KR101478286B1 - Manufacturing method of metal foam and metal foam manufactured thereby - Google Patents

Abstract

The present invention relates to a method for producing a metal foam. Specifically, the present invention provides a method for producing a metal powder, comprising: (a) mixing two or more metal powders; (b) molding the mixed powder obtained in the step (a); (c) sintering the formed body obtained in the step (b); (d) dealloying the sintered body obtained in the step (c); And (e) heat treating the sintered body that has been alloyed in step (d). According to the present invention, a metal alloy is produced through sintering, followed by dealloying the metal alloy and then heat-treating the metal alloy, thereby manufacturing a metal foam at a much lower temperature than a conventional metal foam manufacturing method The metal foam produced by the above production method has a fine structure in which nano-sized pores and micro-sized pores are mixed, and not only has a high specific surface area but also is excellent in fluid flow of liquid, Catalysts, sensors, actuators, fuel cells, gas diffusion layers (GDLs), microfluidic flow controllers, and the like, because they exhibit high performance.

Description

Technical Field [0001] The present invention relates to a method of manufacturing a metal foam,

More particularly, the present invention relates to a method of manufacturing a metal foam which can economically produce a metal foam with a simple process.

Metal foam is also referred to as a foam metal, and refers to a metal containing a plurality of pores. Such metal foams can be applied to various fields such as lightweight structures, transportation machines, building materials, energy absorbing devices and the like by having various useful properties such as light weight, energy absorption, heat insulation, fire resistance or environmental friendliness. Particularly, metal foams having a microstructure in which nano-sized pores and micro-sized pores are mixed together, which have been gradually realized in recent years, not only have a high specific surface area but also can improve the flow of fluids or electrons such as liquids and gases, And can be usefully applied to a substrate for a heat exchanger, a catalyst, a sensor, an actuator, a secondary battery, a fuel cell, a gas diffusion layer (GDL), a microfluidic flow controller, Value added material.

As a general method for producing a metal foam, there is a casting method. The casting method includes a method (bubble generation method) in which a metal ingot is melted to make a molten metal, and then a foaming agent is added to expand and grow bubbles by a chemical reaction at a high temperature And a method of producing a foamed metal by injecting a gas such as hydrogen, argon, or air directly into a molten metal (gas injection method).

However, when a metal foam is produced by a casting method, a relatively large pore size distribution is formed. After the completion of the foaming operation, unfoamed portions are generated on the bottom surface of the foamed material, and coarse pores are formed in the upper portion, There is a problem that the homogeneity of the pores in the foam is deteriorated.

Meanwhile, in recent years, it has been studied to fabricate metal foams having nano pores by using dealloying which removes less noble metal among the metals constituting the alloy in metal alloys .

Specifically, a metal foam made of Au is produced by removing Ag from a binary alloy of Ag-Au by de-alloying, or Al is removed from a binary alloy of Al-Cu by a de-alloy to produce a metal foam made of Cu .

However, in this manufacturing method, when the base alloy to be provided in the de-alloying process is produced, since each constituent metal component is melted at a high temperature to produce an alloy, the process is complicated, oxidation problem and economical It is accompanied by the problem of disadvantage.

Accordingly, there is a need for a new metal foam manufacturing method which can economically produce metal foam with a simpler process, and can form a microstructure in which nano-sized pores and micro-sized pores are mixed in the metal foam.

Korean Registered Patent No. 10-1190384 (registration deadline: Oct. 11, 2012)

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a method of manufacturing a metal foam at a much lower temperature by a simpler process than the conventional method, and a metal foam produced by the method. In particular, the metal foam produced by the present invention is a polymer fuel cell which forms a microporous and nano-sized pore structure and which provides a smooth flow of water and gas as a foam material and a functional material capable of maximizing the catalytic reaction on the surface. The electrode and the gas diffusion layer, and the like.

According to an aspect of the present invention, there is provided a method of manufacturing a metal powder, comprising the steps of: (a) mixing two or more metal powders; (b) molding the mixed metal powder obtained in the step (a); (c) sintering the formed body obtained in the step (b); (d) dealloying the sintered body obtained in the step (c); And (e) heat-treating the sintered body that has been alloyed in step (d), and a metal foam produced by the method.

According to the present invention, a metal alloy is produced through sintering, followed by dealloying the metal alloy and then heat-treating the metal alloy, thereby manufacturing a metal foam at a much lower temperature than a conventional metal foam manufacturing method The metal foam produced by the above production method has a fine structure in which nano-sized pores and micro-sized pores are mixed, and not only has a high specific surface area but also is excellent in fluid flow of liquid, Performance.

1 is a flowchart of a method of manufacturing a metal foam according to the present invention.
2 is a phase diagram of an Al-Cu binary system used in an embodiment of the present invention.
FIG. 3 is a scanning electron microscope (SEM) photograph of a section of a copper (Cu) foam prepared in an embodiment of the present invention and a partial enlarged photograph thereof.

Hereinafter, the present invention will be described in detail.

FIG. 1 is a flow chart showing a method for manufacturing a metal foam according to the present invention. As shown in FIG. 1, the method for manufacturing a metal foam according to the present invention comprises: (a) mixing two or more kinds of metal powders; (b) molding the mixed metal powder obtained in step (a); (c) sintering the formed body obtained in step (b); (d) dealloying the sintered body obtained in step (c); And (e) heat treating the sintered body that has been alloyed in step (d).

Hereinafter, a method of manufacturing a metal foam according to a preferred embodiment of the present invention will be described in more detail.

Step (a) of the present production method is a step of mixing two or more metal powders to prepare a mixed metal powder.

At this time, the two or more types of metal powders for producing the mixed metal powder include at least one selected from the group consisting of Ag, Al, Au, Cu, Mn, Ni, (Al) powder and copper (Cu) powder, ii) manganese (Mn) powder and nickel (Ni) powder, and at least one metal powder selected from the group consisting of zinc oxide Or iii) silver (Ag) powder and gold (Au) powder are more preferable.

In carrying out the step (a), it is possible to mix only two or more kinds of metal powders corresponding to the raw material powder, but it is also possible to add two or more kinds of metal powders in addition to known additives such as binders, release agents, dispersants and plasticizers It is possible.

Step (b) of the present production method is a step of molding the mixed metal powder obtained in step (a). The molding method used in this step is not limited as long as it is a method capable of obtaining a molded body having a shape suitable for sintering such as press molding, cold isostatic pressing, powder injection molding, etc. However, From the viewpoint of ease of production of a molded article.

When a molded article is produced by press molding, the type of apparatus to be used is not particularly limited, but it is preferable to perform molding at a pressure of 0.3 MPa or more. When the press forming is performed at a molding pressure of less than 0.3 MPa, the molded body to be produced does not have a sufficient density and consequently a sintered body having sufficient strength can not be obtained.

On the other hand, the molded body can be manufactured without restriction of the form suitable for the intended use such as pellets, bar, and the like.

Step (c) of the present production method is a step of sintering the formed body obtained in step (b).

At this time, the upper limit of the sintering temperature may be determined in a temperature range in which the solid phase sintering is performed in consideration of the phase balance degree of the two or more kinds of metal powders. For example, a molded article containing 30 at% of copper and 70 at% of aluminum has an eutectic point temperature (Fig. 2) which is a part of the phase equilibrium diagram of a two-component system of copper (Cu) The upper limit of the sintering temperature may be a temperature of less than 546.2 ° C, preferably 400 to 500 ° C.

The lower limit of the sintering temperature can be appropriately selected in consideration of the desired relative density and strength of the sintered body depending on the type of the alloy system. For example, in the case of a two-component system of copper (Cu) -aluminum (Al), it is preferable that the temperature is 300 DEG C or more in terms of minimizing pores included in the sintered body and strength of the sintered body.

On the other hand, it is also possible to keep the sintering temperature constant at the upper and lower limits of the sintering temperature, and to gradually raise or lower the sintering temperature at the upper and lower sintering temperatures.

The sintering time at the above-mentioned sintering temperature is preferably 1 hour to 50 hours taking into consideration sintering property and economic aspect at the same time.

Regarding the sintering atmosphere, sintering may be performed at atmospheric pressure or vacuum, but sintering may be performed in an atmosphere of reducing gas, inert gas, or the like.

Step (e) of the present production method is a step of dealloying the sintered body heat-treated in step (d).

The term "de-alloy" refers to the selective removal of a metal component from two or more components constituting the alloy, and a specific metal component is selectively dissolved according to the difference in ionization tendency between the metal constituting the alloy in the acid solution or the basic solution, One example is the removal.

Step (d) in the present invention can be carried out by holding the sintered body obtained in step (c) in a state of being immersed in an acidic or basic solution for a predetermined time. By doing so, at least one of the two kinds of metal components contained in the sintered body obtained in the step (c) dissolves into the solution and is removed from the sintered body. The step (d) is preferably carried out until at least the generation of the hydrogen gas generated as the at least one metal component dissolves can not be visually observed. For this purpose, the step (d) is preferably carried out for at least 1 hour .

The de-alloy of step (d) can be more effectively performed as the difference in standard electrode potential, which is directly related to the ionization tendency of each of two or more kinds of metals contained in the sintered body, is greater. For example, in the case of a two-component system of copper-aluminum, since the standard electrode potential difference between copper (standard electrode potential: 0.342 V) and aluminum (standard electrode potential: -1.662 V) is large, Can be completely removed. Preferably, the difference in standard electrode potential between two kinds of metals is 1.0 V or more.

Step (e) of the present production method is a step of heat-treating the sintered body that has been alloyed in step (d).

At this time, the heat treatment can be performed at a temperature at which the diffusion and sintering of the remaining metal elements can be appropriately performed in consideration of the phase balance degree of the alloy. For example, in the case of a sintered body containing 30 at% of copper and 70 at% of aluminum, it can be seen from FIG. 2 showing a part of the phase balance degree of the copper-aluminum binary system at a temperature higher than the eutectic point temperature of 546.2 ° C. Heat treatment may be performed so that sufficient copper diffusion may occur, and preferably, the heat treatment may be performed at a temperature of 600 to 1000 캜. As described above, the particles constituting the microstructure of the sintered body are rearranged and filled by heat treatment at a temperature at which sufficient diffusion and sintering can be performed, and grain growth is achieved by diffusion of atoms in the liquid phase and the solid phase.

The heat treatment time at the heat treatment temperature is preferably 1 to 20 hours, taking into consideration economical aspects in addition to microstructure control such as particle size and distribution.

Regarding the heat treatment atmosphere, the heat treatment may be performed at atmospheric pressure or under vacuum, but the heat treatment may be performed in an atmosphere of a reducing gas, an inert gas, etc. Preferably, the sintered body is oxidized The heat treatment can be performed in a reducing gas atmosphere such as a hydrogen atmosphere.

Also, the present invention provides a metal foam produced by the method for producing a metal foam using the sintering and de-alloying.

The metal foam produced by the method for producing a metal foam according to the present invention has a microstructure in which nano-sized pores and micro-sized pores are mixed and distributed, thereby not only having a high specific surface area but also a fluid flow of liquid, (GDL), microfluidic flow controller, and the like, because it exhibits excellent performance in the case of a heat exchanger, a catalyst, a sensor, an actuator, a fuel cell, a gas diffusion layer (GDL) and a microfluidic flow controller.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in detail below on the basis of embodiments. The presented embodiments are illustrative and are not intended to limit the scope of the invention.

<Examples> Preparation of Copper Foam Using Cu-Al Binary Alloy System

A powder mixture consisting of 30 at% of copper powder (manufactured by Metal Chem Tech .; average particle size 1 μm) and 70 at% of aluminum powder (Alfa Aesar, USA; average particle size 1 μm) was mixed with a mixer (SPEX CertiPrep product, 8000-D Mixer Mill) for 10 minutes. The thus obtained mixed powder was pressure-molded using an air presser (DBP-6P, manufactured by Dongjin Machinery) to obtain pellets. The pellets thus obtained were sintered in an air furnace at 450 DEG C for 24 hours. Next, the sintered pellets were cut into flakes using a diamond cutter (Isomet low speed saw, manufactured by Buehler (USA)) and then polished to have a thickness of 200 to 250 mu m. Then, the polished flakes were immersed in a 5 wt% aqueous solution of sodium hydroxide (NaOH) and de-alloyed for 5 hours to remove aluminum from the flakes. The alloyed flakes were then heat treated in a hydrogen atmosphere at 650 DEG C for 2 hours in a tube furnace (MSTF11-500) to produce copper foams.

<Experimental Example> Microstructure observation of the metal foam prepared in the example

The cut microstructure of the copper foam specimen prepared in the example was photographed using a scanning electron microscope (SEM: JEOL (product), JSM7401F), which is shown in FIG.

From the left image taken at a relatively low magnification among the images included in FIG. 3, it can be seen that the copper foams produced in the examples are irregularly distributed in micro-sized pores. In addition, it can be seen from FIG. 3 that the copper foams prepared in the examples also contain nano-sized pores from the right-hand image of a part of the microstructure of the left image. That is, from FIG. 3, it can be seen that the copper foam produced from the embodiment according to the present invention has a microstructure in which nano-sized pores and micro-sized pores are mixed. The copper foams produced according to the present invention have a microstructure in which nano-sized pores and micro-sized pores are mixed. The sintering is performed at a temperature lower than the eutectic point before the de-alloying, In the region where the mixing is uniformly performed well, the alloy is formed well by the sintering process despite the low sintering temperature, and nano-sized pores are formed by the de-alloy, whereas the aluminum is not well mixed with the copper, It appears that aluminum is still ubiquitinated even by sintering because micro-sized pores are formed in the region by the de-alloy.

Claims (14)

(a) is prepared by mixing two or more metal powders selected from the group consisting of (Ag), aluminum (Al), gold (Au), copper (Cu), nickel (Ni), titanium (Ti) and zinc ;
(b) molding the mixed metal powder obtained in the step (a);
(c) sintering the formed body obtained in the step (b);
(d) dealloying the sintered body obtained in the step (c); And
(e) heat treating the sintered body that has been alloyed in step (d) in a reducing gas atmosphere. delete The method according to claim 1,
Wherein the two or more kinds of metal powders in step (a) are aluminum (Al) powder and copper (Cu) powder. The method according to claim 1 or 3,
Wherein the step (b) is carried out using press molding, cold isostatic pressing or powder injection molding. The method of claim 3,
Wherein the step (c) is maintained at a temperature of 400 ° C to 500 ° C for 1 to 50 hours. 6. The method of claim 5,
Wherein the step (c) is maintained at a temperature of 450 DEG C for 24 hours. The method according to claim 1 or 3,
Wherein the step (d) is performed by immersing the heat-treated sintered body in an acid solution or a basic solution for 1 hour or more. The method of claim 3,
Wherein the step (d) is performed by immersing the heat-treated sintered body in an aqueous solution of 5 wt% sodium hydroxide (NaOH) for 5 hours. The method of claim 3,
Wherein the step (e) is maintained at a temperature of 600 ° C to 1000 ° C for 1 hour to 20 hours. 10. The method of claim 9,
Wherein the step (e) is maintained at a temperature of 650 DEG C for 2 hours. delete delete delete delete

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