EP4779043A1

EP4779043A1 - Metal porous body

Info

Publication number: EP4779043A1
Application number: EP24865161.4A
Authority: EP
Inventors: Atsuki MITANI; Ryohei Kobayashi
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 2023-09-11
Filing date: 2024-08-16
Publication date: 2026-07-22
Also published as: JPWO2025057655A1; JP7718613B1; US20260146306A1; WO2025057655A1; CN121794406A

Abstract

A metal porous body composed of a metal in which a plurality of pores is formed; wherein an arithmetic mean of equivalent circle diameters of the pores, M1, is 50 µm or more and 500 µm or less, and a coefficient of variation of the equivalent circle diameters of the pores is 0 or more and 1.3 or less, wherein the arithmetic mean of the equivalent circle diameters of the pores, M1, and the coefficient of variation of the equivalent circle diameters of the pores are measured on a cross section of the metal porous body, the coefficient of variation of the equivalent circle diameters of the pores is a ratio of a standard deviation of the equivalent circle diameters of the pores, σ1, to the arithmetic mean of the equivalent circle diameters of the pores, M1, (σ1/M1) and units of the arithmetic mean M1 and the standard deviation σ1 are each µm; and a percentage (L1/L) × 100 is 0% or more and 2.0% or less in each of at least four of five 4,500 µm × 3,700 µm rectangular measurement fields of view that do not overlap each other and are defined in the cross section of the metal porous body, where L1 is a distance L1 between the center of gravity of the measurement field of view, C1, and the center of gravity of the pores based on all the pores in the measurement field of view, C2, and L is a square root of an area of the measurement field of view, wherein units of the square root L and the distance L1 are each µm.

Description

TECHNICAL FIELD

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

BACKGROUND ART

A metal porous body in which a plurality of pores is formed is lighter than ordinary metals and has high electrical and thermal conductivities. For this reason, the metal porous body is being considered for application to structural parts for automobiles, buildings and others, heat exchangers, electrodes, etc.
NPL 1 discloses a technology for fabricating a metal porous body by mixing metal fine powder as a raw material with spacer particles (such as sodium chloride) and sintering them.

CITATION LIST

NON PATENT LITERATURE

NPL 1: Masataka HAKAMADA and Mamoru MABUCHI (2012), "Fabrication by spacer method and evaluation of porous metals", Journal of The Japan Institute of Light Metals, Vol. 62, No. 8, 313-321

SUMMARY OF INVENTION

The metal porous body of the present disclosure is a metal porous body composed of a metal in which a plurality of pores is formed;
wherein

an arithmetic mean of equivalent circle diameters of the pores, M1, is 50 µm or more and 500 µm or less, and
a coefficient of variation of the equivalent circle diameters of the pores is 0 or more and 1.3 or less,
wherein
the arithmetic mean of the equivalent circle diameters of the pores, M1, and the coefficient of variation of the equivalent circle diameters of the pores are measured on a cross section of the metal porous body,
the coefficient of variation of the equivalent circle diameters of the pores is a ratio of a standard deviation of the equivalent circle diameters of the pores, σ1, to the arithmetic mean of the equivalent circle diameters of the pores, M1, (σ1/ M1) and
units of the arithmetic mean M1 and the standard deviation σ1 are each µm; and
a percentage (L1/L) × 100 is 0% or more and 2.0% or less in each of at least four of five 4,500 µm × 3,700 µm rectangular measurement fields of view that do not overlap each other and are defined in the cross section of the metal porous body, where L1 is a distance between the center of gravity of the measurement field of view, C1, and the center of gravity of the pores based on all the pores in the measurement field of view, C2, and L is a square root of an area of the measurement field of view,
wherein
units of the square root L and the distance L1 are each µm.

DETAILED DESCRIPTION

[Problem to be Solved by the Present Disclosure]

For improvement in the performance of the metal porous body in various applications, it is necessary to improve uniformity of the pore sizes, and uniformity of the spatial distribution of the pores in the metal porous body.
Therefore, an object of the present disclosure is to provide a metal porous body that has improved uniformity of the pore sizes and improved uniformity of the spatial distribution of the pores in the metal porous body.

[Advantageous Effect of the Present Disclosure]

According to the present disclosure, there can be provided a metal porous body that has improved uniformity of the pore sizes and improved uniformity of the spatial distribution of the pores in the metal porous body.

[Description of Embodiments]

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 composed of a metal in which a plurality of pores is formed;

an arithmetic mean of equivalent circle diameters of the pores, M1, is 50 µm or more and 500 µm or less, and
a coefficient of variation of the equivalent circle diameters of the pores is 0 or more and 1.3 or less,
wherein
the arithmetic mean of the equivalent circle diameters of the pores, M1, and the coefficient of variation of the equivalent circle diameters of the pores are measured on a cross section of the metal porous body,
the coefficient of variation of the equivalent circle diameters of the pores is a ratio of a standard deviation of the equivalent circle diameters of the pores, σ1, to the arithmetic mean of the equivalent circle diameters of the pores, M1, (σ1/M1) and
units of the arithmetic mean M1 and the standard deviation σ1 are each µm; and
a percentage (L1/L) × 100 is 0% or more and 2.0% or less in each of at least four of five 4,500 µm × 3,700 µm rectangular measurement fields of view that do not overlap each other and are defined in the cross section of the metal porous body, where L1 is a distance between the center of gravity of the measurement field of view, C1, and the center of gravity of the pores based on all the pores in the measurement field of view, C2, and L is a square root of an area of the measurement field of view,
wherein
units of the square root L and the distance L1 are each µm.

According to the present disclosure, there can be provided the metal porous body that has improved uniformity of the pore sizes and improved uniformity of the spatial distribution of the pores in the metal porous body.
(2) In the above (1), the porosity of the metal porous body may be 40% or more and 85% or less. This allows for obtaining a lightweight metal porous body still having a high thermal conductivity.
(3) In the above (1) or (2), the metal may be: a metal consisting of a metallic element of one selected from the first group consisting of aluminum, magnesium, copper, silver, gold, iron, molybdenum, tungsten, and titanium; an alloy consisting of metallic elements of two or more selected from the first group; a metal in a composite state of metallic elements of two or more selected from the first group; an alloy consisting of metallic elements of one or more selected from the first group and elements of one or more 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 metallic elements of one or more selected from the first group and elements of one or more selected from the second group.
This improves the thermal conductivity of the metal porous body.
(4) In any of the above (1) to (3), the coefficient of variation of the equivalent circle diameters of the pores may be 0 or more and 1.2 or less. This further improves the uniformity of the pore size.
(5) In any of the above (1) to (4), the percentage (L1/L) × 100 may be 0% or more and 1.5% or less in each of at least four of the five 4,500 µm × 3,700 µm rectangular measurement fields of view that do not overlap each other and are defined in the cross section of the metal porous body, where L1 is the distance between the center of gravity of the measurement field of view, C1, and the center of gravity of the pores based on all the pores in the measurement field of view, C2, and L is the square root of the area of the measurement field of view.
This further improves the uniformity of the spatial distribution of the pores in the metal porous body.

[Details of Embodiments of the Present Disclosure]

Herein, the notation "A to B" means a range with the lower limit and the upper limit (i.e., A or more and B or less). If there is no unit described for A but is only a unit described for B, the unit for A and the unit for B are the same.
Herein, a compound or the like may be expressed by a chemical formula. In that case, if an atomic ratio is not limited, the chemical formula encompasses compounds of all conventionally known atomic ratios and is not necessarily be limited only to those within the stoichiometric range.
In the present disclosure, when one or more numerical values are described for each of the lower and upper limits of numerical ranges, it is appreciated that a combination of any one numerical value described for the lower limit and any one numerical value described for the upper limit is also disclosed. For example, in a case where a1 or more, b1 or more, and c1 or more are described for the lower limit and also where a2 or less, b2 or less, and c2 or less are described for the upper limit, it is appreciated that 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 disclosed.

[Embodiment 1: Metal Porous Body]

The metal porous body of an embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") is a metal porous body composed of a metal in which a plurality of pores is formed;
wherein

The metal porous body of Embodiment 1 is composed of a metal in which a plurality of pores is formed. Namely, the metal porous body has a plurality of pores inside.

In the metal porous body of Embodiment 1, the arithmetic mean of the equivalent circle diameters of the pores, M1, is 50 µm or more and 500 µm or less. When the arithmetic mean of the equivalent circle diameters of the pores, M1, is 50 µm or more, the metal porous body can have an increased specific surface area while still having the high thermal conductivity. For the lower limit, the arithmetic mean of the equivalent circle diameters of the pores, M1, may be 60 µm or more, 65 µm or more, or 70 µm or more. When of the arithmetic mean of the equivalent circle diameters of the pores, M1, is 500 µm or less, for the upper limit, the metal porous body can have increased water permeability while still having the high thermal conductivity. For the upper limit, the arithmetic mean of the equivalent circle diameters of the pores, M1, may be 400 µm or less, 300 µm or less, or 200 µm or less. The arithmetic mean of the equivalent circle diameters of the pores, M1, 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.
In the present disclosure, the arithmetic mean of the equivalent circle diameters of the pores, M1, is measured on the cross section of the metal porous body. A specific method for measuring the arithmetic mean of the equivalent circle diameters of the pores, M1, is as follows.
Procedure A1. Cut out the metal porous body by wire electrical discharge machining to obtain a sample for measurement. The cut-out is carried out to obtain the sample for measurement such that at least one side face of the sample for measurement is a rectangle of 10 mm × 10 mm in size. The position of the cut-out can be arbitrary.
Procedure A2. Place the sample for measurement in a dedicated holder, and pour a hardening resin to embed the sample for measurement in the hardening resin.
Procedure A3. Polish the sample for measurement embedded in Procedure A2 with a rotary polisher until a cross section of the metal porous body is exposed.
Procedure A4. Take an image of the cross section of the metal porous body under a microscope at a magnification of 25× to obtain a first image. The size of the first image is a rectangle of 4,500 µm × 3,700 µm. As the microscope, "WRAYCAM-NT500" (TM) manufactured by WRAYMER INC. can be used, for example.
Procedure A5. Binarize the first image using the image analysis software ImageJ (https://imagej.nih.gov/ij/download.html) to obtain a second image. In the second image, the pore region is in a bright field (white) and the metal region is in a dark field (black).
Procedure A6. Identify the bright fields whose entire outer periphery is within the measurement field of view (hereinafter also referred to as the "first bright fields"), among the bright fields corresponding to the pore region in the second image. Calculate the arithmetic mean of the equivalent circle diameters of the first bright fields, m1, using the image analysis software ImageJ. In the second image, even if the shape of the first bright field is formed by a plurality of pores in contact with each other, a continuous first bright field is regarded as one first bright field.
Procedure A7. Perform Procedures A4 to A6 on five first images that do not overlap with each other, and calculate the arithmetic mean (µm) of the equivalent circle diameters of the first bright fields, m1, in each of five second images. Calculate the average M1 (µm) of the arithmetic means (µm) of the equivalent circle diameters of the first bright fields, m1, of the five second images. In the present disclosure, the average M1 (µm) corresponds to the arithmetic mean (µm) of the equivalent circle diameters of the pores, M1.
It has been confirmed that even if the measurement area is changed arbitrarily, there is no variation in the measurement results as long as measurement is carried out by the above-described method on the same metal porous body.

In the metal porous body of Embodiment 1, the coefficient of variation of the equivalent circle diameters of the pores is 0 or more and 1.3 or less. In the present disclosure, the coefficient of variation of the equivalent circle diameters of the pores is the ratio of the standard deviation of the equivalent circle diameters of the pores,σ1, to the arithmetic mean of the equivalent circle diameters of the pores, M1, (σ1/M1). The coefficient of variation of the equivalent circle diameters of the pores is an index of the variation of the pore sizes. The smaller the value of the coefficient of variation of the equivalent circle diameters of the pores, the smaller the variation of the pore sizes, indicating that the pore size is uniform.
For the upper limit, the coefficient of variation of the equivalent circle diameters of the pores is 1.3 or less, in view of improving the uniformity of the pore size, and may be 1.2 or less, 1.17 or less, or 1.15 or less. The coefficient of variation of the equivalent circle diameters of the pores is 0 or more, and may be 0.3 or more from the manufacturing point of view. The coefficient of variation of the equivalent circle diameters of the pores may be 0 or more and 1.2 or less, 0 or more and 1.17 or less, or 0.3 or more and 1.15 or less.
In the present disclosure, the coefficient of variation of the equivalent circle diameters of the pores is measured on the cross section of the metal porous body. A specific method for measuring the coefficient of variation of the equivalent circle diameters of the pores is as follows.
Procedure B1. Measure the arithmetic mean (µm) of the equivalent circle diameters of the pores, M1, in the same manner as in Procedure A1 to Procedure A7 of the method for measuring the arithmetic mean of the equivalent circle diameters of the pores, M1.
Procedure B2. Identify the first bright fields in the second image in the same manner as in Procedure A1 to Procedure A6 of the method for measuring the arithmetic mean of the equivalent circle diameters of the pores, M1. Calculate the standard deviation (µm) of the equivalent circle diameters of the first bright fields, σA, using the image analysis software ImageJ. Calculate the standard deviation (µm) of the equivalent circle diameters of the first bright fields, σA, in each of the second images obtained from the same five first images as in Procedure A7 above. Calculate an average σ1 (µm) of the standard deviations (µm) of the equivalent circle diameters of the first bright fields, σA, in the five second images. In the present disclosure, the average σ1 (µm) corresponds to the standard deviation (µm) of the equivalent circle diameters of the pores, σ1.
Procedure B3. Calculate the ratio of the standard deviation (µm) of the equivalent circle diameters of the pores, σ1, to the arithmetic mean (µm) of the equivalent circle diameters of the pores, M1, (σ1/M1), from the arithmetic mean (µm) of the equivalent circle diameters of the pores, M1, obtained in Procedure B1 and the standard deviation (µm) of the equivalent circle diameters of the pores, σ1, obtained in Procedure B2. In the present disclosure, the ratio (σ1/M1) corresponds to the coefficient of variation of the equivalent circle diameters of the pores.
It has been confirmed that even if the measurement area is changed arbitrarily, there is no variation in the measurement results as long as measurement is carried out by the above-described method on the same metal porous body.

The percentage (L1/L) × 100 is 0% or more and 2.0% or less in each of at least four of the five 4,500 µm × 3,700 µm rectangular measurement fields of view that do not overlap each other and are defined in the cross section of the metal porous body of Embodiment 1, where L1 is a distance (µm) between the center of gravity of the measurement field of view, C1, and the center of gravity of the pores based on all the pores in the measurement field of view, C2, and L is a square root L (µm) of an area of the measurement field of view. The percentage (L1/L) × 100 is an index of the deviation in the spatial distribution of the pores. More specifically, it is the index that correlates with a gap between the center of gravity of the measurement field of view, C1, and the center of gravity of the pores based on all the pores in the measurement field of view C2. The smaller the value of the percentage (L1/L) × 100, the more uniform the spatial distribution of the pores.
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, in each of at least four of the five 4,500 µm × 3,700 µm rectangular measurement fields of view that do not overlap each other and are defined in the cross section of the metal porous body.
In the present disclosure, the percentage (L1/L) × 100 is measured by the following procedures.
Procedure C1. Identify the first bright fields in the second image in the same manner as in Procedure A1 to Procedure A6 of the method for measuring the arithmetic mean of the equivalent circle diameters of the pores, M1. Identify the center of gravity of the measurement field of view, C1, of the second image (the rectangular measurement field of view of 4,500 µm × 3,700 µm) and the center of gravity of the first bright fields, C2', using the image analysis software ImageJ. The center of gravity of the first bright fields, C2', corresponds to the center of gravity of the pores, C2. In the present disclosure, the center of gravity of the pores, C, corresponds to the center of gravity of the first bright fields whose entire outer peripheries are within the measurement field of view, among the bright fields in the second image after binarization of the rectangular first image of 4,500 µm × 3,700 µm size obtained by taking the image of the cross section of the metal porous body under the microscope at a magnification of 25×.
The center of gravity of the first bright fields, C2', corresponds to the center of gravity of the first bright fields, G (x_G, y_G), which is represented by the following expression. $x_{G} = \frac{Σ x_{i} a_{i}}{Σ a_{i}}, y_{G} = \frac{Σ y_{i} a_{i}}{Σ a_{i}}$
In the above expression, a_i represents an area of each first bright field, and (x_i, y_i) represents the coordinates of the center of gravity of each first bright field.
Procedure C2. Measure the distance L1 (µm) between the center of gravity C1 and the center of gravity C2' (the center of gravity of the first bright fields, C2', corresponds to the center of gravity of the pore, C2) in the second image. Calculate the percentage of the distance L1 (µm) to the square root L (µm) of the area of the measurement field of view of the second image (4,500 µm × 3,700 µm), i.e., the percentage (L1/L) × 100.
In the present disclosure, it is determined that the spatial distribution of the pores of the metal porous body is uniform if the percentage (L1/L) × 100 is 0% or more and 2.0% or less in each of at least four of the five 4,500 µm × 3,700 µm rectangular measurement fields of view that do not overlap each other and are defined in the cross section of the metal porous body.
It has been confirmed that even if the measurement area is changed arbitrarily, there is no variation in the measurement results as long as measurement is carried out by the above-described method on the same metal porous body.

The porosity of the metal porous body of Embodiment 1 may be 40% or more and 85% or less. For the lower limit, the porosity of the metal porous body may be 60% or more, 70% or more, or 75% or more in view of increasing open pores and reducing weight. For the upper limit, the porosity of the metal porous body may be 80% or less in view of easy processing in the wire electrical discharge machining of the metal porous body. The porosity of the metal porous 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.
The porosity of the metal porous body is defined by the following expression (1). Porosity = {1 - [Mass of Metal Porous Body [g] / (Volume of Metal Porous Body [cm³] × Material Density [g/cm³])]} × 100 [%] (1)
"Volume of Metal Porous Body [cm³]" in the above expression (1) means the volume based on the external shape of the metal porous body containing pores.

The metal constituting the metal porous body of Embodiment 1 consists of: a metal consisting of a metallic element of one selected from the first group consisting of aluminum, magnesium, copper, silver, gold, iron, molybdenum, tungsten, and titanium; an alloy consisting of metallic elements of two or more selected from the first group; a metal in a composite state of metallic elements of two or more selected from the first group; an alloy consisting of metallic elements of one or more selected from the first group and elements of one or more selected from the 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 metallic elements of one or more selected from the first group and elements of one or more selected from the second group.
In the alloy consisting of metallic elements of one or more selected from the first group and elements of one or more selected from the second group, the kind of the element of the first group is different from the kind of the element of the second group. In the metal in the composite state of metallic elements of one or more selected from the first group and elements of one or more selected from the second group, the kind of the element of the first group is different from the kind of the element of the second group.
Since the above metals have high thermal conductivity, the metal porous body can also have the high thermal conductivity.
In the present disclosure, the "metal" is defined as a concept including a metal consisting of one metallic element, an alloy containing two or more metallic elements, and a metal in a composite state containing two or more metallic elements.
In the present disclosure, the "metal in a composite state of two or more metallic elements" means the state in which each of two or more metals exists as a substance, not as an alloy. Specifically, it means the state in which two or more metal powders are adhered to each other on their surfaces and formed into a shape.
In the present disclosure, in a case where the element of the second group is carbon, the "metal in a composite state of metallic elements of one or more selected from the first group and elements of one or more selected from the second group" may be the state in which metal powders of one or more selected from the first group and graphite or diamond are adhered together, or may be a carbide of metals of one or more selected from the first group. In a case where the element of the second group is boron, the "metal in a composite state of metallic elements of one or more selected from the first group and elements of one or more selected from the second group" may be the state in which metal powders of one or more selected from the first group and boron elementary powder are adhered together, or may be a boride of metals of one or more selected from the first group.
Examples of the alloy include Cu-1%Ag alloy, and Al-1%Mg-0.6%Si-0.5%Fe-0.25%Cu-0.1%Cr alloy (A6061).
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, in view of having high thermal conductivity. The alloy may be in a state in which a constituent element forms a solid solution in copper or aluminum, for example. The alloy may be in a state in which precipitates or different phases are dispersed.
The composition of the metal porous body is measured by an ICP emission analysis.
The metal porous body of Embodiment 1 may contain impurities other than the above-described metals as long as the effect of the present disclosure is not impaired. As defined above, the "metal" here intends a concept including a metal consisting of one metallic element, an alloy containing two or more metallic elements, and a metal in a composite state containing two or more metallic elements. The metal porous body of Embodiment 1 can consist of the above metal and impurities. Examples of the impurities include oxygen, hydrogen, nitrogen, sulfur, phosphorus, and metallic elements other than the metallic elements included in the first and second groups above. The impurities are included in the form of precipitates and the like independently of the mother phase. The content of the impurities may be less than the volume ratio that results in the predetermined thermal conductivity. For example, it may be 3% by atom or less. The content of the impurities is measured by a gas chromatography (GC) analysis or the ICP emission analysis.

An example of a method for manufacturing the metal porous body for a heat transfer system of Embodiment 1 is described below. The method for manufacturing the metal porous body of Embodiment 1 can include the providing step, the mixing step, the premolding step, the sintering step, and the cleaning step.

<<Providing Step>>

In the providing step, raw material powders for the metal porous body and a sodium chloride powder (NaCl powder) are provided.
Examples of the raw material powders include: a metal powder consisting of a metallic element of one selected from the first group consisting of aluminum, magnesium, copper, silver, gold, iron, molybdenum, tungsten, and titanium; an alloy powder consisting of metallic elements of two or more selected from the first group; and a powder consisting of metallic elements of one or more selected from the first group and elements of one or more selected from the second group consisting of iron, cobalt, chromium, nickel, manganese, tin, zinc, silicon, phosphorus, carbon, boron, scandium, molybdenum, tungsten, and titanium.
The median particle diameter of the above raw material powder can be 10 to 85 µm. Here, the median particle diameter of the raw material powder is the particle diameter at which the cumulative volume percentage from the small diameter side is 50% in a histogram where the horizontal axis and the vertical axis are the particle diameter and the volume percentage, respectively. The median particle diameter of the raw material powder is measured by a laser diffraction and scattering method.
The median particle diameter of the NaCl powder can be 45 to 500 µm. Here, the median particle diameter of the NaCl powder is the particle diameter at which the cumulative volume percentage from the small diameter side is 50% in a histogram where the horizontal axis and the vertical axis are the particle diameter and the volume percentage, respectively. The histogram is prepared based on the results obtained by sieving with sieves specified in JIS Z 8801-1:2019 "Test sieves - Part 1: Test sieves of metal wire cloth", and measuring the mass of the sample remaining on each sieve.

<<Mixing Step>>

Next, in the mixing step, the raw material powder and the NaCl powder are put in a plastic container and mixed to obtain a mixed powder. The mixing ratio of the raw material powder and the NaCl powder can be adjusted as appropriate according to the porosity of the metal porous body to be manufactured. For example, the percentage of the NaCl powder in the mixed powder is preferably 40 to 85% by volume.
Ethanol is dropped into the plastic container containing the mixed powder, and the resultant is stirred with a stirring rod for 5 minutes. The mixing ratio of the mixed powder and the ethanol was "mixed powder: ethanol = 10: 1 to 5:1" on a volume basis.

<<Premolding Step>>

In the premolding step, the mixed powder mixed with ethanol is then filled into a graphite mold, and premolding is performed at 15 MPa using a hand press to obtain a premolded product. The premolded product as in the graphite mold is allowed to dry naturally for 480 minutes in an organic draft chamber.

<<Sintering Step>>

In the sintering step, the graphite mold is then placed in plasma pressure sintering equipment and pressure sintering is performed to obtain a sintered body. The conditions for the pressure sintering are as follows: a temperature of 500 to 900°C, a pressure of 10 to 30 MPa, and a time of 5 to 10 minutes.

<<Cleaning Step>>

Then, in the cleaning step, the sintered body is immersed in water, to elute NaCl with the water. Specifically, about 1 L of pure water is provided per 10 g of the sintered body. The pure water is poured into a beaker, and the sintered body is immersed in the pure water, followed by stirring. By immersing it for a total of about 50 hours while changing the pure water every 5 hours, the NaCl is sufficiently eluted outside the sintered body.
The sintered body after immersing in the pure water is then placed on a hot plate heated to 180°C, and dried to remove the moisture. If any sodium chloride remains, water is dropped with a dropper while heating as appropriate, so that the remaining sodium chloride is removed by the power of evaporation.
The sintered body dried on the hot plate is then ultrasonically cleaned for 10 minutes and dried. This results in the metal porous body of Embodiment 1.
In the mixing step in the above-described manufacturing method, ethanol is dropped on the mixed powder, followed by mixing. The present inventors have newly found that the mixing the mixed powder with the ethanol dropped thereon improves the uniformity of the pore sizes, and the uniformity of the spatial distribution of the pores in the resulting metal porous body. The reason is not clear, but can be deduced as follows.
As NaCl is insoluble in ethanol, its particle shape can be maintained during the mixing step. The area of the NaCl in the premolded product corresponds to the area of the pores in the metal porous body. When the NaCl maintains its particle shape in the premolded product, the uniformity of the pore size and the uniformity of the spatial distribution of the pores in the metal porous body are improved.
The surface tension of ethanol can cause the NaCl powder and the raw material powder to adhere. Therefore, even in the premolded product, the NaCl powder and the raw material powder do not separate and the state in which the NaCl and raw material powder are mixed is easily maintained, to improve the uniformity of the pore size and the uniformity of the spatial distribution of the pores in the metal porous body.
Furthermore, the use of ethanol provides the following benefits. Ethanol has favorable drying properties, so the time required for natural drying in the premolding step can be reduced. Ethanol does not remain as impurities, so the sintering can be achived without altering the framework of the metal porous body.

EXAMPLES

The present embodiment will be described in more specifically by way of Examples. However, the present embodiment is not limited to these Examples.

[Preparation of Metal Porous Body]

<<Providing Step>>

In each sample, an aluminum powder or a copper powder as the raw material powder, and a sodium chloride powder were provided. The median particle diameters of these powders used for each sample are as described in the columns "Raw Material Powder" and "NaCl powder" of Table 1.

<<Mixing Step>>

The raw material powder and the NaCl powder were put into a plastic container and mixed to obtain a mixed powder. The content of each of the raw material powders and the NaCl powders in the mixed powders is shown in the column "Mixed powder" of Table 1. The upper row in each cell shows the content in % by mass, and the lower row in each cell shows the content in % by volume.
Ethanol in Sample 1 to Sample 9 and water in Sample 1-1 and Sample 1-2 were then dropped into the plastic container containing the mixed powder, and the resultant was stirred with a stirring rod for 5 minutes. The mixing ratio of the mixed powder and the ethanol or the water was "mixed powder: ethanol or water = 10:1" on a volume basis. In Sample 1-3, any of ethanol and water was not dropped.

<<Premolding Step>>

For Sample 1 to Sample 9 and Sample 1-1 and Sample 1-2, the mixed powder after the mixing step was filled into a graphite mold of 42 mm ϕ and premolding was performed at 15 MPa using a hand press to obtain a premolded product. The premolded product as in the graphite mold was allowed to dry naturally for 480 minutes in an organic draft chamber.
For Sample 1-3, the Cu powder and the NaCl powder for the mixed powder failed to be uniformly mixed, and thus separated from each other, and therefore a premolded product failed to be prepared.

<<Sintering Step>>

The graphite mold was placed in the plasma pressure sintering equipment and the pressure sintering was performed at a pressure of 30 MPa and a temperature of 700°C for 8 minutes, to obtain a sintered body.

<<Cleaning Step>>

The sintered body was immersed in water to elute NaCl with the water. Specifically, the sintered body was placed in a beaker containing 200 ml of water and left for 480 minutes.
The sintered body after immersing in the pure water was then placed on a hot plate heated to 180°C, and dried to remove the moisture. If any sodium chloride remained, water was dropped with a dropper while heating as appropriate, so that the remained sodium chloride was removed by the power of evaporation.
The sintered body dried on the hot plate was then ultrasonically cleaned for 10 minutes and dried. This results in the metal porous body of each sample.

[Table 1]

Table 1

Sample No.	Raw material powder		NaCl powder	Mixed powder		Mixing	Sintering
	Composition	Median particle diameter	Median particle diameter	Raw material powder	NaCl powder	Solution added	Pressure	Temperature	Time
	Composition	µm	µm	% by mass (% by volume)	% by mass (% by volume)	Solution added	MPa	°C	Min.
1	Al	13	75	45.5 (40)	54.5 (60)	Ethanol	30	700	8
2	Al	13	200	34.9 (30)	65.1 (70)	Ethanol	30	700	8
3	Al	13	200	18.1 (15)	81.9 (85)	Ethanol	30	700	8
4	Al	13	500	34.9 (30)	65.1 (70)	Ethanol	30	700	8
5	Cu	75	75	73.3 (40)	26.7 (60)	Ethanol	30	700	8
6	Cu	75	200	64 (30)	36.0 (70)	Ethanol	30	700	8
7	Cu	75	200	42.1 (15)	57.9 (85)	Ethanol	30	700	8
8	Cu	75	500	64.0 (30)	36.0 (70)	Ethanol	30	700	8
9	Cu	85	500	42.1 (15)	57.9 (85)	Ethanol	30	700	8
10	Cu	75	75	77.1 (45)	22.9 (55)	Ethanol	30	700	8
11	Cu	75	75	86.1 (60)	13.9 (40)	Ethanol	30	700	8
12	Al	13	75	50.6 (45)	49.4 (55)	Ethanol	30	700	8
13	Al	13	75	65.2 (60)	34.8 (40)	Ethanol	30	700	8
1-1	Al	13	500	34.9 (30)	65.1 (70)	Water	30	700	8
1-2	Cu	75	500	64.0 (30)	36.0 (70)	Water	30	700	8
1-3	Cu	75	500	64.0 (30)	36.0 (70)	None	Failure in manufacture of premolded product

[Evaluation of Metal Porous Body]

The composition, the arithmetic mean of the equivalent circle diameters or the pores, M1, the coefficient of variation of the equivalent circle diameters of the pores, the percentage (L1/L) × 100, and the porosity were measured for the metal porous bodies obtained. The measurement method of each item is as described for Embodiment 1. The results are shown in Table 2.
The values in the column "Percentage (L1/L) × 100" in Table 2 indicate the fourth smallest value when the percentage (L1/L) × 100 of the five measurement fields of view are listed from smallest to largest. Namely, the percentage (L1/L) × 100 of at least four among the five measurement fields of view are equal to or less than the value shown in the column "Percentage (L1/L) × 100". For example, in Sample 1, the percentages (L1/L) × 100 of at least four among the five measurement fields of view are each 1.2% or less.

[Table 2]

Table 2

Sample No.	Metal porous body
	Composition	Pores			Porosity
		Arithmetic mean of equivalent circle diameters, M1	Coefficient of variation of equivalent circle diameters	Percentage (L1/L)x100	Porosity
		µm	Coefficient of variation of equivalent circle diameters	%	%
1	Al	70	1.2	1.2	60
2	Al	125	1.1	1.5	70
3	Al	206	0.9	1.2	85
4	Al	450	1.2	1.1	70
5	Cu	56	0.8	1.3	60
6	Cu	150	1.2	1.5	70
7	Cu	224	1.1	1.4	85
8	Cu	373	0.9	1.0	70
9	Cu	495	1.1	1.1	85
10	Cu	57	0.8	1.2	55
11	Cu	72	0.8	1.3	40
12	Al	66	0.9	1.1	55
13	Al	65	1.0	1.1	40
1-1	Al	221	3.2	2.7	70
1-2	Cu	191	2.5	3.5	70
1-3	Failure in manufacture

The metal porous bodies of Sample 1 to Sample 13 correspond to Examples. It was confirmed that the metal porous bodies of Sample 1 to Sample 13 had improved uniformity of the pore size and improved uniformity of the spatial distribution of the pores in the metal porous body.
The metal porous bodies of Sample 1-1 and Sample 1-2 correspond to Comparative Examples. It was confirmed that the metal porous bodies of Sample 1-1 and Sample 1-2 had non-uniform pore sizes, and non-uniform spatial distribution of the pores in the metal porous body. For Sample 1-1 and Sample 1-2, it is inferred that the NaCl powder was dissolved in the water dropped into the mixed powder in the mixing step, and that thus the resulting metal porous bodies were non-uniform in the pore size and the spatial distribution of the pores.
In Sample 1-3, the Cu powder and the NaCl powder failed to be mixed uniformly in the mixed powder, and they separated from each other. Therefore, a premolded product failed to be prepared, to result in failure in obtaining the metal porous body.
Although the embodiments and Examples of the present disclosure have been described as above, it has also been contemplated from the outset that the configurations of the embodiments and Examples described above may be combined as appropriate and modified in various ways.
The embodiments and Examples disclosed herein are illustrative in all respects and should not be considered to be restrictive. The scope of the present invention is indicated by the claims, and not by the embodiments and Examples described above, and is intended to also include the scope of the meaning equivalent to the claims as well as all modifications within the scope.

Claims

A metal porous body composed of a metal in which a plurality of pores is formed;
wherein
an arithmetic mean of equivalent circle diameters of the pores, M1, is 50 µm or more and 500 µm or less, and

a coefficient of variation of the equivalent circle diameters of the pores is 0 or more and 1.3 or less,

wherein

the arithmetic mean of the equivalent circle diameters of the pores, M1, and the coefficient of variation of the equivalent circle diameters of the pores are measured on a cross section of the metal porous body,

the coefficient of variation of the equivalent circle diameters of the pores is a ratio of a standard deviation of the equivalent circle diameters of the pores, σ1, to the arithmetic mean of the equivalent circle diameters of the pores, M1, (σ1/M1) and

units of the arithmetic mean M1 and the standard deviation σ1 are each µm; and

a percentage (L1/L) × 100 is 0% or more and 2.0% or less in each of at least four of five 4,500 µm × 3,700 µm rectangular measurement fields of view that do not overlap each other and are defined in the cross section of the metal porous body, where L1 is a distance between the center of gravity of the measurement field of view, C1, and the center of gravity of the pores based on all the pores in the measurement field of view, C2, and L is a square root of an area of the measurement field of view,

wherein

units of the square root L and the distance L1 are each µm.
The metal porous body according to claim 1, wherein a porosity of the metal porous body is 40% or more and 85% or less.
The metal porous body according to claim 1 or 2, wherein the metal is:
a metal consisting of a metallic element of one selected from the first group consisting of aluminum, magnesium, copper, silver, gold, iron, molybdenum, tungsten, and titanium;

an alloy consisting of metallic elements of two or more selected from the first group;

a metal in a composite state of metallic elements of two or more selected from the first group;

an alloy consisting of metallic elements of one or more selected from the first group and elements of one or more selected from the 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 metallic elements of one or more selected from the first group and elements of one or more selected from the second group.
The metal porous body according to any one of claims 1 to 3, wherein the coefficient of variation of the equivalent circle diameters of the pores is 0 or more and 1.2 or less.
The metal porous body according to any one of claims 1 to 4, wherein the percentage (L1/L) × 100 is 0% or more and 1.5% or less in each of at least four of the five 4,500 µm × 3,700 µm rectangular measurement fields of view that do not overlap each other and are defined in the cross section of the metal porous body, where L1 is the distance between the center of gravity of the measurement field of view, C1, and the center of gravity of the pores based on all the pores in the measurement field of view, C2, and L is the square root of the area of the measurement field of view.