 11 modeled as an approximately triangle.

[0032] The nickel-chromium porous body 10 may have a percentage (%) of the adhered portion calculated by the above formula [A] of 80% or more. In the nickel-chromium porous body 10 according to the embodiment of the present disclosure, the surface oxide layer 13 is tightly adhered to the main metal layer 12 without any gaps, and therefore, even when subjected to cutting or other processing, the surface oxide layer 13 is unlikely to peel off from the surface of the skeleton 11 in the vicinity of the fracture surface, and high corrosion resistance can be maintained.

[0033] The thickness of the nickel-chromium porous body 10 can be appropriately selected depending on the intended use of the nickel-chromium porous body. For example, by setting the thickness to 0.5 mm or more and 5.0 mm or less, the nickel-chromium porous body 10 can be made lightweight and strong. The thickness of the nickel-chromium porous body 10 may be 0.5 mm or more and 2.5 mm or less. For example, the thickness can be adjusted by preparing a relatively thick nickel-chromium porous body 10 and compressing it in the thickness direction Z. The nickel-chromium porous body 10 can be manufactured using a nickel porous body as a starting material. In this case, for example, by using Celmet (registered trademark) manufactured by Sumitomo Electric Industries, Ltd. as the nickel porous body, a nickel porous body having a thickness of 5.0 mm or more can be prepared, and a nickel-chromium porous body 10 having a thickness of 5.0 mm or more can be manufactured from this. Furthermore, even when a nickel porous body having a thickness less than 5.0 mm is used, a nickel-chromium porous body 10 having a thickness of 5.0 mm or more can be manufactured. For example, in the step of chromizing the nickel porous body in the manufacturing method of the nickel chrome porous body, two or more nickel porous bodies may be stacked in the thickness direction and chromized with their skeletons in contact with each other. As a result, the two or more nickel porous bodies are alloyed and integrated while their skeletons remain in contact with each other, and a nickel chrome porous body 10 having a thickness of 5.0 mm or more is obtained. The portions where the skeletons of the two or more nickel porous bodies were in contact with each other are firmly joined by welding. The thickness of the nickel chrome porous body 10 can be measured, for example, using a digital thickness gauge.

[0034] The porosity of the nickel-chromium porous body 10 may be appropriately selected depending on the intended use of the nickel-chromium porous body. For example, when the nickel-chromium porous body 10 is used as a filter, it is desirable that the nickel-chromium porous body 10 has excellent object capture properties and low pressure loss. The porosity of the nickel-chromium porous body 10 may be, for example, 60% to 98%, 70% to 98%, or 90% to 98%. In many cases, the porosity of the nickel-chromium porous body 10 immediately after production is approximately 98%, and the porosity can be reduced by compression processing in the thickness direction Z.

[0035] The porosity of the nickel-chromium porous body 10 is defined by the following formula [1]. Porosity (%) = [1-{Mp / (Vp×dp)}]×100 Equation [1] Mp: Mass of the nickel-chromium porous body [g] Vp: Volume of the external shape of the nickel-chromium porous body [cm 3 ] dp: Density of the metal constituting the nickel-chromium porous body [g / cm 3 ]

[0036] The average pore diameter of the nickel-chromium porous body 10 may be appropriately selected depending on the application of the nickel-chromium porous body 10. For example, the average pore diameter of the nickel-chromium porous body 10 may be 50 μm or more and 5000 μm or less, 100 μm or more and 1000 μm or less, or 200 μm or more and 900 μm or less.

[0037] The average pore diameter of the nickel-chromium porous body 10 refers to the value obtained by observing the main surface of the nickel-chromium porous body 10 with a microscope or the like in at least 10 fields of view to determine the average number (nc) of pores 15 per inch (25.4 mm = 25,400 μm) and calculating it using the following formula [2]. Average pore diameter = 25400 μm / nc Equation [2] The number of pores 15 is measured in accordance with the method for determining the number of pores (cell count) of a soft foam material according to JIS K6400-1:2004, Appendix 1 (reference).

[0038] In the nickel-chromium porous body 10 according to the embodiment of the present disclosure, the surface oxide layer 13 is unlikely to peel off from the surface of the skeleton 11 even when cut, and therefore, for example, high corrosion resistance can be maintained even when the body is finely processed. The processed nickel-chromium porous body 10 can be used, for example, as a filter or catalyst support that requires corrosion resistance.

[0039] FIG. 6 shows an example of a processed nickel-chromium porous body 10. The nickel-chromium porous body 10 has a polygonal bottom surface 21 that is curved from the bottom surface 21 to the apex 22. The bottom surface 21 may be either square or rectangular as long as the length of one side is 2 mm or more and 10 mm or less. The height from the bottom surface 21 to the apex 22 may be 0.5 mm or more and 5.0 mm or less. The height is defined as the length of the perpendicular line from the apex 22 to the bottom surface 21. Examples of polygonal shapes include a square, a pentagon, and a hexagon.

[0040] The nickel-chromium porous body 10 can be produced, for example, by cutting the main surface of a flat-plate-shaped nickel-chromium porous body having a thickness of 0.5 mm to 5.0 mm into a rectangular shape with a side length of 2 mm to 10 mm. Nickel-chromium porous bodies with a hollow interior 14 of the skeleton 11 are prone to deformation when pressure is applied, so when cut into a rectangular shape with a side length of 2 mm to 10 mm, the cut portion is crushed and the thickness is reduced. As a result, the center of the rectangle becomes the apex 22, and slopes from there toward the four sides form a curved shape.

[0041] FIG. 7 shows a schematic diagram of another example of a processed nickel-chromium porous body 10. The nickel-chromium porous body 10 has a circular bottom surface 21 and a hemispherical shape extending from the bottom surface 21 to the apex 22. The diameter of the bottom surface 21 may be 2 mm or more and 10 mm or less. The height from the bottom surface 21 to the apex 22 may be 0.5 mm or more and 5.0 mm or less. A nickel-chromium porous body having a circular bottom surface 21 has a higher filling rate for a given volume than one having a rectangular bottom surface 21. Similar to the nickel-chromium porous body shown in FIG. 6, the nickel-chromium porous body 10 can be manufactured by cutting the main surface of a flat plate-shaped nickel-chromium porous body having a thickness of 0.5 mm or more and 5.0 mm or less into a circle having a diameter of 2 mm or more and 10 mm or less. The circular bottom surface may be a perfect circle or an ellipse. In the case of an ellipse, the average diameter of the major and minor axes is treated as the diameter. The height is the length of the perpendicular line from the top 22 to the bottom 21. The above-mentioned hemispherical shape is not limited to a hemisphere, and may be a semi-elliptical sphere.

[0042] The processed nickel-chromium porous body 10 shown in Fig. 6 or 7 can also be produced by cutting a plurality of flat-plate nickel-chromium porous bodies in a state in which they are stacked in the thickness direction. When flat-plate nickel-chromium porous bodies are cut in a stacked state, the skeletons of the portions where a blade has been applied are crushed and entangled, allowing the stacked nickel-chromium porous bodies to be bonded together. Because the size of the bottom surface 21 of the processed nickel-chromium porous body is small compared to the height from the bottom surface 21 to the top portion 22, the adhesive strength provided by the entanglement of the skeletons at the peripheral edges is sufficient, and the stacked nickel-chromium porous bodies can be used in an integrated state without peeling off.

[0043] <Method of manufacturing nickel-chromium porous body> A method for producing a nickel-chromium porous body according to an embodiment of the present disclosure is a method for producing a nickel-chromium porous body according to the embodiment of the present disclosure described above, comprising the steps of preparing a nickel porous body having a skeleton with a three-dimensional network structure, chromizing the nickel porous body by a diffusion infiltration method to obtain a nickel-chromium porous body, and heat-treating the chromized nickel-chromium porous body to form a surface oxide layer on the surface of the skeleton. Furthermore, in the method for producing a nickel-chromium porous body, the heat treatment temperature in the step of obtaining a nickel-chromium porous body by chromizing may be 900°C or higher and 1200°C or lower. This configuration can provide a method for producing a nickel-chromium porous body in which peeling of the oxide film on the skeleton surface is reduced even when processing such as cutting is performed.

[0044] (Step of preparing a nickel porous body) This step is a step of preparing a nickel porous body having a skeleton with a three-dimensional network structure, the skeleton being composed primarily of nickel. Nickel porous bodies are easier to handle when they are in a sheet-like shape overall. The nickel-chromium porous body according to the embodiment of the present disclosure is obtained by alloying the nickel constituting the skeleton of the nickel porous body with chromium. Therefore, the structure (porosity, average pore diameter, etc.) of the nickel porous body may be the same as the structure required for the nickel-chromium porous body 10. Similar to the nickel-chromium porous body 10, the nickel porous body may be prepared such that the interior of the skeleton is hollow and pores are formed by the skeleton. The porosity and average pore diameter of the nickel porous body are defined in the same way as the porosity and average pore diameter of the nickel porous body 10 described above. The skeleton of the nickel porous body being composed primarily of nickel means that the skeleton of the nickel porous body contains nickel in the largest amount.

[0045] (Chromizing process of the nickel porous body) In this process, chromium is diffused and infiltrated into the nickel that constitutes the skeleton of the porous nickel body prepared in the previous process, thereby alloying the nickel and chromium to obtain a nickel-chromium porous body. Known methods can be used to diffuse and infiltrate chromium. For example, a method can be used in which the porous nickel body is filled with powder containing at least chromium (Cr), aluminum oxide (Al2O3), and ammonium chloride (NH4Cl), and then heated to approximately 950°C or higher and 1200°C or lower in an inert gas atmosphere such as Ar gas. For example, when the heating temperature is 1000°C, the heating time can be approximately 10 hours. The heating time and temperature can be appropriately adjusted so that the chromium concentration in the skeleton as a whole is 10% by mass or higher.

[0046] (Step of forming a surface oxide layer) This step involves heat-treating the nickel-chromium porous body obtained by the above step to form an oxide layer on the surface of the skeleton (both the interior side and the pore side of the skeleton). This step yields a nickel-chromium porous body 10 having a skeleton 11 with a surface oxide layer formed on both sides of the main metal layer 12. The heat treatment is carried out in hydrogen gas containing at least water vapor. The hydrogen gas only needs to contain at least water vapor and may further contain nitrogen gas, such as ammonia decomposition gas. This increases the chromium content on the surface (both the interior side and the pore side of the skeleton) of the skeleton (main metal layer 12) composed of nickel-chromium with a chromium content of 10% by mass or more, and also forms a film containing dense chromium oxide (surface oxide layer 13). The surface oxide layer 13 is formed in close contact with the surface of the main metal layer 12 without any gaps. Furthermore, the surface oxide layer 13 formed in this way is highly unlikely to crack or peel off from the main metal layer 12, even when the nickel-chromium porous body is bent or cut. The temperature for the heat treatment may be, for example, about 900° C. to 1200° C., or may be about 950° C. to 1100° C. The atmosphere for the heat treatment may be an atmosphere in which the volume ratio of hydrogen gas to water vapor (H2 / H2O) is, for example, in the range of 0.01 to 1,000, or may be in the range of 1 to 100, or may be in the range of 10 to 50.

[0047] Before the heat treatment in hydrogen gas containing at least water vapor, a heat treatment in an oxidizing atmosphere such as air may be performed. By performing the heat treatment in an oxidizing atmosphere, a surface oxide layer can be formed on the surface of the skeleton of the nickel porous body relatively quickly. However, since the surface oxide layer is likely to peel off from the main metal layer of the skeleton if only the heat treatment is performed in an oxidizing atmosphere, it is necessary to subsequently perform the heat treatment in hydrogen gas containing at least water vapor. [Example]

[0048] The present disclosure will be described in more detail below based on examples, but these examples are merely illustrative and the nickel-chromium porous body and the like of the present disclosure are not limited to these. The scope of the present disclosure is defined by the claims, and includes all modifications within the meaning and scope equivalent to the claims.

[0049] [Example 1] -Preparing a porous nickel body- A nickel porous body having a three-dimensional network structure skeleton was prepared. The nickel porous body had a thickness of 2.0 mm, a porosity of 98%, and an average pore diameter of 850 μm (Celmet #4 manufactured by Sumitomo Electric Industries, Ltd.).

[0050] -Chromizing process- A mixed powder containing 1% by mass of aluminum powder, 50% by mass of chromium powder, 0.5% by mass of ammonium chloride powder, and the remainder of aluminum oxide powder was prepared in a stainless steel furnace. The porous nickel body prepared in the above process was embedded in the mixed powder. Heat treatment was then performed at 1000°C for 10 hours, thereby alloying the nickel that constitutes the skeleton of the porous nickel body with chromium.

[0051] -Process for forming a surface oxide layer- The nickel-chromium porous body obtained in the above process was heat-treated in an atmosphere of hydrogen gas and water vapor with a volume ratio (H2 / H2O) of 32. The heat treatment temperature was 1000°C, and the heat treatment time was 20 minutes. Nickel-chromium porous body No. 1 was thus obtained.

[0052] [Example 2] Nickel-chromium porous body No. 2 was obtained in the same manner as in Example 1, except that in the step of forming the surface oxide layer, an ammonia decomposition mixed gas (H2+N2) containing water vapor was used instead of hydrogen gas containing water vapor. The volume ratio of hydrogen gas to water vapor (H2 / H2O) was 25.

[0053] [Comparative Example 1] Nickel-chromium porous body No. A was produced in the same manner as in Example 1, except that the step of forming a surface oxide layer in the manufacturing method described in Example 1 was carried out as follows. In the step of forming a surface oxide layer, the nickel-chromium porous body obtained in the above step was heat-treated in a nitrogen gas (N2) atmosphere. The heat treatment temperature was 1000°C, and the heat treatment time was 20 minutes.

[0054] Comparative Example 2 Nickel-chromium porous body No. B was produced in the same manner as in Example 1, except that the step of forming a surface oxide layer in the manufacturing method described in Example 1 was carried out as follows. In the step of forming a surface oxide layer, the nickel-chromium porous body obtained in the above step was heat-treated in a hydrogen gas (H2) atmosphere. The heat treatment temperature was 1000°C, and the heat treatment time was 20 minutes.

[0055] Comparative Example 3 Nickel chromium porous body No. C was produced in the same manner as in Example 1, except that in the production method described in Example 1, the heat treatment in the chromizing step was carried out at 800° C. for 2 hours.

[0056] Comparative Example 4 Nickel-chromium porous body No. D was produced in the same manner as in Example 1, except that the step of forming a surface oxide layer in the production method described in Example 1 was omitted.

[0057] [evaluation] Nickel-chrome porous bodies No. 1, No. 2, and No. A to No. D were press-cut in the thickness direction Z, and the skeletons of the fractured surfaces were observed using an electron microscope. Figure 8 shows the results for nickel-chrome porous body No. 1, and Figure 9 shows the results for nickel-chrome porous body No. A. For nickel-chrome porous body No. 1, the main metal layer 12 and the surface oxide layer 13 were firmly adhered with no gaps even on the fractured surface, and the surface oxide layer 13 was hardly peeled off. In other words, it was confirmed that the surface oxide layer 13 was adhered to the main metal layer 12 over 80% or more of the skeleton 11 on the fractured surface. Similar results were also confirmed for nickel-chrome porous body No. 2. The thickness of the surface oxide layer 13 was 0.5 μm for nickel-chrome porous body No. 1 and 1 μm for nickel-chrome porous body No. 2.

[0058] On the other hand, as shown in Figure 9, nickel-chrome porous body No. A, in which the surface oxide layer was formed in a nitrogen gas atmosphere, had a thick surface oxide layer 13, but gaps had formed at the interface with the main metal layer 12, and it was confirmed that most of the surface oxide layer 13 had peeled off. Nickel-chrome porous body No. B, in which the surface oxide layer was formed in a hydrogen gas atmosphere containing no water vapor, and nickel-chrome porous body No. C, which was chromized under conditions such that the chromium content of the main metal layer 12 was less than 10 mass%, also showed gaps at the interface between the surface oxide layer 13 and the main metal layer 12, and the surface oxide layer 13 had peeled off, in the fracture surface skeleton, as with nickel-chrome porous body No. A. Furthermore, nickel-chrome porous body No. D, in which no surface oxide layer was formed, had almost no surface oxide layer 13 formed on the surface of the skeleton, and its thickness was less than 0.1 µm.

[0059] The skeletons of nickel-chrome porous bodies No. 1, No. 2, and No. A to No. D were analyzed by EDX and XRD to determine their respective compositions and alloy components. The results are shown in Table 1 below. For nickel-chrome porous body No. 1, the chromium content of the main metal layer 12 was 25 mass% overall. The chromium content of the main metal layer 12 within a region at least 3 μm from the interface with the surface oxide layer 13 was 23.9 mass%. For nickel-chrome porous body No. 2, the chromium content of the main metal layer 12 within a region at least 3 μm from the interface with the surface oxide layer 13 was 28 mass% overall. The chromium content of the main metal layer 12 within a region at least 3 μm from the interface with the surface oxide layer 13 was 29.7 mass%. For nickel-chrome porous body No. A, the chromium content of the main metal layer 12 was 23 mass% overall. The chromium content of the main metal layer 12 within a region at least 3 μm from the interface with the surface oxide layer 13 was 41.7 mass%. In nickel-chrome porous body No. B, the chromium content of the main metal layer 12 was 24 mass% overall. The chromium content of the main metal layer 12 in the area extending at least 3 μm from the interface in contact with the surface oxide layer 13 was 46.3 mass%. In nickel-chrome porous body No. C, the chromium content of the main metal layer 12 was 7 mass% overall. The chromium content of the main metal layer 12 in the area extending at least 3 μm from the interface in contact with the surface oxide layer 13 was 12 mass%.

[0060] [Table 1]

[0061] The electrical conductivity was evaluated by measuring the electrical resistance of nickel-chrome porous bodies No. 1, No. 2, and No. A to No. D. The electrical resistance of each nickel-chrome porous body was measured by sandwiching a 3 cm x 3 cm test piece between electrode plates from above and below and applying a load of 0.12 MPa to the entire body while measuring the electrical resistance in the thickness direction. The results are shown in Table 1. It was confirmed that nickel-chrome porous bodies No. 1 and No. 2 had lower electrical resistance than nickel-chrome porous bodies No. A to No. C.

[0062] The corrosion resistance of nickel-chrome porous bodies No. 1, No. 2, and No. A to No. D was measured according to ASTM standard (ASTM-G5-94). Specifically, linear sweep voltammetry (LSV) measurements (scan rate: 5 mV / sec) were repeatedly performed using a sodium sulfate aqueous solution (pH 3) at 60°C, and the current value (mA) at 0.8 V vs. Ag / AgCl was measured on the fifth run. The potential scan range was 0.1 V to 1.0 V vs. SHE. Each nickel-chrome porous body was cut into 20 mm x 20 mm pieces and welded to a platinum wire. A platinum mesh was used as the counter electrode. The electrode spacing was uniform at 20 mm. A silver / silver chloride electrode was used as the reference electrode. The results are shown in Table 1. Nickel-chrome porous bodies No. 1 and No. 2 were confirmed to have superior corrosion resistance compared to nickel-chrome porous bodies No. A to No. D. [Explanation of symbols]

[0063] 10 Nickel-chromium porous body 11 Skeleton 12 Main metal layer 13 Surface oxide layer 14 Inside the skeleton 15 Pore 21 Bottom 22 Top R High chromium content area Z thickness direction

Claims

1. A nickel-chromium porous body having a skeleton with a three-dimensional network structure, the skeleton is hollow and has a main metal layer and surface oxide layers formed on both sides of the main metal layer; the surface oxide layer has a thickness of 0.5 μm or more and 1.0 μm or less and is mainly composed of chromium oxide; the main metal layer is nickel chromium with a chromium content of 10% by mass or more as a whole, and the chromium content in a range of at least 3 μm from the interface in contact with the surface oxide layer is 20% by mass or more; the surface oxide layer and the main metal layer are in close contact with each other without any gaps; Nickel-chromium porous body.

2. When cut in the thickness direction, the surface oxide layer is in close contact with the main metal layer over 80% or more of the skeleton of the fracture surface. The nickel-chromium porous body according to claim 1.

3. The thickness is 0.5 mm or more and 5.0 mm or less. The nickel-chromium porous body according to claim 1 or 2.

4. The porosity is 60% or more and 98% or less. The nickel chromium porous body according to any one of claims 1 to 3.

5. The bottom surface is polygonal and curved from the bottom surface to the top surface, The bottom surface has a side length of 2 mm or more and 10 mm or less, The height from the bottom surface to the top is 0.5 mm or more and 5.0 mm or less. The nickel-chromium porous body according to claim 1 or 4.

6. The bottom surface is circular and the top surface is hemispherical, The diameter of the bottom surface is 2 mm or more and 10 mm or less, The height from the bottom surface to the top is 0.5 mm or more and 5.0 mm or less. The nickel-chromium porous body according to claim 1 or 4.

7. A method for producing the nickel chromium porous body according to claim 1, comprising: preparing a nickel porous body having a skeleton with a three-dimensional network structure; a step of chromizing the nickel porous body by a diffusion penetration method to obtain a nickel-chromium porous body; a step of forming a surface oxide layer on the surface of the skeleton by heat treating the nickel-chromium porous body after the chromizing treatment; and In the step of obtaining a nickel-chromium porous body by chromizing, the temperature of the heat treatment is 900°C or higher and 1200°C or lower, The heat treatment is carried out in hydrogen gas containing at least water vapor. A method for manufacturing a nickel-chromium porous body.

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