WO2017171511A1 - Method for producing metal foam - Google Patents

Abstract

The present application provides a method for producing metal foam. The present application can provide a method for producing metal foam which comprises uniformly formed holes and having desired porosity while exhibiting superb mechanical properties, and can provide metal foam having such characteristics. Furthermore, the present application can provide a method which can form, within a short processing time, metal foam into a thin film or sheet while assuring the properties discussed above, and can provide metal foam having such properties.

Description

Manufacturing method of metal foam

This application claims the benefit of priority based on Korean Patent Application No. 10-2016-0040362, filed April 1, 2016 and Korean Patent Application No. 10-2017-0040972, filed March 30, 2017. All contents disclosed in the documents of the Korean patent application are included as part of the present specification.

The present application relates to a method for producing a metal foam.

Metal foam has various useful properties such as light weight, energy absorbency, heat insulation, fire resistance or eco-friendliness, and thus can be applied to various fields including lightweight structures, transportation machines, building materials, or energy absorbing devices. . In addition, the metal foam not only has a high specific surface area but also improves the flow of fluids or electrons such as liquids, gases, and the like, so that substrates, catalysts, sensors, actuators, secondary batteries, fuel cells, and gases for heat exchangers can be further improved. It may be usefully applied to a gas diffusion layer (GDL) or a microfluidic flow controller.

It is an object of the present application to provide a method for producing a metal foam having uniform porosity and excellent mechanical strength while having a desired porosity.

As used herein, the term metal foam or metal skeleton refers to a porous structure containing metal as a main component. In the above, the main component of the metal is that the proportion of the metal is 55% by weight, 60% by weight, 65% by weight, 70% by weight, 75% by weight or more, based on the total weight of the metal foam or metal skeleton. It means when the weight percent or more, 85 weight% or more, 90 weight% or more or 95 weight% or more. The upper limit of the ratio of the metal contained as the main component is not particularly limited, and may be, for example, about 100% by weight, 99% by weight or 98% by weight.

As used herein, the term porosity may refer to a case in which porosity is at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 75%, or at least 80%. The upper limit of the porosity is not particularly limited and may be, for example, less than about 100%, about 99% or less, or about 98% or less. The porosity can be calculated in a known manner by calculating the density of the metal foam or the like.

The method of manufacturing a metal foam of the present application may include sintering a structure including a metal component. In the present application, the term structure refers to a structure before undergoing a process performed to form a metal foam such as the sintering, that is, a structure before the metal foam is produced. In addition, the structure, although referred to as a porous structure does not necessarily have to be porous by itself, and may be called a porous structure for convenience, as long as it can form a metal foam that is finally a porous metal structure.

In the present application, the structure may include a metal component and an organic binder, and may form the structure by molding a mixture including the metal component and the organic binder.

In one example, the metal component may include at least a metal having a predetermined relative permeability and conductivity. Application of such a metal, according to one example of the present application can be smoothly performed sintering according to the method when the induction heating method described later as the sintering is applied.

For example, as the metal, a metal having a relative permeability of 90 or more may be used. The relative permeability (μ _r ) is the ratio (μ / μ ₀ ) of the permeability (μ) of the material to the permeability (μ ₀ ) in the vacuum. The metal has relative permeability of 95 or more, 100 or more, 110 or more, 120 or more, 130 or more, 140 or more, 150 or more, 160 or more, 170 or more, 180 or more, 190 or more, 200 or more, 210 or more, 220 or more, 230 or more Over 240, over 250, over 260, over 270, over 280, over 290, over 300, over 310, over 320, over 330, over 340, over 350, over 360, over 370, over 380, over 390, over 400 410 or more, 420 or more, 430 or more, 440 or more, 450 or more, 460 or more, 470 or more, 480 or more, 490 or more, 500 or more, 510 or more, 520 or more, 530 or more, 540 or more, 550 or more, 560 or more, At least 570, at least 580, or at least 590. The higher the relative permeability, the higher the heat generated upon application of the electromagnetic field for induction heating, which will be described later, so the upper limit is not particularly limited. In one example, the upper limit of the relative permeability may be, for example, about 300,000 or less.

The metal may be a conductive metal. The term conductive metal has a conductivity at 20 ° C. of at least about 8 MS / m, at least 9 MS / m, at least 10 MS / m, at least 11 MS / m, at least 12 MS / m, at least 13 MS / m or 14.5 MS / It may mean a metal that is m or more or such an alloy. The upper limit of the conductivity is not particularly limited, and for example, the conductivity may be about 30 MS / m or less, 25 MS / m or less, or 20 MS / m or less.

In the present application, the metal having the relative permeability and conductivity as described above may simply be referred to as a conductive magnetic metal.

By applying the conductive magnetic metal, sintering can be more effectively performed when the induction heating process described later is performed. As such a metal, nickel, iron or cobalt may be exemplified, but is not limited thereto.

The metal component may comprise a second metal, different from the metal, with the conductive magnetic metal, if necessary. In this case, the metal foam may be formed of a metal alloy. As the second metal, a metal having a relative permeability and / or conductivity in the same range as the above-mentioned conductive magnetic metal may be used, and a metal having a relative permeability and / or conductivity outside such range may be used. In addition, 1 type may be included in a 2nd metal and 2 or more types may be included. The kind of the second metal is not particularly limited as long as it is different from the conductive magnetic metal to which it is applied. For example, copper, phosphorus, molybdenum, zinc, manganese, chromium, indium, tin, silver, platinum, gold, aluminum or One or more metals other than the conductive magnetic metal may be applied in magnesium, but the present invention is not limited thereto.

The proportion of the conductive magnetic metal in the metal component or structure is not particularly limited. For example, the ratio may be adjusted so that proper joule heat can be generated when the induction heating method described below is applied. For example, the metal component or structure may include 30 wt% or more of the conductive magnetic metal based on the weight of the entire metal component. In another example, the proportion of the conductive magnetic metal in the metal component or structure may be at least about 35 wt%, at least about 40 wt%, at least about 45 wt%, at least about 50 wt%, at least about 55 wt%, 60 wt% Or at least 65 wt%, at least 70 wt%, at least 75 wt%, at least 80 wt%, at least 85 wt% or at least 90 wt%. The upper limit of the ratio of the conductive magnetic metal is not particularly limited, and for example, the ratio of the conductive magnetic metal in the metal component or structure may be less than about 100 wt% or less than or equal to 95 wt%. However, the ratio is an exemplary ratio. For example, since the heat generated by induction heating by the application of the electromagnetic field can be adjusted according to the strength of the applied electromagnetic field, the electrical conductivity and resistance of the metal, the ratio may be changed according to specific conditions.

The metal component forming the structure may be in powder form. For example, the metals in the metal component may have an average particle diameter in the range of about 0.1 μm to about 200 μm. The average particle diameter is, in another example, about 0.5 μm or more, about 1 μm or more, about 2 μm or more, about 3 μm or more, about 4 μm or more, about 5 μm or more, about 6 μm or more, about 7 μm or more, or about 8 μm. It may be abnormal. In another example, the average particle diameter may be about 150 μm or less, 100 μm or less, 90 μm or less, 80 μm or less, 70 μm or less, 60 μm or less, 50 μm or less, 40 μm or less, 30 μm or less, or 20 μm or less. As metal in a metal component, what differs in an average particle diameter can also be applied. The average particle diameter may be selected in consideration of the form of the desired metal foam, for example, the thickness and porosity of the metal foam.

The structure may comprise an organic binder together with the metal component. For example, the structure may be manufactured by molding a slurry including the metal component and the organic binder.

The type of organic binder that can be applied in the present application is not particularly limited. As the organic binder, for example, polyalkylene carbonate having an alkylene unit having 1 to 8 carbon atoms such as alkyl cellulose, polypropylene carbonate or polyethylene carbonate having an alkyl group having 1 to 8 carbon atoms such as methyl cellulose or ethyl cellulose or Polyvinyl alcohol-based binders such as polyvinyl alcohol or polyvinylacetate; Polyalkylene oxide including an alkylene group having 1 to 8 carbon atoms such as polyethylene oxide or polypropylene oxide may be exemplified, but is not limited thereto.

In the structure, the organic binder may be included, for example, in a ratio of about 10 parts by weight to 400 parts by weight with respect to 100 parts by weight of the metal component. Finally, the ratio may be 10 parts by weight or more to ensure proper porosity, and 400 parts by weight or less may be used to efficiently advance the firing between metal components, thereby stably maintaining the foam form. The ratio of the binder is, in another example, at least about 20 parts by weight, at least about 30 parts by weight, at least about 40 parts by weight, at least about 50 parts by weight, at least about 60 parts by weight, at least about 70 parts by weight, at least about 80 parts by weight or About 90 parts by weight or more, about 350 parts by weight or less, about 300 parts by weight or less, about 250 parts by weight or less, about 200 parts by weight or less, or about 150 parts by weight or less.

The structure may contain known additives which are additionally required in addition to the above-mentioned components. Examples of such additives include, but are not limited to, solvents and binders.

The manner of forming the structure is not particularly limited. Various methods for forming a structure are known in the manufacturing field of metal foam, and all of these methods may be applied in the present application. For example, the structure may be formed by maintaining a slurry containing the metal component and the organic binder in a suitable template, or by coating the mixture in a suitable manner.

The shape of such a structure is not particularly limited as determined according to the desired metal foam. In one example, the structure may be in the form of a film or sheet. For example, when the structure is in the form of a film or sheet, the thickness may be 5,000 μm or less, 3,500 μm or less, 2,000 μm or less, 1000 μm or less, 800 μm or less, 700 μm or less and 500 μm or less. Metal foams generally have brittle characteristics in terms of their porous structural characteristics, and thus are difficult to manufacture in the form of a film or sheet, in particular in the form of a thin film or sheet, and have a problem of brittleness even when manufactured. However, according to the method of the present application, it is possible to form a metal foam having a thin thickness and uniformly internal pores and excellent mechanical properties.

In the above, the lower limit of the thickness of the structure is not particularly limited. For example, the thickness of the structure in the form of a film or sheet may be at least about 10 μm, at least 50 μm, or at least about 100 μm.

The metal foam may be manufactured by sintering the structure formed in the above manner. In this case, the manner of performing sintering for producing the metal foam is not particularly limited, and a known sintering method may be applied. That is, the sintering may be performed by applying an appropriate amount of heat to the structure in an appropriate manner.

As a method different from the conventional known method, in the present application, the sintering may be performed by an induction heating method. That is, as described above, since the metal component includes a conductive magnetic metal having a predetermined permeability and conductivity, an induction heating method may be applied. In this way, including the pores formed uniformly, the mechanical properties are excellent, and the porosity can also be more smoothly produced metal foam adjusted to the desired level.

Induction heating is a phenomenon in which heat is generated from a specific metal when an electromagnetic field is applied. For example, when an electromagnetic field is applied to a metal having appropriate conductivity and permeability, eddy currents are generated in the metal, and joule heating is generated by the resistance of the metal. In the present application, the sintering process may be performed through such a phenomenon. In the present application, the sintering of the metal foam can be performed in a short time by applying the same method, thereby ensuring processability, and at the same time, a metal foam having high porosity and excellent mechanical strength can be manufactured.

The sintering process may include applying an electromagnetic field to the structure. Joule heat is generated by the induction heating phenomenon in the conductive magnetic metal of the metal component by the application of the electromagnetic field, whereby the structure can be sintered. At this time, the conditions for applying the electromagnetic field are not particularly limited as determined by the type and ratio of the conductive magnetic metal in the structure.

For example, the induction heating may be performed using an induction heater formed in the form of a coil or the like.

Induction heating, for example, may be performed by applying a current of about 100A to 1,000A. In another example, the magnitude of the applied current may be 900 A or less, 800 A or less, 700 A or less, 600 A or less, 500 A or less, or 400 A or less. In another example, the magnitude of the current may be about 150 A or more, about 200 A or more, or about 250 A or more.

Induction heating can be performed, for example, at a frequency of about 100 kHz to 1,000 kHz. In another example, the frequency may be 900 kHz or less, 800 kHz or less, 700 kHz or less, 600 kHz or less, 500 kHz or less, or 450 kHz or less. The frequency may, in another example, be at least about 150 kHz, at least about 200 kHz, or at least about 250 kHz.

Application of the electromagnetic field for the induction heating may be performed, for example, within a range of about 1 minute to 10 hours. The application time is, in another example, about 9 hours or less, about 8 hours or less, about 7 hours or less, about 6 hours or less, about 5 hours or less, about 4 hours or less, about 3 hours or less, about 2 hours or less, about Up to 1 hour or up to about 30 minutes.

The above-mentioned induction heating conditions, for example, the applied current, the frequency and the applied time may be changed in consideration of the type and ratio of the conductive magnetic metal as described above.

The sintering of the structure may be carried out only by the above-mentioned induction heating or, if necessary, by applying appropriate heat with the induction heating, i.e., application of an electromagnetic field.

As the organic binder in the structure is removed by the heat generated in the sintering process as described above, the metal component may be sintered to form a metal foam.

The present application also relates to a metal foam. The metal foam may be prepared by the method described above. Such a metal foam may include, for example, at least the conductive magnetic metal described above. The metal foam may include at least 30 wt%, at least 35 wt%, at least 40 wt%, at least 45 wt%, or at least 50 wt% of the conductive magnetic metal. In another example, the proportion of the conductive magnetic metal in the metal foam may be about 55% by weight, 60% by weight, 65% by weight, 70% by weight, 75% by weight, 80% by weight, 85% by weight or Or 90% by weight or more. The upper limit of the ratio of the conductive magnetic metal is not particularly limited, and may be, for example, less than about 100% by weight or less than 95% by weight.

The metal foam may have a porosity in the range of about 40% to 99%. As mentioned, according to the method of the present application, the porosity and the mechanical strength can be adjusted while including uniformly formed pores. The porosity may be 50% or more, 60% or more, 70% or more, 75% or more, or 80% or more, 95% or less, or 90% or less.

The metal foam may also exist in the form of a thin film or sheet. In one example, the metal foam may be in the form of a film or sheet. The metal foam in the form of a film or sheet has a thickness of 2,000 μm or less, 1,500 μm or less, 1,000 μm or less, 900 μm or less, 800 μm or less, 700 μm or less, 600 μm or less, 500 μm or less, 400 μm or less, 300 μm or less, 200 μm or less, 150 μm or less , About 100 μm or less, about 90 μm or less, about 80 μm or less, about 70 μm or less, about 60 μm or less, or about 55 μm or less. The film or sheet-shaped metal foam has a thickness of about 10 μm, about 20 μm, about 30 μm, about 40 μm, about 50 μm, about 100 μm, about 150 μm, about 200 μm, about 250 μm, about 300 μm or more. , About 350 μm or more, about 400 μm or more, about 450 μm or more, or about 500 μm or more.

The metal foam may be utilized in various applications requiring a porous metal structure. In particular, according to the method of the present application, as described above, it is possible to manufacture a metal foam in the form of a thin film or sheet having a desired porosity and excellent mechanical strength, thereby expanding the use of the metal foam in comparison with the existing. have.

In the present application, it is possible to provide a method for producing a metal foam including a uniformly formed pores, having a desired porosity and capable of forming a metal foam having excellent mechanical properties, and a metal foam having the above characteristics. . In addition, the present application can provide a method and a metal foam that can form a metal foam having the above-described physical properties in the form of a thin film or sheet.

1 and 2 are SEM photographs of the metal foams formed in Examples 1 and 2, respectively.

Hereinafter, the present application will be described in detail with reference to Examples and Comparative Examples, but the scope of the present application is not limited to the following Examples.

Example 1.

Nickel powder (conductivity is about 14.5 MS / m, relative permeability is about 600, average particle diameter is about 10-20 μm) and ethyl cellulose are put in methylene chloride in a weight ratio of about 1: 1, and the co-electromagnetic mixer The slurry was prepared by mixing using. The prepared mixture was coated on a quartz plate with a thickness of about 200 μm to prepare a structure, and a metal foam was prepared by applying an electromagnetic field to the structure with a coil induction heater and sintering. At this time, the electromagnetic field was formed by applying a current of about 350 A at a frequency of about 380 kHz, and the application time was about 3 minutes. The porosity of the prepared metal foam was about 65%, the SEM photograph is shown in FIG.

Example 2.

A metal foam was prepared in the same manner as in Example 1 except that polyethylene carbonate was used instead of ethyl cellulose. The porosity of the prepared metal foam was about 45%, the SEM photograph is shown in FIG.

Example 3.

Polyvinyl alcohol was used instead of ethyl cellulose, and metal foam was prepared in the same manner as in Example 1 except that water was used instead of methylene chloride. The porosity of the prepared metal foam was about 52%.

Example 4.

A metal foam was prepared in the same manner as in Example 1 except that polyethylene oxide was used instead of ethyl cellulose. The porosity of the prepared metal foam was about 57%.

Claims (14)

1. A method of manufacturing a metal foam comprising the step of sintering a structure comprising a metal component and an organic binder comprising a conductive metal having a relative permeability of 90 or more.
2. The method of claim 1, wherein the conductive metal has a conductivity of 20 MS / m or more at 20 ° C.
3. The method of claim 1, wherein the conductive metal is nickel, iron, or cobalt.
4. The method of claim 1, wherein the structure includes 30 wt% or more of the conductive metal by weight.
5. The method of claim 1, wherein the conductive metal has an average particle diameter in the range of 5 μm to 100 μm.
6. The method for producing a metal foam according to claim 1, wherein the organic binder is alkyl cellulose, polyalkylene carbonate, polyvinyl alcohol, polyalkylene oxide or polyvinylacetate.
7. The method of claim 1, wherein the structure comprises 10 to 400 parts by weight of an organic binder based on 100 parts by weight of a metal component.
8. The method for producing a metal foam according to claim 1, wherein the structure is produced by using a slurry containing a metal component and an organic binder.
9. The method for producing a metal foam according to claim 1, wherein the structure is in the form of a film or sheet.
10. The method of claim 9, wherein the film or sheet has a thickness of 5,000 μm or less.
11. The method of claim 1, wherein the sintering of the structure is performed by applying an electromagnetic field to the structure.
12. The method of claim 11, wherein the electromagnetic field is formed by applying a current within a range of 100A to 1,000A.
13. The method of claim 11, wherein the electromagnetic field is formed by applying a current at a frequency within a range of 100 kHz to 1,000 kHz.
14. The method of claim 11, wherein the electromagnetic field is applied for a time within a range of 1 minute to 10 hours.

Images