Metal foam bodies and process for production thereof

Abstract

The present invention relates to processes for producing metal foam bodies, in which metal-containing powders that may comprise aluminium and chromium or molybdenum are applied to metal foam bodies that may comprise nickel, cobalt, copper and iron and then treated thermally, wherein the highest temperature in the thermal treatment of the metal foam bodies is in the range from 680 to 715? C., and wherein the total duration of the thermal treatment within the temperature range from 680 to 715? C. is between 5 and 240 seconds. Following this method of thermal treatment can achieve alloy formation at the contact surface between metal foam body and metal-containing powder, but simultaneously leave unalloyed regions within the metal foam. The present invention further comprises processes comprising the treatment of the alloyed metal foam bodies with basic solution. The present invention further comprises the metal foam bodies obtainable by these processes, which find use, for example, as support and structure components and in catalyst technology.

Claims

1. A process for producing a metal foam body, comprising the following steps: (a) providing a metal foam body A, comprising two metallic components in the form of an alloy, wherein the alloy consists of either nickel and cobalt or nickel and copper; (b) applying a metal-containing powder MP to metal foam body A to obtain metal foam body AX, wherein the metal-containing powder MP is selected from the group consisting of: a mixture consisting of aluminium powder and chromium powder; a mixture consisting of aluminium powder and molybdenum powder; a pulverulent alloy consisting of aluminium and chromium; and a pulverulent alloy consisting of aluminium and molybdenum; (c) treating the metal foam body AX thermally to achieve alloy formation between the metallic components of metal foam body A and the metal-containing powder MP to thereby obtain metal foam body B, wherein: the highest temperature of the thermal treatment of metal foam body AX is in the range from 680 to 715? C.; and the total duration of the thermal treatment in the temperature range from 680 to 715? C. is between 5 and 240 seconds; wherein: after step c), alloy formation is found in the upper regions of the metal foam, but unalloyed regions remain within central areas of the metal foam; the metal-containing powder MP is applied to the metal foam body A using a polyethyleneimine binder with a molecular weight in the range of 700 000 to 800 000 g/mol; the binder is completely converted to gas at a temperature of 100-400? C.; and MP and binder are applied to A in one step as a suspension of MP in binder.

2. The process of claim 1, wherein the metallic components in step (a) are in the form of an alloy, wherein the alloy consists of nickel and copper.

3. The process of claim 1, wherein the metallic components in step (a) are in the form of an alloy, wherein the alloy consists of nickel and cobalt.

4. The process of claim 1, wherein the metal-containing powder MP used in step (b) comprises either: (iii) a mixture consisting of aluminium powder and chromium powder; or (iv) a pulverulent alloy consisting of aluminium and chromium.

5. The process of claim 1, wherein the metal-containing powder MP used in step (b) is a pulverulent alloy consisting of aluminium and chromium.

6. The process of claim 1, wherein the metal foam body A used in step (a) has been obtained by either two successive electrolytic deposition steps, in each of which an individual metallic component is deposited on a substrate, or by a single electrolytic deposition step in which two metallic components are deposited simultaneously on a substrate, wherein the substrate is removed by thermolysis after the conclusion of all electrolytic deposition steps.

7. The process of claim 1, wherein the metal foam body A has a cubic, cuboidal, or cylindrical shape.

8. The process of claim 1, wherein the metal foam body A is a monolith.

9. The process of claim 1, further comprising: (d) treating the metal foam body B with a basic solution.

10. The process of claim 9, wherein the treatment of the metal foam body B with a basic solution is performed for a period of from 5 minutes to 8 hours, at a temperature in the range of 20 to 120? C., and wherein the basic solution is an aqueous NaOH solution having an NaOH concentration between 2% and 30% by weight.

11. The process of claim 1, wherein the ratio V of the masses of metal foam body B to metal foam body A, is in the range of from 1.1:1 to 1.5:1.

12. The process of claim 11, wherein the metallic components in step a) are in the form of an alloy, wherein the alloy consists of nickel and copper.

13. The process of claim 11, wherein the metallic components in step a) are in the form of an alloy, wherein the alloy consists of a combination of nickel and cobalt.

14. The process of claim 11, wherein the metal-containing powder MP used in step (b) is a mixture consisting of aluminium powder and chromium powder, or a pulverulent alloy consisting of aluminium and chromium.

15. The process of claim 11, wherein the metal-containing powder MP used in step (b) is a pulverulent alloy consisting of aluminium and chromium.

16. The process of claim 11, wherein thermal treatment takes place in a stepwise manner under an inert gas or under reductive conditions, wherein the temperature is first increased from room temperature to about 300 to 400? C. for a period of about 2 to 30 minutes to remove moisture and organic constituents, and then the temperature is increased to the range of 680 to 715? C.

17. The process of claim 16, wherein the metal foam body A used in step (a) has been obtained by either two successive electrolytic deposition steps, in each of which an individual metallic component is deposited on a substrate, or by a single electrolytic deposition step in which two metallic components are deposited simultaneously on a substrate, wherein the substrate is removed by thermolysis after the conclusion of all electrolytic deposition steps.

18. The process of claim 16, wherein metal foam body B is treated with a basic solution for a period in the range from 5 minutes to 8 hours at a temperature in the range from 20 to 120? C., and wherein the basic solution is an aqueous NaOH solution having an NaOH concentration between 2% and 30% by weight.

Description

EXAMPLES

(1) 1. Providing of Metal Foam Bodies

(2) Three metal foam bodies (a, b, c) of a cobalt-nickel alloy were provided (Co/Ni=9:1) (manufacturer: AATM, dimensions: 220 mm?180 mm?1.6 mm, weight per unit area: 1000 g/m.sup.2, average pore diameter: 580 ?m), which had been produced by simultaneous electrolytic deposition of nickel and cobalt on a polyurethane foam and subsequent thermolysis of the plastic components.

(3) 2. Applying of Metal-Containing Powders

(4) Subsequently, binder solution (polyethyleneimine (2.5% by weight) in water) was first sprayed onto all metal foam bodies, and then a pulverulent aluminium-chromium alloy (manufacturer: AMG, average particle size: <63 ?m, Al/Cr=70/30, with 3% by weight of added ethylenebis(stearamide)) was applied as a dry powder (about 400 g/m.sup.2).

(5) 3. Thermal Treatment

(6) Thereafter, all metal foam bodies were subjected to a thermal treatment under nitrogen atmosphere in a furnace. First of all, the furnace was heated from room temperature to the maximum temperature within about 15 min, which was maintained for a defined period of time, followed by quenching by contacting with nitrogen atmosphere at 200? C.

(7) Maximum temperature for metal foam body a:

(8) 700? ? C. for 2 minutes

(9) Temperature progression for metal foam body b:

(10) 600? C. for 2 minutes

(11) Temperature progression for metal foam body c:

(12) 750? C. for 2 minutes

(13) 4. Determination of Extent of Alloying

(14) At the end, the extent of alloy formation in the metal foam bodies was determined. For this purpose, cross sections of the metal foam bodies were examined under the microscope and scanning electron microscope.

(15) This gave the following result:

(16) While superficial alloy formation had taken place in metal foam body a, but unalloyed regions remained within the metal foam, no alloy formation took place in the case of metal foam body b, and alloy formation in metal foam body c is so far advanced that no unalloyed regions remained within the metal foam.

(17) This result clearly shows that departure from the thermal treatment conditions according to the invention has the effect that superficial alloy formation leaving unalloyed regions within the metal foam is difficult to achieve.