Fecralloy metal foils

Figure 3.31 Laboratory-scale radiant burner as developed by Redenius etai. [118] top, drawing to scale centre, sketch showing three ducts separated by only the 50 pm Fecralloy metal foil bottom, temperature distribution as determined by numerical calculations, temperatures in K.

Wash-coating techniques for metal foils exist in automotive exhaust treatment technology [646]. Adomaitis et al. has presented the Metreon process, which was developed for coating of unstructured Fecralloy metal foils [646]. The foils wrapped up as coils were processed through rolls, where they received a corrugated structure. 

Metallic monoliths made of both rhodium ([HCR 1]) and FeCrAlloy (72.6% Fe, 22% Cr and 4.8% Al ([HCR 3]) carrying micro channels of 120 pm x 130 pm cross-section at various length (5 and 20 mm) were applied. The monoliths were prepared of micro structured foils by electron beam welding. After bonding, the FeCrAlloy was oxidized in air at 1 000 °C for 4 h to form an a-alumina layer, which was verified by XRD. Its thickness was determined as < 10 pm by SEM/EDX. The alumina layer was impregnated with rhodium chloride and alternatively with a nickel salt solution. The catalyst loading with nickel (30 mg) was much higher than that with rhodium (1 mg) (see Table 2.4). The amount of rhodium on the catalyst surface was determined as 3% by XPS. 

The constmction material of metallic monoliths are alloys of iron, about 15-20 wL % chromium and 5 wt.% aluminium (Fecralloy). The unique feature of these alloys is the formation of a thin alumina layer (0.5 pm) on their outer surface when treated at temperatures above 850 °C [130]. Long alumina whiskers are formed at temperatures of around 900 °C and an oxidation time of greater than 12h (see Figure 10.6). This alumina layer then acts as an adhesion layer for the catalyst coating. On top of this, the alumina layer protects the alloy from corrosion, which allows the operation of ultra-thin Fecralloy foils at high temperatures. 

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