Current catalyst foils for automobile exhaust gas catalytic converters are 50 micrometers thick. By reducing the thickness, the catalyst would reach operating temperature more quickly. In addition, the surface available for the catalytic reaction would be increased. The problem is that up to now reducing foil thickness meant shorter foil life. In addition, common catalyst foils do not exhibit the electrical resistance necessary for pre-heating. Solving this problem was the aim of a research project which involved Krupp VDM, Emitech as the world's biggest manufacturer of metal catalytic converters, the Fraunhofer Institute of Applied Material Research in Bremen and the University of Wuppertal. The result of the research effort, completed at the end of 1998, is a completely new steel alloy designated Aluchrom 7AI YHF. Whereas the chromium-aluminium alloys used at present for catalyst foils contain about 5 % Al, the new metal has 7 % Al and also contains the reactive elements yttrium and hafnium. Using this alloy the thickness of catalyst foils can be reduced to less than 30 micrometers without sacrificing service life. At the same time, the electrical resistance of the catalyst foils is raised to approximately 1.6 ohms per square millimetre. Raining the aluminium content and using yttrium and hafnium additions extend foil life by preventing early aluminium depletion. Besides this, Krupp VDM developed a new cost-efficient process to make thin foils of Aluchrom 7AI YHF. In this, a chromium steel strip is passed through a bath of molten aluminium. Subsequent heat treatment and annealing is carried out to make sure the chromium steel and the aluminium bond intimately. A key advantage of this process is the fact that the aluminium is available where it is needed, at the surface to form the aluminium oxide layer.
New steel for 'cats'
Neuer Stahl für Abgaskatalysatoren
Steel Times ; 227 , 11 ; 423
1999
1 Seite, 1 Bild
Aufsatz (Zeitschrift)
Englisch
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