JPH093566A - Production of metallic porous body - Google Patents

Abstract

PURPOSE: To produce a metallic porous body almost free from closed pores and having satisfactory gas permeability and high strength. CONSTITUTION: Metal powder is stuck to the surface of urethane foam and heat treatment is carried out in a gaseous atmosphere contg. hydrogen as reducing gas for the powder and moisture and/or carbon dioxide as oxidizing gas for carbon to produce the objective porous body. In other way, metal powder of Cr, Ti or Al is stuck to the surface of urethane foam and heat treatment is carried out in a nonoxidizing atmosphere to produce the objective porous body. By such an easy method as heat treatment in the specified gaseous atmosphere, the objective metallic porous body having high porosity and high strength and contg. a chemically active metal such as Cr, Ti or Al is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a metal porous body used for a filter, a catalyst carrier, a battery current collector and the like.

[0002]

2. Description of the Related Art A method for producing a metal porous body by sintering metal powder is disclosed in Japanese Patent Publication No. 61-53417, and this method is foaming having a three-dimensional network structure such as urethane foam as a base. Resin is soaked in a slurry prepared by mixing metal powder, thickening polymer and solvent, the metal powder is applied to the skeleton of the foamable resin, and then heat-treated in a hydrogen atmosphere to decompose and burn off the foamable resin. By sintering the metal powder and the metal powder, a metal porous body in which the shape of the foamable resin substrate is transferred is obtained.

[0003]

In the method for producing a metal porous body by sintering as described above, generally, a powder is suspended in a solution of a high molecular weight organic substance to prepare a slurry, which is applied to a foamable resin substrate. However, it is difficult to uniformly apply the powder because the powder tends to collect at the joint portion of the skeleton as compared with the skeleton portion of the foamable resin substrate due to the surface tension of the applied slurry. This phenomenon seriously affects the strength of the finished porous metal body. That is, when a certain amount of powder is applied, a thin portion is likely to be formed on the skeleton, and the strength is reduced.
Therefore, in order to increase the strength, it is necessary to increase the amount of the slurry to be applied to thicken the skeleton, and there is a problem that it is difficult to obtain a material having high porosity and high strength.

Further, as a problem of using the slurry, there is a drawback that it is easy to form a thin film-like portion (closed portion) which closes the network structure of the foamable resin substrate. This is a phenomenon that occurs because the slurry tends to form a film and depends largely on the viscosity of the slurry, but even when the polymer in the slurry is removed and the substrate is impregnated with the mixture of powder and solvent, the Aggregation occurs and a closed part is generated. Therefore, when used as a filter, there is a problem that pressure loss increases.

On the other hand, in the heat treatment in the hydrogen atmosphere, since the foamed resin is used as the substrate, the foamable resin is thermally decomposed to generate carbon, which remains in the porous metal body. When carbon remains, it generally reacts with a metal to form a brittle carbon alloy, and there is a problem that a porous metal body having high strength cannot be obtained.

The present invention has been made in view of the above circumstances, and provides a method for producing a metal porous body having a small number of closed portions, good air permeability, and high strength.

[0007]

[Means for Solving the Problems] The first invention of the present application is to provide an adhesive property to the skeleton surface of a porous resin which is a base material, to which a powder is applied, and then to reduce the powder. And a metal porous body are manufactured by heat treatment in a gas atmosphere that is oxidative to carbon and carbon.

The second invention of the present application is to provide Cr, Ti, A after the tackiness is imparted to the skeleton surface of the porous resin serving as the substrate.
A powder containing at least one of metals selected from the group 1 or alloys containing these metals is deposited and heat-treated in a non-oxidizing atmosphere to produce a metal porous body.

In the invention of the present application, the porous resin serving as a substrate is a foaming resin having an open cell structure such as urethane foam, or a non-woven fabric or a woven fabric, and the shape is appropriately selected according to the purpose of use. .

The skeleton surface of the substrate is provided with tackiness for the purpose of facilitating the deposition of powder and preventing peeling. The tackiness is imparted by applying an acrylic or rubber adhesive solution or an adhesive resin solution such as a phenol resin, an epoxy resin, or a furan resin. Further, it is possible to give tackiness to the substrate itself by plasma treatment or the like.

After imparting tackiness to the skeleton surface of the substrate, the powder is deposited on the skeleton surface of the substrate by a method such as rocking the substrate in the powder or spraying the powder onto the substrate. Thereby, the dry powder can be directly applied to the skeleton surface of the substrate. The powder is instantly fixed on the skeleton surface of the substrate, and unlike the slurry method, the powder does not move on the skeleton surface of the substrate during the drying process, so that the powder does not collect at the joint portion of the substrate skeleton. Also, since the powder deposition occurs on the skeleton surface of the substrate and does not depend on the thickness of the adhesive layer,
The amount of powder deposited is uniform over the entire substrate, and when a constant weight of powder is deposited, a porous metal body having high strength can be obtained. Further, the powder is selectively adhered only to the portion to which tackiness is imparted, and since no solvent is used, agglomeration of the powder particles does not occur, so that a closed portion is not formed unlike the slurry method.

The first invention of the present application will be described below.
The material of the powder is Ni, Cu, Fe, C which can be reduced with hydrogen.
At least one of pure metals such as o, Ag, Mo, and W, alloys thereof, and oxides thereof is used. The particle size of the powder may be within a range that can be attached to the skeleton surface of the base,
It is desirable to be in the range of 0.01 to 100 microns. Further, the shape of the powder is not particularly limited. In addition, a porous metal body having an arbitrary skeleton thickness can be obtained by repeating the step of imparting tackiness and the step of depositing powder.

After the powder is deposited and before the heat treatment, the substrate is wetted with a liquid and then dried, whereby the powder can be densely deposited on the substrate skeleton. Therefore, a porous metal body having high strength can be obtained by heat treatment. This is to wet the powder on the skeleton surface of the substrate with a liquid and to agglomerate the powder by the surface tension of the liquid in the drying process. The method for wetting the powder is performed by immersing the substrate in a liquid, spraying the liquid on the substrate, or the like. Any type of liquid may be used as long as it does not reduce the adhesive force between the substrate and the powder, but water is the most practical.
Further, a thickening polymer such as methyl cellulose or polyvinyl alcohol, or a metal salt may be added to this liquid.

Preferably, the substrate is wetted with a liquid and dried, and then heat treated. The heat treatment atmosphere is an oxidizing gas atmosphere which has a reducing power for powder and can be reduced to a metal, and carbon has an action of oxidizing a volatile gas such as carbon monoxide to remove it from the porous body. Therefore, an oxidizing gas is added to the heat treatment atmosphere gas together with hydrogen, for example. Generally, water and carbon dioxide are used as the oxidizing gas.
Water reacts with carbon to produce carbon monoxide and hydrogen, and carbon dioxide reacts with carbon to produce carbon monoxide. This makes it possible to remove carbon from the porous body during the heat treatment, and prevent the formation of a brittle carbon alloy.

It is necessary that the amount of the oxidizing gas added is at least a concentration at which a practical carbon oxidation reaction rate can be obtained and at a concentration at which the powder is not oxidized. In the case of water, it is preferable that the gas volume ratio is 0.1 ≦ (H ₂ O volume / H ₂ volume) ≦ 10 although it varies depending on the powder used, and in the case of carbon dioxide, the gas volume ratio also varies depending on the powder. 0.1 ≦ (C
It is preferable that O ₂ volume / H ₂ volume) ≦ 10. These atmosphere gases may be diluted with an inert gas such as argon or nitrogen.

Although the heat treatment temperature varies depending on the powder used, it is generally carried out in a temperature range of 70% to 9.5% of the melting point (T _m ) of the metal shown in absolute temperature. It is preferable to perform the heat treatment at a temperature of 80% or more of T _m , because the higher the heat treatment is, the more the sintering between the metal powders proceeds, and the metal porous body having high strength is obtained.

The second invention of the present application will be described below.
As the material of the powder, a pure metal selected from Cr, Ti, and Al that cannot be reduced by hydrogen, an alloy containing these metals, or a mixture thereof is used. These powders include a chemically non-metallic material that easily forms an oxide, and once an oxide is formed, there is a problem that it cannot be reduced to a metal in a gas atmosphere. Therefore, when these powders are used, it is necessary to prevent the powders from being oxidized in the manufacturing process in order to obtain the metal porous body. The particle size of the powder may be in the range that can be adhered to the skeleton surface of the substrate, and is preferably in the range of 0.01 to 100 microns. Further, the shape of the powder is not particularly limited. Also,
By repeating the step of imparting tackiness and the step of depositing powder, it is possible to obtain a metal porous body having an arbitrary skeleton thickness.

After the powder is deposited and before the heat treatment, the substrate is wetted with a liquid and then dried, whereby the powder can be densely deposited on the substrate skeleton. Therefore, after heat treatment, a metal porous body having high strength can be obtained. This is to wet the powder on the skeleton surface of the substrate with a liquid and to agglomerate the powder by the surface tension of the liquid in the drying process. The method for wetting the powder is performed by immersing the substrate in a liquid, spraying the liquid on the substrate, or the like. Any type of liquid may be used as long as it does not reduce the adhesive force between the substrate and the powder, but water is the most practical. Further, a thickening polymer such as methyl cellulose or polyvinyl alcohol, or a metal salt may be added to this liquid.

Preferably, the substrate is wetted with a liquid and dried, and then heat treated. The heat treatment is intended for sintering the powder, and is performed in a non-oxidizing atmosphere for the purpose of preventing the powder from being oxidized. The non-oxidizing atmosphere is an atmosphere containing no oxidizing agent such as oxygen, carbon dioxide, and water, and a reducing gas atmosphere,
There are an inert gas atmosphere and a vacuum atmosphere. The reducing gas atmosphere is an atmosphere containing a gas having a reducing action such as hydrogen and carbon monoxide, and the inert gas atmosphere is an atmosphere having no reactivity with the metal to be heat-treated, such as argon and nitrogen. The vacuum atmosphere is generally a high vacuum atmosphere having a pressure of 0.1 Pa or less.

By carrying out the heat treatment in a non-oxidizing atmosphere, it becomes possible to carry out sintering without producing oxides, and it is possible to obtain a porous metal body having high strength.
On the other hand, since the heat treatment is performed in a non-oxidizing atmosphere, the porous resin used as the substrate decomposes to generate carbon. Since carbon inhibits the progress of sintering, if the carbon can be removed, it can be expected that a metal porous body having even higher strength can be obtained. However, it is difficult to remove carbon without producing metal oxides. Therefore, when the powder containing Cr, Ti, and Al was examined for the effect of carbon, it was found that even if the amount of carbon remained was such that the porous resin was decomposed, there was no problem in practical use. I understood. It is considered that this is because the amount of carbon solid solution of these materials is large.

The heat treatment temperature varies depending on the metal, and the temperature is in the range of 70% to 9.5% of the melting point (T _m ) indicated by the absolute temperature of the metal used. As the heat treatment is performed at a higher temperature, the sintering between the metal powders progresses and a porous metal body with high strength is obtained.
It is preferably performed at 80% or more of T _m .

[0022]

【Example】

Example 1 A 3 mm thick polyurethane foam (trade name Everlite SF, manufactured by Bridgestone Corporation) was used as the porous resin to be the substrate. This polyurethane foam is dipped in an acrylic adhesive solution with a resin content of 5% by weight using methyl ethyl ketone as a solvent, and then the excess solution is removed through a roll and the adhesive is applied to impart adhesiveness to the substrate skeleton surface. did. After drying at 100 ° C. for 10 minutes to remove the solvent, the Ni powder was deposited by inserting the substrate into carbonyl Ni powder having an average particle size of 5 μm and rocking. After immersion in water and drying, heat treatment was performed at 1150 ° C. for 20 minutes in an atmosphere in which a mixed gas of water: 20% by volume, hydrogen: 60% by volume, nitrogen: 20% by volume was flowed. As a result, a Ni porous body a having a shape in which the Ni powder was sintered and the polyurethane foam was transferred was obtained. Table 1 shows the characteristics of the porous body a.

Example 2 After soaking in water and drying, at 1150 ° C. for 20 minutes, carbon dioxide: 20% by volume, hydrogen: 60% by volume, nitrogen: 20% by volume
A Ni porous body b was obtained in the same manner as in Example 1 except that the heat treatment was performed in the atmosphere in which the mixed gas of 3 was flowed. Table 1 shows the characteristics of the porous body b.

Comparative Example 1 The polyurethane foam of Example 1 was used as the porous resin to be the substrate. This polyurethane foam had the same composition as in Example 1 except that carbonyl Ni powder: 50% by weight, methylcellulose: 2% by weight, water: 48% by weight.
The Ni powder was applied to the surface of the base skeleton by immersing it in the powder slurry and removing the excess Ni powder slurry. 100
After drying at 30 ° C for 30 minutes to remove water, it is kept at 1150 ° C for 20 minutes.
Heat treatment was performed in an atmosphere in which a mixed gas of hydrogen: 75% by volume and nitrogen: 25% by volume was allowed to flow for one minute. As a result, Ni powder is sintered and Ni having a shape in which polyurethane foam is transferred
To obtain a porous body c. Table 1 shows the characteristics of the porous body c.

Comparative Example 2 A comparison was made except that after immersing in water and drying, heat treatment was carried out at 1150 ° C. for 20 minutes in an atmosphere in which a mixed gas of water: 20% by volume, hydrogen: 60% by volume, nitrogen: 20% by volume was flown. In the same manner as in Example 1, a Ni porous body d was obtained. Table 1 shows the characteristics of the porous body d.

Comparative Example 3 After soaking in water and drying, hydrogen was added at 1150 ° C. for 20 minutes and hydrogen: 75
A porous body e of Ni was obtained in the same manner as in Example 1 except that the heat treatment was performed in an atmosphere in which a mixed gas of 25% by volume of nitrogen and 25% by volume of nitrogen was flowed. This mixed gas is reducing for powder and inactive for carbon. Table 1 shows the characteristics of the porous body e.

Table 1 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Apparent density Pressure loss Tensile strength Carbon content ( g / cm ³ ) (mmAq) (kgf / cm ² ) (ppm) ────────────────────────────────── ── Porous body a 0.36 2.6 11.8 11 Porous body b 0.37 2.6 11.5 15 Porous body c 0.38 4.8 1.5 1600 Porous body d 0.38 5.1 4.4 10 Porous body e 0.37 2.6 2.4 2400 ━━━━━━━━━ ━━━━━━━━━━━━━━━━━━━━━━━━━━━ In Table 1, the pressure loss is the value when the wind speed is 1 m / min. Comparing Examples 1 and 2 with Comparative Examples 1 and 2, it can be seen that in the first invention of the present application, a porous body having a small pressure loss and good air permeability can be obtained as compared with the method of applying the powder slurry. . In addition, comparing Examples 1 and 2 with Comparative Examples 3 and 5, in the first invention of the present application, heat treatment in a hydrogen gas atmosphere containing an oxidizing gas results in a porous material having a low carbon content and high strength. It can be seen that a body is obtained.

Example 3 Polyurethane foam (trade name: Everlite SF, manufactured by Bridgestone Co., Ltd.) having a thickness of 3 mm was used as the porous resin to be the substrate. This polyurethane foam is dipped in an acrylic adhesive solution with a resin content of 5% by weight using methyl ethyl ketone as a solvent, and then the excess solution is removed through a roll and the adhesive is applied to impart adhesiveness to the substrate skeleton surface. did. After drying at 100 ° C. for 10 minutes to remove the solvent, SUS304 powder having an average particle size of 5 μm (Cr: 18
Wt%, Ni: 8 wt%, Fe: 74 wt% alloy), and the SUS304 powder was adhered by inserting the substrate and rocking. After soaking in water and drying, 1100 ° C for 20 minutes,
Heat treatment was performed in a reducing atmosphere in which a mixed gas of hydrogen: 75% by volume and nitrogen: 25% by volume was flown. This makes SUS304
A porous body f of SUS304 having a shape in which the powder was sintered and a polyurethane foam was transferred was obtained. Carbon content is 3.
It was 2% by weight. Table 2 shows the characteristics of the porous body f.

Comparative Example 4 The polyurethane foam of the example was used as the porous resin to be the substrate. This polyurethane foam was made of the same SUS304 powder as in the example: 50% by weight, methylcellulose: 2% by weight, water: 48% by weight.
It is immersed in 04 powder slurry and the excess SUS304 powder slurry is removed.
I applied the powder. After drying at 100 ° C. for 30 minutes to remove water, heat treatment was performed at 1100 ° C. for 20 minutes in an atmosphere in which a mixed gas of hydrogen: 75 v% by volume and nitrogen: 25% by volume was flowed. As a result, SUS304 powder was sintered to obtain a porous body g of SUS304 having a shape in which polyurethane foam was transferred. The carbon content was 3.5% by weight. Table 2 shows the characteristics of the porous body g.

Table 2 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Apparent density Pressure loss Tensile strength (g / cm ³ ) (mmAq) ( kgf / cm ² ) ───────────────────────────── Porous body f 0.33 2.6
8.8 Porous body g 0.35 4.5
2.9 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
In Table 2, the pressure loss is the value when the wind speed is 1 m / min. Comparing the example and the comparative example, it is found that a porous body having a small pressure loss and good air permeability can be obtained in the example. Further, it can be seen that in the example, a porous body having high strength can be obtained.

[0031]

According to the first invention of the present application, the skeleton surface of the porous resin serving as the substrate is made to have tackiness, and after the powder is adhered, the powder is reducible, A porous metal body having high porosity and high strength can be obtained by a simple method of heat treating carbon in an oxidizing gas atmosphere. According to the second invention of the present application, the skeleton surface of the porous resin serving as the substrate is provided with tackiness, and after the powder is adhered, the heat treatment is performed in a reducing atmosphere or an inert atmosphere in a vacuum atmosphere. Various methods, high porosity and high strength Cr,
A metal porous body containing a chemically active metal such as Ti or Al can be obtained.

Claims (4)

[Claims] 1. A gas which is adhesive to the skeleton surface of a porous resin serving as a substrate and is coated with a powder, and then a reducing agent for the powder and an oxidizing agent for the carbon. A method for producing a porous metal body, which comprises performing heat treatment in an atmosphere. 2. Hydrogen as a reducing gas for powder,
The method for producing a metal porous body according to claim 1, wherein the heat treatment is performed in a gas atmosphere containing water and / or carbon dioxide as an oxidizing gas for carbon. 3. A powder containing at least one of a metal selected from Cr, Ti, and Al or an alloy containing these metals, after adhesion is imparted to the skeleton surface of a porous resin serving as a substrate. A method for producing a porous metal body, which comprises depositing and performing heat treatment in a non-oxidizing atmosphere. 4. The method for producing a porous metal body according to claim 1, wherein the deposited powder is wetted with a liquid after the powder deposition and before the heat treatment.