DE102007047874A1 - Monolithic, metal oxide molding containing submicron pores, used e.g. as vehicle catalyst, is made by adding carbon nanotubes or fibers to metal powder followed by grinding and oxidation - Google Patents

Abstract

The molding contains pores in a single size range or two different size ranges. The pore size within a range, differs by no more than 50 nm. In the single size range, pore sizes lie within the sizes 2-100 nm or 100-300 nm. Where there are two different size ranges, the pore sizes are less than and greater than 200 nm. In this case, the pore sizes range up to 200 nm, and above 300 nm or alternatively up to 200 nm and above 500 nm. Further variant quantified specifications are provided. The pores are partially- or entirely interconnected. The pores are directionally-orientated, with at least some forming a complete pore cavity directed spatially through the molding. The monolithic foam comprises CuO, NiO, TiC, TiO 2, ZrO, ZrO 2and/or Al 2O 3. To make the molding, metal powder and carbon nanotubes or carbon fibers (the carbon forms) are mixed together and ground in the absence of oxygen. Only sufficient of the carbon form is added, to reach a suitable range of pore sizes whilst preventing agglomeration of the carbon. Their dimensions differ by no more than 20 nm. Alternatively, to reach two different size ranges, sufficient of the carbon form is added, to promote partial agglomeration. At most, submicron agglomerates are formed. The mixture is then compacted or compressed under vacuum, followed by temperature treatment in an oxygen-containing atmosphere. The temperature used is below the melting point of the metals and above a temperature at which oxidation of carbon and the metals occurs. The metal powder added is Cu, Ni, Ti, Zr and/or Al at particle sizes exceeding 250 mu m. The nanotubes are single- or multi-walled and unfilled. They are 1-100 nm in diameter and up to 50 nm in length. Mixing and grinding is under inert gas atmosphere and/or vacuum. Mixing and grinding to produce two different pore size ranges, is carried out in two to five stages, within 30 minutes to 400 hours. Up to 20 vol% of the total volume is added in carbon form; or up to 60 vol% when making two different size ranges of pores. Compaction is by equal channel angular pressing (ECAP), high pressure torsion (HPT), hot isostatic pressing (HIP), cold isostatic pressing (CIP) or extrusion at 400-700[deg] C in 10 s to 10 minutes. The temperature treatment is at 400[deg] C - 1000[deg] C for 30 minutes -100 hours. This continues until oxidation of the carbon form and metal is up to 95% complete. An independent claim IS INCLUDED FOR the method of manufacture.

Description

The This invention relates to the field of materials science and relates to porous shaped bodies of metal oxides, as used, for example, as catalyst material in the automotive industry, as a battery electrode material with a high surface area, in biosensors, in fuel cells, as a filter or membrane material can be applied and a procedure for his Production.

porous Metal foams are widely used in various fields applied to the technique. Such foam materials have the advantage low weight with high specific surface area on.

however the practical application of such materials is limited because their production by achieving a large surface area is limited with cross-sectional dimensions in the submicrometer range.

In order to achieve this, various methods are known, such as, for example, the oxidation on carrier substrates, electrochemical or electrocoating methods (US Pat. X. Jiang, et al., Nano Lett. 2, 1333 (2002) ; PL Taberna, et al., Nature Mater. 5, 567, (2006) ; S. Jung, et al., Adv. Mater. 19, 749, (2007) )

A known method for the preparation of porous metal oxides is template synthesis using silicon and silicon solvents with block copolymers ( P. Yang, et al., Nature 396, 152 (1998) . M. Zukalova, et al., Nano Lett. 5, 1789 (2005) ).

Among the transition metal oxides, copper is very interesting and has been very well studied for its narrow band gap and low surface potential limit at a high superconductor transition temperature ( W. Wang, et al., MRS Bull. 37, 1093 (2002) ; AO Musa. et al., Sol. Energy Mater. Sol. Cells 51 305 (1998) ).

to Production of foams in the form of submicrometer films are known to be very fine powder on a support membrane or applied to a carrier substrate. Due to the low Dimensions of the thin films and the relatively small Surface, their application is very limited.

however the above methods are not applicable for use of CuO in the form of a monolithic porous foam.

It is known that it is very difficult to produce porous oxides by oxidation of porous metals, since they evaporate during the oxidation ( HJ Grabke, Materials and Corrosion 54, no. 10, 736 (2003) ,

The The object of the present invention is to specify a porous one Shaped body having a controllably adjustable pore size range in the Submicrometer range and in the indication of a simple Manufacturing process.

The The object is achieved by the invention specified in the claims solved. Advantageous embodiments are the subject of Dependent claims.

Of the inventive porous shaped body Metal oxides consists of a monolithic foam with pores in the Submicrometer range, the pore structure of the molding is set by pores with only one pore size range or with two different pore size ranges, wherein the pore size is within a pore size range does not differ by more than 50 nm.

advantageously, has in the case of the pore structure with a pore size range the molded body pore sizes in the range from 2 to 100 nm or 100 to 300 nm.

Farther Advantageously, in the case of the pore structure with two different Pore size ranges of the molding pore sizes of <200 nm and> 200 nm or ≤ 200 nm and> 300 nm or of ≤200 nm and ≥500 nm or of ≤100 nm and ≥ 200 nm or ≤ 50 nm and ≥ 200 nm or from ≤20 nm and ≥200 nm or from ≤20 nm and ≥ 300 nm.

Also Advantageously, in the case of the pore structure with two different Pore size ranges of the molding pore sizes within 0.1 to ≤ 20 nm and within ≥ 500 nm to 1 micron.

And also advantageously, the pores are wholly or partially with each other connected.

From It is also an advantage if the pores are arranged directionally and at least parts of the pores have a complete pore space realize in a spatial direction through the pore body.

And it is also advantageous if the monolithic foam consists of CuO, NiO, TiC, TiO ₂ , ZrO, ZrO ₂ and / or Al ₂ O ₃ .

In the inventive method for producing a porous Formköpers of metal oxides are metal powder and carbon nanotubes or carbon fibers are mixed and ground with the exclusion of oxygen, wherein to achieve a pore size range maximum carbon nanotubes or carbon fibers are added so that no agglomeration of carbon nanotubes or carbon fibers occurs, and such carbon nanotubes or carbon fibers are added, the dimensions of which differ by a maximum of 20 nm, or Achieving two different pore size ranges in at least two steps so much carbon nanotubes or carbon fibers are added that at least a partial agglomeration of carbon nanotubes or carbon fibers occurs and maximum submicrometer agglomerates of carbon nanotubes or carbon fibers are produced, then compacting / compression of the mixture under vacuum and then a Temperature treatment is carried out under an oxygen-containing atmosphere, the temperature treatment is carried out at temperatures below the melting temperature of the metals and above a temperature at which the oxidation of the carbon and the metal takes place.

advantageously, are used as metal powders Cu, Ni, Ti, Zr and / or Al.

Also Advantageously, metal powders with particle sizes ≤ 250 microns used.

Farther Advantageously, as carbon nanotubes, a and / or multi-walled unfilled carbon nanotubes used.

And also advantageously carbon nanotubes or Carbon fibers with 1 to 100 nm diameter and ≥ 50 nm length used.

Advantageous It is also when the mixture and grinding under inert gas atmosphere and / or carried out under vacuum.

Farther It is advantageous if the mixture and grinding to achieve of two different pore size ranges is carried out in two to five steps, being still advantageously the quantitative Addition of carbon nanotubes or carbon fibers for mixing in two to five steps becomes.

Also It is advantageous if the mixture and grinding within 30 min to 400 h.

And It is also advantageous if to achieve a pore structure with a maximum pore size range of 20% by volume Carbon nanotubes or carbon fibers related to the total volume is added.

From It is also advantageous if to achieve a pore structure with two different pore size ranges maximum 60 vol.% Carbon nanotubes or carbon fibers be added based on the total volume.

And It is also advantageous if the compaction / compression by ECAP (equal channel angular pressing), HPT (high pressure torsion), HIP (hot isostatic pressing), CIP (cold isostatic pressing) or by extrusion, wherein still advantageously the extrusion at temperatures of 400 to 700 ° C and within from 10 s to 10 min.

Farther it is advantageous if the temperature treatment at temperatures above 400 ° C and below 1000 ° C performed becomes.

And It is also beneficial if the temperature treatment within from 30 minutes to 100 hours.

Also it is beneficial if the temperature treatment is carried out until the oxidation of the carbon nanotubes or Carbon fibers and metal powder in each case at least 95% is completed.

Porous transition metal oxides have great potential when used as a catalyst material in the automotive industry to reduce CO ₂ emissions. The solution according to the invention achieves a very high reaction rate due to the improved accessibility of the porous structure for the gas.

With the solution according to the invention is a porous one Shaped body of metal oxides to produce a desired Having pore structure. The pore structure of submicrometer pores can thereby in a pore size range up to a so-called Hybrid structure of submicrometer pores in two different Pore size ranges over the manufacturing process be set. The pore size ranges differ thereby within a pore size range maximum 20 nm. It is advantageous if these two different Pore size ranges a different possible pore size range such as ≦ 20 nm and ≥ 500 nm.

This pore structure in the porous shaped body according to the invention of metal oxides is determined essentially by the selection of the particle size of the metal powder and the dimensions of the carbon nanotubes, but also by the duration and conditions of mixing and milling and compaction / compaction.

The Pore size structure with a pore size distribution is achieved essentially by the fact that carbon nanotubes with substantially the same dimensions, that is with Dimensions that do not differ by more than 50 nm, be used as starting material and the addition advantageously 20 vol .-% based on the total volume does not exceed.

Under stating "where the pore size is within a pore size range of not more than 50 nm differs "should be understood according to the invention, all pores are within 50 nm of their size distinguished, for example, 1-49 nm, 30-80 nm, 75-125 nm, 50-100 nm, 180-230 nm 250-300 can be nm

Should more carbon nanotubes are used, the Mixing and grinding time can be extended. By the volume Addition and the dependent mixing and grinding time is in Metal powder carbon nanotube mixture an agglomeration prevents the carbon nanotubes, so that the porous Moldings consistently pores within a pore size range having.

Should a porous shaped body according to the invention with two different pore size ranges can be made, so the dimensions of the used Carbon nanotubes differ more clearly from each other. By the gradual addition of the carbon nanotubes during mixing and grinding and a much higher one Amount of carbon nanotubes will be an agglomeration of Carbon nanotubes in the metal powder-carbon nanotube mixture achieved, wherein the agglomerated carbon nanotubes the pores with the larger pore size range form. The size of the agglomerates and their number in the mixture are defined over the mixing and grinding time The mixing and milling are always carried out under exclusion of oxygen, so that no oxidation of the metals and the carbon take place can.

When Metal powder may be an oxidizable powder of a metal or even a mixture of several metals or a metal alloy be used.

It may be single or multi-walled carbon nanotubes be used.

To the preparation of the metal powder carbon nanotube mixture the mixture is compacted or compacted under vacuum. It can at the same time structuring / alignment of the pores within of the shaped body can be achieved, for example in the extrusion direction. Due to the vacuum during compaction / compression Furthermore, an oxidation of the metals and the carbon is prevented.

After compacting / densification, the still relatively dense shaped body is subjected to a temperature treatment under an oxygen-containing atmosphere. In this case, the temperature must be at least so high that an oxidation of the metals to metal oxides and the carbon to CO and / or CO _{2 is} realized and on the other hand, the melting temperature of the metals is not exceeded. The oxidation of the metals and the carbon should be carried out in each case at least 95%.

ever after selection of the carbon nanotubes and the mixed and Grinding time and the type of subsequent compaction / compression can have two different pore size ranges be achieved, in terms of their pore sizes differ relatively clearly from each other. This can be advantageous lead to a pore structure, on the one hand very small Pores and on the other hand much larger pores exhibiting, by both agglomeration of the original Carbon nanotubes and / or even by merger of the original agglomerates have arisen and at one appropriate compaction / compression in a preferred direction are aligned and so to continuous pore channels being able to lead.

following The invention will be closer to several embodiments explained.

example 1

A composite of 60% by volume of Cu powder with a particle size of ≤ 45 μm and 40% by volume of multi-walled carbon nanotubes (CNTs) of 0.5-200 μm in length and with an outer diameter of 10-20 nm and an inner diameter Diameters of 5-10 nm are mixed and ground. The Cu powder (Reade Advanced Materials) had a purity of 99.9% and the multi-walled carbon nanotubes (Sigma Aldrich) had a purity of> 95%. The mixing and milling were carried out in a Retsch Pulverisette for 5,300 hours at a rotation speed of 250 rpm using hardened steel balls as grinding balls and the ratio of balls to powder was 10: 1. Mechanical milling was performed in 5 steps, with 8 vol% carbon nanotubes added at each step. Milling was done under pure Ar atmosphere (less than 3 ppm O ₂ and H ₂ O).

The milled Cu / CNT nanocomposite powder was placed in a copper mold under vacuum and by heat extrusion in an extruder (Innovare Inc. Laboratory Metalworking System) also compacted under vacuum at 510 ° C at an extrusion rate of 9 and a pressure of 700 MPa. The resulting dense, disc-shaped pellets 8 mm in diameter and 5 mm in thickness were then annealed at 450 ° C for 3 hours, wherein the simultaneous oxidation of the Cu and the carbon nanotubes takes place, whereby after cooling porous Cu oxide shaped bodies with a Pore structure have emerged, which has two different pore size range of 5-20 nm and 500-550 nm, wherein the pores are aligned in the extrusion direction and 55% connected to each other and thus completely through the molding body passing pores.

Example 2

A composite of 80% by volume Ni powder with a particle size of ≤ 45 μm and 20% by volume of multi-walled carbon nanotubes (CNTs) of 0.5-200 μm in length and with an outer diameter of 10-20 nm and an inner diameter Diameters of 5-10 nm are mixed and ground. The Ni powder (Reade Advanced Materials) had a purity of 99.9% and the multi-walled carbon nanotubes (Sigma Aldrich) had a purity of> 95%. Mixture and milling was carried out in a Retsch Pulverisette 5 for 50 hours at a rotation speed of 250 rpm using hardened steel balls as grinding balls and the ratio of balls to powder was 10: 1. Milling was done under pure Ar atmosphere (less than 3 ppm O ₂ and H ₂ O).

The Milled Ni / CNT nanocomposite powder was placed in a copper mold Vacuum introduced and by heat extrusion in an extruder (Innovare Inc. Laboratory Metalworking System) also under vacuum 510 ° C with an extrusion rate of 9 and a pressure of Compacted 700 MPa. The resulting dense, formed into a disk Pellets of 8 mm diameter and 5 mm thickness were then at 450 ° C Annealed for 3 h, with the simultaneous oxidation of Ni and the Carbon nanotubes takes place, whereby porous after cooling Ni oxide shaped bodies having a pore structure have been formed, which has a uniform pore size range of 50-100 nm, wherein the pores in the extrusion direction are aligned.

Example 3

A composite of 60% by volume of Ni powder having a particle size of ≦ 45 μm and 40% by volume of multi-walled carbon fibers of 0.5-200 μm in length and having an outer diameter of 10-20 nm are mixed and ground. The Ni powder (Reade Advanced Materials) had a purity of 99.9% and the carbon fibers had a purity of> 95%. The mixing and milling were carried out in a Retsch Pulverisette 5 for 100 h at a rotation speed of 250 rpm, using hardened steel balls as grinding balls and the ratio of balls to powder was 10: 1. Milling was done under pure Ar atmosphere (less than 3 ppm O ₂ and H ₂ O).

The Milled nanocomposite powder was placed in a copper mold under vacuum introduced by heat extrusion in an extruder (Innovare Inc.). Laboratory Metalworking System) also under vacuum at 510 ° C compressed at an extrusion rate of 9 and a pressure of 700 MPa. The resulting dense, disc-shaped pellets of 8 mm in diameter and 5 mm in thickness were thereafter at 450 ° C Annealed for 3 h, with the simultaneous oxidation of Ni and the Carbon fibers takes place, whereby after cooling porous Ni-oxide shaped body were created with a pore structure, which is a uniform Having a pore size range of 10-50 nm, wherein the pores are aligned in the extrusion direction.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited non-patent literature

• - X. Jiang, et al., Nano Lett. 2, 1333 (2002) [0004]
• - PL Taberna, et al., Nature Mater. 5, 567, (2006) [0004]
• - S. Jung, et al., Adv. Mater. 19, 749, (2007) [0004]
• - P. Yang, et al., Nature 396, 152 (1998) [0005]
• - M. Zukalova, et al., Nano Lett. 5, 1789 (2005) [0005]
• - W. Wang, et al., MRS Bull. 37, 1093 (2002) [0006]
• - AO Musa. et al., Sol. Energy Mater. Sol. Cells 51 305 (1998) [0006]
• - HJ Grabke, Materials and Corrosion 54, no. 10, 736 (2003) [0009]

Claims (30)

Porous shaped body of metal oxides consisting of a monolithic foam with sub-micron pores, wherein the pore structure of the shaped body is adjusted pores with a pore size range or with two different pore size ranges, wherein the pore size within a pore size range does not differ by more than 50 nm. Porous molding according to claim 1, wherein in the case of the pore structure having a pore size range the molded body pore sizes in the range from 2 to 100 nm. Porous molding according to claim 1, wherein in the case of the pore structure having a pore size range the molded body pore sizes in the range from 100 to 300 nm. Porous molding according to claim 1, wherein in the case of the pore structure with two different pore size ranges the shaped body pore sizes of <200 nm and> 200 nm. Porous molding according to claim 1, wherein in the case of the pore structure with two different pore size ranges the molded body pore sizes of ≤ 200 nm and ≥ 300 nm. Porous molding according to claim 1, wherein in the case of the pore structure with two different pore size ranges the molded body pore sizes of ≤ 200 nm and ≥ 500 nm. Porous molding according to claim 1, wherein in the case of the pore structure with two different pore size ranges the molded body pore sizes of ≤ 100 nm and ≥ 200 nm. Porous molding according to claim 1, wherein in the case of the pore structure with two different pore size ranges the molded body pore sizes of ≤ 50 nm and ≥ 200 nm. Porous molding according to claim 1, wherein in the case of the pore structure with two different pore size ranges the molded body pore sizes of ≤ 20 nm and ≥ 200 nm. Porous molding according to claim 1, wherein in the case of the pore structure with two different Pore size ranges of the molding pore sizes of ≤ 20 nm and ≥ 300 nm. Porous molding according to claim 1, wherein in the case of the pore structure with two different Pore size ranges of the molding pore sizes within 0.1 to ≤ 20 nm and within ≥ 500 nm to 1 micron. Porous molding according to claim 1, in which the pores are completely or partially connected to each other. Porous molding according to claim 1, in which the pores are arranged directionally and at least parts the pores a complete pore space in a spatial direction realize through the pore body. Porous shaped body according to claim 1, wherein the monolithic foam consists of CuO, NiO, TiC, TiO ₂ , ZrO, ZrO ₂ and / or Al ₂ O ₃ . Process for the preparation of a porous molded body of metal oxides according to at least one of claims 1 to 14, in the metal powder and carbon nanotubes or carbon fibers mixed with each other and exclusion of oxygen be ground, wherein to achieve a pore size range maximum of carbon nanotubes or carbon fibers be admitted that no agglomeration of the carbon nanotubes or carbon fibers, and such carbon nanotubes or carbon fibers are added, whose dimensions are differ by a maximum of 20 nm, or to achieve two different ones Pore size ranges in at least two steps as many carbon nanotubes or carbon fibers added be that at least a partial agglomeration of the carbon nanotubes or carbon fibers and maximum submicrometer agglomerates made of carbon nanotubes or carbon fibers then a compaction / densification of the Mixture under vacuum and then a temperature treatment carried out under an oxygen-containing atmosphere is, wherein the temperature treatment at temperatures below the Melting temperature of the metals and realized above a temperature at which the oxidation of the carbon and the metal takes place. The method of claim 15, wherein as metal powder Cu, Ni, Ti, Zr and / or Al are used. The method of claim 15, wherein the metal powder with particle sizes ≤ 250 μm be used. The method of claim 15, wherein as carbon nanotubes single- and / or multi-walled unfilled carbon nanotubes be used. The method of claim 15, wherein the carbon nanotubes or carbon fibers used with 1 to 100 nm in diameter and ≥ 50 nm in length become. The method of claim 15, wherein the mixture and grinding under inert gas atmosphere and / or under vacuum is carried out. The method of claim 15, wherein the mixture and grinding to achieve two different pore size ranges in two to five steps. The method of claim 21, wherein the quantitative Addition of carbon nanotubes or carbon fibers for mixing in two to five steps becomes. The method of claim 15, wherein the mixture and grinding carried out within 30 min to 400 h becomes. A method according to claim 15, wherein the achievement a pore structure with a pore size range a maximum of 20% by volume of carbon nanotubes or carbon fibers be added based on the total volume. A method according to claim 15, wherein the achievement a pore structure with two different pore size ranges a maximum of 60% by volume of carbon nanotubes or carbon fibers be added based on the total volume. A method according to claim 15, wherein the compaction / densification by ECAP (equal channel angular pressing), HPT (high pressure torsion), HIP (hot isostatic pressing), CIP (cold isostatic pressing) or by extrusion. The method of claim 26, wherein the extrusion at temperatures of 400 to 700 ° C and within 10 s is carried out to 10 min. The method of claim 15, wherein the temperature treatment at temperatures above 400 ° C and below 1000 ° C is carried out. The method of claim 15, wherein the temperature treatment within 30 minutes to 100 hours. The method of claim 15, wherein the temperature treatment is carried out until the oxidation of the carbon nanotubes or carbon fibers and the metal powder in each case at least 95% complete.