Patent Description:
A sheet-shaped metal porous body having a skeleton with a three-dimensional mesh-like structure is used in various applications such as a filter, a catalyst support, a metal composite material, and an electrode plate for a battery. Celmet (manufactured by Sumitomo Electric Industries, Ltd. , registered trade mark), which is a metal porous body made of nickel, is widely used in various industrial fields, for example, an electrode of an alkaline storage battery such as a nickel-hydrogen battery, a support of an industrial deodorizing catalyst.

The metal porous body may be required to have corrosion resistance depending on the application. As a metal porous body having high corrosion resistance, a nickel-chromium porous body in which a skeleton is formed of a nickel-chromium alloy is known. As a method of manufacturing a nickel-chromium porous body, methods disclosed in <CIT> (PTL <NUM>) and <CIT> (PTL <NUM>) are known.

PTL <NUM> discloses a method of manufacturing a nickel-chromium porous body in which a chromium layer is formed on a surface of a skeleton of a nickel porous body whose skeleton is formed of nickel by plating, and then chromium is diffused by heat treatment. PTL <NUM> discloses a method of manufacturing a nickel-chromium porous body by a diffusion coating method in which a nickel porous body is embedded in a powder including Cr and NH<NUM>Cl and subjected to heat treatment in an Ar or H<NUM> gas atmosphere.

<CIT> (PTL <NUM>) discloses that forming an oxide film on the surface of the skeleton of a metal porous body enables the metal porous body to have further improved corrosion resistance. In addition, as a method of forming the oxide film on the surface of the skeleton of the metal porous body, it is disclosed that heat treatment is conducted in an oxidizing atmosphere or heat treatment is conducted after treatment with an acidic solution.

<CIT> Al discloses a metal porous material in sheet form that includes a frame having a three-dimensional network configuration, wherein the frame includes an alloy including at least nickel and chromium, wherein the frame is a solid solution with iron and includes a chromium oxide (Cr2O3) layer as an outermost layer and includes a chromium carbide layer located under the chromium oxide layer.

<NPL> discloses INCONEL <NUM> metal foams produced from alloy powder by the slip-reaction-foam-sinter-process and tested in respect to cyclic oxidation behaviour in air in the temperature range <NUM>-<NUM>. Summary of Invention.

The present invention provides a nickel-chromium porous body according to claim <NUM>.

A method of manufacturing a nickel-chromium porous body is also provided in the disclosure but does not form part of the invention. The method of manufacturing the nickel-chromium porous body includes preparing a nickel porous body having a skeleton with a three-dimensional mesh-like structure, obtaining a nickel-chromium porous body by subjecting the nickel porous body to chromizing treatment by a diffusion coating method, and forming a surface oxide layer on a surface of the skeleton by subjecting the nickel-chromium porous body after the chromizing treatment to heat treatment. The heat treatment is conducted in hydrogen gas containing at least water vapor.

A metal porous body is often subjected to processings of rolling, cutting, grooving, bending, and so on, depending on the application. The present disclosers have studied in detail what kind of changes occurs in a skeleton when a metal porous body having an oxide film on the surface of the skeleton is subjected to the above-described processings (particularly, cutting in which a large force is applied). As a result, it has been confirmed that when a conventional metal porous body having an oxide film on the surface of the skeleton is cut, the oxide film is peeled off from the surface of the skeleton in the vicinity of the cut surface, or the oxide film cracks. The reason for this is considered to be that since the oxide film generally does not have high adhesion to a metal forming the skeleton, a gap is likely to be formed at the interface between the oxide film and the metal when a force applied, and in some cases, a gap may be already formed at the interface between the oxide film and the metal during formation of the oxide film.

Thus, it is an object of the present disclosure to provide a nickel-chromium porous body with less peeling of the oxide film on the surface of the skeleton even when processing such as cutting is performed.

According to the present disclosure, it is possible to provide a nickel-chromium porous body with less peeling of the oxide film on the surface of the skeleton even when processing such as cutting is performed.

A nickel-chromium porous body according to the invention is a nickel-chromium porous body that includes a skeleton having a three-dimensional mesh-like structure. The skeleton has a hollow inner portion and has a main metal layer and a surface oxide layer formed on each surface side of the main metal layer. The surface oxide layer has a thickness of <NUM> or more and contains chromium oxide as a main component. The main metal layer is formed of nickel-chromium having a chromium content of <NUM> mass% or more as a whole and has a chromium content of <NUM> mass% or more in a region extending at least <NUM> from an interface in contact with the surface oxide layer. The surface oxide layer and the main metal layer are in close contact with each other without a gap therebetween. With such a configuration, it is possible to provide a nickel-chromium porous body with less peeling of the oxide film on the surface of the skeleton even when processing such as cutting is performed.

When the nickel-chromium porous body is cut in a thickness direction, the surface oxide layer may be in close contact with the main metal layer in <NUM>% or more of the skeleton in a fracture cross-section of the nickel-chromium porous body. With such a configuration, for example, it is possible to provide a nickel-chromium porous body in which the surface oxide layer is hardly peeled off from the surface of the skeleton even when the nickel-chromium porous body is cut.

The nickel-chromium porous body may have a thickness of <NUM> to <NUM>. With such a configuration, it is possible to provide a nickel-chromium porous body which is lightweight and has high strength.

The nickel-chromium porous body may have a porosity of <NUM>% to <NUM>%. With such a configuration, it is possible to provide a nickel-chromium porous body having a high porosity.

According to a first aspect of the invention, the nickel-chromium porous body has a bottom surface having a polygonal shape and have a curved shape from the bottom surface toward an apex. The bottom surface has a side having a length of <NUM> to <NUM>, and a height from the bottom surface to the apex is <NUM> to <NUM>. With such a configuration, it is possible to provide a nickel porous body having a shape suitable for a filter application or a catalyst support application.

According to a second aspect of the invention, the nickel-chromium porous body has a bottom surface having a circular shape and have a hemispherical shape from the bottom surface toward an apex. The bottom surface has a diameter of <NUM> to <NUM>, and a height from the bottom surface to the apex is <NUM> to <NUM>. With such a configuration, it is possible to provide a nickel porous body having a shape suitable for a filter application or a catalyst support application.

According to an aspect of the disclosure, not forming part of the invention, a method of manufacturing a nickel-chromium porous body includes preparing a nickel porous body having a skeleton with a three-dimensional mesh-like structure, obtaining a nickel-chromium porous body by subjecting the nickel porous body to chromizing treatment by a diffusion coating method, and forming a surface oxide layer on a surface of the skeleton by subjecting the nickel-chromium porous body after the chromizing treatment to heat treatment. The heat treatment is conducted in hydrogen gas containing at least water vapor. With such a configuration, it is possible to provide a method of manufacturing a nickel-chromium porous body with less peeling of the oxide film on the surface of the skeleton even when processing such as cutting is performed.

In the method of manufacturing a nickel-chromium porous body, heat treatment may be conducted at a temperature of <NUM> to <NUM> forming a surface oxide layer on a surface of the skeleton by subjecting the nickel-chromium porous body after the chromizing treatment to heat treatment. With such a configuration, it is possible to provide a method of manufacturing a nickel-chromium porous body with less peeling of the oxide film on the surface of the skeleton even when processing such as cutting is performed.

Examples of a nickel-chromium porous body and a method of manufacturing a nickel-chromium porous body will be described in more detail.

<FIG> is a schematic view of an example of a nickel-chromium porous body <NUM> not forming part of the invention. <FIG> is an enlarged photograph of a skeleton <NUM> of a three-dimensional mesh-like structure of nickel-chromium porous body <NUM> shown in <FIG>. <FIG> is an enlarged schematic view of a cross-section of nickel-chromium porous body <NUM> shown in <FIG>.

As shown in <FIG>, nickel-chromium porous body <NUM> has skeleton <NUM> with a three-dimensional mesh-like structure, and in many cases, has a flat plate-like appearance as a whole.

As shown in <FIG>, skeleton <NUM> of nickel-chromium porous body <NUM> is formed of a main metal layer <NUM> and a surface oxide layer <NUM>. An inner portion <NUM> of skeleton is hollow. Further, a pore portion <NUM> formed by skeleton <NUM> is an interconnected pore that cells, which may be modeled as a regular dodecahedron, are connected to each other from the surface to the interior of nickel-chromium porous body <NUM> to form. <FIG> is a schematic view of a cross-section taken along line A-A of skeleton <NUM>. The cross-sectional shape of skeleton <NUM> can be modeled as a triangular shape whose central portion (an inner portion <NUM> of the skeleton) is hollow. Skeleton <NUM> has main metal layer <NUM> and surface oxide layers <NUM> formed on each surface side of main metal layer <NUM>. Surface oxide layer <NUM> on one surface side faces inner portion <NUM> of the skeleton, and surface oxide layer <NUM> on the other surface side faces pore portion <NUM> of nickel-chromium porous body <NUM>.

<FIG> is an enlarged view of skeleton <NUM> in a region enclosed by the dashed line in <FIG>. Surface oxide layer <NUM> formed on each surface side of main metal layer <NUM> has a thickness of <NUM> or more and contains chromium oxide as a main component. Note that the main component refers to the most abundant component contained in surface oxide layer <NUM>. Surface oxide layer <NUM> may contain nickel, nickel oxide, Fe, or the like in addition to chromium oxide.

The upper limit of the thickness of surface oxide layer <NUM> is not particularly limited, but may be about <NUM> or less in consideration of the cost required for forming surface oxide layer <NUM>. When the thickness of surface oxide layer <NUM> is too large, surface oxide layer <NUM> is easily peeled off from the surface of main metal layer <NUM>. In addition, since surface oxide layer <NUM> increases a surface resistance of nickel-chromium porous body <NUM>, the thickness of surface oxide layer <NUM> may be thin when nickel-chromium porous body <NUM> is used for an application requiring conductivity. From these viewpoints, the upper limit of the thickness of surface oxide layer <NUM> may be <NUM> or less, or <NUM> or less.

Main metal layer <NUM> is formed of nickel-chromium having a chromium content of <NUM> mass% or more as a whole. As the content of chromium increases, main metal layer <NUM> has excellent corrosion resistance. Thus, the upper limit of the chromium content of main metal layer <NUM> is not particularly limited, but may be about <NUM> mass% or less in consideration of the cost required for alloying. From these viewpoints, the content of chromium in main metal layer <NUM> may be <NUM> mass% to <NUM> mass%, or may be <NUM> mass% to <NUM> mass% as a whole. Note that main metal layer <NUM> may intentionally or inevitably contain other components such as nickel and chromium oxide in addition to nickel-chromium.

Main metal layer <NUM> has a chromium content of <NUM> mass% or more as a whole, but has a chromium concentration of <NUM> mass% or more in a region R extending at least <NUM> from an interface in contact with surface oxide layer <NUM>. As will be described later, in the process of manufacturing nickel-chromium porous body <NUM> according to an embodiment of the present disclosure, by having the chromium content in region R extending at least <NUM> from an interface in contact with surface oxide layer <NUM> of <NUM> mass% or more, nickel-chromium porous body <NUM> in which main metal layer <NUM> and surface oxide layer <NUM> are in close contact with each other without a gap therebetween can be obtained. The chromium content in region R may be <NUM> mass% to <NUM> mass%, or may be <NUM> mass% to <NUM> mass%.

In skeleton <NUM> forming nickel-chromium porous body <NUM> according to an embodiment of the present disclosure, main metal layer <NUM> and surface oxide layer <NUM> are firmly in close contact with each other without a gap therebetween. Hence, in nickel-chromium porous body <NUM>, even when a strong force is applied to skeleton <NUM> due to bending or cutting, surface oxide layer <NUM> is hardly peeled off, and high corrosion resistance can be maintained.

For example, when nickel-chromium porous body <NUM> is cut in a thickness direction Z, surface oxide layer <NUM> may be in close contact with main metal layer <NUM> in <NUM>% or more of skeleton <NUM> in a fracture cross-section of nickel-chromium porous body <NUM>. In the fracture cross-section of nickel-chromium porous body <NUM>, the proportion of a portion where surface oxide layer <NUM> is in close contact with main metal layer <NUM> is determined as follows. First, nickel-chromium porous body <NUM> is embedded in a resin and cut in a thickness direction to observe a fracture cross-section thereof with an electron microscope. At this time, an area of "entire region in the thickness direction × <NUM> in a widthwise direction" in the fracture cross-section is observed, and for all skeletons observed in the area of the fracture cross-section, the length of a portion where surface oxide layer <NUM> is in close contact with main metal layer <NUM> is measured. When it can be found at a glance that a portion where surface oxide layer <NUM> is peeled off from main metal layer <NUM> is the lesser in the electron micrograph of the fracture cross-section, the length of the portion where surface oxide layer <NUM> is peeled off may be measured and the length of the portion where surface oxide layer <NUM> is in close contact with main metal layer <NUM> may be calculated as "(total peripheral length of skeleton × <NUM>) - (length of peeled portion)". In this case, the reason for doubling the total peripheral length of the skeleton will be described later. Then, the proportion of the portion where surface oxide layer <NUM> is in close contact with main metal layer <NUM> in the skeleton of the fracture cross-section is calculated by the following Formula (A).

Since surface oxide layer <NUM> is also formed on inner portion <NUM> side of the skeleton, the "length of close contact portion" in the above Formula (A) refers to a length of a portion where surface oxide layer <NUM> is in close contact with each surface on pore portion <NUM> side and inner portion <NUM> side of main metal layer <NUM> forming skeleton <NUM>. Similarly, the "length of peeled portion" refers to a length of a portion where surface oxide layer <NUM> is peeled from each surface on pore portion <NUM> side and inner portion <NUM> side of main metal layer <NUM> forming skeleton <NUM>. In order to determine the "length of close contact portion" as described above, in the above Formula (A) for calculating the "proportion of close contact portion" in the skeleton of the fracture cross-section, the "length of the close contact portion" is divided by a value obtained by doubling the "total peripheral length of skeleton". Similarly, also when the "length of close contact portion" is calculated from the "length of peeled portion", it is necessary to subtract the length of the peeled portion from a value obtained by doubling the total peripheral length of the skeleton. In addition, since the cross-section of skeleton <NUM> can be modeled as a substantially triangular shape as described above, the "total peripheral length of skeleton" in the above Formula (A) can be calculated by the following Formula (B).

In Formula (B), "the number of skeletons" means the number of skeletons present in the observed fracture cross-section, and "total length of three sides" means the sum of the lengths of three sides of skeleton <NUM> modeled as a substantially triangular shape.

In nickel-chromium porous body <NUM>, the proportion (%) of the close contact portion calculated by the above Formula (A) may be <NUM>% or more. In nickel-chromium porous body <NUM> according to an embodiment of the present disclosure, since surface oxide layer <NUM> is firmly in close contact with main metal layer <NUM> without a gap therebetween, surface oxide layer <NUM> is hardly peeled off from the surface of skeleton <NUM> in the vicinity of the fracture cross-section even when processing such as cutting is performed, and high corrosion resistance can be maintained.

The thickness of nickel-chromium porous body <NUM> may be appropriately selected depending on the application of the nickel-chromium porous body. For example, having a thickness of <NUM> to <NUM> allows nickel-chromium porous body <NUM> to be lightweight and to have high strength. Nickel-chromium porous body <NUM> may have a thickness of <NUM> to <NUM>. For example, nickel-chromium porous body <NUM> having a relatively large thickness is prepared and compressed in a thickness direction Z to adjust the thickness. Nickel-chromium porous body <NUM> can be manufactured by using a nickel porous body as a starting material. At this time, for example, Celmet (registered trade mark) manufactured by Sumitomo Electric Industries, Ltd. is used as a nickel porous body to prepare a nickel porous body having a thickness of <NUM> or more, and nickel-chromium porous body <NUM> having a thickness of <NUM> or more can be manufactured using the nickel porous body. Even when a nickel porous body having a thickness of less than <NUM> is used, nickel-chromium porous body <NUM> having a thickness of <NUM> or more can be manufactured. For example, in the step of subjecting a nickel porous body to chromizing treatment in the method of manufacturing a nickel-chromium porous body, two or more nickel porous bodies may be laminated in a thickness direction and subjected to the chromizing treatment with skeletons of the nickel porous bodies in contact with each other. This allows the two or more nickel porous bodies to be alloyed and integrated with the skeletons of the nickel porous bodies in contact with each other, and nickel-chromium porous body <NUM> having a thickness of <NUM> or more per sheet is obtained. The portion where the skeletons of the two or more nickel porous bodies are in contact with each other is firmly bonded by welding. The thickness of nickel-chromium porous body <NUM> can be measured with, for example, a digital thickness gauge.

The porosity of nickel-chromium porous body <NUM> may be appropriately selected depending on the application of the nickel-chromium porous body. For example, when nickel-chromium porous body <NUM> is used as a filter, it is desirable that nickel-chromium porous body <NUM> has an excellent ability to collect an object to be collected and a small pressure loss. Nickel-chromium porous body <NUM> may have a porosity of <NUM>% to <NUM>%, <NUM>% to <NUM>%, or <NUM>% to <NUM>%, for example. In many cases, nickel-chromium porous body <NUM> has a porosity of about <NUM>% immediately after manufacturing, but compression processing in thickness direction Z allows the porosity to be reduced.

The porosity of nickel-chromium porous body <NUM> is defined by the following Formula (<NUM>). [Formula <NUM>] <MAT>.

The average pore size of nickel-chromium porous body <NUM> may be appropriately selected depending on the application of nickel-chromium porous body <NUM>. As an example, nickel-chromium porous body <NUM> may have an average pore size of <NUM> to <NUM>, <NUM> to <NUM>, or <NUM> to <NUM>.

The average pore size of nickel-chromium porous body <NUM> is calculated by the following Formula (<NUM>) using an average number (nc) of pore portions <NUM> per inch (<NUM> = <NUM>) which a main surface of nickel-chromium porous body <NUM> is observed in at least <NUM> fields of view with a microscope or the like to obtain. [Formula <NUM>] <MAT>.

The measurement of the number of pore portions <NUM> is performed in accordance with the determination of the number of pores (number of cells) for flexible cellular polymeric materials according to JIS K6400-<NUM>:<NUM> Annex <NUM> (reference).

In nickel-chromium porous body <NUM> according to an embodiment of the present disclosure, surface oxide layer <NUM> is hardly peeled off from the surface of skeleton <NUM> even when nickel-chromium porous body <NUM> is cut. Therefore, for example, high corrosion resistance can be maintained even when nickel-chromium porous body <NUM> is finely processed. Processed nickel-chromium porous body <NUM> can be used, for example, as a filter or a catalyst support which requires corrosion resistance.

<FIG> is a schematic view of an example of processed nickel-chromium porous body <NUM> according to the invention. Nickel-chromium porous body <NUM> has a bottom surface <NUM> having a polygonal shape and has a curved shape from bottom surface <NUM> toward an apex <NUM>. Bottom surface <NUM> has a side having a length of <NUM> to <NUM> and either a square shape or a rectangular shape. A height from bottom surface <NUM> to apex <NUM> is <NUM> to <NUM>. Note that the height is defined as a length of a perpendicular line from apex <NUM> to bottom surface <NUM>. Examples of the polygonal shape include, for example, a quadrangular shape, a pentagonal shape, a hexagonal shape, and the like.

A main surface of a flat plate-like nickel-chromium porous body having a thickness of, for example, <NUM> to <NUM> is cut so as to form a quadrangular shape with a side having a length of <NUM> to <NUM> to manufacture nickel-chromium porous body <NUM>. Since the nickel-chromium porous body in which inner portion <NUM> of skeleton <NUM> is hollow is easily deformed when a pressure is applied, cutting the nickel-chromium porous body so as to form a quadrangular shape with a side having a length of <NUM> to <NUM> causes the cut portion to be crushed and reduced in thickness. As a result, the center portion of the quadrangular shape becomes apex <NUM>, and slopes are formed from apex <NUM> toward the four sides to form a curved shape.

<FIG> is a schematic view of another example of processed nickel-chromium porous body <NUM> according to the invention. Nickel-chromium porous body <NUM> has a bottom surface <NUM> having a circular shape and has a hemispherical shape from bottom surface <NUM> toward apex <NUM>. Bottom surface <NUM> has a diameter of <NUM> to <NUM>. A height from bottom surface <NUM> to apex <NUM> is <NUM> to <NUM>. A nickel-chromium porous body with bottom surface <NUM> having a circular shape has a higher filling rate into a given volume than a nickel-chromium porous body with bottom surface <NUM> having a quadrangular shape. As in the nickel-chromium porous body shown in <FIG>, a main surface of a flat plate-like nickel-chromium porous body having a thickness of <NUM> to <NUM> is cut so as to form a circular shape having a diameter of <NUM> to <NUM> to manufacture nickel-chromium porous body <NUM>. The circular shape of the bottom surface may be a perfect circle or an ellipse. In the case of an ellipse, an average diameter of the major axis and the minor axis is treated as the diameter. Further, the height is defined as a length of a perpendicular line from apex <NUM> to bottom surface <NUM>. The hemispherical shape may be a hemisphere or a semi-ellipsoid.

Cutting a plurality of flat plate-like nickel-chromium porous bodies laminated in the thickness direction also enables processed nickel-chromium porous body <NUM> shown in <FIG> or <FIG> to be manufactured. Cutting the flat plate-like nickel-chromium porous bodies in the laminated state causes, for example, the skeleton of a portion to which a blade is applied to be crushed and entangled with each other, thereby bonding the laminated nickel-chromium porous bodies to each other. In the processed nickel-chromium porous body, since the size of bottom surface <NUM> is smaller relative to the height from bottom surface <NUM> to apex <NUM>, the adhesive force due to the entanglement of the skeleton in a peripheral portion is sufficient, so that the laminated nickel-chromium porous bodies can be used in an integrated state without being separated from each other.

An aspect of the disclosure, not forming part of the invention, relates to a method of manufacturing a nickel-chromium porous body. The method includes preparing a nickel porous body having a skeleton with a three-dimensional mesh-like structure, obtaining a nickel-chromium porous body by subjecting the nickel porous body to chromizing treatment by a diffusion coating method, forming a surface oxide layer on a surface of the skeleton by subjecting the nickel-chromium porous body after the chromizing treatment to heat treatment. Furthermore, in the method of manufacturing the nickel-chromium porous body, heat treatment may be conducted at a temperature of <NUM> to <NUM> in the step of obtaining the nickel-chromium porous body by the chromizing treatment. With such a configuration, it is possible to provide a method of manufacturing a nickel-chromium porous body with lesser peeling of the oxide film on the surface of the skeleton even when processing such as cutting is performed.

This step is a step of preparing a nickel porous body having a skeleton with a three-dimensional mesh-like structure in which the skeleton contains nickel as a main component. Handling of the nickel porous body is easier when it has a sheet-like shape as a whole. Nickel forming the skeleton of the nickel porous body is alloyed with chromium to obtain the nickel-chromium porous body according to an embodiment of the present disclosure. Therefore, the structure (porosity, average pore size, etc.) of the nickel porous body may be the same as the structure required for nickel-chromium porous body <NUM>. As in nickel-chromium porous body <NUM>, the nickel porous body may be prepared in which the inner portion of skeleton is hollow and the skeleton forms the pore portion. The porosity and average pore size of the nickel porous body are defined in the same manner as the porosity and average pore size of nickel-chromium porous body <NUM> described above. Containing nickel as a main component in the skeleton of the nickel porous body means that nickel is the most abundant component contained in the skeleton of the nickel porous body.

In this step, diffusion coating of chromium is applied to nickel forming the skeleton of the nickel porous body prepared in the above step to alloy nickel and chromium with each other, thereby obtaining a nickel-chromium porous body. As a method of diffusion coating of chromium, a known method can be employed. For example, it is possible to adopt a method in which a nickel porous body is embedded in a powder containing at least chromium (Cr), aluminum oxide (Al<NUM>O<NUM>), and ammonium chloride (NH<NUM>Cl) and heated to about <NUM> to <NUM> in an inert gas atmosphere such as Ar gas. For example, when the heating temperature is <NUM>, the heating time may be about <NUM> hours. The heating time and temperature may be appropriately adjusted so that a chromium concentration in the skeleton is <NUM> mass% or more as a whole.

In this step, the nickel-chromium porous body obtained in the above step is subjected to heat treatment to form an oxide layer on the surface of the skeleton (each surface side of the inner portion side and the pore portion side of the skeleton). Through this step, nickel-chromium porous body <NUM> having skeleton <NUM> in which the surface oxide layer is formed on each surface side of main metal layer <NUM> is obtained. The heat treatment is conducted in hydrogen gas containing at least water vapor. The hydrogen gas may contain at least water vapor, and may further contain nitrogen gas or the like as in ammonia cracked gas, for example. This allows the chromium content of the surface (each surface side of the inner portion side and the pore portion side of the skeleton) of the skeleton (main metal layer <NUM>) formed of nickel-chromium having a chromium content of <NUM> mass% or more to be increased, thereby forming a dense film containing chromium oxide (surface oxide layer <NUM>). At this time, surface oxide layer <NUM> is formed in close contact with the surface of main metal layer <NUM> without a gap therebetween. In addition, surface oxide layer <NUM> formed in this manner is extremely unlikely to crack or peel off from main metal layer <NUM> even when the nickel-chromium porous body is bent or cut. The temperature at which the heat treatment is conducted may be, for example, about <NUM> to <NUM>, and may be about <NUM> to <NUM>. The atmosphere in which the heat treatment is conducted may be, for example, an atmosphere in which a volumetric ratio (H<NUM>/H<NUM>O) of hydrogen gas to water vapor is in a range of <NUM> to <NUM>, may be in a range of <NUM> to <NUM>, or may be in a range of <NUM> to <NUM>.

Before the heat treatment in hydrogen gas containing at least water vapor, heat treatment may be conducted in an oxidizing atmosphere such as an air atmosphere. A surface oxide layer can be relatively rapidly formed on the surface of the skeleton of the nickel porous body by the heat treatment in an oxidizing atmosphere. However, since the surface oxide layer is easily peeled off from the main metal layer of the skeleton when heat treatment is conducted only in the oxidizing atmosphere, heat treatment in hydrogen gas containing at least water vapor needs to follow the heat treatment in the oxidizing atmosphere.

Hereinafter, the present disclosure will be described in more detail 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 thereto.

As a nickel porous body having a skeleton with a three-dimensional mesh-like structure, a nickel porous body (Celmet #<NUM>, Sumitomo Electric Industries, Ltd. ) having a thickness of <NUM>, a porosity of <NUM>%, and an average pore size of <NUM> was prepared.

In a stainless steel furnace, a mixed powder was prepared in which <NUM> mass% of an aluminum powder, <NUM> mass% of a chromium powder, <NUM> mass% of an ammonium chloride powder, and an aluminum oxide powder as a balance were blended. The nickel porous body prepared in the above-mentioned step was embedded in the mixed powder. Subsequently, heat treatment was conducted at <NUM> for <NUM> hours to alloy nickel forming the skeleton of the nickel porous body with chromium.

The nickel-chromium porous body obtained in the above step was subjected to heat treatment in an atmosphere in which the volumetric ratio (H<NUM>/H<NUM>O) of hydrogen gas to water vapor was <NUM>. Heat treatment was conducted at a temperature of <NUM> for <NUM> minutes. As a result, a nickel-chromium porous body No. <NUM> was obtained.

A nickel-chromium porous body No. <NUM> was obtained in the same manner as in Example <NUM> except that an ammonia cracked gas mixture (H<NUM> + N<NUM>) containing water vapor was used instead of hydrogen gas containing water vapor in the step of forming a surface oxide layer in the manufacturing method described in Example <NUM>. The volumetric ratio (H<NUM>/H<NUM>O) of hydrogen gas to water vapor was <NUM>.

A nickel-chromium porous body No. A was manufactured in the same manner as in Example <NUM> except that the step of forming the surface oxide layer was performed as follows in the manufacturing method described in Example <NUM>. In the step of forming a surface oxide layer, the nickel-chromium porous body obtained in the above step was subjected to heat treatment in a nitrogen (N<NUM>) gas atmosphere. Heat treatment was conducted at a temperature of <NUM> for <NUM> minutes.

A nickel-chromium porous body No. B was manufactured in the same manner as in Example <NUM> except that the step of forming a surface oxide layer was performed as follows in the manufacturing method described in Example <NUM>. In the step of forming a surface oxide layer, the nickel-chromium porous body obtained in the above step was subjected to heat treatment in a hydrogen (H<NUM>) gas atmosphere. Heat treatment was conducted at a temperature of <NUM> for <NUM> minutes.

A nickel-chromium porous body No. C was manufactured in the same manner as in Example <NUM> except that the heat treatment in the step of the chromizing treatment was conducted at <NUM> for <NUM> hours in the manufacturing method described in Example <NUM>.

A nickel-chromium porous body No. D was manufactured in the same manner as in Example <NUM> except that the step of forming a surface oxide layer was not performed in the manufacturing method described in Example <NUM>.

Nickel-chromium porous bodies No. <NUM> and No. <NUM> and nickel-chromium porous bodies No. A to No. D were press-cut in thickness direction Z, and the skeleton of each fracture cross-section was observed with an electron microscope. <FIG> shows the result of nickel-chromium porous body No. <NUM>, and <FIG> shows the result of nickel-chromium porous body No. A. In the fracture cross-section of the nickel-chromium porous body No. <NUM>, main metal layer <NUM> and surface oxide layer <NUM> were firmly in close contact with each other without a gap therebetween, and surface oxide layer <NUM> was hardly peeled off. That is, it was confirmed that surface oxide layer <NUM> was in close contact with main metal layer <NUM> in <NUM>% or more of skeleton <NUM> of the fracture cross-section. The same result was also confirmed for nickel-chromium porous body No. <NUM>. Surface oxide layer <NUM> had a thickness of <NUM> in nickel-chromium porous body No. <NUM> and a thickness of <NUM> in nickel-chromium porous body No. <NUM>.

On the other hand, as shown in <FIG>, it was confirmed that in nickel-chromium porous body No. A in which the surface oxide layer was formed in a nitrogen gas atmosphere, although nickel-chromium porous body No. A had a thick surface oxide layer <NUM>, a gap was formed at the interface between surface oxide layer <NUM> and main metal layer <NUM> and that most of surface oxide layer <NUM> was peeled off. In nickel-chromium porous body No. B in which the surface oxide layer was formed in a hydrogen gas atmosphere containing no water vapor, and nickel-chromium porous body No. C in which the chromizing treatment was performed under a condition in which the chromium content of main metal layer <NUM> was less than <NUM> mass%, it was confirmed that a gap was formed at the interface between surface oxide layer <NUM> and main metal layer <NUM> in the skeleton of the fracture cross-section and that surface oxide layer <NUM> was peeled off, as in nickel-chromium porous body No. A. In addition, in nickel-chromium porous body No. D which was manufactured without forming a surface oxide layer, surface oxide layer <NUM> was hardly formed on the surface of the skeleton, and surface oxide layer <NUM> had a thickness of less than <NUM>.

The skeletons of nickel-chromium porous bodies No. <NUM> and No. <NUM> and the nickel-chromium porous bodies No. A to No. D were analyzed by EDX and XRD to examine the compositions and alloy components of the respective skeletons. In nickel-chromium porous body No. <NUM>, main metal layer <NUM> had a chromium content of <NUM> mass% as a whole. In addition, main metal layer <NUM> had a chromium content of <NUM> mass% in a region extending at least <NUM> from the interface in contact with surface oxide layer <NUM>. In nickel-chromium porous body No. <NUM>, main metal layer <NUM> had a chromium content of was <NUM> mass% as a whole. In addition, main metal layer <NUM> had a chromium content of <NUM> mass% in a region extending at least <NUM> from the interface in contact with surface oxide layer <NUM>. In nickel-chromium porous body No. A, main metal layer <NUM> had a chromium content of <NUM> mass% as a whole. In addition, main metal layer <NUM> had a chromium content of <NUM> mass% in a region extending at least <NUM> from the interface in contact with surface oxide layer <NUM>. In nickel-chromium porous body No. B, main metal layer <NUM> had a chromium content of <NUM> mass% as a whole. In addition, main metal layer <NUM> had a chromium content of <NUM> mass% in a region extending at least <NUM> from the interface in contact with surface oxide layer <NUM>. In nickel-chromium porous body No. C, main metal layer <NUM> had a chromium content of <NUM> mass% as a whole. In addition, main metal layer <NUM> had a chromium content of <NUM> mass% in a region extending at least <NUM> from the interface in contact with surface oxide layer <NUM>.

Electrical resistances of nickel-chromium porous bodies No. <NUM> and No. <NUM> and nickel-chromium porous bodies No. A to No. D were measured to evaluate conductivities. The electrical resistance of each nickel-chromium porous body was measured in a thickness direction using a test piece having a size of <NUM> × <NUM> with electrodes holding the top and bottom of the test piece to sandwich the test piece and a load of <NUM> MPa applied to the entire test piece. The results are shown in Table <NUM>. It was confirmed that nickel-chromium porous bodies No. <NUM> and No. <NUM> had lower electrical resistances than nickel-chromium porous bodies No. A to No. C.

Claim 1:
A nickel-chromium porous body comprising a skeleton having a three-dimensional mesh-like structure,
wherein the skeleton has a hollow inner portion and has a main metal layer and a surface oxide layer formed on each surface side of the main metal layer,
the surface oxide layer has a thickness of <NUM> or more and contains chromium oxide as a main component,
the main metal layer is formed of nickel-chromium having a chromium content of <NUM> mass% or more as a whole and has a chromium content of <NUM> mass% or more in a region extending at least <NUM> from an interface in contact with the surface oxide layer, and
the surface oxide layer and the main metal layer are in close contact with each other without a gap therebetween,
characterised in that:
the nickel-chromium porous body has a bottom surface having a polygonal shape and has a curved shape from the bottom surface toward an apex, the bottom surface has a side having a length of <NUM> to <NUM>, and a height from the bottom surface to the apex is <NUM> to <NUM>, or
the nickel-chromium porous body has a bottom surface having a circular shape and has a hemispherical shape from the bottom surface toward an apex, the bottom surface has a diameter of <NUM> to <NUM>, and a height from the bottom surface to the apex is <NUM> to <NUM>.