Surface modified metallic foam body, process for its production and use thereof

Abstract

A metallic foam body containing an alloy skin which is up to 50 m thick can be obtained by a process including (a) providing a metallic foam body comprising a first metallic material; (b) applying a second metallic material which contains a first metallic compound that is leachable as such and/or that can be transformed by alloying into a second metallic compound that is leachable and different from the first metallic compound on a surface of the foam body (a), by coating the metallic foam body with an organic binder and a powder of the second metallic material; (c) forming a skin on foam body (b) by alloying the first and the second metallic material; and (d) leaching out with a leaching agent at least a part of the first and/or the second metallic compound.

Claims

1. A surface modified metallic foam body containing an unmodified core and an alloy skin on surface of the unmodified core, obtained by a process comprising the steps: (a) providing a metallic foam body, as a core, comprising a first metallic material, wherein the metallic foam body of (a) has an apparent density in the range of from 300 to 1200 kg/m.sup.3 as determined as weight per volume unit according to ISO 845; (b) applying a second metallic material which is different from the first metallic material of (a) and which contains a first metallic compound that is leachable as such and/or that can be transformed by alloying into a second metallic compound that is leachable and different from the first metallic compound on a surface of the metallic foam body of (a), by coating the surface of the metallic foam body of (a) with an organic binder and a powder of the second metallic material, wherein the second metallic material contains A1 as the first metallic compound; (c) forming the alloy skin by alloying the first metallic material and the second metallic material of step (b) to give an alloyed metallic foam body comprising the core that is unmodified and an alloy skin formed on the surface of the unmodified core; and (d) treating the alloyed metallic foam body obtained in step (c) with an agent that is capable of leaching out the leachable first and/or second metallic compound from the alloy skin of the metallic foam body, to leach out at least a part of the first and/or the second metallic compound from the alloy skin of the alloyed metallic foam body; wherein the thickness of the alloy skin is in the range of up to 50 m as determined by electron microscopy, and wherein the unmodified core of the alloyed metallic foam body comprises pores with a pore size between 100 and 5000 m as determined by a Visiocell analysis method from Recticel, a specific surface area in the range of from 100 to 20000 m.sup.2/m.sup.3 as determined in accordance with DIN 9277 via gas adsorption and a porosity in the range of from 0.50 to 0.95 as determined by using the following equation:
Porosity (%)=100/VT(VTW(1000/), wherein VT is the foam sheet sample W is the foam sheet sample weight; and is the density of the foam material.

2. The surface modified metallic foam body according to claim 1, wherein the first metallic material contains at least one metal selected from the group consisting of Ni, Fe, Cr, Co, Cu, Ag, Au, Pt, and Pd.

3. The surface modified metallic foam body according to claim 2, wherein the metal is selected from the group consisting of Ni, Cr, Co, Cu, and Ag.

4. The surface modified metallic foam body according to claim 1, wherein the second metallic material contains Si or Zn as the second metallic compound.

5. The surface modified metallic foam body according to claim 1, wherein the metallic foam body of (a) is obtained by coating a polyurethane foam with the first metallic material and then burning off the polyurethane foam.

6. A process for producing a surface modified metallic foam body containing an unmodified core and an alloy skin on surface of the unmodified core, comprising the steps: (a) providing a metallic foam body, as a core, comprising a first metallic material, wherein the metallic foam body of (a) has an apparent density in the range of from 300 to 1200 kg/m.sup.3 as determined as weight per volume unit according to ISO 845; (b) applying a second metallic material which is different from the first metallic material of (a) and which contains a first metallic compound that is leachable as such and/or that can be transformed by alloying into a second metallic compound that is leachable and different from the first metallic compound on a surface of the metallic foam body of (a), by coating the surface of the metallic foam body of (a) with an organic binder and a powder of the second metallic material, wherein the second metallic material contains Al as the first metallic compound; (c) forming the alloy skin by alloying the first metallic material and the second metallic material of step (b) to give an alloyed metallic foam body comprising the core that is unmodified and an alloy skin formed on the surface of the unmodified core; and (d) treating the alloyed metallic foam body obtained in step (c) with an agent that is capable of leaching out the leachable first and/or second metallic compound from the alloy skin of the alloyed metallic foam body, wherein the thickness of the alloy skin is in the range of up to 50 m as determined by electron microscopy, and wherein the unmodified core of the alloyed metallic foam body comprises pores of a pore size between 100 and 5000 m as determined by a Visiocell analysis method from Recticel, a specific surface area in the range of from 100 to 20000 m.sup.2/m.sup.3 as determined in accordance with using the following equation:
Porosity (%)=100/VT(VTW(1000/), wherein VT is the foam sheet sample volume; W is the foam sheet sample weight; and is the density of the foam material.

7. The process according to claim 6, wherein in alloying in step (c) a heating temperature and time as well as a cooling time are adjusted in order to control the leachability of the alloy skin obtained.

8. The process according to claim 6, wherein the first metallic material comprises nickel and the second metallic material comprises aluminum.

9. The process according to claim 6, wherein the step (b) further comprises applying at least one promoter element to the surface of the metallic foam body of (a).

10. A catalyst formulation comprising the surface-modified metallic foam body of claim 1.

11. A hydrogenation process which comprises subjecting a chemical compound to a chemical reaction in the presence of the catalyst formulation of claim 10.

12. The process according to claim 6, wherein the first metallic material consists of nickel and the second metallic material comprises aluminum.

13. The process according to claim 6, which further comprises a step (e) of applying at least one promoter element to the surface of the alloyed metallic foam body obtained in step (d).

14. The surface modified metallic foam body according to claim 1, wherein the second metallic material consists of A1 as the first metallic compound.

15. The surface modified metallic foam body according to claim 1, wherein the treatment (d) is carried out at a temperature between 50 and 95 C. for a period of 2 to 10 minutes.

16. The method according to claim 6, wherein the treatment (d) is carried out at a temperature between 50 and 95 C. for a period of 2 to 10 minutes.

17. The surface modified metallic foam body according to claim 1, wherein the second metallic material powder has an average particle size in a range of from 30 m to 50 m.

18. The method according to claim 6, wherein the second metallic material power in (b) has an average particle size in a range of from 30 m to 50 m.

Description

EXAMPLE 1

(1) A Ni foam body with dimensions of 75 mm75 mm1.7 mm with a surface area of 0.0222 m.sup.2/g, corresponding to a surface area density of 450 g/m.sup.2 and pores with a medium pore size of 580 m and a porosity of 93.8%, a strut thickness of 10 m, an apparent density of 552 kg/m.sup.3, and a geometrical surface area (GSA) of 3100 m.sup.2/m.sup.3 was sprayed with a 1 wt.-% aqueous solution of polyvinylpyrrolidone as binder. The binder was used in an amount to obtain a final layer with a thickness of the polyvinylpyrrolidone of 15 m.

(2) After drying the sprayed Ni foam body at room temperature, the binder coated foam body was coated with an Al powder with an average particle diameter of from 30 to 50 m. To this end, Al powder was poured on the binder coated foam body in an amount such that the weight ratio powder/foam was 1. The coated metallic foam was vibrated such that the Al powder could be uniformly distributed on the open-porous structure.

(3) The binder was then removed by heating in a hydrogen atmosphere with a heating rate of 5 K/min up to 600 C. The temperature was then kept at 600 C. for 0.5 hours.

(4) A NiAl alloy was then formed by heating continuously with a heating rate of 5 K/min to a temperature of 700 C. After reaching this temperature, the heated foam body was then cooled to room temperature by natural cooling. In this way it was possible to obtain a 50:50 mol-% Ni:Al composition layer on the foam body.

(5) The cooled foam body was then treated with a 5 M solution of NaOH at 70 C. for 3 to 5 minutes.

(6) As a result a surface modified metallic foam body was obtained. The obtained surface modified metallic foam body had an alloy skin with a thickness of up to 10 m and a specific (BET) surface area of 57.4 m.sup.2/g as determined via BET measurement in accordance with DIN 9277 via gas adsorption.

EXAMPLE 2

(7) Unless specified otherwise, Example 1 was repeated with the difference that a NiCrAl foam (73 wt. % Ni, 21 wt. % Cr and 6 wt % Al) was used. Moreover, alloying was effected in an Ar atmosphere at 900 C. for 30 minutes.

(8) A NiCrAl foam body with dimensions of 75 mm75 mm1.7 mm with a surface area of 0.00084 m.sup.2/g, corresponding to a surface area density of 1180 g/m.sup.2 and pores with a medium pore size of 580 m and a porosity of 89.6%, a strut thickness of 15 m, an apparent density of 821 kg/m.sup.3, and a geometrical surface area (GSA) of 6860 m.sup.2/m.sup.3 was sprayed with a 1 wt.-% aqueous solution of polyvinylpyrrolidone as binder. The binder was used in an amount to obtain a final layer with a thickness of the polyvinylpyrrolidone of 15 m.

(9) After drying the sprayed Ni foam body at room temperature, the binder coated foam body was coated with an Al powder with an average particle diameter of from 30 to 50 m. To this end, Al powder was poured on the binder coated foam body in an amount such that the weight ratio powder/foam was 1. The coated metallic foam was vibrated such that the Al powder could be uniformly distributed on the open-porous structure.

(10) The binder was then removed by heating in a hydrogen atmosphere with a heating rate of 5 K/min up to 600 C. The temperature was then kept at 600 C. for 0.5 hours.

(11) A NiAl alloy was then formed by heating continuously with a heating rate of 5 K/min to a temperature of 900 C. After reaching this temperature, the heated foam body was kept on this temperature for 30 minutes and then cooled to room temperature by natural cooling.

(12) The cooled foam body was then treated with a 5 M solution of NaOH at 70 C. for 3 to 5 minutes.

(13) As a result a surface modified metallic foam body was obtained. The obtained surface modified metallic foam body had an alloy skin with a thickness of up to 10 m and a specific surface area (SSA) of 10.8 m.sup.2/g as determined via BET measurement in accordance with DIN 9277 via gas adsorption.