JP3868546B2 - Method for producing porous silver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing porous silver . More specifically, the present invention relates to various mechanical parts such as catalyst materials, anti-seismic materials, shock-absorbing materials, electromagnetic shielding materials, automobiles, silencers, filters, self-lubricating bearings, heat exchangers, electrolytic cells, liquid separations. The present invention relates to a method for producing porous silver which is useful for a vessel , a lightweight panel of space material, an oxygen treatment device for water purification, and the like.
[0002]
[Prior art and its problems]
Conventionally, various types of porous materials such as inorganic and metal are known as products such as shirasu porous glass, cermet, and arpora, and the fields of application of these porous materials are diverse. However, naturally, porous glass is extremely inferior in strength, workability, and moldability compared to metals, and in the case of Celmet in which a foamed resin is filled with metal, or the use of a porous glass using a hydrogen gas foaming method. In this case, the applicable metal is limited, and application to many metals is impossible.
[0003]
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. For this reason, it has been treated as detrimental 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 machine parts, lightweight structural panels, anti-vibration materials, silencers, electromagnetic shielding materials, hydrogen storage alloys, catalysts, bearings, heat exchangers, electrolysis cells, etc. In addition, as described above, satisfactory results have not been obtained in terms of strength, workability, formability, etc., especially as a metal porous material, despite the expected expansion of applications in various fields. Therefore, the range of application cannot be expanded with conventional products.
[0004]
Accordingly, the present invention provides a method for producing a porous metal by a new method that can solve the above-mentioned problems of the prior art and realize a metal porous material having excellent workability, formability, machinability and the like. It is intended to provide.
[0005]
[Means for Solving the Problems]
The present invention, as to solve the above problems, to provide a method for manufacturing a porous silver, characterized in that solidify by melting under pressure oxygen gas atmosphere.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, porous silver is produced by utilizing a metal-gas eutectic reaction under an isobaric gas atmosphere. And in this invention, the porous silver which controlled the form and the magnitude | size of the pore (hole) is provided. More specifically, as shown in FIG. 1, when the metal-gas phase diagram has a eutectic point under a certain isobaric pressure, the eutectic reaction represented by the cooling process indicated by the arrow (L (liquid) → α + G (gas)) produces a gaseous lamellar structure in the metal during the solidification process. This creates a porous metal. That is, the present invention utilizes the fact that oxygen gas atoms dissolve in molten silver and do not dissolve in solid silver as a metal-gas eutectic reaction. When a molten metal in which oxygen gas is dissolved is cooled, the gas becomes bubbles inside the metal material, and porous silver having pores (pores) of uniform size is generated.
[0007]
Actually, in the production method of the present invention, a metal is melted and solidified in an oxygen gas atmosphere pressurized from normal pressure to high pressure.
In this case, melting and solidification, the casting method, a Czochralski method, Ru can be performed by a pulling method such as improved Czochralski method.
[0008]
Oxygen gas may be used alone, but by using in admixture with an inert gas such as argon (Ar), as described below, the advantage of facilitating the control of pores (holes).
FIG. 2 exemplifies (a) and (b) casting into a mold and (c) pulling up as methods of the manufacturing method of the present invention.
[0009]
For example, in the casting method, for example, the apparatus shown in FIGS. 2 (a) and 2 (b) is placed in a high-pressure oxygen gas container up to about 20 atmospheres, and metallic silver is dissolved in the melting crucible (2). It is heated and melted by the coil (1) and cast into the mold (4) cooled by the water cooling part (5) through the on-off valve (3). By cooling, it is solidified to produce porous silver (6).
[0010]
Similarly, in the pulling method, the apparatus shown in FIG. 2 (c) is placed in a high-pressure gas container and is melted by a high-frequency coil (1) in a melting pot (2) where silver is melted. Porous silver solidified by being pulled up by (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 gas type, gas pressure, or solidification rate, and further by applying a temperature gradient. Can be controlled. As possible forms, as shown in FIG. 3, (a) randomly distributed spherical pores, (b) needle-shaped pores directed toward the center, (c) lotus-shaped pores parallel to the generatrix, Discontinuous pores, spiral pores, and the like are exemplified, and the layer made of these pores may have a multilayer structure with a non-porous layer.
[0011]
As for the form of these pores, those having needle-like pores oriented in the central direction as a permeable porous metal, or lotus-like pores (through-type) parallel to the busbars are used for blood filtration filters, air purification, catalyst carriers. It is used for the structure of lightweight construction materials, batteries, electrodes, emulsified products, and has random distribution pores as non-permeable porous metal, lotus-like pores (non-penetrating type) parallel to the busbar, spiral pores, etc. The thing will be used for the weight reduction of a structural material, a sound-absorbing material, a building material, an acoustic device, and an electromagnetic wave shielding material.
[0012]
The pressure of the oxygen gas is appropriately selected within the range of, for example, several atmospheres to several tens of atmospheres according to the type of the target metal and the shape and size of the target pore (hole). . The metal may naturally be an alloy.
The method of the present invention is epoch-making in that it can be applied to any metal or alloy system that undergoes a metal-gas eutectic reaction, and since the produced porous metal has a eutectic structure, workability is improved. Excellent in moldability and machinability.
[0013]
Furthermore, it is conceivable to increase the added value by combining porous metals having various forms. For example, high-temperature gas carburization or the like is performed on the porous metal to harden or strengthen the inner wall of the pore, and a composite material is prepared by filling the pore with a different 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.
[0014]
Hereinafter, examples will be shown, and the embodiments of the present invention will be described in more detail.
[0015]
【Example】
Example 1
From a phase diagram (not shown) of an Ag—O based isobaric atmosphere, it has an eutectic point of Ag—O at 931 ° C., and in the molten state, Ag absorbs a large amount of oxygen. It can be seen that it is solidified and separated into two phases of silver and oxygen at a temperature below ℃, and that oxygen hardly dissolves in silver at room temperature.
[0016]
Therefore, Ag is dissolved and solidified in an oxygen atmosphere from 0.1 MPa to 11 MPa by the improved Czochralski method using a high-pressure high-frequency melting apparatus having a pressure resistance up to 100 atm. It was. The condition was about 0.1 mm / sec to 1 mm / sec by natural cooling. When pure silver (99.99%) is dissolved under oxygen at 0.1 MPa (1 atm), many spots are observed on the surface of the molten silver in the crucible. This is because oxygen is blown out. Further, the solidified silver rod-like surface being pulled upward showed rough traces of oxygen solidified by blowing out.
[0017]
Similarly, silver samples were prepared by pulling up under oxygen pressures of 0.6 MPa and 1.1 MPa. When the samples in these cases are compared, the surface of Ag is relatively smooth at 0.1 MPa, but it is observed that the surface is uneven like lava stone at 0.6 MPa and 1.1 MPa. Is done.
On the other hand, for comparison, in a pressurized atmosphere of a mixed gas of 0.55 MPa oxygen and 0.55 MPa argon so that the total pressure becomes 1.1 MPa, the oxygen pressure is approximately the same, but the oxygen pressure is 0. It is noted that the surface of the ingot is smooth when the unreacted argon gas of 55 MPa is pressurized. This is considered to be because oxygen blowing out during solidification was suppressed by loading 0.55 MPa of unreacted argon gas.
[0018]
The porous silver sample thus produced was cut by an electric discharge machine without causing distortion. 4 and 5 are each a cross-sectional view and a vertical cross-section of a rod in the upper part of porous silver produced under oxygen pressure of 0.1 MPa, as observed by a scanning electron microscope. As can be seen from FIGS. 4 and 5, the pores grow in the pulling direction, that is, the solidification direction. The pores are divided into two types: large pores having a diameter of 200 μm to several 100 μm and small pores having a diameter of about 50 to 100 μm. It is made up. The length of the pore was 250-1500 μm. However, under a mixed gas of oxygen of 0.55 MPa and argon of 0.55 MPa, a uniform size pore having a diameter of 50 to 200 μm is shown in FIG. It can be seen that is generated. Practically, it is desired that the pore size is uniform, so solidification under the 1.1 MPa mixed gas is considered preferable for the production of porous silver.
[0019]
Of course, the present invention is not limited to the above examples. Various aspects are possible in detail.
[0020]
【The invention's effect】
As described above in detail, according to the present invention, a wide variety of uses such as lightweight structural materials, aerospace materials, porous catalysts, anti-vibration materials, sound deadening materials, filters, bearings, heat exchangers, electrolytic cells, etc. This makes it possible to produce a new porous metal having excellent properties such as strength, workability and machinability as a metallic material.
[0021]
In this production, means such as casting or pulling can be used, and simple production is possible.
[Brief description of the drawings]
FIG. 1 is a relationship diagram illustrating a metal-gas system phase diagram as a basic principle of the present invention.
FIGS. 2 (a), (b) and (c) are schematic views illustrating an apparatus mounted in a high-pressure vessel as an apparatus for the method of the present invention, respectively.
FIGS. 3A, 3B, and 3C are conceptual views illustrating various types of pores. FIG.
FIG. 4 is a scanning electron micrograph in place of a drawing, showing a cross section of a rod in the upper part of porous silver under oxygen of 0.1 MPa.
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 in place of a drawing showing a transverse cross section of porous silver produced under a mixed gas of 0.55 MPa oxygen and 0.55 MPa argon.
[Explanation of symbols]
1 dissolve high-frequency coil 2 soluble seen pot 3 off valve 4 template 5 water cooling unit 6 porous silver 7 for pulling the metal rod

Claims (5)

Method for producing a porous silver, characterized in that solidify by melting silver oxygen gas atmosphere which is pressurized.   The manufacturing method of Claim 1 which is made to melt and solidify in a casting method.   The manufacturing method of Claim 1 which is made to melt and solidify in the pulling-up method. The production method according to any one of claims 1 to 3, wherein the mixed gas atmosphere of oxygen gas and inert gas is used. The manufacturing method in any one of Claim 1 thru | or 4 which is rapidly solidified .

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