Porous metal

Abstract

A metal porous body made of metal having a plurality of pores formed therein, wherein the arithmetic mean M1 of the equivalent circle diameters of the pores is 50 μm or more and 500 μm or less, and the coefficient of variation of the equivalent circle diameters of the pores is 0 or more and 1.3 or less, the arithmetic mean M1 of the equivalent circle diameters of the pores and the coefficient of variation of the equivalent circle diameters of the pores are measured on a cross section of the metal porous body, and the coefficient of variation of the equivalent circle diameters of the pores is a ratio (σ1 / M1) of the standard deviation σ1 of the equivalent circle diameters of the pores to the arithmetic mean M1 of the equivalent circle diameters of the pores, The units of M1 and the standard deviation σ1 are μm, and in at least four of the five non-overlapping rectangular measurement fields of 4500 μm × 3700 μm set on the cross section of the metal porous body, the percentage (L1 / L) × 100 of the distance L1 between the center of gravity C1 of the measurement field and the center of gravity C2 of the pores based on all the pores in the measurement field to the square root L of the area of the measurement field is 0% or more and 2.0% or less, and the units of the square root L and the distance L1 are μm.

Description

[Technical Field]

[0001] The present disclosure relates to a metal porous body. This application claims priority to Japanese Patent Application No. 2023-146885, filed on September 11, 2023. The entire contents of the Japanese Patent Application are incorporated herein by reference. [Background technology]

[0002] Porous metal bodies, which have multiple pores formed inside, are lighter than ordinary metals and have high electrical and thermal conductivity. For this reason, their application to construction components for automobiles and buildings, heat exchangers, electrodes, and the like is being considered.

[0003] Non-Patent Document 1 discloses a technique for producing a porous metal body by mixing a raw metal powder with spacer particles (such as sodium chloride) and sintering the mixture. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Hakamada, M., Mabuchi, M. (2012). Creation of microporous metals by the spacer method and their characterization. Light Metals, Vol. 62, No. 8, 313-321 Summary of the Invention

[0005] The metal porous body of the present disclosure is a metal porous body made of a metal having a plurality of pores formed therein, wherein the arithmetic mean M1 of the equivalent circle diameters of the pores is 50 μm or more and 500 μm or less, and the coefficient of variation of the equivalent circle diameters of the pores is 0 or more and 1.3 or less, the arithmetic mean M1 of the equivalent circle diameters of the pores and the coefficient of variation of the equivalent circle diameters of the pores are measured on a cross section of the metal porous body, and the coefficient of variation of the equivalent circle diameters of the pores is the ratio (σ1 / M1) of the standard deviation σ1 of the equivalent circle diameters of the pores to the arithmetic mean M1 of the equivalent circle diameters of the pores, The metal porous body is characterized in that the unit of the square root L and the unit of the standard deviation σ1 are μm, and in at least four of five non-overlapping rectangular measurement fields of 4500 μm × 3700 μm set on the cross section of the metal porous body, the percentage (L1 / L) × 100 of the distance L1 between the center of gravity C1 of the measurement field and the center of gravity C2 of the pores based on all the pores in the measurement field to the square root L of the area of the measurement field is 0% or more and 2.0% or less, and the unit of the square root L and the distance L1 is μm. DETAILED DESCRIPTION OF THE INVENTION

[0006] [Problem to be solved by this disclosure] In order to improve the performance of porous metal bodies in various applications, it is necessary to improve the uniformity of the pore size and the spatial distribution of the pores in the porous metal body.

[0007] Therefore, an object of the present disclosure is to provide a porous metal body having improved uniformity in pore size and in the spatial distribution of pores in the porous metal body.

[0008] [Effects of this disclosure] According to the present disclosure, it is possible to provide a porous metal body with improved uniformity in pore size and spatial distribution of pores in the porous metal body.

[0009] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described. (1) The metal porous body of the present disclosure is a metal porous body made of a metal having a plurality of pores formed therein, wherein the arithmetic mean M1 of the circle-equivalent diameters of the pores is 50 μm or more and 500 μm or less, and the coefficient of variation of the circle-equivalent diameters of the pores is 0 or more and 1.3 or less, the arithmetic mean M1 of the circle-equivalent diameters of the pores and the coefficient of variation of the circle-equivalent diameters of the pores are measured in a cross section of the metal porous body, and the coefficient of variation of the circle-equivalent diameters of the pores is the ratio (σ1 / M1) of the standard deviation σ1 of the circle-equivalent diameters of the pores to the arithmetic mean M1 of the circle-equivalent diameters of the pores, and the standard deviation σ1 is in μm, and the unit of the square root L and the distance L1 is in μm. The metal porous body is characterized in that, in at least four of five non-overlapping rectangular measurement fields of 4500 μm × 3700 μm set on the cross section of the metal porous body, the percentage (L1 / L) × 100 of the distance L1 between the center of gravity C1 of the measurement field and the center of gravity C2 of the pores based on all the pores in the measurement field, relative to the square root L of the area of the measurement field, is 0% or more and 2.0% or less, and the unit of the square root L and the distance L1 is μm.

[0010] According to the present disclosure, it is possible to provide a porous metal body with improved uniformity in pore size and spatial distribution of pores in the porous metal body.

[0011] (2) In the above (1), the porosity of the porous metal body may be 40% or more and 85% or less, thereby making it possible to obtain a lightweight porous metal body while maintaining high thermal conductivity.

[0012] (3) In the above (1) or (2), the metal may be a metal consisting of one metal element selected from a first group consisting of aluminum, magnesium, copper, silver, gold, iron, molybdenum, tungsten, and titanium; an alloy consisting of two or more metal elements selected from the first group; a metal in a composite state of two or more metal elements selected from the first group; an alloy consisting of one or more metal elements selected from the first group and one or more elements selected from a second group consisting of iron, cobalt, chromium, nickel, manganese, tin, zinc, silicon, phosphorus, carbon, boron, scandium, molybdenum, tungsten, and titanium; or a metal in a composite state of one or more metal elements selected from the first group and one or more elements selected from the second group.

[0013] This improves the thermal conductivity of the porous metal body.

[0014] (4) In any of the above (1) to (3), the coefficient of variation of the equivalent circle diameter of the pores may be 0 or more and 1.2 or less, thereby further improving the uniformity of the pore size.

[0015] (5) In any of (1) to (4) above, in each of at least four of five non-overlapping rectangular measurement fields of 4500 μm × 3700 μm set on the cross section of the metal porous body, the percentage (L1 / L) × 100 of the distance L1 between the center of gravity C1 of the measurement field and the center of gravity C2 of the pores based on all the pores in the measurement field to the square root L of the area of the measurement field may be 0% or more and 1.5% or less.

[0016] This further improves the uniformity of the spatial distribution of pores in the porous metal body.

[0017] [Details of the embodiments of the present disclosure] In this specification, the expression "A to B" means the upper and lower limits of a range (i.e., A or more and B or less), and when no unit is specified for A and a unit is specified only for B, the unit of A and the unit of B are the same.

[0018] In the present specification, when a compound or the like is represented by a chemical formula, unless the atomic ratio is particularly limited, it is understood to include any conventionally known atomic ratio, and is not necessarily limited to only those within the stoichiometric range.

[0019] In the present disclosure, when one or more numerical values are recited as the lower limit and the upper limit of a numerical range, a combination of any one numerical value recited as the lower limit and any one numerical value recited as the upper limit is also considered to be disclosed. For example, when a1 or more, b1 or more, and c1 or more are recited as the lower limit and a2 or less, b2 or less, and c2 or less are recited as the upper limit, a1 or more and a2 or less, a1 or more and b2 or less, a1 or more and c2 or less, b1 or more and a2 or less, b1 or more and b2 or less, b1 or more and c2 or less, c1 or more and a2 or less, c1 or more and b2 or less, and c1 or more and c2 or less are considered to be disclosed.

[0020] [Embodiment 1: Metallic porous body] A metal porous body according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") is a metal porous body made of metal having a plurality of pores formed therein, wherein the arithmetic mean M1 of the equivalent circle diameters of the pores is 50 μm or more and 500 μm or less, and the coefficient of variation of the equivalent circle diameters of the pores is 0 or more and 1.3 or less, the arithmetic mean M1 of the equivalent circle diameters of the pores and the coefficient of variation of the equivalent circle diameters of the pores are measured in a cross section of the metal porous body, and the coefficient of variation of the equivalent circle diameters of the pores is determined by the ratio (σ1 / M 1), wherein the arithmetic mean M1 and the standard deviation σ1 are expressed in units of μm, and in at least four of five non-overlapping rectangular measurement fields of 4500 μm × 3700 μm set on a cross section of the metal porous body, the percentage (L1 / L) × 100 of the distance L1 between the center of gravity C1 of the measurement field and the center of gravity C2 of the pores based on all the pores in the measurement field to the square root L of the area of the measurement field is 0% or more and 2.0% or less, and the square root L and the distance L1 are expressed in units of μm.

[0021] <Structure of porous metal body> The porous metal body of the first embodiment is made of a metal having a plurality of pores formed therein, that is, the porous metal body has a plurality of pores therein.

[0022] <Arithmetic mean of equivalent circular pore diameter M1> In the metal porous body of embodiment 1, the arithmetic mean M1 of the equivalent circle diameter of the pores is 50 μm or more and 500 μm or less. When the arithmetic mean M1 of the equivalent circle diameter of the pores is 50 μm or more, the specific surface area can be increased while maintaining the high thermal conductivity of the metal porous body. The lower limit of the arithmetic mean M1 of the equivalent circle diameter of the pores may be 60 μm or more, 65 μm or more, or 70 μm or more. When the upper limit of the arithmetic mean M1 of the equivalent circle diameter of the pores is 500 μm or less, the water permeability can be increased while maintaining the high thermal conductivity of the metal porous body. The upper limit of the arithmetic mean M1 of the equivalent circle diameter of the pores may be 400 μm or less, 300 μm or less, or 200 μm or less. The arithmetic mean M1 of the equivalent circle diameter of the pores may be 60 μm or more and 400 μm or less, 65 μm or more and 300 μm or less, or 70 μm or more and 200 μm or less.

[0023] In the present disclosure, the arithmetic mean M1 of the equivalent circle diameter of the pores is measured in the cross section of the metal porous body. The specific method for measuring the arithmetic mean M1 of the equivalent circle diameter of the pores is as follows.

[0024] Step A1: A measurement sample is obtained by cutting out the porous metal body using wire electric discharge machining. The measurement sample is cut out so that at least one side of the measurement sample is a rectangle measuring 10 mm x 10 mm. The cutting position can be set arbitrarily.

[0025] Step A2: Place the measurement sample in a dedicated holder, pour in hardening resin, and embed the measurement sample in the hardening resin.

[0026] Step A3: The measurement sample embedded in step A2 is polished with a rotary polisher until the cross section of the metal porous body is exposed.

[0027] Step A4: The cross section of the metal porous body is photographed using a microscope at 25x magnification to obtain a first image. The size of the first image is a rectangle of 4500 μm × 3700 μm. As the microscope, for example, the "WRAYCAM-NT500" (trademark) manufactured by Raymer Co., Ltd. can be used.

[0028] Step A5: The first image is binarized using the image analysis software ImageJ (https: / / imagej.nih.gov / ij / download.html) to obtain the second image. In the second image, the pores appear as bright field (white) and the metal appears as dark field (black).

[0029] Step A6. In the second image, among the bright fields corresponding to the pores, identify the bright field whose entire outer edge is located within the measurement field (hereinafter also referred to as the "first bright field"). Using the image analysis software ImageJ, calculate the arithmetic mean m1 of the circle-equivalent diameter of the first bright field. Even if the shape of the first bright field in the second image is formed by multiple adjacent pores, the continuous first bright field is considered to be a single first bright field.

[0030] Step A7: Perform steps A4 to A6 above based on five non-overlapping first images, and calculate the arithmetic mean m1 (μm) of the equivalent circle diameters in the first bright field for each of the five second images. Calculate the average M1 (μm) of the arithmetic mean m1 (μm) of the equivalent circle diameters in the first bright field for the five second images. In the present disclosure, this average M1 (μm) corresponds to the arithmetic mean M1 (μm) of the equivalent circle diameters of the pores.

[0031] It has been confirmed that as long as measurements are made using the above method on the same porous metal body, there is no variation in the measurement results even if the measurement area is changed arbitrarily.

[0032] <Coefficient of variation of pore equivalent circle diameter> In the metal porous body of embodiment 1, the coefficient of variation of the equivalent circle diameter of the pores is 0 or more and 1.3 or less. In the present disclosure, the coefficient of variation of the equivalent circle diameter of the pores is the ratio (σ1 / M1) of the standard deviation σ1 of the equivalent circle diameter of the pores to the arithmetic mean M1 of the equivalent circle diameter of the pores. The coefficient of variation of the equivalent circle diameter of the pores is an index showing the variation in pore size. A smaller value of the coefficient of variation of the equivalent circle diameter of the pores indicates a smaller variation in pore size and more uniform pore size.

[0033] The upper limit of the coefficient of variation of the equivalent circle diameter of the pores is 1.3 or less, or may be 1.2 or less, 1.17 or less, or 1.15 or less, from the viewpoint of improving the uniformity of the pore sizes. The coefficient of variation of the equivalent circle diameter of the pores is 0 or more, or may be 0.3 or more, from the viewpoint of manufacturing. The coefficient of variation of the equivalent circle diameter of the pores may be 0 or more and 1.2 or less, or 0 or more and 1.17 or less, or 0.3 or more and 1.15 or less.

[0034] In the present disclosure, the coefficient of variation of the equivalent circle diameter of pores is measured in a cross section of a metal porous body. A specific method for measuring the coefficient of variation of the equivalent circle diameter of pores is as follows.

[0035] Step B1: Measure the arithmetic mean M1 (μm) of the pore equivalent circle diameter using the same method as steps A1 to A7 of the measurement method for the arithmetic mean M1 of the pore equivalent circle diameter.

[0036] Step B2: Identify the first bright field in the second image using the same method as steps A1 to A6 of the method for measuring the arithmetic mean M1 of the pore circle-equivalent diameter. Calculate the standard deviation σA (μm) of the circle-equivalent diameter in the first bright field using image analysis software ImageJ. Calculate the standard deviation σA (μm) of the circle-equivalent diameter in the first bright field for each of the second images acquired based on the same five first images as in step A7 above. Calculate the average σ1 (μm) of the standard deviations σA (μm) of the circle-equivalent diameter in the first bright field for the five second images. In the present disclosure, this average σ1 (μm) corresponds to the standard deviation σ1 (μm) of the circle-equivalent diameter of the pore.

[0037] Step B3: Based on the arithmetic mean M1 (μm) of the equivalent circle diameter of the pores obtained in Step B1 and the standard deviation σ1 (μm) of the equivalent circle diameter of the pores obtained in Step B2, calculate the ratio (σ1 / M1) of the standard deviation σ1 (μm) of the equivalent circle diameter of the pores to the arithmetic mean M1 (μm) of the equivalent circle diameter of the pores. In the present disclosure, the ratio (σ1 / M1) corresponds to the coefficient of variation of the equivalent circle diameter of the pores.

[0038] It has been confirmed that as long as measurements are made using the above method on the same porous metal body, there is no variation in the measurement results even if the measurement area is changed arbitrarily.

[0039] <Percentage (L1 / L)×100> In each of at least four of the five non-overlapping rectangular measurement fields of 4500 μm × 3700 μm set on the cross section of the metal porous body of embodiment 1, the percentage (L1 / L) × 100 of the distance L1 (μm) between the center of gravity C1 of the measurement field and the center of gravity C2 of all pores within the measurement field relative to the square root L (μm) of the area of the measurement field is 0% or more and 2.0% or less. The percentage (L1 / L) × 100 is an index indicating the bias in the spatial distribution of pores. More specifically, it is an index correlating with the deviation between the center of gravity C1 of the measurement field and the center of gravity C2 of all pores within the measurement field. A smaller value of the percentage (L1 / L) × 100 indicates a more uniform spatial distribution of pores.

[0040] In each of at least four of the five non-overlapping rectangular measurement fields of 4500 μm × 3700 μm set on the cross section of the metal porous body, the percentage (L1 / L) × 100 may be 0% or more and 1.5% or less, 0% or more and 1.4% or less, 0% or more and 1.3% or less, or 0% or more and 1.2% or less.

[0041] In the present disclosure, the percentage (L1 / L)×100 is measured by the following procedure.

[0042] Step C1: Identify the first bright field in the second image using the same method as steps A1 to A6 of the method for measuring the arithmetic mean M1 of the circle-equivalent diameter of the pores. Using the image analysis software ImageJ, identify the center of gravity C1 of the measurement field of view (a rectangular measurement field of view of 4500 μm × 3700 μm) of the second image and the center of gravity C2' of the first bright field. The center of gravity C2' of the first bright field corresponds to the center of gravity C2 of the pores. In the present disclosure, the center of gravity C of the pores corresponds to the center of gravity of the first bright field in the second image after binarization of the rectangular first image of 4500 μm × 3700 μm obtained by imaging the cross section of the metal porous body with a microscope at 25x magnification, with the entire outer edge of the bright field located within the measurement field.

[0043] The center of gravity C2' of the first bright field is the center of gravity G(x G ,y G ) and is expressed by the following formula:

[0044]

number

[0045] In the above formula, a i indicates the area of each primary bright field, and (x i ,y i ) indicate the coordinates of the center of gravity of each first bright field.

[0046] Step C2: In the second image, measure the distance L1 (μm) between the center of gravity C1 and the center of gravity C2' (the center of gravity C2' in the first bright field corresponds to the center of gravity C2 of the pore). Calculate the percentage of the distance L1 (μm) relative to the square root L (μm) of the area of the measurement field of the second image (4500 μm × 3700 μm) (L1 / L) × 100.

[0047] In the present disclosure, the spatial distribution of pores in a metal porous body is determined to be uniform when the percentage (L1 / L)×100 is 0% or more and 2.0% or less in each of at least four of five non-overlapping rectangular measurement fields of 4500 μm × 3700 μm set on the cross section of the metal porous body.

[0048] It has been confirmed that as long as measurements are made using the above method on the same porous metal body, there is no variation in the measurement results even if the measurement area is changed arbitrarily.

[0049] <Porosity of porous metal bodies> The porosity of the porous metal body of embodiment 1 may be 40% or more and 85% or less. The lower limit of the porosity of the porous metal body may be 60% or more, 70% or more, or 75% or more, from the viewpoints of increasing open pores and reducing weight. The upper limit of the porosity of the porous metal body may be 80% or less, from the viewpoint of ease of machining the porous metal body by wire electric discharge machining. The porosity of the porous metal body may be 60% or more and 85% or less, 70% or more and 85% or less, or 75% or more and 80% or less.

[0050] The porosity of a porous metal body is defined by the following formula (1). Porosity = {1 - [mass of porous metal body [g] / (volume of porous metal body [cm 3 ]×Material density [g / cm 3 ])]}×100[%] (1) The volume of the porous metal body in the above formula (1) [cm 3 ]" means the volume based on the outer shape of the metal porous body including pores.

[0051] <Composition of porous metal body> The metal constituting the metal porous body of embodiment 1 is a metal consisting of one metal element selected from Group 1 consisting of aluminum, magnesium, copper, silver, gold, iron, molybdenum, tungsten, and titanium; an alloy consisting of two or more metal elements selected from Group 1; a metal in a composite state of two or more metal elements selected from Group 1; an alloy consisting of one or more metal elements selected from Group 1 and one or more elements selected from Group 2 consisting of iron, cobalt, chromium, nickel, manganese, tin, zinc, silicon, phosphorus, carbon, boron, scandium, molybdenum, tungsten, and titanium; or a metal in a composite state of one or more metal elements selected from Group 1 and one or more elements selected from Group 2.

[0052] In an alloy consisting of one or more metal elements selected from Group 1 and one or more elements selected from Group 2, the type of element in Group 1 is different from the type of element in Group 2. In a metal in a composite state consisting of one or more metal elements selected from Group 1 and one or more elements selected from Group 2, the type of element in Group 1 is different from the type of element in Group 2.

[0053] Since the above metals have high thermal conductivity, the metal porous body can also have high thermal conductivity.

[0054] In the present disclosure, the term "metal" is defined as a concept including metals consisting of one type of metal element, alloys containing two or more types of metal elements, and composite metals containing two or more types of metal elements.

[0055] In the present disclosure, the term "a metal in a composite state of two or more metal elements" refers to a state in which two or more metals exist as individual substances, rather than as an alloy. Specifically, it refers to a state in which the surfaces of two or more metal powders are bonded together and molded.

[0056] In the present disclosure, "a metal in a composite state of one or more metal elements selected from Group 1 and one or more elements selected from Group 2" means, when the element of Group 2 is carbon, powder of one or more metals selected from Group 1 bonded to graphite or diamond, or carbides of one or more metals selected from Group 1. When the element of Group 2 is boron, powder of one or more metals selected from Group 1 bonded to powder of boron alone, or borides of one or more metals selected from Group 1.

[0057] Examples of alloys include Cu-1%Ag alloy and Al-1%Mg-0.6%Si-0.5%Fe-0.25%Cu-0.1%Cr alloy (A6061).

[0058] From the viewpoint of high thermal conductivity, the metal may be pure copper, pure aluminum, a copper alloy containing 90% by mass or more of copper, or an aluminum alloy containing 90% by mass or more of aluminum. The alloy may be in a state where the constituent elements are solid-solved in copper, aluminum, etc. The alloy may be in a state where precipitates or heterogeneous phases are dispersed.

[0059] The composition of the porous metal body is measured by ICP emission spectrometry.

[0060] The metal porous body of embodiment 1 may contain impurities other than the above metals, as long as the effects of the present disclosure are not impaired. Here, as defined above, the term "metal" encompasses metals consisting of one metal element, alloys containing two or more metal elements, and composite metals containing two or more metal elements. The metal porous body of embodiment 1 can be composed of the above metals and impurities. Examples of such impurities include oxygen, hydrogen, nitrogen, sulfur, phosphorus, and metal elements other than the metal elements in the first and second groups. The impurities are contained independently from the matrix phase in the form of precipitates or the like. The content of the impurities need only be less than the volume fraction required to achieve a predetermined thermal conductivity. For example, it can be 3 atomic % or less. The content of the impurities is measured by gas chromatography (GC) analysis or ICP atomic emission spectrometry.

[0061] <Method of manufacturing a porous metal body> The following describes an example of a method for manufacturing the metal porous body of the heat transfer system of Embodiment 1. The method for manufacturing the metal porous body of Embodiment 1 can include a preparation step, a mixing step, a preforming step, a sintering step, and a cleaning step.

[0062] ≪Preparation process≫ In the preparation step, a raw material powder of the metal porous body and sodium chloride powder (NaCl powder) are prepared.

[0063] Examples of the raw material powder include metal powders consisting of one metal element selected from Group 1 consisting of aluminum, magnesium, copper, silver, gold, iron, molybdenum, tungsten, and titanium; alloy powders consisting of two or more metal elements selected from Group 1; and powders consisting of one or more metal elements selected from Group 1 and one or more elements selected from Group 2 consisting of iron, cobalt, chromium, nickel, manganese, tin, zinc, silicon, phosphorus, carbon, boron, scandium, molybdenum, tungsten, and titanium.

[0064] The average particle size of the raw material powder can be 10 to 85 μm. Here, the average particle size of the raw material powder is the particle size at which the cumulative volume fraction from the smallest diameter side is 50% in a histogram where the horizontal axis represents particle size and the vertical axis represents volume fraction. The average particle size of the raw material powder is measured by a laser diffraction / scattering method.

[0065] The average particle size of the NaCl powder can be 45 to 500 μm. Here, the average particle size of the NaCl powder is the particle size at which the cumulative volume fraction from the smallest diameter side is 50% in a histogram where the horizontal axis represents particle size and the vertical axis represents volume fraction. The histogram is created based on the results of sieving a sample using sieves specified in JIS Z 8801-1:2019 "Test sieves - Part 1: Metal mesh sieves" and measuring the mass of the sample remaining on each sieve.

[0066] ≪Mixing process≫ Next, in the mixing step, the raw material powder and NaCl powder are placed in a plastic container and mixed to obtain a mixed powder. The mixing ratio of the raw material powder and NaCl powder can be adjusted appropriately depending on the porosity of the porous metal body to be produced. For example, the percentage of NaCl powder in the mixed powder is preferably 40 to 85% by volume.

[0067] Add ethanol dropwise to the mixed powder in a plastic container and stir for 5 minutes with a stirring rod. The mixing ratio of the mixed powder to ethanol is 10:1 to 5:1 by volume.

[0068] <Pre-molding process> Next, in the preforming process, the mixed powder mixed with ethanol is filled into a graphite mold and preformed using a hand press at 15 MPa to obtain a preformed product, which is then naturally dried in an organic draft chamber for 480 minutes while still in the graphite mold.

[0069] <Sintering process> Next, in the sintering step, the graphite mold is placed in a plasma pressure sintering apparatus and pressure sintering is carried out to obtain a sintered body. The pressure sintering conditions are a temperature of 500 to 900°C, a pressure of 10 to 30 MPa, and a time of 5 to 10 minutes.

[0070] <Cleaning process> Next, in the washing process, the sintered body is immersed in water to dissolve the NaCl into the water. Specifically, approximately 1 L of pure water is prepared for 10 g of sintered body. The pure water is placed in a beaker, and the sintered body is immersed in the pure water and stirred. By immersing the body for a total of approximately 50 hours, changing the pure water every 5 hours, the NaCl is sufficiently dissolved out of the sintered body.

[0071] Next, the sintered body after immersion in pure water is placed on a hot plate heated to 180°C and dried to remove moisture. If sodium chloride remains, add water dropwise with a dropper while heating as needed, and remove the remaining sodium chloride by evaporation.

[0072] Next, the sintered body dried on the hot plate is subjected to ultrasonic cleaning for 10 minutes and then dried, thereby obtaining the metal porous body of the first embodiment.

[0073] In the above manufacturing method, ethanol is added dropwise to the mixed powder in the mixing step. The present inventors have newly discovered that adding ethanol dropwise to the mixed powder improves the uniformity of the pore size and the uniformity of the spatial distribution of the pores in the resulting porous metal body. The reason for this is not clear, but is presumed to be as follows.

[0074] Because NaCl is insoluble in ethanol, it can maintain its granular shape during the mixing process. The NaCl regions in the preform correspond to the pore regions of the porous metal body. If the NaCl maintains its granular shape in the preform, the uniformity of the pore size and spatial distribution of the pores in the porous metal body will be improved.

[0075] The surface tension of ethanol allows the NaCl powder and the raw material powder to adhere to each other, so that even in the preform, the NaCl powder and the raw material powder do not separate and tend to remain mixed together, improving the uniformity of the pore size and spatial distribution of the pores in the porous metal body.

[0076] Furthermore, the use of ethanol has the following advantages: Ethanol dries quickly, so the time required for natural drying in the preforming process can be shortened; and because ethanol does not remain as an impurity, the metal porous body can be sintered without altering its skeleton. [Example]

[0077] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0078] [Preparation of porous metal bodies] ≪Preparation process≫ For each sample, aluminum powder or copper powder and sodium chloride powder were prepared as raw material powders. The average particle sizes of these powders used for each sample are listed in the "Raw Powder" and "NaCl Powder" columns in Table 1.

[0079] ≪Mixing process≫ The raw material powders and NaCl powder were placed in a plastic container and mixed to obtain a mixed powder. The raw material powder and NaCl powder contents of the mixed powder are shown in the "Mixed Powder" column of Table 1. The upper row of each column shows the content in mass %, and the lower row of each column shows the content in volume %.

[0080] Next, ethanol was added dropwise to the plastic container containing the mixed powder for Samples 1 to 9, and water was added dropwise to Samples 1-1 and 1-2, and the mixture was stirred for 5 minutes with a stirring rod. The mixing ratio of the mixed powder to ethanol or water was 10:1 by volume. Neither ethanol nor water was added dropwise to Sample 1-3.

[0081] <Pre-molding process> For Samples 1 to 9, 1-1, and 1-2, the mixed powders after the mixing process were filled into a graphite mold with a diameter of 42 mm and preformed at 15 MPa using a hand press to obtain preformed products. The preformed products were left in the graphite molds and allowed to air dry for 480 minutes in an organic draft chamber.

[0082] In Sample 1-3, the Cu powder and NaCl powder in the mixed powder could not be mixed uniformly and separated, so that a preform could not be produced.

[0083] <Sintering process> The graphite mold was placed in a plasma pressure sintering apparatus and pressure sintered at a pressure of 30 MPa and a temperature of 700°C for 8 minutes to obtain a sintered body.

[0084] <Cleaning process> The sintered body was immersed in water to dissolve NaCl into the water. Specifically, the sintered body was placed in a beaker containing 200 ml of water and left to stand for 480 minutes.

[0085] Next, the sintered body after immersion in pure water was placed on a hot plate heated to 180°C and dried to remove moisture. If sodium chloride remained, water was added dropwise with a dropper while heating as needed, and the remaining sodium chloride was removed by evaporation.

[0086] Next, the sintered body was dried on a hot plate, ultrasonically cleaned for 10 minutes, and then dried, thereby obtaining a metal porous body for each sample.

[0087] [Table 1]

[0088] [Evaluation of porous metal bodies] The resulting metal porous body was measured for composition, arithmetic mean pore diameter M1, coefficient of variation of pore diameter equivalent to a circle, percentage (L1 / L) x 100, and porosity. The measurement methods for each item were as described in embodiment 1. The results are shown in Table 2.

[0089] The value in the "Percentage (L1 / L) × 100" column in Table 2 indicates the fourth smallest value when the percentages (L1 / L) × 100 of the five measurement visual fields are arranged in ascending order. In other words, the percentages (L1 / L) × 100 of at least four of the five measurement visual fields are equal to or less than the value in the "Percentage (L1 / L) × 100" column. For example, for Sample 1, the percentages (L1 / L) × 100 of at least four of the five measurement visual fields are equal to or less than 1.2%.

[0090] [Table 2]

[0091] The porous metal bodies of Samples 1 to 13 correspond to Examples. It was confirmed that the porous metal bodies of Samples 1 to 13 had improved uniformity in pore size and in the spatial distribution of pores in the porous metal body.

[0092] The porous metal bodies of Samples 1-1 and 1-2 correspond to comparative examples. It was confirmed that the porous metal bodies of Samples 1-1 and 1-2 had non-uniform pore sizes and that the spatial distribution of the pores in the porous metal bodies was also non-uniform. It is presumed that the non-uniform pore sizes and spatial distribution of Samples 1-1 and 1-2 were due to the NaCl powder dissolving in the water added dropwise to the mixed powder during the mixing process.

[0093] In Sample 1-3, the Cu powder and NaCl powder in the mixed powder could not be mixed uniformly and separated, so that a preform could not be produced and a metal porous body could not be obtained.

[0094] Although the embodiments and examples of the present disclosure have been described above, it is originally intended that the configurations of the above-described embodiments and examples may be appropriately combined or modified in various ways. The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the embodiments and examples described above, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

Claims

1. A porous metal body made of a metal having a plurality of pores formed therein, The arithmetic mean M1 of the equivalent circle diameter of the pores is 56 μm or more and 495 μm or less, the coefficient of variation of the equivalent circle diameter of the pores is 0.8 or more and 1.2 or less; The arithmetic mean M1 of the equivalent circle diameter of the pores and the coefficient of variation of the equivalent circle diameter of the pores are measured in a cross section of the metal porous body, the coefficient of variation of the equivalent circle diameter of the pores is a ratio (σ1 / M1) of the standard deviation σ1 of the equivalent circle diameter of the pores to the arithmetic mean M1 of the equivalent circle diameter of the pores, The arithmetic mean M1 and the standard deviation σ1 are in μm, In each of at least four of five non-overlapping rectangular measurement fields of 4500 μm × 3700 μm obtained by imaging the cross section of the metal porous body with a microscope at a magnification of 25 times, the percentage (L1 / L) × 100 of the distance L1 between the center of gravity C1 of the measurement field and the center of gravity C2 of the pores based on all the pores in the measurement field to the square root L of the area of the measurement field is 1.0% or more and 1.5% or less, The square root L and the distance L1 are in μm, The porosity of the metal porous body is 40% or more and 85% or less, The metal is a metal consisting of one metal element selected from the first group consisting of aluminum, magnesium, copper, silver, gold, iron, molybdenum, tungsten, and titanium; an alloy consisting of two or more metal elements selected from the first group; a metal in a composite state of two or more metal elements selected from the first group; an alloy comprising one or more metal elements selected from the first group and one or more elements selected from a second group consisting of iron, cobalt, chromium, nickel, manganese, tin, zinc, silicon, phosphorus, carbon, boron, scandium, molybdenum, tungsten, and titanium; or, A metal porous body comprising a composite metal of one or more metal elements selected from the first group and one or more elements selected from the second group.

2. A metal porous body as described in claim 1, wherein the metal is aluminum or copper.

Images