DE102014009371A1 - Process for the production of metal nanofoams - Google Patents

Abstract

The invention relates to a process for the production of metal nanofoams. In this case, at least at least one metal salt (MS), citric acid (ZS) and water (W) and starch (S) are used as starting materials, which are mixed to a rheopexen, non-Newtonian fluid, wherein the resulting rheopexe, non-Newtonian fluid at least is formed with an exothermic reaction within an inert environment to form a block of metal nanofoam.

Description

The invention relates to a process for the production of metal nanofoams.

As metal foam, a form of the metal is called, which consists of at least 50% of cavities. The cavities may be filled with gas or evacuated. The density of the metal foams can be less than one-thousandth of the density of the underlying metal, which means that one block of this metal is 99.9% air. Therefore also the designation Airgel, which is often used for all highly porous solids, as in the Tappen et al.: Nanoporous Metal Foams, Angewandte Chemie Int. Ed., 2010, 49, 4544-4565 is described.

It is different between nanofoams and metal foams in the narrower sense. The latter have been known for about 50 years and serve as structural material in the aerospace industry. Strength at low weight is here in the foreground. They are not the subject of the present invention. The difference to nanofoams shows in the size of the inner pore surface, the porosity. This size is not only the most important distinguishing criterion, but also a measure used to compare the quality of different aerogels.

Metal foams used as building material have substantially less than 1 square meter of internal surface area per gram. On the other hand nanofoams can have over 100 m ² / g. It is this enormous inner surface that determines the fields of application of nanofoams. The name itself is due to the size of the characteristic structures (these are filaments and cavities) of these materials. It lies in the nanometer range, in contrast to conventional metal foams in which the cavities are located in the micro to millimeter range.

In the Tappan et al: Nanoporous Metal Foams, Angewandte Chemie Int. Ed., 2010, 49, 4544-4565 is a review article on metal nanofoams described with an indication of the state of research in this field. Here is just a brief summary of the main issues and perspectives.

The biggest problem in the production of highly porous metals is the high surface energy of the metals compared to other substance classes. Roughly speaking, metals tend to be as compact as possible. Therefore, foams made of natural and synthetic materials or ceramics have long been known and in the Kistler: Coherent expanded aerogels and jellies, Nature 1931, 127, page 741 and Pekala, Alviso and LeMay: Organic aerogels, Non-Cryst. Solids, 1990, 125, p. 57 described. The known foams can have very high internal surfaces and volumes, while the nanofoams of corresponding metals are still quite new.

A numerical example may illustrate this: Porous forms of carbon, activated carbons, have internal surfaces above 1000 m ² / g and have been known since ancient times. Raney nickel, a highly porous form of nickel widely used as a catalyst in the chemical industry, has a surface area of at most 100 m ² / g even after more than a century of targeted research and development.

It is a high surface energy spent during the synthesis, which is why high-energy starting materials or synthesis methods must be used. At present, there are only two classes per process that allow production of metal aerogels with surface areas of the order of tens of m ² / g. The first class concerns a synthesis of metal nanoparticles and careful coagulation followed by drying with supercritical carbon dioxide. A particularly successful variant is in the Publication Liu, Herrmann, et al .: High-performance electrocatalysts on palladium aerogels, Angewandte Chemie Int. Ed., 2012, vol. 51 (23), pp. 5743-5767 described. It synthesizes aerogels made of platinum, palladium, gold and silver with surfaces up to 150 m ² / g. The disadvantage is the long synthesis time and the high cost. These factors make the aerogels so created more expensive until they become inefficient, at least for most applications.

The second class of methods for producing metal nanofoams is a combustion synthesis, and to this belongs the present invention. This is a highly exothermic reaction of metal precursors, which is a kind of controlled explosion that provides the needed energy. This is in the Tappan et al .: Ultralow-density nanostructural metal foams combustion synthesis, morphology and composition, Journal of the American Chemical Society, 2006, 128 (20) 6589-6594 , a method known as bisaminotetrazole method. It is first a high-energy ligand, the Bisaminotetrazol prepared, then reacted with metal salts to form a complex and reacted by ignition under inert gas. Iron, cobalt, nickel, gold and copper are used as metals for nanofoams. Surfaces of up to 278 m ² / g are achieved. The disadvantage is that a complex synthesis of ligands is required, which uses extremely toxic chemicals (cyanamide) and large amounts of solvent used.

• 1) Chemische Katalyse: Hier ist der Zusammenhang einfach – je größer die Oberfläche des Katalysators, desto höher die Reaktivität und desto weniger wird davon gebraucht, was bei Platinmetallen durchaus ins Gewicht fällt.
• 2) Elektroden: Hier sind die Zusammenhänge nicht anders als bei Katalysatoren. Besonders vielversprechend ist der Einsatz in Berennstoffzellen, dort kann eine Metall-Aerogel-Elektrode den Unterschied zwischen dem Zustand wirtschaftlich lebensfähig und dem Zustand nicht rentabel ausmachen.
• 3) Wärmetauscher: Das stellt eine noch nicht sehr weit entwickelte, jedoch sehr interessante Anwendung dar. Effektive Wärmetauscher werden im Elektronikbereich, z. B. CPU von Personalcomputern benötigt, bei denen große Wärmemengen schnell abgeführt werden müssen, in der – chemischen und nuklearen – Reaktortechnik, für Wärmekraftmaschinen (z. B. Stirling-Motoren, solare und geothermische Wärmepumpen) und in der Kühltechnik.

Applications of metal aerogels primarily make use of their large internal surfaces. That is, their use is especially useful in technological processes that run on surfaces.
These are:

• 1) Chemical catalysis: Here the connection is simple - the larger the surface area of the catalyst, the higher the reactivity and the less is needed, which is quite important for platinum metals.
• 2) Electrodes: Here the connections are no different than with catalysts. Particularly promising is the use in fuel cells, where a metal airgel electrode can make the difference between the state economically viable and the state not profitable.
• 3) Heat exchanger: This is a not yet very developed, but very interesting application. Effective heat exchangers are used in the electronics sector, eg. B. CPU of personal computers in which large amounts of heat must be dissipated quickly, in the - chemical and nuclear - reactor technology, for heat engines (eg Stirling engines, solar and geothermal heat pumps) and in the cooling technology.

In addition, other applications are possible, where the price of nanofoam is crucial. If this is sufficiently small, for example, use in the construction industry can also be considered as an insulating material. Numerous niche applications, such as the use for electromagnetic shielding, are also possible.

The invention is therefore based on the object of specifying a method for the production of metal nanofoams, which is designed so suitable that metal nanofoams can be produced with a larger inner surface of high quality from very cheap starting materials, with little effort and in a short time. The process should also be applicable to a broad class of metallic materials that hitherto can not be represented in airgel form. In addition, the production of the metal nanofoams and the metal nanofoams themselves should be environmentally friendly.

The object is achieved at least with the features of claim 1. In the process for producing metal nanofoams
be according to the characterizing part of claim 1
used as starting materials at least at least one metal salt (MS), citric acid (ZS) and water (W) and starch (S), which are mixed to a rheopexen, non-Newtonian fluid, wherein
the resulting rheopaque, non-Newtonian fluid is formed into a block of metal nanofoam at least with an exothermic reaction within an inert environment.

The starting materials - at least at least one metal salt (MS), citric acid (ZS) and water (W) and starch (S) - are essentially at a weight ratio
MS: ZS: W: S = 5: 3: 10: 24 and mixed to the rheopex, non-Newtonian fluid.

The following weight-related tolerance limits of the starting materials are specified for the production: Metal salt / metal salts (MS) 5 g ± 1 g, Citric acid (ZS) 3 g ± 1 g, Water (W) 10 g ± 2 g, Strength (S) 24 g ± 10 g.

• – Umsetzung mindestens eines Metallsalzes mit Zitronensäure in Wasser zu einer wässrigen Lösung,
• – Verrühren der wässrigen Lösung mit Stärke solange, bis ein rheopexes, nicht-Newtonsches Fluid entsteht,
• – Verflüssigung zu einem vergießbaren Gel-Rohling,
• – Gießen des Gel-Rohlings in eine vorgegebene Form,
• – Erhitzen des in der Form befindlichen Gel-Rohlings in einem als Ofen ausgebildeten hochtemperierten Reaktionsbehälter mit Schutzgas-Umgebung oder im Vakuum zur Durchführung einer exothermen Reaktion,
• – Entnahme des durch die exotherme Reaktion entstandenen Metallnanoschaumblocks,
• – Abkühlung des Metallnanoschaumblocks.

In detail, the following steps are carried out for the production of the metal nanofoams:

• Conversion of at least one metal salt with citric acid in water to an aqueous solution,
• Stirring the aqueous solution with starch until a rheopexes, non-Newtonian fluid is formed,
• Liquefaction into a pourable gel blank,
• Casting the gel blank into a predetermined shape,
• Heating of the gel blank in the mold in a high-temperature reaction vessel formed as a furnace with a protective gas environment or in a vacuum for carrying out an exothermic reaction,
• Removal of the metal nanofoam block resulting from the exothermic reaction,
• - cooling of the metal nanofoam block.

Corn starch can be used in particular as starch.

The removal of the metal nanofoam block from the oven after the exothermic reaction can, depending on the dimensions of the gel blank after about 20 minutes to be made after about 2 hours for subsequent cooling.

The exothermic reactions can be carried out in a high-temperature reaction vessel with an internal inert reaction space, an oven with protective gas or a furnace with vacuum.

The metal nanofoam blocks can be formed of platinum metals and iron group metals.

The metal nanofoams produced by the process according to the invention have as starting materials at least one metal salt (MS), citric acid (ZS) and water (W) and starch (S) essentially having a weight ratio
MS: ZS: W: S = 5: 3: 10: 27.5.

The following tolerance limits of the starting materials for production are specified on weight units (GWE): Metal salt / metal salts 5 GWE ± 1 GWE, citric acid 3 GWE ± 1 GWE, water 10 GWE ± 2 GWE, Strength 27.5 GWE ± 12.5 GWE.

The metal nanofoams according to the invention have the following tolerance limits of the starting materials, based on the weight unit (GWE) grams, for the preparation: Metal salt / metal salts 5 g ± 1 g, citric acid 3 g ± 1 g, water 10 g ± 2 g, Strength 27.5 g ± 12.5 g.

With the nanometer cavities triggering reaction system, which consists of the predetermined weight ratio of starch and citric acid, non-toxic starting materials for the production of metal nanofoams are advantageously used according to the invention.

Hereinafter, a detailed description will be given of the manufacture with subsequent embodiments. The salt of a given metal or two or more salts of predetermined metals, if an alloy foam is sought, preferably a nitrate, is reacted with citric acid in water and dissolved.

The salts used are in particular metal nitrates.

According to the invention, starting materials used are 5 grams of metal salt, 3 grams of citric acid and 10 milliliters of water, and an aqueous solution is prepared therefrom. The aqueous solution is stirred with 15 to 40 grams of corn starch, more preferably 30 grams. From the aqueous solution and the starch stirred into it, a rheopexes, non-Newtonian fluid is formed, which can be shed, but at rest represents a solid gel. This gel blank is poured into a predetermined shape and placed in an oven under inert gas, for. As nitrogen, or in vacuo at 400 to 600 ° C, more preferably at 500 ° C, reacted and burned. The reaction is exothermic, so it releases heat, which is to be considered with larger beginnings of the starting materials. Depending on the dimensions of the gel, the metal nanofoam block can be removed from the high-temperature reaction vessel and cooled after only half an hour residence time in the oven operating as a high-temperature reaction vessel. If the dimensions of the gel are larger, a residence time of up to 2 hours is required.

Variations of the stated basic method refer to the shape of the final product and to the process management, which can be discrete and continuous.

With the method according to the invention z. Example, nanofoams of the following metals are prepared: iron, cobalt, nickel, platinum, palladium, gold, silver, copper and alloys with one of these metals.

In summary, it can be stated
that it is possible with the inventive method to produce high quality metal nanofoams from very cheap starting materials, with little effort and in a short time. The method can also be applied to a broad class of metallic materials which hitherto can not be represented in airgel form. In addition, the production of the metal nanofoams and the produced metal nanofoams themselves are environmentally friendly.

Further developments and advantageous embodiments are specified in the subclaims.

The invention will be explained in more detail by means of exemplary embodiments.

The process for producing metal nanofoams has as starting materials at least at least one metal salt (MS), citric acid (ZS) and water (W) and starch (S) essentially having a basic weight unit ratio MS: ZS: W: S = 5: 3: 10: 27.5, wherein the starting materials are mixed to a rheopexen, non-Newtonian fluid, wherein the resulting rheopex non-Newtonian fluid at least with an exothermic reaction in an inert environment (also vacuum) to a block of metal nanofoam is trained.

The following tolerance limits of the starting materials based on weight units (GWE) can be specified for production: Metal salt / metal salts 5 GWE ± 1 GWE, citric acid 3 GWE ± 1 GWE, water 10 GWE ± 2 GWE, Strength 27.5 GWE ± 12.5 GWE.

It can be z. One unit of weight (GWE) may be one gram or one kilogram.

• – Umsetzung mindestens eines Metallsalzes mit Zitronensäure in Wasser zu einer Lösung,
• – Verrühren der wässrigen Lösung mit Stärke solange, bis ein rheopexes, nicht-Newtonsches Fluid entsteht,
• – Verflüssigung zu einem vergießbaren Gel-Rohling,
• – Gießen des Gel-Rohlings in eine vorgegebene Form,
• – Erhitzen des in der Form befindlichen Gel-Rohlings in einem hochtemperierten Reaktionsbehälter mit Schutzgas-Reaktionsraum oder mit Vakuum zur Durchführung einer exothermen Reaktion,
• – Entnahme des durch die exotherme Reaktion entstehenden Metallnanoschaumblocks,
• – Abkühlung des Metallnanoschaumblocks.

In detail, at least the following steps are performed:

• Conversion of at least one metal salt with citric acid in water to a solution,
• Stirring the aqueous solution with starch until a rheopexes, non-Newtonian fluid is formed,
• Liquefaction into a pourable gel blank,
• Casting the gel blank into a predetermined shape,
• Heating of the in-mold gel blank in a high-temperature reaction vessel with protective gas reaction space or with a vacuum for carrying out an exothermic reaction,
• Removal of the metal nanofoam block resulting from the exothermic reaction,
• - cooling of the metal nanofoam block.

In the following several embodiments are given.

Embodiment 1

• – Umsetzung von 5 Gramm Nickel-Nitrat Hexahydrat zusammen mit 3 Gramm Zitronensäure in 10 Milliliter Wasser zu einer wässrigen Lösung,
• – Verrühren der wässrigen Lösung mit 20 Gramm Maisstärke solange, bis ein rheopexes, nicht-Newtonsches Fluid entsteht,
• – Verflüssigung zu einem vergießbaren Gel-Rohling,
• – Gießen des Gel-Rohlings in eine vorgegebene Form,
• – Erhitzen des in der Form befindlichen Gel-Rohlings in einem Ofen bei 450°C mit Schutzgas-Umgebung unter Argon für 20 Minuten zur Durchführung einer exothermen Reaktion,
• – Entnahme des durch die exotherme Reaktion entstehenden Nickelnanoschaumblocks,
• – Abkühlung des Nickelnanoschaumblocks.

The production of nickel nanofoam takes place as follows:

• Conversion of 5 grams of nickel nitrate hexahydrate together with 3 grams of citric acid in 10 milliliters of water to an aqueous solution,
• Stirring the aqueous solution with 20 grams of corn starch until a rheopexes, non-Newtonian fluid is formed,
• Liquefaction into a pourable gel blank,
• Casting the gel blank into a predetermined shape,
• Heating the in-mold gel blank in an oven at 450 ° C with inert gas atmosphere under argon for 20 minutes to effect an exothermic reaction,
• Removal of the nickel nanofoam block resulting from the exothermic reaction,
• - cooling of the nickel nanofoam block.

The subsequent porosimetric analysis of the nickel nanofoam block gives an internal surface area of 304 m ² / g and an internal volume of 98 cm ³ / g. The density is 10 kg / m ³ .

Embodiment 2

• – Umsetzung von 5 Gramm Nickel-Nitrat Hexahydrat zusammen mit 3 Gramm Zitronensäure in 10 Milliliter Wasser zu einer wässrigen Lösung,
• – Verrühren der wässrigen Lösung mit 30 Gramm Maisstärke (gegenüber 20 Gramm Maisstärke im Ausführungsbeispiel 1) solange, bis ein rheopexes, nicht-Newtonsches Fluid entsteht,
• – Verflüssigung zu einem vergießbaren Gel-Rohling,
• – Gießen des Gel-Rohlings in eine vorgegebene Form,
• – Erhitzen des in der Form befindlichen Gel-Rohlings in einem Ofen bei 450°C mit Schutzgas-Umgebung unter Argon für 20 Minuten zur Durchführung einer exothermen Reaktion,
• – Entnahme des durch die exotherme Reaktion entstehenden Nickelnanoschaumblocks,
• – Abkühlung des Nickelnanoschaumblocks.

The production of a further second nickel nanofoam takes place as follows:

• Conversion of 5 grams of nickel nitrate hexahydrate together with 3 grams of citric acid in 10 milliliters of water to an aqueous solution,
• Stirring the aqueous solution with 30 grams of corn starch (compared to 20 grams of corn starch in Example 1) until a rheopexes, non-Newtonian fluid is formed,
• Liquefaction into a pourable gel blank,
• Casting the gel blank into a predetermined shape,
• Heating the in-mold gel blank in an oven at 450 ° C with inert gas atmosphere under argon for 20 minutes to effect an exothermic reaction,
• Removal of the nickel nanofoam block resulting from the exothermic reaction,
• - cooling of the nickel nanofoam block.

The subsequent porosimetric analysis of the nickel nanofoam block gives an internal surface area of 329 m ² / g and an internal volume of 107 cm ³ / g.

Embodiment 3

• – Umsetzung von jeweils 1 Gramm Nickel-Nitrat, Eisen-Nitrat und Cobalt-Nitrat zusammen mit 2 Gramm Zitronensäure in 7 Milliliter Wasser zu einer wässrigen Lösung,
• – Verrühren der wässrigen Lösung mit 15 Gramm Maisstärke solange, bis ein rheopexes, nicht-Newtonsches Fluid entsteht,
• – Verflüssigung zu einem vergießbaren Gel-Rohling,
• – Gießen des Gel-Rohlings in eine vorgegebene Form,
• – Erhitzen des in der Form befindlichen Gel-Rohlings in einem Ofen bei 450°C mit Schutzgas-Umgebung unter Argon für 20 Minuten zur Durchführung einer exothermen Reaktion,
• – Entnahme des durch die exotherme Reaktion entstehenden FeCoNi-Legierungs-Nanoschaumblocks,
• – Abkühlung des FeCoNi-Legierungs-Nanoschaumblocks.

The production of FeCoNi alloy nanofoam takes place as follows:

• Reacting 1 gram each of nickel nitrate, iron nitrate and cobalt nitrate together with 2 grams of citric acid in 7 milliliters of water to form an aqueous solution,
• - Stir the aqueous solution with 15 grams of corn starch until a rheopexes, non-Newtonian fluid is formed,
• Liquefaction into a pourable gel blank,
• Casting the gel blank into a predetermined shape,
• Heating the in-mold gel blank in an oven at 450 ° C with inert gas atmosphere under argon for 20 minutes to effect an exothermic reaction,
• Removal of the FeCoNi alloy nanofoam block resulting from the exothermic reaction,
• - Cooling of the FeCoNi alloy nanofoam block.

The subsequent porosimetric analysis of the resulting FeCoNi alloy nanofoam block results in an inner surface area of 180 m ² / g.

Embodiment 4

• – Umsetzung von 1 Gramm Platin-Acethylacetonat zusammen mit 0,6 Gramm Zitronensäure in 2 Milliliter Wasser zu einer Lösung,
• – Verrühren der wässrigen Lösung mit 4 Gramm Maisstärke solange, bis ein rheopexes, nicht-Newtonsches Fluid entsteht,
• – Verflüssigung zu einem vergießbaren Gel-Rohling,
• – Gießen des Gel-Rohlings in eine vorgegebene Form,
• – Erhitzen des in der Form befindlichen Gel-Rohlings in einem Ofen bei 450°C mit Schutzgas-Umgebung unter Argon für 20 Minuten zur Durchführung einer exothermen Reaktion,
• – Entnahme des durch die exotherme Reaktion entstehenden Platinnanoschaumblocks,
• – Abkühlung des Platinnanoschaumblocks.

The production of platinnano foam takes place as follows:

• Conversion of 1 gram of platinum acetoacetonate together with 0.6 gram of citric acid in 2 milliliters of water to a solution,
• Stirring of the aqueous solution with 4 grams of corn starch until a rheopexes, non-Newtonian fluid is formed,
• Liquefaction into a pourable gel blank,
• Casting the gel blank into a predetermined shape,
• Heating the in-mold gel blank in an oven at 450 ° C with inert gas atmosphere under argon for 20 minutes to effect an exothermic reaction,
• Removal of the platinum nanofoam block resulting from the exothermic reaction,
• - Cooling of the platinum foam block.

The subsequent porosimetric analysis of the platinum nanofoam block gives an inner surface area (on a gram) of 253 m ² / g.

The exothermic reactions can be carried out in a high-temperature reaction vessel with an internal inert reaction space - an oven with inert gas or a furnace with vacuum.

• 1) Das erfindungsgemäße Verfahren ist kostengünstiger, weil keine aufwändige Synthese des energetischen Liganden benötigt wird.
• 2) Das erfindungsgemäße Verfahren ist sicherer in der Anwendung, weil keine brisanten Komponenten – Bisamotetrazol und seine Metallkomplexe – eingesetzt werden.
• 3) Das erfindungsgemäße Verfahren ist nachhaltiger, weil erstens nur nachwachsende Rohstoffe oder Mineralien als Ausgangsstoffe eingesetzt werden, und zweitens die aufwändige chemische Synthese des Liganden entfällt, die extrem giftige Chemikalien (Cyanamid) und große Mengen Lösungsmittel zum Einsatz gelangen.
• 4) Schließlich liefert das erfindungsgemäße Verfahren Metall-Aerogele mit durchschnittlich größerer innerer Oberfläche pro Gramm Metallnanoschaum (329 m²/g im Ausführungsbeispiel 4 gegenüber im Stand der Technik angegebenen 278 m²/g).

The advantages of the method according to the invention are:
Because only in the Tappan et al .: Ultralow-density nanostructural metal foams combustion synthesis, morphology and composition, Journal of the American Chemical Society, 2006, 128 (20) 6589-6594 , method described is comparable to the method according to the invention and similarly high quality aerogels or nanofoams supplies, the advantages of the method according to the invention over the known method are mentioned:

• 1) The inventive method is less expensive because no complex synthesis of the energetic ligand is needed.
• 2) The inventive method is safer to use because no explosive components - bisamotetrazole and its metal complexes - are used.
• 3) The inventive method is more sustainable because, firstly, only renewable raw materials or minerals are used as starting materials, and secondly eliminates the complex chemical synthesis of the ligand, the extremely toxic chemicals (cyanamide) and large amounts of solvent used.
• 4) Finally, the process according to the invention provides metal aerogels having an average inner surface area per gram of metal nanofoam (329 m ² / g in the exemplary embodiment 4 compared to 278 m ² / g stated in the prior art).

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• Tappen et al.: Nanoporous Metal Foams, Angewandte Chemie Int. Ed., 2010, 49, 4544-4565 [0002]
• Tappan et al: Nanoporous Metal Foams, Angewandte Chemie Int. Ed., 2010, 49, 4544-4565 [0005]
• Kistler: Coherent expanded aerogels and jellies, Nature 1931, 127, page 741 and Pekala, Alviso and LeMay: Organic aerogels, Non-Cryst. Solids, 1990, 125, p. 57 [0006]
• Publication Liu, Herrmann, et al .: High-performance electrocatalysts on palladium aerogels, Angewandte Chemie Int. Ed., 2012, vol. 51 (23), pp. 5743-5767 [0008]
• Tappan et al .: Ultralow-density nanostructural metal foams combustion synthesis, morphology and composition, Journal of the American Chemical Society, 2006, 128 (20) 6589-6594 [0009]
• Tappan et al .: Ultralow-density nanostructural metal foams combustion synthesis, morphology and composition, Journal of the American Chemical Society, 2006, 128 (20) 6589-6594 [0047]

Claims (14)

Process for the production of metal nanofoams, characterized by that at least at least one metal salt (MS), citric acid (ZS) and water (W) and starch (S) are used as starting materials, which are mixed to a rheopexen, non-Newtonian fluid, wherein the resulting rheopaque, non-Newtonian fluid is formed into a block of metal nanofoam at least with an exothermic reaction within an inert environment. Method according to claim 1, characterized by that the starting materials - at least at least one metal salt (MS), citric acid (ZS) and water (W) and starch (S) - essentially with a weight ratio MS: ZS: W: S = 5: 3: 10: 27.5 and mixed to form the rheopex non-Newtonian fluid. A method according to claim 2, characterized in that the following on weight units (GWE) related tolerance limits of the starting materials are predetermined for the preparation: Metal salt / metal salts (MS), 5 GWE ± 1 GWE, Citric acid (ZS) 3 GWE ± 1 GWE, Water (W) 10 GWE ± 2 GWE, Strength (S) 27.5 GWE ± 12.5 GWE. Process according to claims 1 to 3, characterized in that the following steps are carried out in detail: - reaction of at least one metal salt with citric acid in water to an aqueous solution, - stirring of the aqueous solution with starch until a rheopexes, non-Newtonian fluid - Liquefaction into a pourable gel blank, - Casting the gel blank in a predetermined shape, - Heating the in-mold gel blank in a high-temperature reaction vessel with inert gas reaction space or with a vacuum reaction chamber to perform an exothermic reaction - removal of the metal nanofoam block resulting from the exothermic reaction, - cooling of the metal nanofoam block. Method according to one of claims 1 to 4, characterized in that the exothermic reactions in a high-temperature reaction vessel with an inner intertem reaction space, an oven with inert gas or a furnace with vacuum, are performed. Method according to one of claims 1 to 5, characterized in that corn starch is used as starch. A method according to claim 4, characterized in that the removal of the metal nanofoam block is carried out after the exothermic reaction from the high-temperature reaction vessel depending on the dimensions of the gel blank after about 20 minutes to 2 hours for subsequent cooling. Method according to one of claims 1 to 7, characterized in that platinum metals and metals of the iron group are used for the formation of the metal nanofoam blocks. Method according to one of the preceding claims 1 to 8, characterized in that the following steps are carried out for the preparation of a nickel nanofoam: - reaction of 5 grams of nickel nitrate hexahydrate together with 3 grams of citric acid in 10 milliliters of water to an aqueous solution, - stirring the aqueous solution with 20 grams of corn starch until a rheopexes, non-Newtonian fluid is formed, - liquefaction into a pourable gel blank, Casting the gel blank into a predetermined shape, heating the gel blank in the mold in a high temperature reaction vessel at 450 ° C. with protective gas atmosphere under argon for 20 minutes to carry out an exothermic reaction, removing the gel by the exotherm Reaction of the resulting nickel nanofoam block, - cooling of the nickel nanofoam block. Method according to one of claims 9, characterized in that for the production of a further nickel nanofoam the following steps are carried out: reaction of 5 grams of nickel nitrate hexahydrate together with 3 grams of citric acid in 10 milliliters of water to an aqueous solution, stirring of the aqueous Solution with 30 grams of corn starch until a rheopexes, non-Newtonian fluid is formed, - liquefaction into a pourable gel blank, - pouring the gel blank into a predetermined shape, - heating the in-mold gel blank in the high-temperature Reaction vessel at 450 ° C with inert gas atmosphere under argon for 20 minutes to carry out an exothermic reaction, - Removing the nickel foam block formed by the exothermic reaction, - Cooling of the nickel foam block. Method according to one of claims 1 to 8, characterized in that the following steps are carried out for the preparation of a FeCoNi alloy nanofoam: - Implementation of 1 gram of nickel nitrate, iron nitrate and cobalt nitrate together with 2 grams of citric acid in 7 Milliliters of water to an aqueous solution, - stirring the aqueous solution with 15 grams of corn starch until a rheopexes, non-Newtonian fluid is formed, - liquefaction into a pourable gel blank, - pouring the gel blank into a predetermined shape, - heating of the in-mold gel blank in the high-temperature reaction vessel at 450 ° C with inert gas atmosphere under argon for 20 minutes to carry out an exothermic reaction, - Removing the FeCoNi alloy nanofoam block resulting from the exothermic reaction, - Cooling of FeCoNi Alloy Nano foam block. Method according to one of claims 1 to 8, characterized in that for the preparation of a Platinnanoschaums the following steps are carried out: - Implementation of 1 gram of platinum acetoacetonate together with 0.6 grams of citric acid in 2 milliliters of water to an aqueous solution, - stirring the aqueous Solution with 4 grams of corn starch until a rheopexes, non-Newtonian fluid is formed, - liquefaction into a pourable gel blank, - pouring the gel blank into a predetermined shape, - heating the in-mold gel blank in the high-temperature Reaction vessel at 450 ° C with inert gas atmosphere under argon for 20 minutes to carry out an exothermic reaction, - Removing the platinum nanoshoam block resulting from the exothermic reaction, - Cooling of Platinnanoschaumblocks. Metal nanofoams, produced by the process according to one of claims 1 to 12, characterized in that as starting materials at least one metal salt (MS), citric acid (ZS) and water (W) and starch (S) substantially with a weight ratio MS: ZS: W: S = 5: 3: 10: 27.5 are used. Metal nanofoams according to Claim 13, characterized in that the following tolerance limits of the starting materials, based on weight units (GWE), are predetermined for production: Metal salt / metal salts 5 GWE ± 1 GWE, citric acid 3 GWE ± 1 GWE, water 10 GWE ± 2 GWE, Strength 27.5 GWE ± 12.5 GWE.