JP2012001808A - Method for producing porous metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous metal with a large surface area which can be effectively used for a catalytic reaction or electrode reaction, and a method of producing the porous metal equipped with an oxide film on a surface by rolling.SOLUTION: The porous metal production method includes: a mixing step of mixing metal powder and support powder of a grain size of 10 times or more of the metal powder in the volume ratio of the metal powder: the support powder =3:7 to 1:19; a rolling step of rolling the mixed powder or the rolling step of rolling the green compact after a pressure forming step of making the mixed powder into the green compact by carrying out pressure forming; and a supporting powder removing process to form a gap by eliminating the support powder.

Description

  The present invention relates to a method for producing a porous metal, and more particularly to a production method capable of mass-producing a porous metal having a large surface area and a porous metal having an oxide film on its surface by performing a surface treatment.

  As a method for producing a porous metal, (1) a molten metal foaming method in which a foaming agent such as titanium hydride is mixed in a molten metal and solidified in a state containing the generated gas (Patent Document 1), (2) A spacer method (Patent Document 2) that removes the spacer material after mixing and extruding or rolling a metal powder and a spacer material such as sodium chloride, and a spacer method (Patent Document 3) that uses sintering by energization or plasma, etc. Are known.

JP-A-11-302765 Japanese Patent No. 4048251 Japanese Patent Laid-Open No. 03-285880

  The porous metal produced by the molten metal foaming method has a closed cell structure in which the pores are independent, and since the inside of the pores does not communicate with the outside, the surface area is small, and it is used as a battery current collector, a catalyst, or a carrier thereof. I couldn't. Further, in the spacer method using conventional rolling, the porosity is as low as less than 70%, and some spacer materials that exist independently without being communicated with the outside may remain inside. For example, when sodium chloride is used as a spacer, there is a problem in that corrosion of the porous metal substrate is promoted when sodium chloride that cannot be completely removed is exposed to the external environment. In addition, although a porous metal having a high porosity can be manufactured by a manufacturing method using energization or plasma sintering, it is not suitable for mass production because it is a batch process.

  As a result of intensive studies in view of the above problems, the present inventors increase the porosity as compared with the conventional method using rolling by adjusting the particle size of the metal powder and the supporting powder in the spacer method using rolling. And a method for producing a porous metal having a large surface area. Specifically, the particle size of the support powder is specified to be 10 times or more that of the metal powder, and in addition, the mixing ratio of the support powder is specified by a volume ratio of metal powder: support powder = 3: 7 to 1:19. is there. Thereby, it is possible to produce a porous metal having a large porosity without being separated into individual metal powders. Moreover, it can process continuously by utilizing rolling as a manufacturing method, and mass production is attained. In addition, it has also been found that by subjecting the porous metal to a surface treatment, an oxide film is formed on the surface of the bonded metal powder, and a porous metal having continuous pores and excellent corrosion resistance can be obtained.

  That is, according to a first embodiment of the present invention, in claim 1, the metal powder and the support powder having a particle size of 10 times or more of the metal powder are mixed in a volume of metal powder: support powder = 3: 7 to 1:19. A method for producing a porous metal comprising: a mixing step of mixing at a ratio; a rolling step of rolling the mixed powder mixture; and a support powder removing step of removing the support powder to form voids; did.

  The present invention according to claim 2, wherein the metal powder and the support powder having a particle size of 10 times or more of the metal powder are mixed in a volume ratio of metal powder: support powder = 3: 7 to 1:19, A pressure forming step of pressing the mixed powder mixture into a green compact; a rolling step of rolling the green compact; and a support powder removing step of removing the support powder to form a void. It was set as the manufacturing method of the porous metal characterized by including.

  According to a third aspect of the present invention, in the first or second aspect, the metal powder is made of at least one of pure aluminum and an aluminum alloy, and the support powder is a water-soluble salt.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the mixed powder or the green compact is less than the melting point of the supporting powder and the metal powder is recycled before the rolling step. A preheating step of preheating to a temperature higher than the crystal temperature and lower than the melting point is provided.

  Next, a second embodiment of the present invention is the method according to claim 5, wherein the metal powder and the support powder having a particle size of 10 times or more of the metal powder have a volume of metal powder: support powder = 3: 7 to 1:19. The mixed powder is mixed to obtain a mixed powder, the mixed powder is rolled into a rolled body, and then the rolled body is subjected to at least one surface treatment using water, an alkaline solution, and an acid solution. It was set as the manufacturing method of the porous metal to do.

  The present invention provides the mixed powder according to claim 6 by mixing the metal powder and the support powder having a particle size of 10 times or more of the metal powder in a volume ratio of metal powder: support powder = 3: 7 to 1:19. The mixed powder is rolled into a rolled body, and then the support powder is removed from the rolled body to form voids, and at least one surface treatment using water, an alkali solution, an acid solution, and water vapor is performed. It was set as the manufacturing method of the porous metal characterized by performing.

  According to a seventh aspect of the present invention, in the fifth or sixth aspect, the metal powder is made of at least one of pure aluminum and an aluminum alloy, and the support powder is a water-soluble salt.

  According to an eighth aspect of the present invention, in any one of the fifth to seventh aspects, the mixed powder is pressure-molded into a green compact before the rolling step.

  According to a ninth aspect of the present invention, the mixed powder or the green compact is less than the melting point of the support powder and the metal powder is recycled before the rolling step. A preheating step of preheating to a temperature higher than the crystal temperature and lower than the melting point is provided.

  According to a tenth aspect of the present invention, in any one of the fifth to ninth aspects, the surface treatment is performed in any one of water, an alkali solution, and an acid solution at 50 ° C to 100 ° C for 1 minute to 60 minutes. It was assumed to be immersed for less than a minute. Furthermore, the present invention according to claim 11 is the surface treatment according to any one of claims 6 to 9, in which the rolled body is exposed to water vapor of 100 ° C or higher and 300 ° C or lower for 10 minutes or longer and 180 minutes or shorter.

  According to the present invention, it is possible to provide a method capable of mass-producing a porous metal having a large surface area by rolling a mixed powder in which the particle sizes of the metal powder and the supporting powder and the mixing ratio thereof are adjusted, or this green compact. Furthermore, the present invention manufactures a composite material in which a porous metal and a plate-like or band-like metal are stacked and integrated by rolling together the plate-like or belt-like metal and the mixed powder or green compact. You can also Furthermore, a porous metal having excellent corrosion resistance can be produced by forming an oxide film on the surface of the bonded metal powder of the porous metal. The porous metal produced in this way can increase the reaction efficiency by utilizing the surface of a large area as a reaction site for adsorption reaction, catalytic reaction, electrode reaction, photoreaction and the like. Moreover, it can utilize also for the part which requires a smooth surface by setting it as a composite_body | complex.

It is a SEM photograph showing the cross section of the porous aluminum manufactured by the method of this invention. It is explanatory drawing which shows the cross section of FIG. 1 by the relationship with a rolling direction.

(A) Porous metal The porous metal produced according to the first embodiment of the present invention forms voids and voids obtained by removing the support powder after rolling the mixture of metal powder and support powder. And a bonded metal powder wall. The support powder is deformed together with the metal powder by rolling, and the void formed by removing the support powder has a shape crushed in the direction perpendicular to the rolling surface. The voids formed by the support powder have a structure in which they are communicated by a hole opened in a part of the bonded metal powder wall. Therefore, unlike the structure in which the voids are isolated without being communicated with each other, it is possible to remove the support powder at a position not originally in contact with the outside.

(B) Metal powder In the present invention, since the mixed powder of the metal powder and the support powder is rolled, the metal is required to be a stretched material that is plastically deformed by rolling. Examples of the stretched material include aluminum, magnesium, zinc, tin, copper, iron, and alloys thereof. Among these, an aluminum material is preferable, and pure aluminum or an aluminum alloy is preferably used. As the aluminum alloy, 1000 series, 2000 series, 3000 series, 4000 series, 5000 series, 6000 series, and 7000 series aluminum alloys are used. Since the particle size of the support powder needs to be 10 times or more that of the metal powder, it is preferable that the metal powder has a small particle size so that the support powder having various particle sizes can be used. The particle size of the metal powder used in the present invention is preferably 1 to 50 μm. The particle diameter here is the median diameter of the particle diameter measured by the laser diffraction / scattering method.

(C) Support powder The support powder used in the present invention may be a substance that is pulverized and / or deformed together with the deformation of the metal powder during rolling and can be easily removed after rolling. For removing the support powder after rolling, a method of elution with water is simple, and for this reason, a water-soluble salt is preferably used as the support powder. Examples of the water-soluble salt include alkali metal and alkaline earth metal chlorides and carbonates. Sodium chloride and potassium chloride are preferable from the viewpoint of availability. Further, since the support powder is removed and the space in which the support powder existed is left as a void, the particle size of the support powder directly affects the pore size of the porous metal. In the present invention, the particle size of the support powder needs to be 10 times or more that of the metal powder. If it is less than 10 times, the support powder is not sufficiently covered with the metal powder, and the bonding between the metal powders is likely to be interrupted. For this reason, when the support powder is removed, the metal powder becomes a single or several lumps at the portion where the bonding is interrupted, and is separated from other metal powders. The support powder used in the present invention preferably has a particle size of 10 to 1000 μm. The particle diameter here is a median diameter of the particle diameter measured by a sieve opening or a laser diffraction / scattering method.

(D) Mixing step The mixing ratio of the mixed powder composed of the metal powder and the support powder is a volume ratio, and is metal powder: support powder = 3: 7 to 1:19. That is, the volume content of the metal powder in the mixed powder is 5 to 30%, and the volume content of the support powder is 95 to 70%, preferably 95 to 75%, and more preferably 90 to 80%. Since this mixing ratio is reflected in the porosity of the porous metal, the porosity of the porous metal that can be produced by the present invention is about 70 to 95%.

  If the volume content of the supporting powder exceeds 95%, the bonding metal powder wall constituting the porous metal is too few, so that the strength of the wall is weakened and the possibility that the wall is interrupted increases. When removed, the porous metal splits. On the other hand, when the volume content of the support powder is less than 70%, the support powder content is too small to be present without contact between the support powders. The possibility of remaining in the porous metal increases. In addition, it takes a long time to remove the residual support powder. For example, a pure aluminum powder is used as a metal powder and a sodium chloride powder is used as a support powder, and a mixed powder of pure aluminum powder: sodium chloride powder = 35: 65% in a volume ratio is rolled, and this is mixed with running tap water. Even when immersed in time, the removal rate of sodium chloride was about 95%. Accordingly, it takes a long time for the elution removal, and the production efficiency is remarkably lowered. Therefore, the volume mixing ratio of the metal powder and the support powder is metal powder: support powder = 3: 7 to 1:19, preferably 1: 3 to 1:19, more preferably 2: 8 to 1: 9. is there.

  As a mixing means, various mixers such as a tumbler mixer and a drum mixer, a V-type mixer, a W-type mixer, a vibration stirrer, a container rotary mixer and the like are used, but are particularly limited as long as a sufficient mixture can be obtained. It is not something.

(E) Rolling step In the present invention, the mixed powder of the metal powder and the support powder is rolled cold or hot. When the metal powder is plastically deformed by rolling, the oxide film covering the metal powder is broken, a new metal surface appears, and the metal powders are bonded to each other. At this time, the support powder is also deformed together with the metal powder, and a space that becomes a void later is maintained. Rolling is performed by adjusting the roll gap so that the ratio of the bulk specific gravity to the theoretical specific gravity of the rolled product (bulk specific gravity / theoretical specific gravity) is 80% or more, preferably 85% or more. Here, the theoretical specific gravity is calculated from the true specific gravity of the metal powder and the support powder, assuming that the rolled body has no voids. On the other hand, bulk specific gravity is calculated | required from the mass and volume of the rolling body actually measured. Any known rolling technique can be used as the rolling technique, but a powder rolling machine is preferably used. A lubricant may be used during rolling, and the type thereof is not particularly limited. However, when a water-soluble salt is used as the support powder, an aqueous lubricant cannot be used.

  Moreover, in order to accelerate | stimulate the coupling | bonding of the metal powder which comprises a rolling body, you may heat and sinter a rolling body to the melting | fusing point vicinity of raw material metal powder after rolling. As the atmosphere at this time, air, an inert atmosphere such as nitrogen or argon, or a vacuum atmosphere can be used, but an inert atmosphere or a vacuum atmosphere is preferable.

(F) Rolling process using pressure molding Instead of the method of directly rolling the mixed powder of the metal powder and the support powder as described above (powder rolling), the mixed powder is pressure-molded in advance using a mold. A method of forming a green compact and rolling the green compact may be adopted. In this case, there exists an advantage that it can roll using rolling mills other than a powder rolling mill. Further, by forming the green compact in advance, it is possible to solve the problem that the supply amount is biased when the powder is supplied. The green compact only needs to be hardened to such an extent that it is not difficult to handle. For that purpose, a pressure of about 10 to 200 MPa may be applied and pressure-molded.

(G) Preheating process When rolling is carried out hot, it is preferable to preheat the mixed powder or green compact before rolling. The same effect can be obtained by rolling using a heating roll and heating the mixed powder or green compact during rolling. Preheating is not always necessary, and it may be cold as long as sufficient bonding can be generated between the metal powders. However, the higher the temperature, the easier the deformation of the metal powder and the support powder, and it is preferable to preheat because the metal bonding is likely to proceed. The preheating temperature is lower than the melting point of the supporting powder to be used, and is higher than the recrystallization temperature of the metal powder and lower than the melting point. The preheating temperature is adjusted to reach such a temperature range during rolling. For example, when pure aluminum is used as the metal powder and sodium chloride is used as the support powder, the preheating temperature is preferably 300 to 500 ° C. When a heating roll is used, the temperature of the heating roll must not exceed the melting points of the support powder and the metal powder.

(H) Support Powder Removal Step For removal of the support powder in the rolled body, a method such as elution is used. When a water-soluble salt is used as the support powder, it can be easily eluted and removed by a method such as immersing the rolled body in a sufficient amount of water bath or flowing water bath. In this case, it is preferable to use water of 30 ° C. or higher because elution is faster when the temperature is higher, such as warm water, for the elution. The water from which the water-soluble salt is eluted preferably has less impurities, such as ion-exchanged water or distilled water, depending on the application destination, but there is no particular problem with tap water.

(I) Composite porous metal of porous metal and plate-like or belt-like metal Next, a composite porous metal which is an applied technique of the present invention is a porous metal produced by the invention according to an embodiment of the present invention. It is a composite material in which a plate-like or strip-like metal is integrated. This composite porous metal is a two-layer structure obtained by placing the mixed powder on one side of a plate-like or strip-like metal and rolling it, or between two plate-like or strip-like metals. A three-layer structure in which the mixed powder is sandwiched and rolled, or a multilayer structure in which a plurality of the plate-like or strip-like metal and the mixed powder are alternately laminated and rolled. In addition, a plate-like or strip-shaped metal is fed to the rolling mill together with the powder and rolled by passing a hopper that supplies the powder to the rolling mill to form a multilayer structure in which the plate-shaped or strip-shaped metal is sandwiched between the powders. You can also. Similarly to the embodiment of the present invention, a green compact obtained by previously press-molding this can be used instead of the mixed powder. It is also possible to place green compacts having different support powder diameters and mixing ratios and to roll them to form a multilayer structure having different pore sizes and different porosity. Of course, a stack of green compacts can be placed on a plate-like or belt-like metal, or rolled in a sandwiched state to form a multilayer structure. In this composite porous metal, the metal powder to be used and the supporting powder, and the mixing method, the pressure forming method, and the removing method of the supporting powder are the same as those of the porous metal produced by the invention according to the embodiment of the present invention. Same as the case. Below, only the point peculiar to the composite porous metal which is an applied technique of this invention is demonstrated.

(J) Plate-like or strip-like metal The plate-like or strip-like metal used for the composite porous metal is not particularly limited as long as it is a material exhibiting stretchability in rolling, such as expanded metal and punching metal. It can be a hole. Examples of the stretched material include aluminum, magnesium, zinc, tin, copper, iron, and alloys thereof. Among these, an aluminum material is preferable, and pure aluminum or an aluminum alloy is preferably used. As the aluminum alloy, 1000 series, 2000 series, 3000 series, 4000 series, 5000 series, 6000 series, and 7000 series aluminum alloys are used.

(K) Rolling step In the composite porous metal, the mixed powder of the metal powder and the supporting powder is placed on a plate-shaped or strip-shaped metal and is rolled cold or hot. Rolling is in the state of a two-layer structure in which the mixed powder is in contact with one side of a plate-shaped or band-shaped metal, or in the state of a three-layer structure in which the mixed powder is sandwiched between two plate-shaped or band-shaped metals. Alternatively, it is carried out in a state of a multilayer structure in which a plurality of layers of mixed powder and plate-like or strip-like metal are alternately stacked. When the metal powder and the plate-shaped or band-shaped metal are plastically deformed by rolling, the respective oxide films are broken and a new metal surface appears, and the metal powders and the metal powder and the plate-shaped or band-shaped metal are bonded. At this time, the support powder is also deformed together with the metal powder, and a space that becomes a void later is maintained. The rolling is performed so that the ratio of the bulk specific gravity to the theoretical specific gravity of the rolled product (bulk specific gravity / theoretical specific gravity) is 80% or more, preferably 85% or more. Any known rolling technique can be used as the rolling technique. A lubricant is preferably used during rolling, and the type thereof is not particularly limited. However, when a water-soluble salt is used as the support powder, an aqueous lubricant cannot be used.
As in the present invention, it is possible to use a green compact that has been pressure-molded in advance instead of the mixed powder, and to roll the green compacts in layers. In addition, a plate-like or strip-shaped metal is fed to the rolling mill together with the powder and rolled by passing a hopper that supplies the powder to the rolling mill to form a multilayer structure in which the plate-shaped or strip-shaped metal is sandwiched between the powders. You can also. Furthermore, in order to promote the bonding between the metal powders constituting the rolled body, after the rolling, the rolled body may be heated and sintered to the vicinity of the melting point of the raw metal powder or the plate-shaped or strip-shaped metal. As the atmosphere at this time, air, an inert atmosphere such as nitrogen or argon, or a vacuum atmosphere can be used, but an inert atmosphere or a vacuum atmosphere is preferable.

(L) Preheating process Also in this composite porous metal, when rolling is carried out hot, it is preferable to preheat the mixed powder and / or the plate-like or strip-like metal before rolling. Similar to the first embodiment, preheating is not necessarily required, and may be cold as long as sufficient bonding can be generated between the metal powders. However, it is generally preferable to preheat the metal powder, the supporting powder, and the plate-shaped or strip-shaped metal as the temperature is higher, and the metal bonding is more likely to proceed. The same effect can be obtained by rolling using a heating roll and heating the mixed powder or green compact during rolling. The preheating temperature is lower than the melting point of the supporting powder to be used, and is equal to or higher than the recrystallization temperature of the metal powder and the plate-like or strip-like metal and lower than the melting point. The preheating temperature is adjusted to reach such a temperature range during rolling. For example, when using pure aluminum as the metal powder, sodium chloride as the support powder, and pure aluminum as the strip metal, the preheating temperature is preferably 300 to 500 ° C. When a heating roll is used, the temperature of the heating roll must not exceed the melting point of the support powder, metal powder and plate or strip metal.

(M) Porous metal Next, the porous metal produced by the second embodiment of the present invention is oxidized on the surface of the bonded metal powder wall in the porous metal produced by the invention according to the first embodiment. A film is formed. In the porous metal produced by the invention according to the second embodiment (hereinafter referred to as “surface-treated porous metal”), the metal powder and supporting powder used, and the mixing method, rolling method, and pressurization thereof are used. The forming method, the preheating method, and the removal method of the support powder are the same as those of the porous metal produced by the invention according to the first embodiment, and only different points will be described below.

(N) Oxide film The oxide film formed on the surface of the bonded metal powder wall includes at least one of an anhydrous oxide film and a hydrated oxide film of metal powder. Hereinafter, the term “oxide film” refers to both an anhydrous oxide film and a hydrated oxide film unless otherwise specified. Examples of the non-hydration film include Al ₂ O ₃ . The hydrated oxide film is generally represented by Al ₂ O ₃ (nH ₂ O), and specific examples thereof include AlOOH. These oxide films may contain a compound containing an element such as chromium, nickel, cobalt, phosphorus, or fluorine.

(O) Surface Treatment Method The surface treatment of the porous body is performed by combining at least any one treatment using water, an alkaline solution, an acid solution and water vapor, or a combination of a plurality of treatments. In the solution system treatment, the porous metal is immersed in water, an alkaline solution or an acid solution. In the steam system treatment, the porous metal is exposed to water vapor. In the solution system treatment, treatment with water, treatment with an acid solution, treatment with an alkaline solution may be used alone or in combination. Furthermore, you may perform combining these solution type | system | group processes and water vapor type | system | group processes.

  As water used for the solution system treatment, so-called pure water such as ion-exchanged water, distilled water, or ultrapure water is preferably used. As the acid solution, a solution of sodium silicofluoride, chromic acid, phosphoric acid, carbonic acid or the like is preferably used. These acid solutions are preferably aqueous solutions. As the alkaline solution, a solution of chromate, permanganate, phosphate, carbonate, ammonia or the like is preferably used. As these alkaline solutions, aqueous solutions are preferred. As the acid and alkali aqueous solution, it is more preferable to use the above pure water solution. You may add heavy metal salts, such as zinc, nickel, cobalt, copper, to an acid solution or an alkali solution. As the treatment liquid, seawater including artificial seawater can be used in addition to the above solution. On the other hand, steam is used in the steam processing. As the water vapor, steam generated from water such as pure water is used. In addition, you may use the vapor | steam containing the alkali component and acid component which were generated from the above-mentioned alkali solution and acid solution. Further, when solution processing is performed, washing and drying are preferably performed because there is a concern that the treatment liquid may remain in the pores, thereby promoting corrosion and causing problems during use.

  The processing temperature of the solution processing is preferably 50 ° C. or higher and 100 ° C. or lower. When the treatment temperature is less than 50 ° C., it takes time to form an oxide film, and sufficient corrosion resistance may not be exhibited. On the other hand, when the temperature exceeds 100 ° C., excessive energy is consumed to maintain the temperature, and the generation of steam may be remarkably severe and the working environment may be severe. The treatment time of the solution treatment is preferably 1 minute or more and 60 minutes or less. If the treatment time is less than 1 minute, a sufficient oxide film may not be formed, and the corrosion resistance may be inferior. On the other hand, if it exceeds 60 minutes, the effect may be saturated even if the treatment is further performed. When the solution system treatment is performed, it is preferable to perform washing such as washing in order to remove the treatment liquid.

  The treatment temperature for the water vapor treatment is preferably 100 ° C. or more and 300 ° C. or less, and more preferably 110 ° C. or more and 200 ° C. or less for ease of implementation. When the treatment temperature is less than 100 ° C., an oxide film may not be formed up to the inside due to aggregation of water vapor on the outer surface of the porous metal. When the temperature of water vapor exceeds 300 ° C., the effect of increasing the temperature may be saturated. The treatment time for the water vapor treatment is preferably 10 minutes or more and 180 minutes or less. When the treatment time is less than 10 minutes, a sufficient oxide film may not be formed, and the corrosion resistance may be inferior. On the other hand, if it exceeds 180 minutes, the effect may be saturated even if the treatment is further performed.

  In the production of the surface-treated porous metal by the solution system treatment, the supporting powder can be usually removed together with the surface treatment of the porous metal described in detail above, and therefore the supporting powder removing step need not be provided. On the other hand, if the support powder cannot be sufficiently removed together with the surface treatment in the solution treatment or in the case of the steam treatment, it is necessary to remove the support powder separately. The step of removing the supporting powder to form voids must be provided.

  Prior to the above surface treatment, degreasing and washing with an alkaline solution such as an aqueous sodium hydroxide solution or an acid solution such as nitric acid for the purpose of removing an oxide film or oil on the metal surface in order to form a film efficiently. Processing may be performed. Commercially available degreasing agents and cleaning agents can be used for these degreasing treatments and cleaning treatments.

The first embodiment of the present invention will be specifically described below based on examples and comparative examples.
Examples 1-14 and Comparative Examples 1-4
The following pure aluminum powders (A1 to A3) having different particle diameters were used as the metal powder. As the supporting powder, sodium chloride powders (B1 to B3) having different particle sizes depending on the median sieve opening, and potassium chloride (B4) having a median particle size of 550 μm in the median sieve aperture were used. As shown in Table 1 and Table 2, a mixture in which pure aluminum powder and support powder were mixed at a predetermined mixing volume ratio was prepared. The prepared mixture was rolled without being heated or heated in advance to the temperatures shown in Tables 1 and 2 to prepare rolled body samples having a thickness of 1.5 to 4 mm. In Examples 1, 2, 4, 7, 8, 11, 12 to 14 and Comparative Examples 1, 2, and 4, the mixture was pressure-molded and rolled.

<Pure aluminum powder A (aluminum purity 99.7% or more)>
A1: Particle size 3μm
A2: Particle size 20 μm
A3: Particle size 30 μm

<Sodium chloride powder B>
B1: Particle size 120 μm
B2: Particle size 550 μm
B3: Particle size 780 μm
<Potassium chloride powder B>
C1: Particle size 550 μm

The following evaluation was performed using the rolled body sample produced as described above.
(A) Shape maintenance property The rolled body sample cut out to 20 mm x 20 mm was immersed in flowing water (tap water) at 20 ° C for 24 hours to elute the supporting powder to obtain a porous metal. The volume reduction ratio before and after the elution was used as an index for maintaining the shape, and evaluated according to the following criteria.
○: Volume reduction ratio <10%
×: 10% ≦ Volume reduction ratio ○ was accepted and x was rejected.

(B) Support powder removability In order to investigate the removability of the support powder, the residual amount of sodium chloride or potassium chloride in the porous metal after the elution was measured and evaluated according to the following criteria.
○: Residual amount <0.5%
Δ: 0.5% ≦ residue amount <1%
×: 1% ≦ residual amount ○ and Δ were acceptable, and x was unacceptable.

  The evaluation results are shown in Tables 1 and 2. As shown in Table 1 and Table 2, in each of Examples 1 to 14, the shape maintenance property and the support powder removability were acceptable. Here, the cross-sectional SEM photograph of the porous metal produced in Example 2 is shown to (a)-(c) of FIG. (A) is the SEM photograph of the cross section 1 of FIG. Cross section 1 represents a cross section parallel to the rolling surface of green compact 4, cross section 2 represents a cross section perpendicular to rolling direction L, and cross section 3 represents a cross section parallel to rolling direction L. Moreover, in FIG. 1, A shows the space | gap from which the support powder was removed, B shows a joint metal powder wall.

In Comparative Example 1 and Comparative Example 2, the metal powder cannot sufficiently cover the support powder because the particle size of the sodium chloride powder that is the support powder is too small, and the bonding between the metal powders is interrupted and the shape collapses. did.
In Comparative Example 3, since the mixing ratio of the supporting powder was too small, the supporting powder that existed independently in the rolled body remained after washing with water.
In Comparative Example 4, since the mixing ratio of the support powder was too large, the bonding frequency of the metal powders was low, and the shape collapsed.

Next, based on an Example and a comparative example, the 2nd embodiment of this invention is described concretely.
Examples 15-29 and Comparative Examples 5-7
The sample produced in Example 13 was used as the porous aluminum sample before the surface treatment. That is, the aluminum powder of Al and the sodium chloride powder of B2 were mixed at a volume ratio of aluminum powder: sodium chloride powder = 1: 9 to prepare a porous aluminum sample. The mixed powder was pressure-molded at 50 MPa to form a plate-like green compact, heated to 500 ° C. in the preheating step, and then rolled. Elution of sodium chloride was performed by immersing in flowing water (tap water) at 20 ° C. for 24 hours.

  The porous aluminum sample thus produced was subjected to a surface treatment using the treatment liquids or vapors shown in Tables 3 and 4 at different treatment temperatures and treatment times. Ion exchange water was used as a solvent for the treatment liquid. In Examples 24 and 25, artificial seawater (according to ASTM D1141) was used as the treatment liquid. In Example 25, the surface treatment was performed without performing the step of eluting the support powder.

  The following evaluation was performed using the porous aluminum sample produced as described above.

(C) Corrosion resistance 100 ml of 20% hydrochloric acid was passed through the surface-treated porous aluminum sample, and the Al concentration in hydrochloric acid that passed through the porous aluminum was measured and evaluated according to the following criteria.
A: 3 mg / L> Al concentration O: 10 mg / L> Al concentration ≧ 3 mg / L
Δ: 18 mg / L> Al concentration ≧ 10 mg / L
×: Al concentration ≧ 18 mg / L
◎, ○ and △ were accepted, and x was rejected.

  The evaluation results are shown in Tables 3 and 4. As shown in Tables 3 and 4, in Examples 15 to 29, the corrosion resistance was acceptable. However, in Examples 26, 27, and 28, the treatment temperature was low, and in Example 29, the treatment time was short. Therefore, the corrosion resistance was inferior to the other examples.

In Comparative Example 5, since the surface treatment was not performed, the corrosion resistance was unacceptable.
In Comparative Example 6, a film was not formed even when the treatment was performed with hexane, which is an organic solvent, and the corrosion resistance was unacceptable.
In Comparative Example 7, since it was only heat-treated in the air atmosphere, a corrosion-resistant film was not formed on the surface, and the corrosion resistance was unacceptable.

  Since the porous metal according to the present invention has a high porosity and a large pore surface area, it exhibits excellent performance when used in adsorbents, catalysts, sound absorbing materials, battery electrodes, electromagnetic wave absorbers, light absorbers, etc. To do. Moreover, the composite porous metal of a porous metal and a strip | belt-shaped or plate-shaped metal has the characteristic as a structural material of a strip | belt-shaped or plate-shaped metal in addition to the characteristics which porous metal has, such as adsorption property. Furthermore, the surface-treated porous metal has excellent corrosion resistance due to the oxide film on the surface, even when corroded by fluid components.

  1, 2, 3 ... Cross section, 4 ... Green compact, A ... Air gap, B ... Bonded metal powder wall, L ... Roll direction

Claims (11)

  A mixing step of mixing a metal powder and a support powder having a particle size of 10 times or more of the metal powder in a volume ratio of metal powder: support powder = 3: 7 to 1:19, and rolling to roll the mixed powder A method for producing a porous metal, comprising: a step; and a support powder removing step of removing the support powder to form voids.   A mixing step of mixing a metal powder and a support powder having a particle size of 10 times or more that of the metal powder in a volume ratio of metal powder: support powder = 3: 7 to 1:19, and press-molding the mixed powder And a pressure forming step for forming a green compact, a rolling step for rolling the green compact, and a support powder removing step for removing the support powder to form voids. Metal manufacturing method.   The method for producing a porous metal according to claim 1 or 2, wherein the metal powder is composed of at least one of pure aluminum and an aluminum alloy, and the support powder is a water-soluble salt.   2. A preheating step of preheating the mixed powder or the green compact before the rolling step to a temperature lower than the melting point of the support powder and higher than the recrystallization temperature of the metal powder and lower than the melting point. The manufacturing method of the porous metal as described in any one of -3.   A metal powder and a support powder having a particle size of 10 times or more than the metal powder are mixed at a volume ratio of metal powder: support powder = 3: 7 to 1:19 to obtain a mixed powder, and the mixed powder is rolled. A method for producing a porous metal, characterized in that the rolled body is subjected to at least one surface treatment using water, an alkaline solution and an acid solution.   A metal powder and a support powder having a particle size of 10 times or more than the metal powder are mixed at a volume ratio of metal powder: support powder = 3: 7 to 1:19 to obtain a mixed powder, and the mixed powder is rolled. A porous body characterized by forming a rolled body, and then removing the support powder from the rolled body to form voids, and performing at least one surface treatment using water, an alkaline solution, an acid solution, and water vapor. Metal manufacturing method.   The method for producing a porous metal according to claim 5 or 6, wherein the metal powder is composed of at least one of pure aluminum and an aluminum alloy, and the support powder is a water-soluble salt.   The method for producing a porous metal according to any one of claims 5 to 7, wherein the mixed powder is pressed to form a green compact before the rolling step.   6. A preheating step of preheating the mixed powder or green compact before the rolling step to a temperature below the melting point of the support powder and above the recrystallization temperature of the metal powder and below the melting point. The manufacturing method of the porous metal as described in any one of -8.   The porous according to any one of claims 5 to 9, wherein the surface treatment immerses the rolled body in water, an alkali solution or an acid solution at 50 ° C or higher and 100 ° C or lower for 1 minute or longer and 60 minutes or shorter. A method for producing a solid metal.   The method for producing a porous metal according to any one of claims 6 to 9, wherein the surface treatment exposes the rolled body to water vapor of 100 ° C or higher and 300 ° C or lower for 10 minutes or longer and 180 minutes or shorter.

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