JPH1088254A - Production of porous metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a porous metal excellent in workability, formability, machinability, etc., by melting and solidifying a metal, having an eutectic point in the metal-gas phase diagram under a uniform pressure gas atmosphere under a pressurized gas atmosphere. SOLUTION: A metal having an eutectic point in the metal-gas phase diagram under a uniform pressure gas atmosphere, (e.g. Ag-O), is placed in a melting crucible 2 in a high pressure gas vessel of <=about 20atm. As the gas, hydrogen, oxygen, inert gas, etc., are used. This crucible 2 is heated under pressure by means of a high frequency coil 1 for melting to melt the metal, and the resultant molten metal is cast via an opening/closing valve 3 in a mold 4 cooled by means of a water cooling part 5, followed by solidification by cooling. By this method, a porous metal 6, useful for lightweight structural material, aerospace and aircraft material, catalyst material, etc., can be obtained.

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 porous metal. More specifically, the present invention relates to a catalyst material, a hydrogen storage alloy, an anti-seismic material, a shock absorbing material, an electromagnetic wave shielding material, various mechanical parts such as automobiles, a silencer device, a filter, a self-lubricating bearing, a heat exchanger, an electrolytic device. The present invention relates to a method for producing a porous metal useful for a cell, a liquid separator, a ceramic support for a rocket jet engine, a lightweight panel of a space material, an oxygenator for purifying water, and the like.

[0002]

2. Description of the Related Art Conventionally, as products such as Shirasu porous glass, Celmet, and Alporus, etc.
Various types of inorganic and metal porous materials are known, and the fields of use of these porous materials are also wide-ranging. However, naturally, porous glass is extremely inferior in strength, workability and moldability as compared to metal.Also, in the case of Celmet where the metal is filled in the foamed resin or Alporus using the foaming method with hydrogen gas. If
Applicable metals are limited, and application to many metals is impossible.

On the other hand, a porous (porous) structure is also generated in the powder metallurgy sintering method and the melt casting process.
In these cases, the porous structure becomes a source of cracks in the forming and rolling processes, and so on.
It has been treated as a hazardous material that significantly impairs the mechanical and functional properties of the material. Porous (porous) materials are applied to a wide range of fields such as various mechanical parts, lightweight structural panels, earthquake-proof materials, sound-absorbing materials, electromagnetic wave shielding materials, hydrogen storage alloys, catalysts, bearings, heat exchangers, and electrolytic cells. In spite of the expected expansion of applications in various fields, satisfactory results have not been obtained in terms of strength, workability, moldability, etc., as described above, especially for metal porous materials. Thus, conventional products cannot expand the range of application.

Therefore, the present invention solves the above-mentioned problems of the prior art and realizes a porous metal material having excellent workability, formability, machinability, and the like by a new method. It is intended to provide a manufacturing method.

[0005]

The present invention solves the above-mentioned problems by providing a metal-gas phase diagram under an equal-pressure gas atmosphere in which a metal having a eutectic point is formed under a pressurized gas atmosphere. The present invention provides a method for producing a porous metal, characterized by being melted and solidified.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is to produce a porous metal by utilizing a metal-gas eutectic reaction under an equal pressure gas atmosphere. Further, the present invention provides a porous metal in which the shape and size of pores (holes) are controlled. More specifically, as shown in FIG. 1, when a metal-gas phase diagram has a eutectic point under a certain isobar pressure, the eutectic reaction (L (liquid) → α + G (gas)) causes a gaseous phase. Lamellar tissue is formed in the metal during the solidification process. This results in the generation of a porous metal. In other words, the present invention utilizes, as the metal-gas eutectic reaction, the fact that gas atoms dissolve in metal in a molten state but do not dissolve in metal in a solid state. When the molten metal in which the gas is dissolved is cooled, the gas becomes bubbles inside the metal material, and a porous metal having pores of uniform size is generated.

Actually, in the manufacturing method of the present invention, metal is melted and solidified in a gas atmosphere pressurized from normal pressure to high pressure. In this case, melting and solidification can be performed by a casting method, a Czochralski method, a lifting method such as an improved Czochralski method, and the like. Any gas that is easy to handle and obtain and that has a good correlation with the metal is used. Of course, the selection of the type of gas must have a eutectic point in the metal-gas phase diagram under an equal-pressure gas atmosphere in relation to the type of metal.

[0008] Hydrogen and oxygen are typical examples of gases to be used. These gases may be used alone. However, when they are used by mixing with an inert gas such as argon (Ar), they will be described later. Thus, there is an advantage that the control of the pores (holes) is facilitated. FIGS. 2A, 2B and 2C exemplify a method of casting into a mold and pulling up as a method of the manufacturing method of the present invention.

For example, in the casting method, FIG.
(A) The apparatus of (b) is placed in a high-pressure gas container up to about 20 atm, and the metal is heated and melted by the melting high-frequency coil (1) in the melting crucible (2), and is opened and closed. Through (3), it is cast into the mold (4) cooled by the water cooling unit (5). Then, by cooling, it is solidified to generate a porous metal (6).

In the lifting method, similarly, the apparatus shown in FIG. 2 (c) is placed in a high-pressure gas container, and the metal is melted by a high-frequency coil (1) in a melting crucible (2). Porous metal solidified by being pulled up by the metal rod (7) is generated. For example, in such a system, the shape and size of pores derived from the eutectic reaction product gas can be changed by changing the type and gas pressure of the gas or the solidification rate, and further by applying a temperature gradient. Can be controlled. As shown in FIG. 3, possible forms are (a) spherical pores with random distribution, (b) needle-like pores oriented toward the center, (c) lotus-like pores parallel to the generating line, and lotus-like pores. Examples thereof include discontinuous pores, spiral pores, and the like, and a layer formed of these pores may have a multilayer structure with a nonporous layer.

Regarding the form of these pores, those having needle-like pores facing the center direction as a transmission type porous metal and lotus-like pores (penetration type) parallel to the generatrix, include a blood filtration filter, an air purification filter, and the like. It is used for the structure of batteries, electrodes, emulsified products, and has a random distribution of pores as a non-permeable porous metal, a lotus-shaped pore parallel to the bus (non-penetrating type), and a spiral-shaped pore. Those having such properties are used for weight reduction of structural materials, sound absorbing materials, building materials, acoustic equipment, and electromagnetic wave shielding materials.

The pressure of the gas is appropriately selected, for example, in the range of several atmospheres to several tens of atmospheres according to the type of the target metal and the shape and size of the target pore. become. The metal may of course be an alloy. The present invention is epoch-making in that it can be applied to all metals or alloys that cause a metal-gas eutectic reaction, and since the produced porous metal has a eutectic structure, it has processability, formability, Excellent cutting properties.

Further, it is conceivable to increase the added value by combining porous metals having various forms.
For example, the method includes carburizing a porous metal with a high-temperature gas to harden or strengthen the inner wall of the pore, and filling the inside of the pore with a different material to produce a composite material. By performing such a treatment, it is possible not only to prevent the deterioration as a negative effect caused by the formation of the porous material, but also to develop a material having more excellent characteristics than the bulk material.

Hereinafter, examples will be shown, and embodiments of the present invention will be described in more detail.

[0015]

【Example】

(Example 1) From a phase diagram under an equal pressure atmosphere of an Ag-O system, it has a eutectic point of Ag─O at 931 ° C, and in a molten state, Ag absorbs a large amount of oxygen. It can be seen that when the temperature is lower than 0 ° C., the solidification separates into two phases of silver and oxygen, and oxygen hardly dissolves in silver at room temperature.

Therefore, using a high-pressure high-frequency melting apparatus having a pressure resistance up to 100 atm, the pressure is increased from 0.1 MPa to 11 MPa by the improved Czochralski method shown in FIG.
Ag was dissolved and solidified in an oxygen atmosphere up to the above. The condition was set to about 0.1 mm / sec to 1 mm / sec by natural cooling. When pure silver (99.99%) is dissolved under oxygen of 0.1 MPa (1 atm), a number of spots are observed on the surface of the molten silver in the crucible. This is due to the blowing of oxygen. Further, the rod-shaped surface of the solidified silver which was being pulled upward showed a rough trace of the solidification due to the blowing of oxygen.

Similarly, 0.6 MPa and 1.1 M
The sample was pulled up under an oxygen pressure of Pa to produce a silver sample. Comparing the samples in these cases, it was found that 0.1 MPa
The surface is relatively smooth, but 0.6 MPa and 1.
At 1 MPa, it is observed that the surface is rough like lava rock. On the other hand, for comparison, under a pressurized atmosphere of a mixed gas of 0.55 MPa of oxygen and 0.55 MPa of argon so that the total pressure becomes 1.1 MPa, while maintaining the same oxygen pressure, the pressure is 0.1 MPa. It is notable that when the unreacted argon gas of 55 MPa is pressurized, the surface of the ingot is smooth. this is,
It is considered that the supply of the unreacted argon gas of 0.55 MPa suppressed the blowing of oxygen during coagulation.

The porous silver sample thus produced was cut by an electric discharge machine without causing distortion. FIG. 4 and FIG. 5 are observations of a cross section and a vertical section of a rod on an upper portion of porous silver produced under an oxygen pressure of 0.1 MPa, respectively, by a scanning electron microscope. As can be seen from FIGS. 4 and 5, pores grow in the pulling direction, that is, in the solidification direction. The pores are divided into two types: large pores ranging from 200 μm to several hundred μm in diameter and small pores having a diameter of about 50 to 100 μm. Made up of Further, the length of the pore was 250 to 1500 μm. However, 0.55MPa of oxygen and 0.55MPa
Under the mixed gas with argon gas a, as shown in FIG.
It can be seen that pores having a uniform size of about 200 μm are generated. Practically, it is desired that the pores have a uniform size. Therefore, it is considered that solidification under a mixed gas of 1.1 MPa is more preferable for formation of porous silver.

Of course, the present invention is not limited by the above examples. Various aspects are possible in detail.

[0020]

As described above in detail, according to the present invention, a lightweight structural material, an aerospace material, a porous catalyst, an anti-vibration material, a sound deadening material, a filter, a bearing, a heat exchanger, an electrolytic cell, etc. A wide variety of applications can be opened, and the production of a new porous metal having excellent properties such as strength, workability, and machinability as a metallic material becomes possible.

In this production, means such as a casting method and a pulling-up method can be used, and simple production can be achieved.

[Brief description of the drawings]

FIG. 1 is a relationship diagram illustrating a metal-gas phase diagram as a basic principle of the present invention.

FIGS. 2 (a), (b) and (c) are schematic diagrams each illustrating a device mounted in a high-pressure vessel as a device for the method of the present invention.

FIGS. 3A, 3B, and 3C are conceptual diagrams illustrating various types of pores; FIG.

FIG. 4 is a scanning electron micrograph instead of a drawing showing a cross section of a rod of the upper part of porous silver under 0.1 MPa of oxygen.

FIG. 5 is a scanning electron microscope observation photograph instead of a drawing showing a longitudinal section corresponding to FIG. 4;

FIG. 6 is a scanning electron micrograph instead of a drawing showing a cross section of porous silver produced under a mixed gas of 0.55 MPa of oxygen and 0.55 MPa of argon.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 High frequency coil for melting 2 Melting crucible 3 On-off valve 4 Mold 5 Water cooling unit 6 Sample 7 Metal rod sample for lifting

Claims (6)

[Claims] 1. A method for producing a porous metal, wherein a metal having a eutectic point in a metal-gas phase diagram under an equal-pressure gas atmosphere is melted and solidified in a pressurized gas atmosphere. 2. The production method according to claim 1, wherein the mixture is melted and solidified in a casting method. 3. The production method according to claim 1, wherein the material is melted and solidified in a pulling method. 4. The method according to claim 1, wherein the gas is hydrogen, oxygen or an inert gas. 5. The method according to claim 1, wherein the gas is a mixed gas of hydrogen or oxygen and an inert gas. 6. The method according to claim 1, wherein the solidification is carried out rapidly.