EP3684531A1

EP3684531A1 - Method for producing an open-pore molded body which has a modified surface and which is made of a metal, and a molded body produced using said method

Info

Publication number: EP3684531A1
Application number: EP18769696.8A
Authority: EP
Inventors: Tilo BÜTTNER; Gunnar Walther; Hans-Dietrich BÖHM; Thomas WEISSGÄRBER; Bernd Kieback; Christian Immanuel Müller; Robin Kolvenbach; Lars Torkuhl
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV; Alantum Europe GmbH
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV; Alantum Europe GmbH
Priority date: 2017-09-19
Filing date: 2018-09-14
Publication date: 2020-07-29
Also published as: RU2020111282A3; RU2020111282A; CN111432962B; JP2020534434A; CN111432962A; CA3076513A1; US20200276644A1; KR102612696B1; KR20200124210A; WO2019057625A1; DE102017216566A1; JP7383601B2

Abstract

The invention relates to a method for producing open-pore molded bodies which have a modified surface and which are made of a metal. The surface of an open-pore molded body which is made of a metal, said molded body being used as a semi-finished product, is coated with particles of a chemical compound of a metal which can be reduced or thermally or chemically decomposed in a thermal treatment, and particles of the respective metal are produced by means of the thermal treatment, said particles being obtained by means of a chemical reduction or a thermal or chemical decomposition. After the coating process, at least one thermal treatment is carried out, in which the produced metal particles are connected to the surface of the semi-finished product and/or adjacent produced particles via sintered necks or sintered bridges such that the specific surface area of the obtained open-pore molded body is increased to at least 30 m²/l and/or at least by a factor of 5 in comparison to the starting material of the uncoated metal semi-finished product.

Description

A process for the preparation of an open-porous shaped body with a modified surface, which is formed with a metal and a molded body produced by the process

The invention relates to a process for the production of an open-porous molded body with a modified surface, which is formed with metal and a molded body produced by the process.

It is known to coat metallic porous moldings on their surface, in particular to improve the properties. For this powdery materials are usually used, which are applied by means of a binder or suspension on surfaces of the molding and removed in a heat treatment organic components and then formed at higher temperatures on surfaces of the molding a coating or surface area, which has a different chemical composition than the Material with which the molding was formed have. With these known possibilities, the specific surface of a shaped body can be increased, but this was only possible to a limited extent with the known possibilities.

For many industrial applications, however, very large specific surfaces are advantageous, as is very desirable, for example, in catalytically assisted processes, filtration or even in electrodes in electrochemical applications.

In addition, it is often also other properties of surfaces of open-porous moldings, which affects their properties to influence.

It is therefore an object of the invention to provide open-porous moldings made of a metallic material which can have an increased specific surface and also different surface properties than is possible with the base material with which a surface-modified open-pore shaped body is formed.

According to the invention, this object is achieved by a method having the features of claim 1. Claim 10 relates to a molded article produced by the method. Advantageous embodiments and further developments can be realized with features described in the subordinate claims.

In the invention, open-porous body made of a metallic material are used as semifinished product. This may be a metal grid, a metal net, a metal mesh, a metal foam, a metal garbage or a semi-finished product formed with metallic fibers.

However, the semifinished product may also advantageously be an open-pore shaped body in which a polymer material has been galvanically (electrochemically) coated with a metal. A semifinished product produced in this way can be subjected to a thermal treatment in which the organic constituents of this polymer are removed as a result of pyrolysis. However, this removal of organic components may also occur later in a similar timely removal of a binder, which will be discussed in more detail below.

Before or after this thermal treatment takes place in an embodiment of the invention, a coating of the open-porous body with particles of a chemical compound of a metal on surfaces of the resulting open-porous formed with metal molding. In this case, the particles should also be introduced into the interior of the shaped body, that is to say into the pores or free spaces of the semifinished product.

The particles of a chemical compound of a metal can be used for the process of coating as a powder, as a powder mixture, as a suspension or as a dispersion. The coating of the surface of the semifinished product with a powder, a powder mixture and / or a suspension / dispersion can be effected by dipping, spraying, pressure-assisted, electrostatic and / or magnetic.

In further alternatives according to the invention, the powders, powder mixtures, suspensions or dispersions used for the coating of the open-pore semifinished product can contain, in addition to particles of a chemical compound of a metal, an inorganic and / or organic binder which is finely distributed in the form of the powder, the powder mixture, the suspension or dispersion a solid powder or dissolved in a liquid phase of a solution containing suspension / dispersion of metallic particles or particles of a chemical compound of a metal.

The coating of the surface of the semifinished product with a binder in the form of a solution or a suspension / dispersion can be effected by dipping or spraying. The thus prepared open-porous molded body is coated as a semifinished product with a powder of a chemical compound of a chemical element. This powder contains a chemical compound that can be converted to a metal by thermal reduction, chemical or chemical decomposition.

By the action of mechanical energy, in particular a vibration, the distribution of powder particles can wet with the liquid binder Surfaces and their adhesion to the surface can be improved.

The application of particles as powder, powder mixture and / or suspension / dispersion can be repeated several times, preferably at least three times, more preferably five times. This also applies to the particular vibration to be performed and possibly the application of a binder.

However, the coating of the surface of the semifinished product can also be carried out before the thermal treatment in which the organic constituents of the polymeric material with which the semifinished product has been produced are removed. Subsequent to the application of the particle-containing material, a thermal treatment is carried out in which organic and volatile constituents of the polymeric material and at the same time any binder used are removed.

After thermal treatment and particle deposition, sintering is performed in which sintered bridges are formed between the particles of the metal particles formed in the thermal treatment formed in the reduction or decomposition and the metallic surface of the open-porous metallic shaped body.

In this case, the specific surface of the thus coated and sintered open-pore shaped body is to be increased to at least 30 m ² / l, however, at least 5 times compared to the starting material of the uncoated metallic molded body as a semi-finished product.

Here, the porous skeleton with a pore size between 450 μιη and 6000 μιη and a specific surface area of 1 m ² / l - 30 m ² / l with particles (particle size d ₅₀ between 0.1 μιη to 250 μιη) depending on the application either starting from one side (porosity gradient) or completely filled or the webs of the porous metallic shaped body have been superficially coated.

The coating with particles can be carried out on different sides of the surface, in particular on opposing surfaces of the semifinished product, with different amounts in order to avoid because to get a different porosity, pore size and / or specific surface area. This can be achieved, for example, by a different number of application of particles as powder, powder mixture or in suspension / dispersion, with or without binder use, on the surfaces arranged on different sides. So can a graded

Formation of a shaped article produced according to the invention can be achieved.

The pore size within the applied particle layer of the coated and sintered open-pore shaped body corresponds to a maximum of 10,000 times the particle size used. This can be additionally influenced by the maximum height of the sintering temperature and its holding time, since with increasing temperature and holding time the diffusion-related mass transfer and thus the sintering, which is accompanied by a reduction of the pore volume, is promoted.

The material with which the molding produced according to the invention is formed should contain a maximum of 3% by weight, preferably a maximum of 1% by weight of O ₂ . For this purpose, preferably an inert or reducing atmosphere during the execution of the thermal treatment for the removal of organic components, the possibly carried out chemical reduction and / or sintering from affects.

In the case of a thermal or chemical decomposition, a respectively suitable atmospheric condition for the respective decomposition process can be selected. Thus, the thermal treatment in an inert atmosphere, e.g. Argon, under vacuum or reducing atmosphere, e.g. Hydrogen containing carried out, for example, in which unused decomposition products are removed.

Such an open-porous shaped body produced according to the invention can be used in the field of (i) filtration, (ii) as a catalyst (for example in US Pat

Ethylene oxide synthesis - Ag-particle coated Ag foam catalyst), (iii) electrode material or (iv) support for a catalytic active substance. The increase in the specific surface area results in better filtration performance in application (i) since adsorption tendency and capacity are markedly increased.

In application (ii), increasing the specific surface area results in a disproportionate increase in catalytic activity, since not only does the number of active sites increase, but the surface has a much more faceted structure. In addition, the increased surface energy leads to a significant increase in the catalytic activity compared to the unfaceted surface of the open-pored starting material.

In use case (iii), increasing the specific surface area also leads to an increase in active sites, which in combination with the faceted structure of the surface leads to a significant reduction of the electrical overvoltage compared to commercial electrodes (e.g., nickel or carbon). As a specific application further mention should be made of the electrolysis - e.g. Ni- or Mo-foam coated with Ni particles or Mo particles. Particularly in this application, it is also advantageous to use a sintered and metallic open-pore shaped body coated on one side with metallic particles, since here the grading of the pore size ensures good removal of the gas bubbles.

In the case of application (iv), increasing the specific surface area leads to an improved adhesion of the active component, e.g. a catalytic washcoat, to the support surface which significantly increases the mechanical, thermal and chemical resistance of a catalyst material.

Suitable metals for applied particles and semi-finished products with which moldings produced according to the invention can be produced are: Ni, Fe, Cr, Al, Nb, Ta, Ti, Mo, Co, B, Zr, Mn, Si, La, W, Cu, Ag, Au, Pd, Pt, Zn, Sn, Bi, Ce or Mg.

Chemical compounds of the metals Ni, Fe, Cr, Al, Nb, Ta, Ti, Mo, Co, B, Zr, Mn, Si, La, W, Cu, Ag, Au, Pd, Pt, Zn, Sn, Bi, Ce, Mg, V, by chemical Reduction, thermal or chemical decomposition in a thermal treatment can be converted into particles of the respective metal, in particular their oxides, nitrides, hydrides, carbides, sulfides, sulfates, phosphates, fluorides, chlorides, bromides, iodides, azides, nitrates, amines, Amides, organometallic complexes, salts of organometallic complexes, or decomposable salts for the particle-containing material with which the surface of the present as a semi-finished open-porous shaped body to be coated can be used. Particularly suitable as chemical compounds are chemical compounds of: Ni, Fe, Ti, Mo, Co, Mn, W, Cu, Ag, Au, Pd or Pt.

In the thermal or chemical decomposition of a chemical compound in the respective metal is until the successful thermal or chemical decomposition of the chemical compound into the metal, a suitable decomposition atmosphere, which may be inert, oxidizing or reducing, maintained. For the chemical reduction of a chemical compound into the respective metal, the thermal treatment, which is to lead to the chemical reduction, may preferably be carried out at least temporarily until the chemical reduction has been carried out in a reducing atmosphere, in particular a hydrogen atmosphere.

For chemical decomposition by oxidation, atmospheres are particularly suitable which contain oxygen, fluorine, chlorine, any mixtures of these gases as well as any mixtures with inert gases, for example nitrogen, argon or krypton.

In the case of a thermal or chemical decomposition of a corresponding chemical compound of a metal forming the particles, it is possible to proceed analogously by maintaining the corresponding atmospheric conditions during the thermal treatment at least until the respective decomposition process has been sufficiently completed and sufficient metallic particles for the sintering compound on Material of the semifinished product have been obtained due to decomposition.

In a chemical decomposition, metal cations for the formation of elemental metals can be reduced. The anion component can however be oxidized be diert. A chemical decomposition of a compound of noble metals in the elemental metals (Au, Pt, Pd) is also conceivable under air, so rather oxidizing atmosphere. Also, disproportionations modeled on the equation: 2 gel <-> Ge (s) + gel (g) are possible for aluminum, titanium, zirconium and chromium. It is also possible to use crystalline, organometallic complexes or salts thereof in which the metal center is already present in oxidation state 0.

By means of the metal particles formed by chemical reduction, thermal or chemical decomposition and sintered with the surface of the semifinished product, the surface properties of an open-porous molded article produced according to the invention can be influenced, for example the thermal resistance, the resistance to corrosion, the chemical resistance, the adhesion a catalytic washcoat and the catalytic functionality. In this case, a graded transition between the metallic material of the semifinished product and the material of the metal particles formed advantageously also has an advantageous effect. In this case, starting from the surface up to the webs of the semi-finished product different phases can form, as is clear from subsequent embodiments.

Porosity, pore size and specific surface area can be significantly affected by the morphology of the particles used for the coating. To obtain a high specific surface area and a fine porous structure, particles of small size and dendritic form, e.g.

Electrolyte powder, advantageous. Due to their irregular geometry, which allows no gap-free arrangement, adjacent particles form free spaces between contact points and particle bodies, which are partially connected to channels. Furthermore, the use of particles from a chemical compound in thermal decomposition or chemical decomposition creates an additional microporous space left by the volatile component. The proportion of the microporous space in the total pore space is higher, the greater the proportion and thus also the volume requirement of the volatile component of the chemical compound. For the coating with metal oxide particles, therefore, the use of a oxide with a high oxidation state, and consequently a high oxygen content, is advantageous. Because the Sinteractivity of structures increases with increase in the specific surface area, the atmosphere, the holding time and the material-dependent sintering temperature are chosen so that the particles ansaintern mechanically stable to each other and to the semi-finished, but the fine pores are not significantly compacted.

The invention will be explained in more detail by way of examples.

Embodiment 1

There was obtained by electroplating a porous foam made of polyurethane open-porous molded body made of silver as a semifinished product with a mean pore size of 450 μιη, a porosity of 95%, the dimensions 70 mm x 63 mm, thickness 1.6 mm of a thermal treatment for removal of the organic components as in the embodiment.

Subsequently, a coating of surfaces of the semi-finished product freed of organic components with a suspension of the following composition:

48% Ag ₂ 0 metal oxide powder <5 μιη,

1.5% binder polyvinylpyrrolidone (PVP)

49.5% solvent water

1% dispersing agent

by spraying.

For this purpose, the powdery binder was first dissolved in water and then added all other components and mixed in a speed mixer 2 x 30 s at 2000 rev / min to a suspension.

The semi-finished product was sprayed on both sides several times using a wet powder spray method with the prepared powder suspension. The suspension is atomized in a spraying device and applied on both surfaces on surfaces of the semifinished product. Due to the discharge pressure from the spray nozzle, the suspension is distributed evenly in the porous network of the semifinished product. The suspension only sticks to the web surface, so that the webs are completely covered with the suspension and the porosity of the semifinished product is largely retained. The thus-coated semi-finished product was then dried at room temperature in air. For debinding, reduction and sintering, a thermal treatment was carried out under a hydrogen atmosphere and then in an oven. For this purpose, the oven is heated at a heating rate of 5K / min. The reduction of the silver oxide begins even at below 100 ° C and is completed at 200 ° C and a holding time of about 30 minutes under hydrogen. The remaining debinding and sintering process can then be carried out in an oxygen-containing atmosphere, for example air in the temperature range from 200 ° C to 800 ° C with a holding time of 1 min to 180 min.

During the further thermal treatment, the silver oxide was first reduced to metallic silver, which is nanocrystalline. By the remaining debindering and sintering of the then metallic silver particles to the silver foam webs grow on the one hand, the particles to larger and coarser crystalline conglomerates, on the other hand, the Ag diffused from the powder particles in the web material until the powder particles on themselves forming Sinterhälse or Sinterbrücken fixed to the webs the surface of the open-pore shaped body are connected.

After the further thermal treatment, there is a homogeneous open-pore shaped body which is formed with 100% silver.

The porosity is about 93%.

The surface of the webs is characterized by a high roughness. The reason for this is that the applied powder particles are only connected to the surfaces of the semifinished product via sintered necks / sintered bridges, so that the original particle morphology is retained. The specific inner surface area (measured by the BET method) of the finished open-porous molded article could be determined by the previously performed process

(uncoated condition) 10.8 m ² / l to be subsequently increased (coated condition) to 82.5 m ² / l. Embodiment 2

The semifinished product was an open-porous nickel shaped body having an average pore size of 450 μm, with a porosity of about 95%, the dimensions 200 mm × 80 mm, thickness 1.6 mm (produced by electrolytic

Depositing Ni onto PU foam, a MoS ₂ powder having an average particle size <60 μm and a mass of 15 g, using as B a 1% strength aqueous solution of polyvinylpyrrolidone with a volume of 20 ml, Das Semi-finished nickel was sprayed on one side with the binder solution, so that the previously open pores are closed by the binder on one side. Subsequently, the semi-finished product wetted with the binder is fixed in a vibration device and sprinkled on the bindered side with the MoS ₂ powder. By agglomeration of the near-surface pore space was completely filled. Due to the vibration, the powder was partly distributed in the interior of the semifinished product. The underside of the thus coated semifinished product remained uncoated. As a result, the powder loading in the foam is graded from top to bottom. The debindering (removal of the organic components) was carried out in a thermal treatment in an argon atmosphere. For this purpose, the oven is heated at a heating rate of 5 K / min. The

Debinding begins at about 300 ° C and is completed at 600 ° C and a holding time of about 30 min. This is followed by further heating to 1100 ° C with a holding time of 1 h at this maximum temperature, wherein the MoS _{2 is} decomposed in Mo and S and the sulfur is transported away in the vapor phase by the argon gas stream. Subsequently, the atmosphere was converted to hydrogen during the thermal treatment of argon and further heated. The sintering process took place at a temperature of 1260 ° C to and a holding time of 60 minutes.

During sintering, the Mo diffuses out of the powder particles into the web material until the powder particles are firmly connected to the webs of the semifinished product via sintering necks or sinter bridges which form. However, a complete compensation of the element concentration does not take place. After this thermal treatment, there is an open-pore shaped body with graded porosity and pore size. At the side previously wetted with binder and applied powder, the porosity is <30% and the pore size is in the range 5 μιη - 50 μιη and increases to the uncoated side of the mold continuously to 95% porosity and a pore size of 450 μιη.

The molybdenum-coated foam webs have a graded phase composition as follows:

Composition / phases: Mo (porous layer on the outside of the web and in the filled pore space)

MoNi (transition area outside)

MoNi ₃ (transition area central)

MoNi ₄ (transition area inside)

Ni (bridge heart)

The surface of the webs is characterized by a high roughness. The reason for this is that the applied powder particles are only connected via sintered necks or sinter bridges with the carrier foam, so that the original particle morphology is maintained.

Embodiment 3

The semifinished product was an open-pore shaped body of nickel with an average pore size of 580 μm, a porosity of about 95%, dimensions of 75 mm × 70 mm, thickness 1.9 mm (produced by electrolytic deposition of Ni on PU foam) Powder TiH ₂ titanium hydride powder having a mean particle size <45 μιη, a mass of 12 g, a steramide wax having an average particle size <80 μιη, a mass of 0.12 g and as binder 1% - aqueous solution of polyvinylpyrrolidone with a volume of 20 ml used.

Powder and steramide wax were mixed for 10 minutes with a Turbula mixer.

The semi-finished product was sprayed on both sides with the binder solution. It was then fixed in a vibration device and fitted with titanium on both sides. hydride powder sprinkled. The vibration distributes the powder in the porous network of the semifinished product. The binder and powder coating was repeated five times so that the pore spaces were completely filled. The thus treated semi-finished product was then dried at room temperature in air.

Debinding was carried out under hydrogen atmosphere conditions. For this purpose, the oven is heated at a heating rate of 5K / min. Debinding begins at about 300 ° C and is completed at 600 ° C and a holding time at this temperature of about 30 min. This was followed under vacuum conditions at 700 ° C and 60 min hold time, the decomposition of the titanium hydride to hydrogen and titanium in the thermal treatment. Thereafter, a further heating up to the sintering temperature of 900 ° C at a holding time of 30 min.

The titanium hydride coated webs of the semifinished product had a graded phase composition following the thermal treatment resulting in sintering as follows:

Composition / phases: Ti (porous layer on the outside of the web and in the filled pore space)

Ti ₂ Ni (transition area outside)

TiNi (transition area central)

TiNi ₃ + TiNi (transition area inside)

Ni (bridge heart)

The porosity of the open-pore shaped article treated in this way is 48% and the specific surface area is 55 m ² / l.

Claims

claims

Anspruch [en] A process for producing open-porous modified-surface molded articles formed with metal in which a metal-formed open-porous shaped body as a semifinished product thermally or chemically decomposes on its surfaces with particles of a chemical compound of a metal which reduces upon thermal treatment be coated and with the particles of the respective metal obtained by chemical reduction, thermal or chemical decomposition, is coated; and after the coating at least one thermal treatment is carried out, in which the metal particles formed are connected to the surface of the semifinished product and / or adjacent formed metal particles via sintered necks or sintered bridges, so that the specific surface of the resulting open-pore shaped body to at least 30 m ² / l and / or at least 5 times compared to the starting material of the uncoated metallic semifinished product is increased.

2. The method according to claim 1, characterized in that the particles of said chemical compound of a metal are used as powder, powder mixture and / or suspension / dispersion.

3. The method according to claim 1 and 2, characterized in that the application of the particles of said chemical compound of a metal in the form of a powder, a powder mixture and / or a suspension / dispersion by dipping, spraying, pressure-assisted, electrostatic and / or magnetic ,

4. The method according to claim 1 to 3, characterized in that an organic and / or inorganic binder in solution, suspension / dispersion or as a powder for improving the adhesion of particles is used.

5. The method according to claim 1 to 4, characterized in that the application of the particles of the chemical compound of a metal is repeated several times, in particular at least three times.

6. The method according to claim 1 to 5, characterized in that in the case of multiple coating with particles of the chemical compound of the metal when using a binder, the binder application is repeated several times, in particular at least three times.

7. The method according to claim 1 to 6, characterized in that the application of a binder and the application of the particles of a chemical compound of a metal on different sides of the surface, in particular on oppositely arranged surfaces of the semifinished product is carried out with a different amount, so that On the differently arranged surfaces in each case a different porosity, pore size and / or specific surface is obtained.

8. The method according to any one of the preceding claims, characterized in that as metal for the semifinished product and the particles to be applied Ni, Fe, Cr, Al, Nb, Ta, Ti, Mo, Co, B, Zr, Mn, Si, La, W, Cu, Ag, Au, Pd, Pt, Zn, Sn, Bi, Ce or Mg, or as a metal for a reducible, thermally or chemically decomposable compound, a chemical compound of Ni, Fe, Cr, Al, Nb, Ta, Ti , Mo, Co, B, Zr, Mn, Si, La, W, Cu, Ag, Au, Pd, Pt, Zn, Sn, Bi, Ce or Mg, in particular a salt, an oxide, a nitride, a hydride, a carbide, a sulfide, a sulfate, a fluoride, a chloride, a bromide, an iodide, a phosphate, an azide, a nitrate, an amine, an amide, an organometallic complex or a salt of an organometallic complex.

9. The method according to any one of the preceding claims, characterized in that a semi-finished product is used, which has been obtained by electroplating an open-porous body of a polymeric material with the respective metal.

10. Open porous molded body produced by a method according to one of the preceding claims, characterized in that the shaped body with sintered necks or sintered bridges with the surface of the semifinished product and / or the surface of adjacent particles associated metallic particles has a specific surface area of at least 30 m ² / l having.

11. Shaped body according to the preceding claim, characterized in that the pore size within the coated and sintered open-pore shaped body corresponds to a maximum of 10,000 times the particle size of the chemical compound of a metal used.

12. Shaped body according to the two preceding claims, characterized in that in the material of the shaped body a maximum of 3% by mass, preferably at most 1% by mass of oxygen are contained.