Vertical freeze casting manufacture of metal foam

Abstract

A metal foam structure is used for numerous energy applications such as battery, electrolyzer, fuel cell, carbon capture, thermal management, and others due to its enhanced surface area to be utilized for improved efficiency. A net-shape metal foam sheet or plate production with desired thicknesses without cutting process is thus required to significantly reduce the manufacturing cost and to be more price competitive against other types of existing similar materials such as carbon paper, metal foil, mesh, plate, and others. In order to achieve this, a vertical freeze casting is described where the freeze casting of the metal slurry takes place with the metal slurry plate mold being placed vertically with respect to the ground, whereas the conventional freeze casting process takes place with the metal slurry plate mold being placed horizontally with respect to the ground.

Description

[0001] Vertical Freeze Casting Manufacture of Metal Foam Description

[0002] Cross-Reference to Related Applications

[0003]

[0001] This application claims the benefit of U.S. patent application 63 / 721,983, filed November 18, 2024.

[0004] Background of the Invention

[0005]

[0002] This invention relates to the production of metal foam sheet or plate for energy areas such as the electrodes of battery, fuel cell, thermal management systems, and techniques of making and using such metal foam sheets or plates, such as for use in anodes and cathodes of battery, electrolyzer, fuel cell, and similar and related devices.

[0006]

[0003] There is a need for improved quality and reduced manufacturing cost for metal foam sheet production by directly forming net-shape metal foam without the need of machining.

[0007] Brief Summary of the Invention

[0008]

[0004] A metal foam structure is used for numerous energy applications such as battery, electrolyzer, fuel cell, carbon capture, thermal management, and others due to its enhanced surface area to be utilized for improved efficiency. A net-shape metal foam sheet or plate production with well controlled thickness without cutting process is thus required to significantly reduce the manufacturing cost and to be more price competitive against other types of existing similar materials such as carbon paper, metal foil, mesh, or plate, and others.

[0009]

[0005] In an implementation, a manufacturing process includes vertical freeze casting of metal foam to form a net-shape metal foam. The process includes freezing a net-shaped clamped mold containing metal or metal oxide slurry vertically placed into a cooling liquid without applying cutting process.

[0010]

[0006] In an implementation, a method includes: preparing a metal or metal oxide powder slurry to obtain a prepared slurry; providing a prepared clamped mold including a space of intended geometry between gaskets of the prepared clamped mold; pouring the prepared slurry into the space of the prepared clamped mold, where the mold comprises an opening at a top side of the mold where the prepared slurry is poured in, a bottom side surface opposite to the top side and below the top side, and the bottom side is closed; immersing the mold into a vessel containing a cooling liquid (e.g., polypropylene glycol) for about 5 minutes to about 30 minutes to freeze the metal or metal oxide powder slurry; disassembling the clamped mold to remove a frozen green-body metal or metal oxide powder slurry; and drying and sintering the green-body into a three-dimensionally (3D) connected metal foam structure.

[0011]

[0007] Other objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed description and the accompanying drawings, in which like reference designations represent like features throughout the figures.

[0012] Brief Description of the Drawings

[0013]

[0008] Figure 1 shows processing sequence of vertical freeze casting manufacture of metal foam.

[0014]

[0009] Figure 2 shows prepared clamped mold containing metal or metal oxide powder slurry between gaskets in the mold.

[0015]

[0010] Figure 3 shows flexibly clamped mold containing metal or metal oxide powder slurry between gaskets, which is made possible by using spring-type bolts that can allow metalfoam slurry to expand freely during freezing.

[0016]

[0011] Figure 4 shows immersion of the clamped mold into polypropylene glycol cooling liquid for about 5 to 30 minutes to freeze the metal or metal oxide powder slurry.

[0017]

[0012] Figure 5 shows removal of the clamps and disassembling the mold to take out the frozen green-body metal or metal oxide powder slurry.

[0018]

[0013] Figure 6 shows scanning electron microscopic images of iron foam with about 70 percent porosity after sintering at about 750 degrees Celsius for about 90 minutes.

[0019]

[0014] Figure 7 shows a cross-sectional optical image of iron foam produced in this invention using a vertical freeze casting. The thickness was well controlled within the error range of plus or minus 2 percent without machining. This iron foam was sintered at about 900 degrees Celsius for about 60 minutes in vacuum.

[0020] Detailed Description of the Invention

[0021]

[0015] Geometries of the components required for energy applications such as battery, electrolyzer, fuel cell, and the like tend to be extreme; therefore, cutting or post-machining is often required. If the required component is a metal foam consisting of three-dimensionally structured pores on the scale of microns, cutting or machining is likely to cause closure of the surface pores of the metal foam and significantly degrade its electrochemical performance. This invention can solve this issue by directly forming a net-shape metal foam with a desired thickness and the elimination of the cutting process.

[0016] Figure 1 shows processing sequence of vertical freeze casting manufacture of metal foam. Here, a vertical freeze casting means that the freeze casting of the metal slurry takes place with the metal slurry plate mold being placed vertically with respect to the ground. The conventional freeze casting process takes place with the metal slurry plate mold being placed horizontally with respect to the ground.

[0022]

[0017] The process includes: (1) Preparing metal or metal oxide powder slurry. (2) Pouring prepared slurry into the space of intended geometry between gaskets of the prepared clamped mold. (3) Immersing the clamped mold into cooling liquid for about 5 to 30 minutes to freeze the metal or metal oxide powder slurry. (4) Disassembling the clamped mold to take out the frozen green-body metal or metal oxide powder slurry. (5) Drying and sintering the greenbody into three-dimensionally (3D) connected metal foam.

[0023]

[0018] In an implementation, a manufacturing process includes vertical freeze casting of metal foam to form a net-shape metal foam. The process includes freezing a net-shaped clamped mold (e.g., see figure 2) containing metal or metal oxide slurry vertically placed into a cooling liquid (e.g., see figure 4) without applying cutting process.

[0024]

[0019] The filling of slurry into the mold can be conducted using the gravity feeding. The clamping mold (e.g., see figure 2) can be made of a metallic material such as aluminum, copper, nickel, titanium, zinc, steel, or their alloys. A flexible mold clamping can be achieved using spring-type bolts (e.g., see figure 3).

[0025]

[0020] Further, the vertical freeze casting is carried out with the vertical immersion of a net-shaped mold containing slurry into polypropylene glycol cooling liquid for about 5 minutes to about 30 minutes (e.g. see figure 4).

[0026]

[0021] The metal or metal oxide slurry can include metal or metal oxide powder, ranging from about 50 weight percent to about 80 weight percent, a binder ranging from about 3 weight percent to about 10 weight percent, dispersant ranging from about 0.2 weight percent to about 1.0 weight percent, defoaming agent ranging from about 0.1 weight percent to about 0.5 weight percent, anti-settling agent ranging from about 0.7 weight percent to about 2.0 weight percent, pH controlling agent ranging from 0.3 weight percent to 1.2 weight percent, and water or H2O as a solvent.

[0027]

[0022] The frozen green-body metal foam slurry is subjected to sublimation, reduction, and sintering to form a three-dimensionally connected metal foam with microscale pores. The reduction temperature ranges from about 300 degrees Celsius to about 600 degrees Celsius from about 2 hours to about 7 hours, and the sintering temperature ranges from about 600 degrees Celsius to about 1200 degrees Celsius for about 0.5 hours to about 5 hours.

[0023] A final metal foam sheet or plate after sintering process has thickness of about 200 microns to about 15 millimeters. The final metal foam sheet or plate after sintering process has net shape with a tolerance of about 10 microns to about 50 microns flatness variation.

[0028]

[0024] A method includes: preparing a metal or metal oxide powder slurry to obtain a prepared slurry; providing a prepared clamped mold including a space of intended geometry between gaskets of the prepared clamped mold; pouring the prepared slurry into the space of the prepared clamped mold, where the mold comprises an opening at a top side of the mold where the prepared slurry is poured in, a bottom side surface opposite to the top side and below the top side, and the bottom side is closed; immersing the mold into a vessel containing a cooling liquid (e.g., polypropylene glycol) for about 5 minutes to about 30 minutes to freeze the metal or metal oxide powder slurry; disassembling the clamped mold to remove a frozen green-body metal or metal oxide powder slurry; and drying and sintering the green-body into a three-dimensionally (3D) connected metal foam structure.

[0029]

[0025] An intended geometry can be a net-shaped structure. Then, the three-dimensionally (3D) connected metal foam structure will be net-shape sheet or plate having a thickness from about 10 microns to about 50 microns.

[0030]

[0026] In an implementation, the net-shape structure will be an open-meshed structure having openings defined by metal structure at regular intervals. The metal structure of the net will be porous metal or three-dimensionally connected metal foam. The metal structure of the net can crisscross at right angles to each others, and then the openings in the net can be squares or rectangles. The metal structure of the net can crisscross at transverse angles to each others, and then the openings in the net can be parallelograms or trapezoids. Further in other implementations, the openings of the net can include triangles.

[0031]

[0027] The prepared clamped mold can include spring-type bolts that allow the metal foam slurry to expand during the freezing process. The sintering temperature ranges from about 600 degrees Celsius to about 1200 degrees Celsius for about 0.5 hours to about 5 hours. The drying and sintering the green-body into a three-dimensionally (3D) connected metal foam structure can include: reducing the green-body at a reduction temperature ranges from about 300 degrees Celsius to about 600 degrees Celsius from about 2 hours to about 7 hours. For example, an oxide can be reduced into a metal.

[0032]

[0028] Referring to figures 2-5, the prepared clamped mold can further include a first rectangular outer plate, a second rectangular outer plate, a first side surface, and a second side surface, the first and second rectangular outer plates are opposite to each other, the first and second side surfaces are parallel to each other and perpendicular to first the rectangular outer plate, the bottom side surface is perpendicular to first the rectangular outer plate and first and second side surfaces, and a number of of spring-type bolts (e.g., two per edge as in figure 3), positioned along edges of the second rectangular outer plate that can be screwed to couple the second rectangular outer plate to the first rectangular outer plate together, and a screwing direction of the spring-type bolts is perpendicular to a surface of the second rectangular outer plate.

[0033]

[0029] Figure 2 shows prepared clamped mold containing metal or metal oxide powder slurry between gaskets in the mold. An image of a clamped mold is also presented. Metal or metal oxide powder slurry is poured into the space between gaskets of the clamped mold. The filling of slurry into the mold can be performed simply using the gravity feeding. The mold can be made of a metallic material with decent thermal conductivity such as aluminum, copper, nickel, titanium, zinc, steel, or their alloys. The thickness of the gaskets should be about 10 to 30 percent greater than the desired final thickness of the net-shape metal foam by taking into account of the volume shrinkage of the metal foam during sintering.

[0034]

[0030] Figure 3 shows another clamped mold containing metal or metal oxide powder slurry between gaskets. Flexibly clamped mold containing metal or metal oxide powder slurry between gaskets, which is made possible by using spring-type bolts that can allow metalfoam slurry to expand freely during freezing. The filling of slurry into the mold can be performed similarly using the gravity feeding. The mold can also be made of a metallic material with decent thermal conductivity such as aluminum, copper, nickel, titanium, zinc, steel, or their alloys. Here, a flexible mold clamping can be achieved by using spring-type bolts instead of using regular, tightening bolts so that the spring-type bolts can allow the metal-foam slurry to expand during the freezing process. The spring-type bolts can also allow easier demolding after the freezing process is finished.

[0035]

[0031] Figure 4 shows immersion of the clamped mold into polypropylene glycol cooling liquid for about 5 to 30 minutes to freeze the metal or metal oxide powder slurry. The figure shows a clamped mold immersed in a cooling liquid. The temperature of the cooling liquid can influence the freezing time and speed as well as the final microstructure of the metal foam after sintering. In general, the freezing speed of polypropylene glycol liquid is fast enough that the powder slurry can uniformly freeze without forming voids or even microstructure. The freezing point can vary depending on the concentration of propylene glycol mixed with water, as desired. For example, the polypropylene glycol can be at a temperature from about -59 degrees Celsius to about 0 degrees Celsius, or from about -40 degrees Celsius to about 0 degrees Celsius.

[0032] Figure 5 shows removal of the clamps and disassembling the mold to take out the frozen green-body metal or metal oxide powder slurry. The frozen green-body is then subjected to sublimination prior to sintering to remove water molecules and leave microscale pores in the green body. Sintering is subsequently applied to chemically connect the metal or metal oxide powder and result in three-dimensionally (3D) connected pore structured metal foam. No microstructural damage or disruption is generally observed after the freezing, drying, or sintering process if a right processing is performed.

[0036]

[0033] Figure 6 shows scanning electron microscopic (SEM) images of an exemplary iron foam with about 70 percent porosity after sintering at about 750 degrees Celsius for about 90 minutes. It is particularly noted that the surface pores on the iron (Fe) foam are completely open, which is an important for use as an electrode for energy cells. The desired thickness of the metal foam sheet or plate can be obtained without a cutting process.

[0037]

[0034] Figure 7 shows a cross-sectional optical image of iron foam produced according to a vertical freeze casting technique of this disclosure. The thickness was well controlled within the error range of about plus or minus 2 percent without machining. This iron foam was sintered at about 900 degrees Celsius for about 60 minutes in vacuum.

[0038]

[0035] U.S. patent applications 62 / 194,564, filed July 20, 2015, 15 / 215,519, filed July 20, 2016, 62 / 194,677, filed July 20, 2015, 15 / 215,541, filed July 20, 2016, 62 / 641,223, filed March 9, 2018, PCT / US2019 / 021704, filed March 11, 2019, 61 / 700,793, filed July 19, 2018, and PCT / US2019 / 042686, filed July 19, 2019 describe various techniques of manufacturing a metal form, including freeze casting. These techniques, in whole or in part, can be used to in a vertical freeze casting manufacture of metal foam.

[0039]

[0036] This patent describes some examples of implementations with specific dimensions, measurements, temperatures, and values. These are not intended to be exhaustive or to limit the invention to the precise form described. The values, percentages, times, and temperatures are approximate (e.g., about) values. These values can vary due to, for example, measurement or manufacturing variations or tolerances or other factors (e.g., engineering variation). For example, depending on the tightness of the manufacturing and measurement tolerances, the temperature and time values can vary plus or minus 2.5 percent, plus or minus 5 percent, plus or minus 7.5 percent, plus or minus 10 percent, plus or minus 15 percent, plus or minus 20 percent, or plus or minus 25 percent.

[0040]

[0037] Further, the values are for a specific implementation, and other implementations can have different values, such as certain values made larger for a larger-scaled sized process or product, or smaller for a smaller-scaled product. A device, apparatus, or process may be made proportionally larger or smaller by adjusting relative measurements proportionally (e.g., maintaining the same or about the same ratio between different measurements). In various implementations, the values can be the same as the value given, about the same of the value given, at least or greater than the value given, or can be at most or less than the value given, or any combination of these.

[0041]

[0038] Some techniques or flows are described. A flow may have additional steps (not necessarily described in this patent), different steps which replace some of the steps presented, fewer steps or a subset of the steps presented, or steps in a different order than presented, or any combination of these. Further, the steps in other implementations may not be exactly the same as the steps presented and may be modified or altered as appropriate for a particular application or based on the situation.

[0042]

[0039] This description of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form described, and many modifications and variations are possible in light of the teaching above. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications. This description will enable others skilled in the art to best utilize and practice the invention in various embodiments and with various modifications as are suited to a particular use. The scope of the invention is defined by the following claims.

Claims

ClaimsWhat is claimed is:

1. A manufacturing process of vertical freeze casting of metal foam to form a net-shape metal foam by freezing a net-shaped clamped mold containing metal or metal oxide slurry vertically placed into a cooling liquid without applying cutting process.

2. The manufacture of claim 1 wherein the filling of slurry into the mold is conducted using the gravity feeding.

3. The manufacture of claim 1 wherein the clamping mold is made of a metallic material such as aluminum, copper, nickel, titanium, zinc, steel, or their alloys.

4. The manufacture of claim 1 wherein a flexible mold clamping is achieved using spring-type bolts.

5. The manufacture of claim 1 wherein vertical freeze casting is carried out with the vertical immersion of a net-shaped mold containing slurry into polypropylene glycol cooling liquid for about 5 minutes to about 30 minutes.

6. The manufacture of claim 1 where the metal or metal oxide slurry comprises metal or metal oxide powder ranging from 50 weight percent to 80 weight percent, a binder ranging from 3 weight percent to 10 weight percent, dispersant ranging from 0.2 weight percent to 1.0 weight percent, defoaming agent ranging from 0.1 weight percent to 0.5 weight percent, antisettling agent ranging from 0.7 weight percent to 2.0 weight percent, pH controlling agent ranging from 0.3 weight percent to 1.2 weight percent, and water as a solvent.

7. The manufacture of claim 1 wherein the frozen green-body metal foam slurry is subjected to sublimation, reduction, and sintering to form a three-dimensionally connected metal foam with microscale pores. The reduction temperature ranges from 300 degrees Celsius to 600 degrees Celsius form 2 hours to 7 hours, and the sintering temperature ranges from 600 degrees Celsius to 1200 degrees Celsius for about 0.5 hours to about 5 hours.

8. The manufacture of claim 6 wherein the final metal foam sheet or plate after sintering process has thickness of 200 microns to 15 millimeters.

9. The manufacture of claim 6 wherein the final metal foam sheet or plate after sintering process has net shape with a tolerance of 10 to 50 microns flatness variation.

10. A method comprising:preparing a metal or metal oxide powder slurry to obtain a prepared slurry; providing a prepared clamped mold comprising a space of intended geometry between gaskets of the prepared clamped mold;pouring the prepared slurry into the space of the prepared clamped mold, wherein the mold comprises an opening at a top side of the mold where the prepared slurry is poured in, a bottom side surface opposite to the top side and below the top side, and the bottom side is closed;immersing the mold into a vessel containing a cooling liquid for about 5 minutes to about 30 minutes to freeze the metal or metal oxide powder slurry;disassembling the clamped mold to remove a frozen green-body metal or metal oxide powder slurry; anddrying and sintering the green-body into a three-dimensionally (3D) connected metal foam structure.

11. The method of claim 10 wherein the intended geometry comprises a net-shaped structure.

12. The method of claim 10 wherein the intended geometry comprises a net-shaped mold, and the three-dimensionally (3D) connected metal foam structure a net-shape sheet or plate comprising a thickness from about 10 microns to about 50 microns.

13. The method of claim 10 wherein the metal or metal oxide slurry comprises metal or metal oxide powder, ranging from about 50 weight percent to about 80 weight percent, a binder ranging from about 3 weight percent to about 10 weight percent, dispersant ranging from about 0.2 weight percent to about 1.0 weight percent, defoaming agent ranging from about 0.1 weight percent to about 0.5 weight percent, anti-settling agent ranging from about 0.7 weight percent to about 2.0 weight percent, pH controlling agent ranging from 0.3 weight percent to 1.2 weight percent, and water as a solvent.

14. The method of claim 10 wherein the prepared clamped mold comprises springtype bolts that allow the metal foam slurry to expand during the freezing process.

15. The method of claim 10 wherein the sintering temperature ranges from about 600 degrees Celsius to about 1200 degrees Celsius for about 0.5 hours to about 5 hours.

16. The method of claim 10 wherein the drying and sintering the green-body into a three-dimensionally (3D) connected metal foam structure comprisesreducing the green-body at a reduction temperature ranges from about 300 degrees Celsius to about 600 degrees Celsius from about 2 hours to about 7 hours.

17. The method of claim 10 wherein the prepared clamped mold comprises a first rectangular outer plate, a second rectangular outer plate, a first side surface, and a second side surface,the first and second rectangular outer plates are opposite to each other,the first and second side surfaces are parallel to each other and perpendicular to first the rectangular outer plate,the bottom side surface is perpendicular to first the rectangular outer plate and first and second side surfaces, anda plurality of spring-type bolts, positioned along edges of the second rectangular outer plate that can be screwed to couple the second rectangular outer plate to the first rectangular outer plate together, and a screwing direction of the spring-type bolts is perpendicular to a surface of the second rectangular outer plate.

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