Metal foam and method for producing same

Abstract

A method for manufacturing a metal foam is provided. The present invention relates to a method for applying a metal-containing powder, which may include aluminum and chromium or molybdenum, to a metal foam, which may include nickel, cobalt, copper, and iron, followed by heat treatment, wherein the maximum temperature of the heat treatment of the metal foam is in the range of 680-715°C, and the total duration of the heat treatment at the temperature range of 680-715°C is between 5 and 240 seconds. By taking into account this heat treatment specification, alloy formation occurs at the contact surface between the metal foam and the metal-containing powder, while leaving non-alloyed regions inside the metal foam. The present invention also includes a method comprising treating the alloyed metal foam with a basic solution. The present invention also includes the metal foam obtained by this method, which can be used, for example, as a support or structural element and in catalytic technology.

Description

[Technical field]

[0001] background The invention relates to a method for the production of metallic compacts, which comprises the preparation of a metal foam consisting of two metal components, the subsequent application of a metal-containing powder and a final heat treatment for alloy formation. By suitable temperature regulation of the heat treatment and the selection of the metals involved, it is possible to limit the alloy formation to the upper layer of the metal foam, so that non-alloyed regions remain in the central region of the metal foam. The invention further relates to a method for the heat treatment for alloy formation followed by a treatment in a basic solution, which method is used in particular in the production of catalysts. The invention further relates to metal foams obtainable by the method of the invention, which are used, for example, as support and structural elements and in catalytic technology.

[0002] Prior Art Methods for producing metal foams are known from the prior art, for example from WO 2019 / 057533, where metal powder is applied to a foam-like metal body and subsequently heat-treated, so that an alloy is formed in the contact area between the foam-like metal body and the metal powder. WO 2019 / 057533 discloses a large number of metals and metal combinations that can be selected for the foam-like metal body and the metal powder, as well as a general description of the implementation of the heat treatment for alloy formation, and some specific examples for treating aluminum powder on nickel foam.

[0003] The degree of alloy formation depends on the heat treatment conditions: heat treatment at high temperatures results in alloy formation in deeper regions of the metal foam, whereas heat treatment at lower temperatures results in alloy formation only in the upper regions of the metal foam, leaving non-alloyed regions inside the metal foam. Moreover, the choice of metals for the foam and metal powder has a large effect on alloy formation.

[0004] Because the survival of non-alloyed regions in metal foams is critical for many applications of such metal foams, a need exists for a method to ensure this. The method of the present invention satisfies this need.

[0005] The present invention The method for producing a metal foam according to the present invention comprises the steps of: (a) preparing a metal foam A consisting of two metal components, the metal components being: (i) Exist as an alloy; or (ii) may exist as a composition of two overlapping layers of two individual metal components, where one of the metal components forms an inner layer of the metal foam and the other metal component forms an outer layer of the metal foam; In the case of option (i), the metallic components present as alloys are selected from the following list of combinations: nickel and cobalt, nickel and copper; In the case of option (ii), the metal components shall be selected from the following list of combinations: nickel inner and cobalt outer, nickel inner and copper outer, iron inner and nickel outer; (b) applying a metal-containing powder MP to the metal foam A to obtain a metal foam AX, the metal-containing powder MP being either a mixture of aluminum powder and chromium powder, or a mixture of aluminum powder and molybdenum powder, or a powdered alloy of aluminum and chromium, or a powdered alloy of aluminum and molybdenum; (c) heat treatment of the metal foam AX to achieve alloy formation between the metal components of the metal foam A and the metal-containing powder MP to obtain a metal foam B, The maximum temperature for heat treatment of metal foam AX is in the range of 680-715°C. and the total duration of the heat treatment in the temperature range of 680 to 715°C is between 5 and 240 seconds. Includes.

[0006] The experimental results obtained in the context of the present invention show that the choice of the conditions of the heat treatment for alloy formation, in particular the choice of metals in the metal foam and the metal powder, as well as the temperature conditions, have a significant influence on the results. The method according to the invention makes it possible to confine the alloy formation in said metal combinations to the upper layer of the metal foam, so that a non-alloyed region remains in the central region of the metal foam. The presence of this non-alloyed region affects in particular the chemical and mechanical stability of the resulting metal foam.

[0007] In the context of the present invention, metal foam A is understood to mean a foam-like metal body. Foam-like metal bodies are disclosed, for example, in Ullmann's Encyclopedia of Industrial Chemistry, chapter "Metallic Foams" (published online 15 July 2012, DOI: 10.1002 / 14356007.c16_c=01.pub2). In principle, metal foams with different morphological properties in terms of pore size, pore shape, layer thickness, areal density, geometric surface area, porosity, etc. are suitable. Preferably, the metal foam A has a density of 400 to 1500 g / m 2The foam has a density in the range of 400-3000 μm, preferably 400-800 μm, and a thickness in the range of 0.5-10 mm, preferably 1.0-5.0 mm. Its production can be carried out in a manner known per se. For example, a foam made of an organic polymer can be coated with two metal components one after the other or simultaneously, and then the polymer is removed by pyrolysis, whereby a metal foam is obtained. To coat with at least one first metal or its precursor, the foam made of an organic polymer can be brought into contact with a solution or suspension containing the first metal, for example by spraying or immersion. Deposition by means of chemical vapor deposition (CVD) is also possible. That is, for example, a polyurethane foam can be coated with two metals one after the other, and then the polyurethane foam can be pyrolyzed. Polymer foams suitable for the production of shaped bodies in the form of foams preferably have a pore size in the range of 100-5000 μm, particularly preferably 450-4000 μm, in particular 450-3000 μm. Suitable polymer foams preferably have a layer thickness of 5 to 60 mm, particularly preferably 10 to 30 mm. Suitable polymer foams preferably have a layer thickness of 300 to 1200 kg / m 3 The specific surface area is preferably 100 to 20,000 m 2 / m 3 , particularly preferably 1000 to 6000 m 2 / m 3 The porosity is preferably in the range of 0.50 to 0.95.

[0008] The metal foam A used in step (a) of the method according to the invention may have any arbitrary shape, for example a cube, a rectangular prism, a cylinder, etc. However, the metal foam may also be shaped, for example, into a monolith.

[0009] The application of the metal-containing powder MP in step (b) of the method according to the invention can be carried out in various ways, for example by contacting the metal foam A with the composition of the metal-containing powder MP by rolling or immersion, or by applying the composition of the metal-containing powder MP by spraying, sprinkling or pouring. For this purpose, the composition of the metal-containing powder MP can be present in the form of a suspension or a powder.

[0010] In this case, the actual application of the composition of metal-containing powder MP to the metal foam A in step (b) of the method according to the invention is preferably preceded by a pre-impregnation of the metal foam A with a binder. The impregnation can be carried out, for example, but not limited to, by spraying the binder or immersing the metal foam A in the binder. The composition of metal-containing powder MP can then be applied to the metal foam A thus prepared.

[0011] Alternatively, the binder and the composition of metal-containing powder MP may be applied in one step, either by suspending the composition of metal-containing powder MP in the liquid binder itself prior to application, or by suspending the composition of metal-containing powder MP and the binder in an auxiliary liquid F.

[0012] The binder is a composition that can be completely converted into a gaseous product by heat treatment in the temperature range of 100-400 ° C, containing an organic compound that promotes the adhesion of the composition of the metal-containing powder MP to the metal foam. In this case, the organic compound is preferably selected from the following group: polyethyleneimine (PEI), polyvinylpyrrolidone (PVP), ethylene glycol, mixtures of these compounds. PEI is particularly preferred. The molecular weight of the polyethyleneimine is preferably in the range of 10000 to 1300000 g / mol. The molecular weight of the polyethyleneimine (PEI) is preferably in the range of 700,000 to 800,000 g / mol.

[0013] The auxiliary liquid F must be suitable for suspending the composition of metal-containing powder MP and the binder and for completely converting them into gaseous products by heat treatment in the temperature range of 100-400° C. Preferably, the auxiliary liquid F is selected from the following group: water, ethylene glycol, PVP and mixtures of these compounds. When using an auxiliary liquid, the binder is typically suspended in water at a concentration in the range of 1-10% by weight and then the composition of metal-containing powder MP is suspended in said suspension.

[0014] The metal-containing powder MP used in step (b) of the method according to the invention may contain, besides the powdered metal components, additives that contribute to increasing the flowability or water stability. Such additives must be completely convertible into gaseous products by heat treatment in the temperature range of 100-400 ° C. The metal-containing powder MP used in step (b) of the method according to the invention comprises one or more powdered metal components selected from the following group: a mixture of aluminum powder and chromium powder, a mixture of aluminum powder and molybdenum powder, a powdered alloy of aluminum and chromium, a powdered alloy of aluminum and molybdenum. Preferably, the metal-containing powder MP used in step (b) of the method according to the invention comprises as the only metal component either (i) a mixture of aluminum powder and chromium powder or (ii) a powdered alloy of aluminum and chromium. Particularly preferably, the metal-containing powder MP used in step (b) of the method according to the invention comprises as the only metal component a powdered alloy of aluminum and chromium.

[0015] The composition of the metal-containing powder MP preferably has a metal component content in the range of 80-99.8% by weight. In this case, a composition in which the metal component particles have a particle size of 5 μm to 200 μm is preferred. A composition in which 95% of the metal component particles have a particle size of 5 μm to 75 μm is particularly preferred. In addition to the metal components in elemental form, the composition may further contain metal components in oxidized form. The oxidized components are usually present in the form of oxide compounds, for example oxides, hydroxides and / or carbonates. Typically, the mass fraction of the oxidized components is in the range of 0.05-10% by weight of the total mass of the metal powder composition.

[0016] Step (c) of the method according to the invention involves a heat treatment to achieve the formation of one or more alloys. Experimental results obtained in the context of the present invention have shown that the choice of metals in the metal foam A and the metal-containing powder MP has a significant effect on the progress of the alloy formation. The results further show that a relatively strict temperature control is essential to restrict the alloy formation to the upper region of the metal foam and leave non-alloyed regions inside the metal foam.

[0017] In step (c) of the method according to the invention, the metal foam AX is heat-treated to achieve alloy formation between the metal components of the metal foam A and the metal-containing powder MP to obtain a metal foam B, wherein the maximum temperature of the heat treatment of the metal foam AX is in the range of 680-715°C and the total duration of the heat treatment in the temperature range of 680-715°C is between 5 and 240 seconds.

[0018] The heat treatment comprises a usually stepwise heating of the metal foam AX and subsequent cooling to room temperature. The heat treatment is carried out under inert gas or under reducing conditions. By reducing conditions is understood the presence of a gas mixture containing hydrogen and at least one gas that is inert under reaction conditions, suitable being, for example, a gas mixture containing 50% by volume of N2 and 50% by volume of H2. As inert gas, nitrogen is preferably used. The heating may be carried out, for example, in a belt furnace. Suitable heating rates are in the range of 10-200 K / min, preferably 20-180 K / min. During the heat treatment, typically, the temperature is first increased from room temperature to approximately 300-400 ° C, at which temperature moisture and organic components are removed from the coating for approximately 2-30 minutes, then the temperature is increased to the range of 680-715 ° C, whereby alloy formation takes place between the metal components of the metal foam AX and the composition of the metal-containing powder MP, and then the metal foam is quenched by contact with a protective gas environment at a temperature of approximately 200 ° C.

[0019] In order to limit the alloy formation to the upper region of the metal foam and to leave non-alloyed regions inside the metal foam, it is essential that the maximum temperature of the heat treatment of the metal foam AX in step (c) is in the range of 680-715°C and that the total duration of the heat treatment in the temperature range of 680-715°C is between 5 and 240 seconds for the metal foam concerned according to the invention. Although the duration of the heat treatment can compensate to some extent for the height of the maximum treatment temperature and vice versa, it has been observed that the frequency of experiments in which alloy formation in the upper region of the metal foam and the remaining non-alloyed regions inside the metal foam are simultaneously achieved drops significantly when the maximum temperature of the heat treatment is outside the temperature range between 680-715°C and / or the duration of the heat treatment in the temperature range between 680-715°C is outside the range of 5-240 seconds. If the maximum temperature is too high and / or the metal foam is too long in the range of the maximum temperature, the alloy formation proceeds to the deepest layer of the metal foam and no non-alloyed regions remain. If the maximum temperature is too low and / or the metal foam is too short in the maximum temperature range, the alloy formation does not start at all. A different choice of metals from those involved according to the invention for the metal foam A and the metal-containing powder MP can likewise lead to no alloy formation being obtained or no non-alloyed regions remaining inside the foam, despite a heat treatment in the temperature range between 680 and 715 °C for a duration of 5 to 240 seconds.

[0020] In a preferred embodiment, the mass ratio of the two metal components in metal foam A is in the range of 1:1 to 20:1, the ratio of the mass of aluminum to the mass of all other metal components in the metal-containing powder MP is in the range of 4:1 to 50:1, and the mass ratio V of metal foam B to metal foam A (V=m(metal foam B) / m(metal foam A)) is in the range of 1.1:1 to 1.5:1.

[0021] In a further preferred embodiment, the mass ratio of the two metal components in metal foam A is in the range of 1:1 to 10:1, the ratio of the mass of aluminum to the mass of all other metal components in the metal-containing powder MP is in the range of 10:1 to 20:1, and the mass ratio V of metal foam B to metal foam A (V=m(metal foam B) / m(metal foam A)) is in the range of 1.2:1 to 1.4:1.

[0022] In a further aspect, the invention further comprises a method comprising the step (d) of treating the metal foam B with a basic solution. The treatment of the metal foam B with the basic solution may serve to at least partially dissolve and thus remove from the metal foam the metal components of the composition of the applied metal-containing powder MP and the alloy between the metal components of the metal foam and the composition of the metal-containing powder MP. Typically, the treatment with the basic solution removes from the metal foam 30-70% of the total mass of the metal components of the composition of the applied metal-containing powder MP and the alloy between the metal components of the metal foam and the composition of the metal-containing powder MP. As the basic solution, typically, a basic aqueous solution of NaOH, KOH, LiOH, or a mixture thereof is used. The temperature in the basic treatment is usually kept in the range of 25-120° C. The duration of the treatment with the basic solution is typically in the range of 5 minutes to 8 hours. If the metal component is appropriately selected, the metal foam obtained as a result of treatment with a basic solution can be used as a catalyst, for example, as disclosed in WO 2019 / 057533.

[0023] In a preferred embodiment, the treatment of the metal foam B with the basic solution is carried out at a temperature in the range of 20-120°C for a time in the range of 5 minutes to 8 hours, where the basic solution is an aqueous NaOH solution having a NaOH concentration of 2-30% by weight.

[0024] In a further aspect, the present invention further comprises a coated metal foam obtainable by one of the methods according to the present invention.

[0025] In a further preferred embodiment, the present invention further relates to a method and to a metal foam obtainable thereby, wherein in the metal foam A the two metal components are present as a composition of two overlapping layers of the individual metals, with nickel forming the inner layer and cobalt forming the outer layer, and wherein in step (d) the metal foam B is treated with a basic solution.

[0026] In a further preferred embodiment, the present invention further relates to a method, wherein in metal foam A nickel and cobalt are present as an alloy and in step (d) metal foam B is treated with a basic solution, as well as to a metal foam obtainable thereby.

[0027] In a further preferred embodiment, the present invention further relates to a method and a metal foam obtainable thereby, wherein the metal-containing powder MP used in step (b) comprises either (i) a mixture of aluminum powder and chromium powder or (ii) a powdered alloy of aluminum and chromium as the only metal component, and in step (d) the metal foam B is treated with a basic solution.

[0028] In a further preferred embodiment, the present invention further relates to a method, as well as to a metal foam obtainable thereby, in which the metal-containing powder MP used in step (b) comprises a powdered alloy of aluminum and chromium as the only metal components and in step (d) the metal foam B is treated with a basic solution.

[0029] In a further preferred embodiment, the present invention further relates to a method and a metal foam obtainable thereby, wherein in the metal foam A the two metal components are present as a composition of two overlapping layers of the individual metals, with nickel forming the inner layer and cobalt forming the outer layer, and the metal-containing powder MP used in step (b) comprises as the only metal component either (i) a mixture of aluminium powder and chromium powder or (ii) a powdered alloy of aluminium and chromium.

[0030] In a further preferred embodiment, the present invention further relates to a method and a metal foam obtainable thereby, wherein in the metal foam A the two metal components are present as a composition of two overlapping layers of the individual metals, with nickel forming the inner layer and cobalt forming the outer layer, and the metal-containing powder MP used in step (b) comprises as the only metal component either (i) a mixture of aluminum powder and chromium powder or (ii) a powdered alloy of aluminum and chromium, and in step (d) the metal foam B is treated with a basic solution.

[0031] In a further preferred embodiment, the present invention further relates to a method and to a metal foam obtainable thereby, wherein in the metal foam A the two metal components are present as a composition of two overlapping layers of the individual metals, with nickel forming the inner layer and cobalt forming the outer layer, and the metal-containing powder MP used in step (b) comprises a powdered alloy of aluminium and chromium as the only metal component.

[0032] In a further preferred embodiment, the present invention further relates to a method and a metal foam obtainable thereby, wherein in the metal foam A the two metal components are present as a composition of two overlapping layers of individual metals, with nickel forming the inner layer and cobalt forming the outer layer, and the metal-containing powder MP used in step (b) comprises a powdered alloy of aluminum and chromium as the only metal components, and in step (d) the metal foam B is treated with a basic solution.

[0033] In a further preferred embodiment, the present invention further relates to a method and a metal foam obtainable thereby, in which in the metal foam A nickel and cobalt are present as an alloy and the metal-containing powder MP used in step (b) comprises as the only metal component either (i) a mixture of aluminum powder and chromium powder or (ii) a powdered alloy of aluminum and chromium.

[0034] In a further preferred embodiment, the present invention further relates to a method and a metal foam obtainable thereby, in which in the metal foam A nickel and cobalt are present as an alloy and the metal-containing powder MP used in step (b) comprises as the only metal component either (i) a mixture of aluminum powder and chromium powder or (ii) a powdered alloy of aluminum and chromium, and in step (d) the metal foam B is treated with a basic solution.

[0035] In a further preferred embodiment, the present invention further relates to a method and a metal foam obtainable thereby, in which in the metal foam A nickel and cobalt are present as an alloy and the metal-containing powder MP used in step (b) comprises a powdered alloy of aluminium and chromium as the only metal components.

[0036] In a further preferred embodiment, the present invention further relates to a method and a metal foam obtainable thereby, in which in the metal foam A nickel and cobalt are present as an alloy and the metal-containing powder MP used in step (b) comprises a powdered alloy of aluminum and chromium as the only metal components and in step (d) the metal foam B is treated with a basic solution.

[0037] Working Example 1. Metal Foam Preparation Three metal foams (a, b, c) made of cobalt-nickel alloy were prepared by simultaneous electrolytic deposition of nickel and cobalt on polyurethane foam followed by pyrolysis of the plastic components (Co / Ni=9:1), (manufacturer: AATM, dimensions: 220mmx180mmx1.6mm, areal density: 1000g / m 2 , average pore size: 580μm).

[0038] 2. Application of metal-containing powder Subsequently, all metal foams were first sprayed with a binder solution (polyethyleneimine (2.5 wt%) in water) and then powdered aluminum-chromium alloy (manufacturer: AMG, average particle size: <63 μm, Al / Cr=70 / 30, 3 wt% ethylenebis(stearamide) added) was applied as a dry powder (approximately 400 g / m 2 ).

[0039] 3.Heat treatment All metal foams were then heat treated under nitrogen in a furnace by first heating from room temperature to a maximum temperature within approximately 15 minutes, holding that temperature for a period of time, and then quenching by contact with a 200°C nitrogen atmosphere.

[0040] Maximum temperature for metal foam a: 700°C, 2 minutes Temperature change of metal foam b: 600°C, 2 minutes Temperature change of metal foam c: 750°C, 2 min

[0041] 4. Identifying the degree of alloying Finally, the extent of alloy formation in the metal foams was determined by examining cross-sections of the foams under a microscope and a scanning electron microscope, with the following results: in metal foam a, alloy formation occurred on the surface but non-alloyed regions remained inside the foam, whereas in metal foam b, no alloy formation occurred, and in metal foam c, alloy formation had progressed to the point where no non-alloyed regions remained inside the foam.

[0042] This result clearly shows that deviations from the conditions for heat treatment according to the invention make it difficult to achieve alloy formation at the surface while leaving non-alloyed regions in the interior of the metal foam.

Claims

1. A method for producing a metal foam, comprising: (a) providing a metal foam A consisting of two metal components, nickel and cobalt, said metal components (i) being present as an alloy; (b) applying a metal-containing powder MP to the metal foam body A to obtain a metal foam body AX, The metal-containing powder MP is (iii) a mixture of aluminum powder and chromium powder; (c) A step of heat-treating the metal foam AX to achieve alloy formation between the metal components of the metal foam A and the metal-containing powder MP to obtain a metal foam B, The maximum temperature of the heat treatment of the metal foam body AX is in the range of 680 to 715 ° C., and the total duration of said heat treatment at a temperature range of 680-715° C. is between 5 and 240 seconds. It consists of: wherein the mass ratio of cobalt to nickel in said metal foam A is in the range of 1:1 to 10:1, and further wherein the mass ratio of the aluminum to the mass of the chromium in said metal-containing powder MP is in the range of 10:1 to 20:

1.

2. The method described in claim 1, wherein the mass ratio V of metal foam B to metal foam A (V = m(metal foam B) / m(metal foam A)) is in the range of 1.1:1 to 1.5:

1.

3. A method for producing a metal foam, comprising: (a) providing a metal foam A consisting of two metal components, nickel and cobalt, said metal components (i) being present as an alloy; (b) applying a metal-containing powder MP to the metal foam body A to obtain a metal foam body AX, The metal-containing powder MP is (iii) a mixture of aluminum powder and chromium powder; (c) A step of heat-treating the metal foam AX to achieve alloy formation between the metal components of the metal foam A and the metal-containing powder MP to obtain a metal foam B, The maximum temperature of the heat treatment of the metal foam body AX is in the range of 680 to 715 ° C., and the total duration of said heat treatment at a temperature range of 680-715°C is between 5 and 240 seconds; (d) treating the metal foam body B with a basic solution; wherein the mass ratio of cobalt to nickel in the metal foam A is in the range of 1:1 to 10:1, and further wherein the mass ratio of the aluminum to the mass of the chromium in the metal-containing powder MP is in the range of 10:1 to 20:

1.

4. A metal foam obtainable by the method according to claim 1 or 2.

5. A metal foam obtainable by the method according to claim 3.