BARBEE BRENT (US)
MURRAY JOSEPH (US)
BURGESS DARREN R (US)
US5112697A | 1992-05-12 | |||
SU594181A1 | 1978-02-25 | |||
RU2371498C1 | 2009-10-27 | |||
RU2123052C1 | 1998-12-10 | |||
EP1266973A2 | 2002-12-18 |
CLAIMS What is claimed is: 1 . A method of constructing a loaded metal foam, the method comprising: melting a portion of metal to produce a metal melt within an interior of a closed vessel; purging oxygen, oxygenated molecule-based gases, or both from the interior of the vessel; injecting a forming gas into the metal melt to form channels therein; maintaining the injection of the forming gas for a predetermined amount of time; and cooling the metal melt to form the loaded metal foam. 2. The method of claim 1 , further comprising adding one or more additives to the metal melt prior to injecting of the forming gas. 3. The method of claim 2, wherein the one or more additives are selected from metal oxides, ceramic compounds, or combinations thereof. 4. The method of claim 3, wherein the metal oxides are selected from one or more of aluminum oxide, magnesium oxide, calcium oxide, silicone oxide, or zirconium oxide. 5. The method of claim 3, wherein the ceramic compounds are selected from one or more of silicon carbide, zirconium carbide, silicon nitride, aluminum nitride, boron nitride, titanium carbide, or tungsten carbide. 6. The method of claim 1 , wherein the forming gas is selected from hydrogen, deuterium, or combinations thereof. 7. The method of claim 1 , wherein the forming gas is injected using one or more rotating impellers, nozzles, vibrating nozzles, or spargers. 8. The method of claim 1 , wherein the injecting comprises a flow rate of about 0.1 - 1000 standard cubic centimeters per minute. 9. The method of claim 1 , wherein the predetermined amount of time is about 1 -72 hours. 10. The method of claim 1 , wherein the metal is selected from one or more of palladium, nickel, lanthanum, titanium, zirconium, halfnium, zinc, or alloys thereof. 1 1 . The method of claim 1 , wherein the vessel is selected from an electric arc furnace, induction furnace, cupola furnace, blast furnace, reverberatory furnace, or crucible furnace. 12. The method of claim 1 , wherein the purging comprises displacing the oxygen, oxygenated molecule-based gases, or both with one or more inert gases. 13. The method of claim 12, wherein the one or more inert gases are selected from nitrogen, helium, argon, krypton, or xenon. 14. The method of claim 1 , wherein the purging comprises removing the oxygen, oxygenated molecule-based gases, or both from the vessel interior and maintaining a vacuum within the vessel interior. 15. The method of claim 1 , wherein the metal melt is cooled at a rate of about 10°C to 100°C per second. 16. A metallic foam produced by the method of claim 1 . 17. The metallic foam of claim 16, wherein the foam has a surface-to-volume ratio of about 90 or less. 18. The metallic foam of claim 16, wherein the foam is loaded with deuterium, hydrogen, or both. 19. The metallic foam of claim 16, having a void space of about 75% to 95% of the total volume of the metallic foam. 20. The metallic foam of claim 16, having an average pore size of about 3-25 millimeters. |
METHOD FOR MANUFACTURING LOADED METALLIC FOAMS
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority to U.S. Provisional Patent Application No.
62/567,896, filed October 4, 2017, the entire content of which is hereby incorporated by reference.
TECHNICAL FIELD
The presently disclosed subject matter relates to a method for manufacturing loaded metallic foams, and to the foam produced therefrom.
BACKGROUND
It has long been desirable to engineer metallic foam materials. Metallic foam structures (metallic solid foam or metallic cellular solids) are known to have interesting combinations of physical properties. For example, metallic foams offer high stiffness in combination with very low specific weight, high gas permeability, and a high energy absorption capability. As a result, metallic foam materials have found widespread use as engineering materials. However, the broad use of metallic foams is hindered by the associated difficulty in producing uniform and consistent foam structures. Specifically, prior manufacturing methods for producing metallic foams result in an undesirably wide distribution of cell and/or pore sizes that cannot be controlled satisfactorily. As a result, the functional and structural characteristics of metallic foam materials are limited. It would therefore be beneficial to provide an improved method for manufacturing metallic foams that overcomes the shortcomings in the prior art. It would further be beneficial to provide a method that enables the loading of metallic foams during manufacture.
SUMMARY
In some embodiments, the presently disclosed subject matter is directed to a method of constructing a loaded metal foam. Particularly, the method comprises melting a portion of metal to produce a metal melt within an interior of a closed vessel. The method further comprises purging oxygen, oxygenated molecule-based gases, or both from the interior of the vessel. The method includes injecting a forming gas into the metal melt to form channels therein, and maintaining the injection of the forming gas for a predetermined amount of time. The metal melt is then cooled to form the loaded metal foam.
In some embodiments, the method further comprises adding one or more additives to the metal melt prior to injecting of the forming gas. In some embodiments, the one or more additives are selected from metal oxides, ceramic compounds, or combinations thereof. The metal oxides can be selected from one or more of aluminum oxide, magnesium oxide, calcium oxide, silicone oxide, or zirconium oxide. The ceramic compounds can be selected from one or more of silicon carbide, zirconium carbide, silicon nitride, aluminum nitride, boron nitride, titanium carbide, or tungsten carbide.
In some embodiments, the forming gas is selected from hydrogen, deuterium, or combinations thereof.
In some embodiments, the forming gas is injected using one or more rotating impellers, nozzles, vibrating nozzles, or spargers.
In some embodiments, the injecting comprises a flow rate of about 0.1 -1000 standard cubic centimeters per minute.
In some embodiments, the predetermined amount of time is about 1 -72 hours.
In some embodiments, the metal is selected from one or more of palladium, nickel, lanthanum, titanium, zirconium, halfnium, zinc, or alloys thereof.
In some embodiments, the vessel is selected from an electric arc furnace, induction furnace, cupola furnace, blast furnace, reverberatory furnace, or crucible furnace.
In some embodiments, the purging comprises displacing the oxygen, oxygenated molecule-based gases, or both with one or more inert gases. The one or more inert gases can be selected from nitrogen, helium, argon, krypton, or xenon. In some embodiments, the purging comprises removing the oxygen, oxygenated molecule-based gases, or both from the vessel interior and maintaining a vacuum within the vessel interior.
In some embodiments, the metal melt is cooled at a rate of about 10°C to 100°C per second.
In some embodiments, the presently disclosed subject matter is directed to a metallic foam produced by the disclosed method.
In some embodiments, the metallic foam has a surface-to-volume ratio of about 90 or less.
In some embodiments, the metallic foam is a loaded foam. In some embodiments, the foam is loaded with deuterium, hydrogen, or both.
In some embodiments, the metallic foam has a void space of about 75% to 95% of the total volume of the metallic foam.
In some embodiments, the metallic foam has an average pore size of about 3-25 millimeters.
BRIEF DESCRIPTION OF THE DRAWINGS
The previous summary and the following detailed descriptions are to be read in view of the drawings, which illustrate some (but not all) embodiments of the presently disclosed subject matter.
Fig. 1 is a flowchart of a method of producing loaded metallic foam in accordance with some embodiments of the presently disclosed subject matter.
Fig. 2a is an image of an open celled foam produced in accordance with some embodiments of the presently disclosed subject matter.
Fig. 2b is an image of a closed celled foam produced in accordance with some embodiments of the presently disclosed subject matter.
DETAILED DESCRIPTION
The presently disclosed subject matter is introduced with sufficient details to provide an understanding of one or more particular embodiments of broader inventive subject matters. The descriptions expound upon and exemplify features of those embodiments without limiting the inventive subject matters to the explicitly described embodiments and features. Considerations in view of these descriptions will likely give rise to additional and similar embodiments and features without departing from the scope of the presently disclosed subject matter.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the presently disclosed subject matter pertains. Although any methods, devices, and materials similar or equivalent to those described herein can be used in the practice or testing of the presently disclosed subject matter, representative methods, devices, and materials are now described.
Following long-standing patent law convention, the terms "a", "an", and "the" refer to "one or more" when used in the subject specification, including the claims. Thus, for example, reference to "a vessel" can include a plurality of such vessels, and so forth.
Unless otherwise indicated, all numbers expressing quantities of components, conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the instant specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the presently disclosed subject matter.
As used herein, the term "about", when referring to a value or to an amount of mass, weight, time, volume, concentration, and/or percentage can encompass variations of, in some embodiments +/-20%, in some embodiments +/-10%, in some embodiments +/-5%, in some embodiments +/-1 %, in some embodiments +/-0.5%, and in some embodiments +/-0.1 %, from the specified amount, as such variations are appropriate in the disclosed packages and methods.
A foam is a material that has gas-solid structures, comprising a plurality of gas cells inside a solid matrix. Metallic foams are a class of foam that include a multitude of pores in a metal material. Metallic foams exhibit very low densities and have desirable mechanical, thermal, electrical, and acoustic properties. Particularly, they are lightweight, recyclable, and non-toxic when compared to conventional solid and polymer foams. Further, metallic foams offer high specific stiffness, high strength, enhanced energy absorption, sound and vibration dampening, and tolerance to high temperatures. Moreover, by altering the size and shape of the cells in metal foams, mechanical properties of the foam can be engineered to meet the demands of a wide range of applications.
Conventional metal foams are typically manufactured by injecting gas into a melted metal from an external source or mixing gas-releasing agents (blowing agents) into the liquid metal. However, such prior art methods suffer from the inability to control cell size, shape, and distribution in the resulting foam. As a result, the production of consistently reproducible metallic foams with known properties has proven to be challenging.
The presently disclosed subject matter is directed to a method of manufacturing loaded metallic foams with reliably consistent properties. Loaded metal foams include a gas (such as hydrogen or deuterium) present in the bulk metal foam. The gas can form a metal hydride with the metal atoms of the foam and/or can become interstitial gas atoms.
The disclosed method comprises a first step of melting a desired metal to its molten (e.g., liquid) state, as shown in step 100 of Fig. 1 . The term "metal" refers to an electropositive chemical element, and can be selected from one or more of palladium, nickel, lanthanum, titanium, zirconium, halfnium, zinc, and/or alloys thereof. It should be appreciated that suitable metals are not limited to the group set forth above, and any desired metal can be used. The melting point of a metal can be determined using standard techniques well known to those of ordinary skill in the art.
The metal can be housed in a heating vessel and heated using any known technique. For example, in some embodiments, a furnace can be used. The furnace can be configured as a lined vessel that houses the metal and provides the melting energy. Suitable furnace types can include (but are not limited to) electric arc furnaces, induction furnaces, cupola furnaces, blast furnaces, reverberatory furnaces, and crucible furnaces. For low temperature melting point metals (such as zinc), the vessel can be heated to about 500°C through the use of electricity, propane, and/or natural gas. For higher melting point metals, the vessel can be designed for temperatures over about 1 ,600°C through the use of electricity and/or coke.
The vessel should be configured to maintain the molten metal at a desired temperature for a set amount of time. Further, the vessel can be controlled to maintain the reaction at any desired pressure, temperature, agitation (mixing), and time to control the reaction.
In some embodiments, one or more additives can be added to the molten metal to provide desirable characteristics at optional step 200 of the method of Fig. 1 . The additive(s) can be mixed with the metal prior to melting, during melting, or after the metal has transformed to the molten state. The term "additive" refers to a solid or liquid component admixed with the metal for the purpose of affecting one or more properties of the molten metal or the resultant metal foam. For example, a metal oxide and/or a ceramic compound can be added to the melt to increase melt viscosity and thereby increase the travel time for gas bubbles through the melt. Normally, gas bubbles in molten metal are highly buoyant and quickly rise to the surface. The rise of the gas bubbles can be slowed by increasing the viscosity of the molten metal to form stabilizing particles in the melt.
Suitable metal oxides can be selected from one or more of aluminum oxide, magnesium oxide, calcium oxide, silicone oxide, zirconium oxide, and combinations thereof.
Suitable ceramic compounds can be selected from one or more of silicon carbide, zirconium carbide, silicon nitride, aluminum nitride, boron nitride, titanium carbide, or tungsten carbide.
The additive(s) can be provided in any desired form, such as liquid, solid (e.g., powder), or combinations thereof.
The additive(s) can be added to the metal at any desired concentration. In some embodiments, the additives can be present at about 0.1 -25 weight percent, based on the total weight of the melt. For example, the additive can be present in an amount of about 0.1 -5, 0.1 -10, 0.5-10, 0.5-15, or 1 -15 weight percent. Thus, the additive can be present in an amount of at least about (or no more than about) 0.1 , 0.5, 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, or 25 weight percent.
The additive(s) can be mixed with the metal (e.g., into the metal melt) using any desired method, such as the use of an impeller or other mixing device. In some embodiments, the mixing component is part of the reaction vessel. The term "metal melt" as used herein refers to the melted state of the metal. For example, in some embodiments, all or substantially all of the metal is melted (e.g., 90%, 91 %, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% or greater).
After the metal has reached the molten state, all or substantially all of the oxygen gas and/or oxygenated molecule-based gases capable of reacting with the forming gas (e.g., the gas to be injected in the molten metal) is then purged (removed) from the vessel to avoid catastrophic reaction during phase transition between liquid to solid, as illustrated in step 300 of Fig. 1 . Oxygenated molecule-based gases can include (but are not limited to) carbon dioxide, hydrogen peroxide, ozone, nitrous oxide, nitrogen dioxide, and the like that include an oxygen molecule.
Any desired method can be used to evacuate the gas from the vessel. For example, in some embodiments, the vessel can be purged by flowing an inert gas therethrough to displace the oxygen and/or oxygenated molecule-based gases. The term "inert gas" refers to a gas that does not substantially react with any component of the system to which it is exposed (e.g., the vessel, molten metal, injected gas, and/or additives). In some embodiments, the inert gas can be one or more Group VII gases (noble gases) that form very few stable compounds with other atoms. Thus, suitable inert gases can be selected from one or more of nitrogen, helium, argon, krypton, xenon, or with any other gas that does not react substantially with the system components. By backfilling with an inert gas, the risk of reaction with the forming gas as described below is minimized.
Alternatively, a vacuum pump can be used to remove the oxygen gas and/or oxygenated molecule-based gases from the vessel interior. In some embodiments, the vessel interior can be kept at vacuum after the oxygen gas/oxygenated-based gases have been removed. By holding the vessel at a vacuum, the flow of forming gas through the melt creates a finer foam and more surface area.
The vessel housing the molten metal can therefore include an input and/or exit to allow the flow of the inert gas and/or removal of the oxygen gases.
Next, the disclosed method comprises injecting a forming gas into the molten metal, as shown in step 400 of Fig. 1 . Injection of the forming gas produces bubbles and/or channels throughout the molten metal that cool to form the foam structure. In some embodiments, the forming gas can be hydrogen, deuterium, or combinations thereof. Deuterium is commonly referred to as "hydrogen-2" or 2 H and is one of the two stable isotopes of hydrogen, with a nucleus comprising one proton and one neutron.
In some embodiments, the forming gas is introduced to the molten metal through an input in the reaction vessel. The input can be connected to a gas source through any known configuration. The input can be positioned at any desired location of the vessel (e.g., top, middle, bottom). In some embodiments, an impeller or other mixing element can be used to evenly distribute the forming gas throughout the molten metal.
The forming gas can be injected using any known device. For example, in some embodiments, rotating impellers, nozzles, vibrating nozzles, spargers, and the like can be used. In some embodiments, more than one device can be used, such as multiple impellers or an impeller and a sparger. The device used to inject the gas into the melt can be configured to generate fine or large bubbles/channels in the melt and distribute them uniformly. Further, in some embodiments, the gas conduits are numbered and positioned to allow the gas to diffuse evenly through the melt.
The forming gas can be injected into the melt at a flow rate of about 0.1 -1000 seem (standard cubic centimeters per minute) to cause flow channels to form in the melt. Thus, the flow rate can be about 0.1 -1000, 10-1000, 50-900, 60-800, 70-700, 60- 600, 50-500, 40-400, 30-300, or 20-200 seem.
Flow of the forming gas can be maintained for a period of about 1 -72 hours to allow for the diffusion (i.e., loading) of individual gas atoms (e.g., deuterium and/or hydrogen) into the metal bulk. Thus, the forming gas can flow into the melt for about 1 - 72, 2-60, 3-50, 4-40, 5-30, 6-20, or 7-10 hours. However, it should be appreciated that the forming gas can flow for longer or shorter periods of time than set forth in the range above. In some embodiments, the flow is maintained while the metal is in the molten state. However, in some embodiments, the flow is maintained through cooling of the metal.
The forming gas allows the creation of a metal foam, while simultaneously loading the metal structure with the gas. The term "loading" refers to the diffusion of the forming gas (e.g., hydrogen and/or deuterium) into the bulk metal. For example, the hydrogen or deuterium can react with the metal atoms and form a metal hydride and/or can become interstitial gas atoms. The loaded metal foams can be customized as needed, such as to provide optimal reactive, electromagnetic, etc. properties. Further, loaded porous materials have found widespread applications in mixture separations, catalysis, and ion exchange.
In some embodiments, the disclosed method can be performed at atmospheric pressure. However, the presently disclosed subject matter also includes embodiments wherein the method is performed at pressures greater than or less than atmospheric pressure.
The disclosed method further comprises cooling the melt as shown in step 500 of Fig. 1 . The melt is cooled to ensure that the gas flow channels remain as a permanent part of the solid structure. In some embodiments, the metal is quickly cooled (e.g., solidified) at a rate of about 10°C-100°C per second to create gas-filled pores and/or channels within the structure. For example, the pores and channels can be filled with deuterium and/or hydrogen. Quickly cooling the metal solidifies the foam before the gas escapes and before the gas pores and/or channels have the opportunity to coalesce and/or collapse. In some embodiments, the metal melt can be cooled by traveling on a cooled conveyor belt or transferring to a cooled mold or form, although any known method can be used.
Metal foams produced from the disclosed method exhibit high porosity. The term "porosity" refers to the amount of void space in a foam material. The term "void space" refers to the actual or physical space in a porous material comprising a metal matrix. The total volume of the metallic foam therefore is based on the metal matrix space and the void space. The void space (e.g., pores) can comprise about 75% to about 95% of the total volume of the metallic foam. Thus, the pores can comprise about 80-94%. 85- 93%, or 90-92% of the total volume of the foam. The pores can therefore comprise at least about (or no more than about) 75, 76, 77, 78, 79, 80, 81 , 82, 83, 84, 85, 86, 87, 88, 89, 90, 91 , 92, 93, 94, or 95 percent of the volume of the metallic foam. The disclosed highly porous metallic foams therefore have a high surface-to-volume ratio. The term "surface-to-volume ratio" refers to the amount of surface area per unit volume of the foam. In some embodiments, the disclosed metallic foams have a surface-to- volume ratio of about 90 or less (e.g., about 85 or less, or from about 60-90, 60-85, or 60-80).
In some embodiments, metal foams produced by the disclosed method can have an average pore size of about 3-25 mm, such as about 4-20, 5-15, 7-12, or 6-10 mm. Thus, the loaded metallic foam can have an average pore size of at least about (or no more than about) 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, or 25 mm. However, it should be appreciated that the presently disclosed subject matter also includes foams produced with an average pore size smaller or larger than the range given above, such as pores in the nano size range. The term "average pore size" refers to the average internal radius of the pores and/or channels of the foam material. The average pore size can be increased or decreased as desired by the user using known methods.
As a result of the high porosity of the disclosed metallic foams, the materials are ultra-light. For example, in some embodiments, the produced foam has a weight of less than about 5 pounds per cubic foot. Thus, the produced foam can have a weight of less than about 5, 4.5, 4, 3.5, 3, 2.5, 2, 1 .5, 1 , or 0.5 pounds per cubic foot.
In some embodiments, the porosity or density gradient over the profiled cross section of the metal foam obtained using the disclosed method can be selected as desired within wide ranges by selecting different process parameters. By way of example, the quantity of deuterium and/or hydrogen added and the cooling rate can affect porosity. In some embodiments, the disclosed method can produce an open cell foam material, which can also be referred to as a "metal sponge." One example of an open celled metallic foam is illustrated in Fig. 2a. Open celled metal foam has frequently been used in heat exchangers (compact electronics cooling, cryogen tanks, PCM heat exchangers, etc.), energy absorption, flow diffusion, and lightweight optic in the advanced technology, aerospace, and manufacturing areas.
Alternatively, in some embodiments, a closed cell foam can be produced. Thus, the pores can remain filled with a gas used to create a "closed cell" foam structure. One example of a closed cell metallic foam structure is illustrated in Fig. 2b. Closed cell metallic foams retain the fire resistance and recycling potential of other metallic foams, and add the property of floatation in water.
In some embodiments, similar treatment of melts for the creation of metallic foams and loading them with deuterium gas to support low energy nuclear reactions can be envisioned for platinum, nickel, iridium, copper, silver, gold and zinc.
Further, many industrial applications require the loading of large amounts of hydrogen or deuterium into a crystalline metal structure. The loading of hydrogen requires that hydrogen first adsorb onto the metal surface before diffusing into the structure. A large surface-to-volume ratio would substantially increase the number of hydrogen atoms adsorbed on a surface with potential to diffuse into the bulk.
Vapor deposition is a commonly known method to create metallic coatings or structures. However, metallic structures created by vapor deposition typically do not have large surface areas that allow easy loading of gases into the bulk metal.
Physical or chemical vapor deposition can create a material of relatively high surface to volume ratio, however, the need for a substrate as the base for a film results in there only being one surface, facing away from the surface.
The above description is intended to be illustrative and not limiting. Various changes and modifications in the embodiment described herein may occur to those skilled in the art. Those changes can be made without departing from the scope and spirit of the invention. EXAMPLES
The following Examples have been included to provide guidance to one of ordinary skill in the art for practicing representative embodiments of the presently disclosed subject matter. In light of the present disclosure and the general level of skill in the art, those of skill can appreciate that the following Examples are intended to be exemplary only and that numerous changes, modifications, and alterations can be employed without departing from the scope of the presently disclosed subject matter.
EXAMPLE 1
Construction of Palladium Foam Material Loaded with Deuterium
A sample of palladium metal was melted in a vessel at about 1 ,550°C. All oxygen gas and/or oxygenated molecule-based gases capable of reacting with deuterium were purged from the vessel and replaced with an inert gas. Deuterium gas was injected into the melt at a flow rate of about 10-1000 seem (standard cubic centimeters per minute) for about 1 -72 hours to cause flow channels to form in the melt, and to allow for the loading of individual deuterium atoms into the palladium bulk. The melt was then cooled such that the flow channels remained in the solid foam structure.
A deuterium loaded palladium foam was thereby created. EXAMPLE 2
Construction of Dueterium-Loaded Palladium Foam Material A sample of palladium was melted as in Example 1 . About 1 -25 weight percent aluminium oxide powder was added to the melt to increase its viscosity and thereby increase the travel time for bubbles through the melt. Deuterium gas was injected into the melt mixture at a flow rate of about 0.1 -100 seem for 1 to 72 hours to allow the individual deuterium atoms to diffuse into the palladium bulk. The mixture was then solidified at a high rate of speed between 10°C and 100°C per second to create deuterium filled pores within the structure.
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