JP5825598B2 - Metal porous body and method for producing metal porous body. - Google Patents

Description

The present invention relates to a metal porous body and a method for producing a metal porous body.
About.

  A metal porous body is expected to be used in a wide range of industrial fields because it has both the heat resistance, electrical conductivity, and thermal conductivity of a metal and the large specific surface area, light weight, and fluid permeability of the porous body.

  Although the required characteristics differ depending on the application, when light weight and fluid permeability are required, the porous body needs to have a high porosity. Further, when a large specific surface area is required, a fine pore diameter is required.

  As for the relationship between the porosity and the pore diameter of the metal porous body that has been announced, there has been no porous metal having a porosity of 55% or more and an average pore diameter of 0.15 mm or less, and a method for producing the same (Non-Patent Document). 1).

  Conventionally, a method for producing a porous body having a pore size about a fraction of the size of powder particles to be used by forming a powder of a predetermined material and sintering it at a temperature lower than the densification temperature is known. The obtained metal porous body is used for a filter or the like. However, with this method, the porosity is 40% or less.

  For this reason, there has been proposed a method for obtaining a mean pore diameter of 2 μm and a porosity of about 50% by mixing a pore-forming agent that burns away in the firing process in such a technique to increase the porosity (Patent Document 1). Moreover, a method for producing a microporous nickel porous body by preparing a nickel-manganese alloy and selectively dissolving and removing only manganese in an aqueous solution after molding has been proposed (Patent Document 2). However, although the porous body produced by these techniques can obtain a fine pore diameter, the porosity is at most about 50%.

  The following is known as a method for producing a metal porous body having a higher porosity.

  A method for producing a porous metal body obtained by mixing a molten metal and a foaming agent such as titanium hydride and extruding from a heated cylinder (Patent Document 3).

  A method for producing a high porosity porous body prepared by mixing metal powder, a water-soluble polymer, and a hydrocarbon-based foaming agent, gelling, foaming, and then sintering (Patent Document 4).

  A high-strength sponge by forming a foamed slurry by adding surfactant and volatile organic solvent to a slurry consisting of water-soluble resin binder, plasticizer, and water, with a uniform particle size and nickel oxide. (Patent Document 5) A method for producing a cylindrical porous metal plate.

  A coating containing at least one kind of fine particles selected from oxide, carbide and nitride particles is applied to the skeleton surface of a three-dimensional network resin porous body having continuous pores formed by resin foaming, and A method for producing a porous metal body, in which fine metal particles are dispersed in a plating layer by further heat treatment after forming a metal plating layer such as Ni on the coating film (Patent Document 6).

  However, these methods all utilize foaming, and a material having a porosity exceeding 80% can be easily prepared. However, since the foaming phenomenon is utilized, the pore diameter is the size of the generated foam. The size of the typical pores was limited to a few hundred μm to several mm.

  As a method for producing a high-porosity porous body that does not use foaming, a method has been proposed in which a porous metal is produced by depositing chips generated during machining and sintering (Patent Document 7). Although this method can also obtain a high-porosity porous body, since the chip size is on the order of mm, the pore diameter is several hundred μm.

  On the other hand, as a method for producing a ceramic porous body, a slurry in which ceramic powder is dispersed in an aqueous solution of a water-soluble polymer that can be gelled is gelled, frozen, thawed, dried and sintered, and has a communication hole of 10 μm to 300 μm. A method for producing a ceramic porous body having a porosity of 72% to 99% has been proposed (Patent Document 8). In this method, a ceramic sintered body having a high porosity and a pore diameter of 100 μm or less can be produced, but it was difficult to directly apply to a metal having a higher density and inferior oxidation resistance as compared with ceramics.

JP 2003-526006 A JP 2010-144246 A JP 2004-35961 A Japanese Patent No. 3858096 JP-A-11-269506 Japanese Patent Laid-Open No. 7-150270 JP 2003-105406 A JP 2008-201636 A

Research report on the possibility of using porous metals (March 2006) Japan Mechanical Systems Promotion Association

  As described above, a porous metal body having both a high porosity and a small average pore diameter, specifically, for example, a metal porous body having a porosity of 55% or more and an average pore diameter of 0.15 mm or less. No body has been reported, nor has the technology for its manufacture been established. However, as the performance of filters, heat exchange parts, and battery electrodes is improved, a porous metal body having a fine average pore diameter and a high porosity is desired.

  Therefore, in view of the above-mentioned problems of the prior art, the present invention aims to provide a metal porous body having both a high porosity of 55% or more and 99% or less and an average pore diameter of 0.001 mm or more and 0.15 mm or less. To do.

The present invention is a porosity of 99% or less than 55% and an average pore diameter of Ri der than 0.15mm below 0.001 mm, to provide a metal porous body and having a micro-honeycomb structure.
The present invention also provides a metal porous body having a sponge-like structure having a porosity of 55% or more and 99% or less and an average pore diameter of 0.001 mm or more and 0.15 mm or less. To do.

  According to the present invention, the porous metal body has both a high porosity and a small average pore diameter. For this reason, it can be set as the metal porous body which made the heat resistance, electrical conductivity, and heat conductivity which a metal has and the large specific surface area which a porous body has, lightweight property, and fluid permeability compatible.

Flow diagram of a method for producing a metal porous body according to the second embodiment of the present invention SEM image of porous metal body according to Example 1 of the present invention SEM image of porous metal body according to Example 2 of the present invention SEM image of porous metal body according to Example 3 of the present invention Appearance photograph of porous metal body according to Example 3 of the present invention SEM image of porous metal body according to Example 4 of the present invention

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and the following embodiments are not departed from the scope of the present invention. Various modifications and substitutions can be made.
[First Embodiment]
In this embodiment, the metal porous body of the present invention will be described.

  The porous metal body of the present invention is characterized in that the porosity is 55% or more and 99% or less, and the average pore diameter is 0.001 mm or more and 0.15 mm or less.

  As described above, the porosity of the metal porous body of the present invention is preferably 55% or more and 99% or less. This means that the higher the porosity, the lighter the light and the higher the fluid permeability.However, if the porosity is too high, the strength of the material will be extremely lowered, so the balance between the strength of the metal porous body and the required performance will be balanced. The above range is more preferable in consideration. In particular, from the viewpoint of lightness, fluid permeability, and material strength, it is more preferably 70% or more and 90% or less.

  The porosity can be adjusted, for example, by adjusting the amount of water-soluble polymer aqueous solution added in the production method described later, and can be in the above range.

  As described above, the average pore diameter of the metal porous body of the present invention is preferably 0.001 mm or more and 0.15 mm or less. This is because it is preferable that the average pore diameter is smaller because the specific surface area of the metal porous body is higher, but if it is less than the lower limit, the fluid permeability deteriorates. The average pore diameter is more preferably 0.005 mm or more and 0.13 mm or less, and particularly preferably 0.005 mm or more and 0.1 mm or less from the viewpoint of specific surface area and fluid permeability.

  The average pore diameter can be adjusted by, for example, the freezing temperature of the slurry and the time required for freezing in the production method described later, and can be within the above range.

  In the metal porous body of this invention which concerns, the high porosity which was not able to be achieved conventionally and the small average pore diameter can be made compatible. For this reason, the heat resistance, electrical conductivity, and thermal conductivity of metals can be combined with the large specific surface area, lightness, and fluid permeability of porous materials, and these characteristics are required, such as filters and reactors. It can be preferably used for applications such as a catalyst carrier, a solid catalyst, a shock absorber, a lightweight material, a heat exchange component, and a battery electrode.

  The metal porous body of the present invention is not particularly limited with respect to the shape and structure of the pores therein, but preferably has communication holes. This is because the fluid can pass through the porous metal body by having the communication hole. The open porosity, which is an index of communication, is preferably 70% or more, more preferably 90% or more, and particularly preferably 95% or more.

  The porous metal body of the present invention preferably has a micro honeycomb structure. This is a honeycomb in a broad sense, and the shape of the opening may be a polygon or a circle such as a rectangle or a hexagon, and a collection of hole arrays, that is, the pores of the porous body have orientation. It has a shape in which openings are arranged in one section. By having such a structure, the strength of the metal porous body can be increased. Moreover, since the pores have orientation, the fluid permeability can be increased, which is preferable.

The porous metal body of the present invention preferably has a sponge-like structure. That is, it preferably has a spongy structure. By having such a shape, the specific surface area of the metal porous body can be increased, which is preferable.
[Second Embodiment]
In the present embodiment, a method for producing a porous metal body of the present invention will be described.

  The metal porous body of the present invention can be produced by a method for producing a metal porous body having the following steps. Thereby, the metal porous body demonstrated in 1st Embodiment can be obtained.

  A porous metal body can be produced by the flow shown in FIG. 1, and specifically includes the following steps.

A slurry preparation step of dispersing a metal raw material powder in a water-soluble polymer aqueous solution capable of gelation;
A gelation step of gelling the slurry obtained in the slurry adjustment step;
A freezing step of freezing the gel obtained in the gelation step;
A drying step of removing ice from the frozen body to obtain a dried body;
A degreasing step of heating and drying the dried body in an inert gas;
An oxidative atmosphere degreasing step of degreasing by heating in an oxidative atmosphere;
A method for producing a porous metal body, comprising: a sintering step.

  First, the slurry preparation process which disperse | distributes metal raw material powder to the water-soluble polymer aqueous solution which can be gelatinized is demonstrated. This corresponds to the step of mixing and dispersing the metal raw material powder in the water-soluble polymer (aqueous solution) in FIG.

  Here, the water-soluble polymer used for the gelable water-soluble polymer aqueous solution is not particularly limited, but the water-soluble polymer aqueous solution gels under a predetermined condition and can be frozen. Can be preferably used. In particular, a material that gels by adding the catalyst or cooling the aqueous polymer aqueous solution is preferable. As specific water-soluble polymers, for example, polyethyleneimine, agar, and gelatin can be preferably used.

  Also, the metal raw material powder is not particularly limited, and various metals can be used. However, from the viewpoint of operability, it is preferably a metal that does not react (oxidize) rapidly even when contacted with water, and can be easily reduced even when oxidized, or on the metal surface during sintering. The resulting oxide film is preferably a metal that does not inhibit sintering.

  Specifically, for example, noble metal powders such as gold, platinum, palladium, silver, alloy powders thereof, nickel, copper, or alloys thereof, stainless steel, cemented carbide, tool steel, high speed steel, titanium alloy And the like. Further, an oxide powder can be used as long as it becomes a metal by performing a reduction treatment. In this case, in order to make the oxide powder a metal, it is preferable to perform a reduction treatment after an oxidizing atmosphere degreasing step described later.

  Since the volume fraction of the metal raw material powder and the water-soluble polymer aqueous solution in this step is the porosity of the molded body, the mixing ratio and addition amount of both can be selected according to the target porosity. Specifically, the porosity after sintering is preferably adjusted to be 55% or more and 99% or less, and the porosity is preferably adjusted to be 70% or more and 90% or less. By adjusting the porosity so as to be in such a range, the obtained porous metal body can ensure the strength of the material while improving the lightness and fluid permeability. In order to obtain a structure having communication holes as the metal porous body, it is preferable to reduce the amount of metal raw material powder added, that is, to increase the porosity. This is because when the amount of the metal raw material powder is increased, the pores are easily blocked and are not easily formed as communication holes.

  The amount of the water-soluble polymer that can be gelled is not limited because it varies depending on the material used, etc., and depending on the amount of water added, the slurry obtained by mixing can be gelled. What is necessary is just to add.

  When the particle size of the metal raw material powder is sufficiently small and the metal powder does not settle before it gels after being dispersed in the water-soluble polymer aqueous solution, that is, for example, when it becomes a colloidal solution, only the above materials are used. Can be implemented. However, when the metal powder settles before it gels after being dispersed in the water-soluble polymer aqueous solution, a thickener is added (to the slurry) in the slurry preparation process as shown by the dotted line in FIG. It is preferable to do.

  The thickener is not particularly limited as long as it can increase the viscosity of the slurry, and polyvinyl alcohol compounds, cellulose compounds, polysaccharides, and the like can be preferably used. Specifically, for example, methyl cellulose or starch can be used. Further, the amount of addition varies depending on the type of thickener and metal raw material powder used, the particle size, etc., and is not limited until the slurry is gelled according to the state of the metal raw material powder in the slurry. During this period, an amount that does not allow the metal raw material powder to settle in the aqueous solution can be selected and added.

  In addition to the above components, various additives can be added to the slurry. Specifically, for example, a material that lowers the freezing point such as aluminum nitrate can be added.

  This is because the pore shape of the porous metal body depends on the shape of ice crystals generated in the freezing process, which will be described later. It will not become. For this reason, when it is set as a metal porous body, a part of pore is obstruct | occluded and it can be set as the metal porous body which made the open porosity 20% or less.

  In addition, a component that does not inhibit the sintering and can suppress the grain growth of the metal component, specifically, for example, alumina, zirconia, magnesia, or the like can be added. Since these can suppress the growth of metal grains, the size of the particles constituting the metal porous body can be reduced, and the strength of the entire metal porous body can be increased.

  Next, the gelation process and the freezing process will be described. The steps are a step of gelling and freezing the slurry obtained in the slurry adjustment step, respectively.

  Prior to gelling and freezing the slurry, it is preferable to put the slurry in a predetermined container so as to have the shape of the intended porous metal body. In this case, the container to be used is not particularly limited as long as it can hold the slurry for a certain period of time, that is, not soaked with water. A tall container is preferred. For example, a metal container, a resin container (plastic container), etc. can be used. As for the shape, those according to the shape of the intended porous body can be used.

  Moreover, when manufacturing a thin plate-shaped thing as a metal porous body, it is preferable to perform the gelatinization and freezing process, for example after carrying out the tape casting of the slurry obtained at the slurry adjustment process.

  That is, the gelation step can be performed after the slurry is formed into a tape shape by the doctor blade method.

  The gelation step varies depending on the type of water-soluble polymer to be used, but gelates by adding a catalyst or cooling at a temperature of 0 ° C. or higher.

  In the freezing step, the temperature at which the gel is frozen is not particularly limited, but is preferably cooled to a temperature range of -10 ° C to -80 ° C. Specific freezing means is not limited, and for example, a low temperature bath, a freezer, etc. can be used.

  Due to the freeze-concentration phenomenon during freezing, the metal raw material powder and the gelling agent in the gel are pushed out of the ice, and the metal raw material powder and the like concentrate in a wall shape so as to surround the columnar ice crystals. When the freezing temperature is high, the ice crystals are large, so the pore diameter is large. Conversely, when the freezing temperature is lowered, the ice crystals are fine, and the average pore diameter of the metal porous body is equivalent to that.

  In addition, the cooling rate during freezing also affects the average pore size of the metal porous body. This is because, for example, when the entire slurry is uniformly and rapidly cooled to a low temperature, a large number of ice nuclei are generated, and the growth rate of the nuclei is slowed, so that a uniform metal porous body with a small average pore diameter is produced. Because it can.

  For this reason, in order to control the average pore diameter of the metal porous body, it is preferable to select and control the cooling temperature and the cooling rate, and the average pore diameter of the metal porous body is 0.001 mm to 0.15 mm. It is preferable to select the cooling rate and the cooling temperature. This is because it is preferable that the average pore diameter is smaller because the specific surface area of the metal porous body is higher, but if it is less than the lower limit, the fluid permeability deteriorates. In particular, it is more preferable to select the cooling rate and the cooling temperature so that the average pore diameter is 0.005 mm to 0.13 mm, and the average pore diameter is selected to be 0.005 mm to 0.1 mm. It is particularly preferable to do this.

  In addition, since the pore structure changes depending on the cooling direction during freezing, it is preferable to select the cooling direction according to the required porous structure. For example, in order for the metal porous body to have a micro honeycomb structure, it is preferable to cool and freeze from one direction. This is because, as described above, the shape of the pores of the porous metal body depends on the shape of ice that is generated when the slurry is gelled and frozen, and when ice is cooled from one direction, the ice is oriented along the cooling direction. Grow with sex. That is, columnar ice grows, which acts as a pore-forming agent as described above.

  When cooled from a plurality of directions or when the cooling rate is not uniform, the pore structure and the average pore diameter are not uniform and vary.

  In addition, when the porosity is high for a low cooling temperature (when the amount of added metal raw material powder is small), the wall material (metal) that forms the pores is insufficient, so that the wall portion cannot be sufficiently formed. Since a hole is formed in the surface, a sponge structure tends to be formed.

  When the gel is frozen, the volume is expanded because water is frozen. Therefore, when freezing in a mold or the like, the part to be frozen last, for example, when cooling in one direction, the end opposite to the part being cooled is cooled in two directions. A singular point having a structure different from that of the other part is generated at the point (part) where ice is generated and collides from the direction. For this reason, when it is necessary to remove the singular point (the part that freezes last), the cooling direction can be selected so that the place where the singular point occurs does not affect the product (for example, the end). preferable.

  Next, a drying process for removing ice from the frozen body to obtain a dried body will be described.

  The frozen gel is dried so as not to melt the ice. The drying method is not particularly limited as long as it can be removed without melting the ice, and examples thereof include humidity drying, freeze drying, or a method of replacing ice with a solvent.

  Humidity-controlled drying is a method of removing moisture while adjusting humidity in a freezer, and freeze-drying is a method of sublimating and removing only moisture while reducing the pressure in a frozen state. The method of replacing ice with a solvent is a method in which a frozen sample is placed in an organic solvent cooled to below the melting point of ice (0 ° C. or less), and water and the organic solvent are replaced. Any organic solvent may be used as long as it has a freezing point of 0 ° C. or lower. For example, acetone can be used.

  Then, the degreasing process which heats a dry body in inert gas and removes organic substance will be performed.

  The degreasing step is a step of removing the gelling agent and thickener remaining in the dried body, and the heating temperature is not limited, but the temperature is higher than the boiling point of these components contained in the dried body. It is preferable to carry out the heating at a high temperature. For example, it is preferable to raise the temperature to 600 ° C. or higher and hold it for a certain time.

  This step is preferably performed in an inert gas atmosphere since heating in the air causes combustion of the gelling agent and oxidation of the metal powder, and a sound molded body cannot be obtained. The inert gas is not particularly limited as long as the metal component does not react. For example, nitrogen, argon, helium, or the like can be used.

  Moreover, since it is preferable to discharge | emit the gas containing the organic component generated at this time out of the system, it is preferable to carry out in an inert gas stream.

  Next, an oxidative atmosphere degreasing step is performed in which defatting is performed by heating in an oxidizing atmosphere.

  This is because the organic component (carbon-containing component) may not be sufficiently removed only by the degreasing step of heating and degreasing in an inert gas, which may inhibit the sintering. For this reason, it is a process of removing an organic component reliably by performing an oxidation atmosphere degreasing process.

  The oxidizing gas used at this time may contain oxygen, and for example, air, a mixed gas of oxygen and an inert gas, oxygen, or the like can be used. This step is also preferably performed in an oxidizing gas stream.

The heating temperature here is not particularly limited. However, since the metal component may be oxidized, it is preferably performed at a lower temperature among the temperatures at which the organic component is oxidized. It is particularly preferred to carry out at the lowest temperature at which it is oxidized. For example, the temperature can be easily calculated by measuring thermogravimetric analysis and differential thermal analysis (TG / DTA) in advance in an oxygen atmosphere with respect to the sample. ) Is oxidized, or when an oxide component is contained in the sample, as shown by a dotted line in FIG. 1, in a reducing atmosphere between the oxidizing atmosphere degreasing step and the sintering step described later. It is preferable to perform a reduction process in which a heat treatment is performed in the reduction process. The reduction process is a process in which a heat treatment is performed in a reducing atmosphere. The oxide is reduced to a metal. Moreover, also when an oxide powder is contained in the metal raw material powder, it can be reduced to a metal by this step.

  The heating conditions in this case are not particularly limited, and may be performed under a temperature that is not higher than the temperature at which the sample is densified and that can sufficiently reduce the oxide contained in the sample. Specifically, for example, exhaust gas generated from a heating furnace is monitored, and after the generation of a product due to the reduction reaction ceases, the reaction may be terminated after a predetermined time has elapsed.

  If the sintering process is performed without performing this step when the metal component (metal raw material) in the sample is oxidized, the sample may not sinter or may crack, but this step is performed. Thus, the occurrence of such a phenomenon can be prevented. However, this step is not necessary in the case of a metal that hardly oxidizes, such as a noble metal, or a metal whose oxide film does not affect the sintering.

  Next, the sintering process is not limited as long as the sintering conditions are selected according to the metal component used. However, if the temperature is too high, the pores produced by the previous steps will be blocked, so it is preferable to perform the sintering step at a lower temperature among the sinterable temperatures. Such temperature can be calculated by conducting a preliminary experiment or the like in advance.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to the Example which concerns.
[Example 1]
First, as a slurry preparation step, gelatin is used as a gelling agent, and after making an aqueous solution, copper powder (particle size 0.5 μm) is added as a metal raw material powder so as to be 10% by volume with respect to water. For 5 minutes. Methyl cellulose was added as a thickener so that it might become 1 weight% with respect to the water contained in aqueous solution.

  Next, as a gelling step and a freezing step, the slurry is cast into a resin mold and gelled in a refrigerator maintained at 7 ° C. Then, as shown in Table 1, a low temperature bath of −40 ° C. is used. It was frozen by cooling from one direction.

  After freezing, the sample was removed from the mold, and then freeze-dried as a drying step.

  After the drying process, as a degreasing process, the dried product was heated in a nitrogen stream at 600 ° C. for 2 hours to remove organic substances.

  Subsequently, as an oxidative atmosphere degreasing step, heating was performed in an air stream at 300 ° C. for 10 hours to remove residual carbon and the like.

  Thereafter, a reduction process was performed at 500 ° C. for 4 hours in a hydrogen-nitrogen mixed gas stream as a reduction process, and a sintering process was performed at 600 ° C. as a sintering process. The SEM image of the obtained metal porous body is shown in FIG. Further, Table 1 shows the porosity and average pore diameter of the obtained metal porous body.

  In this example, the porosity was calculated from the compact density calculated from the metal raw material powder and water volume fraction, and the volume shrinkage calculated by measuring the length of the sample after the sintering step. . Specifically, in this example, since the metal raw material powder is added in an amount of 10% by volume with respect to water, the density of the compact is 10% (porosity 90%). When the size when the slurry was put into the mold was compared with the size after the sintering process, it was confirmed that 50% volume contracted after the sintering process. For this reason (since the mass of the metal raw material powder does not change and the volume is halved), the sintered density is 20% and the porosity is 80%. The same calculation was performed in other examples.

  For the average pore diameter, 200 aperture diameters were measured by image analysis on a photograph of a cross section perpendicular to the freezing direction observed by SEM, and the average pore diameter was calculated. The average pore diameter was measured in the same manner in the other examples.

  2A shows a cross-sectional image when FIG. 2A is cut along a plane perpendicular to the freezing direction, and FIG. 2B shows a cross-sectional image when cut along a plane parallel to the freezing direction. 2A shows that a plurality of openings having substantially the same shape are arranged, and in FIG. 2B, the pores are arranged in a straight line. Therefore, it was confirmed that the porous metal body of this example had a micro honeycomb structure.

Further, as shown in Table 1, it was confirmed that the porous metal body of the present example had a high porosity of 80%, and the average pore diameter was as small as 30 μm.
[Example 2]
In this example, a porous metal body was produced in the same manner as in Example 1 except that the temperature of the low temperature bath at the time of freezing the gel in the freezing step was −60 ° C. The SEM image of the obtained metal porous body is shown in FIG. Further, Table 1 shows the porosity and average pore diameter of the obtained metal porous body.

  According to FIG. 3, it was confirmed that it had a sponge-like structure.

  This is because the average pore diameter is small because the cooling temperature is lower than that in Example 1, and the material of the metal component that forms the pores is insufficient, so that the shape of the hole is not the microhoneycomb structure as in Example 1. Is considered to have a random sponge-like structure.

Further, as shown in Table 1, it was confirmed that the porous metal body of the present example had a high porosity of 80%, and the average pore diameter was as small as 10 μm.
[Example 3]
In this example, nickel powder (particle size 0.5 μm) was used as the metal raw material powder, the nickel powder was added at 5% by volume with respect to water, and the temperature at which the gel was frozen in the freezing step was −10 ° C. A porous metal body was produced in the same manner as in Example 1 except that the sintering temperature was 750 ° C. FIG. 4 shows an SEM image of the obtained porous metal body, and FIG. 5 shows an external appearance photograph of the obtained porous metal body. Further, Table 1 shows the porosity and average pore diameter of the obtained metal porous body.

  From the SEM image, it was confirmed that the metal porous body of this example had a micro honeycomb structure.

As shown in Table 1, it was confirmed that the porous metal body of the present example had a high porosity of 90%, and the average pore diameter was 120 μm.
[Example 4]
In this example, a porous metal body was produced in the same manner as in Example 3 except that the temperature of the low-temperature bath at the time of freezing the gel in the freezing step was −75 ° C. The SEM image of the obtained metal porous body is shown in FIG. Further, Table 1 shows the porosity and average pore diameter of the obtained metal porous body.

  In FIG. 6, FIG. 6A shows a cross-sectional image when cut along a plane perpendicular to the freezing direction, and FIG. 6B shows a cross-sectional image when cut along a plane parallel to the freezing direction. 6A and 6B that the openings are randomly arranged. From this result, it was confirmed that the metal porous body of this example had a sponge-like structure.

  This is because, in the metal porous body of this example as well as in Example 2, the cooling temperature is lower than that of Example 3 and the amount of added metal raw material powder is further reduced. It is considered that the metal component forming the wall of the porous body was insufficient, resulting in a sponge-like structure.

Further, as shown in Table 1, it was confirmed that the porous metal body of the present example had a high porosity of 90%, and the average pore diameter was as very small as 8 μm.
[Comparative Example 1]
In this comparative example, a porous metal body was produced in the same manner as in Example 1 except that the oxidizing atmosphere degreasing process was not performed. In other words, a metal porous body was not obtained.

This is presumably because the thickener and the like remained in the sample even in the sintering step, and the sintering was hindered.
[Comparative Example 2]
In this comparative example, the metal porous body was produced in the same manner as in Example 3 except that the thickener was not added. However, the slurry cast into the resin mold in the gelation step was gelled. Previously, the metal powder settled and the sample could not be prepared.

Claims (7)

In porosity of 99% or less than 55% and an average pore diameter of Ri der than 0.15mm below 0.001 mm, metal porous body and having a micro-honeycomb structure.   A porous metal body having a sponge-like structure having a porosity of 55% to 99% and an average pore diameter of 0.001 mm to 0.15 mm. Porous metal body according to claim 1 or 2, characterized in that it has a communication hole. A slurry adjustment step of dispersing the metal raw material powder in a water-soluble polymer aqueous solution capable of gelation;
A gelation step of gelling the slurry obtained in the slurry adjustment step;
A freezing step of freezing the gel obtained in the gelation step;
A drying step of removing ice from the frozen body to obtain a dried body;
A degreasing step of heating and drying the dried body in an inert gas;
An oxidative atmosphere degreasing step of degreasing by heating in an oxidative atmosphere;
A method for producing a porous metal body, comprising: a sintering step. The method for producing a porous metal body according to claim 4 , wherein a thickener is added in the slurry adjustment step. Wherein during oxidizing atmosphere degreasing step and the sintering step, the manufacturing method of the metal porous body according to claim 4 or 5, characterized in that a reducing step of performing heat treatment in a reducing atmosphere. The method for producing a porous metal body according to any one of claims 4 to 6 , wherein the gelling step is performed after the slurry obtained in the slurry adjusting step is tape-cast.