Process For Producing A Catalyst

Abstract

A process for producing a catalyst having a heating element that is formed from an electrically conductive metal alloy. In the production process, the catalyst undergoes at least a first heat treatment, during which the catalyst is at least partly heated in defined fashion and cooled in a defined fashion. The steps include heating at least a subregion of the catalyst to a predeterminable temperature of at least 550 degrees celsius, holding the temperature at a constant temperature level for at least two minutes, and cooling the at least one subregion of the catalyst at a temperature transient of at least 500 Kelvin per minute.

Claims

1.-9. (canceled)

10. A process for producing a catalyst comprising at least one heating element that is formed from an electrically conductive metal alloy having at least a first heat treatment during which the catalyst is at least partly heated in a defined fashion and cooled in a defined fashion, comprising: heating at least a subregion of the catalyst to a predeterminable temperature of at least 550 degrees Celsius; holding the temperature at a constant temperature level for a hold time of at least two minutes; and cooling the at least a subregion of the catalyst at a temperature transient of at least 500 Kelvin per minute [K/min].

11. The process as claimed in claim 10, wherein a heating to at least 700 degrees Celsius is performed.

12. The process as claimed in claim 10, wherein the hold time at the temperature level to which the catalyst has been heated is at least four hours.

13. The process as claimed in claim 10, wherein the temperature transient during the cooling is at least 2400 Kelvin per minute [K/min].

14. The process as claimed in claim 10, wherein the at least the first heat treatment is downstream of at least a second heat treatment, wherein the first heat treatment at least partly reverses a change in a metal microstructure of the metal alloy resulting from the upstream second heat treatment.

15. The process as claimed in claim 14, wherein the upstream second heat treatment converts the metal alloy into an alpha-prime phase, wherein the downstream first heat treatment achieves a dissolution of the alpha-prime phase in the metal alloy.

16. The process as claimed in claim 14, wherein the second heat treatment is a joining process or a coating process.

17. The process as claimed in claim 14, wherein a coating of inner and/or outer surfaces of the catalyst with a surface-area-increasing coating is carried out upstream of the second heat treatment.

18. A catalyst comprising at least one electrically heatable element, wherein the electrically heatable element is formed by an electrically conductive metal alloy and is heatable by utilization of ohmic resistance, wherein the catalyst is at least partly producible by a process comprising: heating at least a subregion of the catalyst to a predeterminable temperature of at least 550 degrees Celsius; holding the temperature at a constant temperature level for at least two minutes; and cooling the at least one subregion of the catalyst at a temperature transient of at least 500 Kelvin per minute [K/min].

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The invention will be discussed in detail below using exemplary embodiments and with reference to the drawings. In the drawings:

[0031] FIG. 1 is a diagram showing the change in the resistance value for a metal alloy (material 1.4767), wherein a heating to about 600 degrees celsius and a hold time of about four hours is followed by a cooling at a temperature transient of 1 K/min;

[0032] FIG. 2 is a diagram showing the change in the resistance value for a metal alloy (material 1.4767), wherein a heating to 700 degrees celsius has been carried out and after a hold time of four hours a cooling at a temperature transient of 2400 K/min has been performed; and

[0033] FIG. 3 shows a block diagram for elucidating the process according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0034] FIG. 1 shows a diagram which along the x-axis depicts the temperature 1, in particular the hold temperature, of the metal alloy. In the case of FIG. 1 the metal alloy is heated to about 600 degrees celsius during the hold time provided for in the process. For cooling, the metal alloy, formed from material 1.4767 in the present case, is cooled at a temperature transient of 1 Kelvin per minute [K/min]. This may preferably be effected by simple cooling in air at room temperature.

[0035] Curve 3 shows the respective percentage change in the resistance coefficient of the metal alloy at different starting temperatures provided that from this starting level a cooling of approximately one Kelvin per minute is effected. The change in the resistance coefficient is plotted as a percentage change from the starting state along the y-axis 4.

[0036] It can be read-off along the arrows 2 that in the case of a starting temperature of 600 degrees celsius and the above-described cooling a reduction in the resistance value of about 5.5% results.

[0037] This correlation relates in particular to material 1.4767 which is chosen by way of example and is an aluminum-chromium alloy. Similar materials result in divergent but qualitatively similar correlations and the chosen example must therefore be regarded as representative.

[0038] Depending on other boundary conditions, for example the expected stress in later operation or the corrosive properties of the fluid flowing through the catalyst, it may be necessary to specify a particular metal alloy. If an excessively low end resistance then is achieved on account of the negative change in the resistance value during the heat treatment, the necessary heating power cannot be achieved with the available current.

[0039] FIG. 2 shows a diagram similar to FIG. 1. The hold temperature of the metal alloy is again plotted along the x-axis 5. In FIG. 2 the hold temperature in the chosen example is about 700 degrees celsius, wherein a cooling at a transient of about 2400 Kelvin per minute is performed. The diagram of FIG. 2 corresponds to the change in resistance during the process according to the invention while the diagram of FIG. 1 reflects by way of example the change in resistance during a heat treatment in an upstream process step.

[0040] The percentage change in the resistance value is plotted along the y-axis 8. It is possible to read-off along the curve 7 the percentage changes in the resistance value during the above-described cooling of 2400 Kelvin per minute for the respective starting temperatures on the x-axis.

[0041] A starting temperature of 700 degrees celsius thus results, in accordance with the arrows 6, in a percentage change in the resistance value of about 1%.

[0042] Since the change in the resistance value is reversible, a strong reduction in the resistance value, as shown in FIG. 1, may for example be compensated or reversed again by a process as proposed in accordance with the invention and employed in FIG. 2. This is advantageous since in this way the necessary process steps for achieving other material properties can be performed unchanged and any negative effect on the resistance value can be corrected retrospectively.

[0043] FIG. 3 is a block diagram of the process according to the invention. In block 9 the metal alloy is heated to a target temperature. In block 10 this target temperature is held for a predetermined time. In block 11 the metal alloy is finally cooled at a predefined temperature transient.

[0044] The diagrams in FIGS. 1 and 2 by way of example relate to a certain material (1.4767) and in particular do not have any limiting character. Related metal alloys may likewise be utilized for the application of the process according to the invention. The choice of the temperature transients and the hold temperature is likewise exemplary and may be varied within the limits according to the invention.

[0045] The figures shown serve to elucidate the inventive concept and do not have any limiting character.

[0046] Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.