Claims
- 1. A method of making monolithic support structures for catalytic converters for internal combustion engine exhaust systems, comprising the steps of:
- hot dip coating a ferritic base metal strip in a bath of molten aluminum, said strip having a thickness of at least 0.25 mm and containing from 10% to about 35% chromium, up to 3% aluminum, up to 1% silicon, and balance essentially iron;
- finishing the molten aluminum coating to provide a coating thickness ranging from 0.013 to 0.13 mm on each side and a total aluminum content of at least 4% by weight;
- cold reducing the aluminum coated strip to a foil having a thickness not greater than 0.13 mm without intermediate annealing;
- heating said foil in an oxidizing atmosphere within the range of about 600.degree. to about 1200.degree. C. with a time at temperature ranging from about 1 second to about 1 hour in accordance with the relationship:
- 1210>temperature (.degree.C.)+1/6.times.time (seconds)>600,
- whereby to produce a porous surface having a matte gray appearance; and
- applying a washcoat of a heat resistant catalyst support material to said porous surface on each side of said foil.
- 2. The method claimed in claim 1, wherein the step of heating said foil in an oxidizing atmosphere causes diffusion of a portion of the aluminum coating into the ferritic base metal and formation of a porous aluminum oxide layer on the surfaces of said foil having a thickness of at least about 500 angstroms.
- 3. The method claimed in claim 1, wherein said ferritic base metal strip contains from about 11.0% to about 14.5% chromium and about 0.5% to 1.0% silicon.
- 4. The method claimed in claim 1, wherein said ferritic base metal strip has a thickness of about 0.4 to about 1.0 mm, the aluminum coating has a thickness of about 0.04 to about 0.10 mm before cold reduction, and said strip is cold reduced to a foil thickness of about 0.04 to about 0.10 mm.
- 5. The method claimed in claim 1, wherein the composition of said ferritic base metal strip is based on the intended operating temperature of said foil in accordance with the formula:
- Operating temperature (.degree.C.)=15 [% Cr+1.5.times.% Si+3.times.% Al]+800.degree. C.
- 6. The method claimed in claim 1, wherein said heat resistant catalyst support material is at least one of gamma aluminum oxide, alkaline earth metal oxides, scandium oxide, and yttrium oxide.
- 7. The method of claim 1, wherein the step of heating said foil in an oxidizing atmosphere is conducted within the range of about 700.degree. to about 1000.degree. C. with a time at temperature ranging from about 1 second to about 20 seconds in accordance with the relationship:
- 1100>temperature (.degree.C.)+15 .times.time (seconds)>1000.
- 8. The method of claim 1 or 7, including the step of impregnating said washcoat with a catalyst comprising at least one of platinum, rhodium, and palladium.
Parent Case Info
This is a division, of application Ser. No. 06/741,282, filed June 4, 1985, U.S. Pat. No. 4,686,155.
US Referenced Citations (7)
Foreign Referenced Citations (1)
Number |
Date |
Country |
4909982 |
Sep 1974 |
JPX |
Divisions (1)
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Number |
Date |
Country |
Parent |
741282 |
Jun 1985 |
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