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Article

Oxidation Induced Lifetime Limits of Chromia Forming Ferritic Interconnector Steels

[+] Author and Article Information
P. Huczkowski

 IWV-2, Forschungszentrum Jülich, D-52425, Jülich, Germanyp.huczkowski@fz-juelich.de

N. Christiansen

 Haldor Topsoe A/S, Nymollevej 55, DK-2800 Lyngby, Denmark

V. Shemet, J. Piron-Abellan, L. Singheiser, W. J. Quadakkers

  Forschungszentrum Jülich, Institute for Materials and Processes in Energy Systems, D-52425 Germany

J. Fuel Cell Sci. Technol 1(1), 30-34 (May 07, 2004) (5 pages) doi:10.1115/1.1782925 History: Received March 15, 2004; Revised May 07, 2004

For planar solid oxide fuel cell (SOFC) designs chromia forming ferritic steels are being considered as possible construction materials for the interconnections. In accordance with SOFC market requirements it is in many cases necessary to reduce the size of the fuel cell and thus the thickness of the interconnect. Therefore, long term, cyclic oxidation studies of ferritic interconnector steels were carried out at 800°C and 900°C in air thereby putting main emphasis on the effect of specimen thickness on the oxidation behaviour. It was observed that with decreasing sample thickness the life time of the mentioned alloys decreases due to breakaway phenomena. This effect is caused by the smaller chromium reservoir in the alloy in case of thinner components. The observed life time limits can be predicted with reasonable accuracy by a theoretical model, using oxide growth rate parameters, initial alloy Cr content and critical Cr content for protective chromia scale formation. It also has to be taken into account that the oxidation rates of the steels increase with decreasing specimen thickness.

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Copyright © 2004 by American Society of Mechanical Engineers
Topics: Steel , oxidation , Thickness
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Figures

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Figure 1

Comparison of mass change data during cyclic oxidation of the three studied steels (thick specimens) at 900°C in air

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Figure 2

Metallographic cross-sections (SEM images) of the three studied steels (thick specimens, compare Fig. 1) after 1000h cyclic oxidation at 900°C in air: (a) JS-3, (b) Crofer 22 APU, and (c) ZMG232

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Figure 3

SNMS profiles of the steel JS-3 (main elements) after isothermal oxidation at 800°C in air: (a) 10min; and (b) 1h

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Figure 4

SNMS profiles of the steel Crofer 22 APU (main elements) after isothermal oxidation at 800°C in air: (a) 10min; and (b) 1h

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Figure 5

SNMS profiles of Ti, Al, Si for the two studied materials after 1h isothermal oxidation at 800°C in air: (a) JS-3; and (b) Crofer 22 APU

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Figure 6

Mass change during cyclic oxidation of Crofer 22 APU and ZMG232 specimens of various thickness at 900°C in air: (a) Crofer 22 APU; and (b) ZMG232. Arrows indicate occurrence of breakaway oxidation.

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Figure 7

Measured kp-values as a function of specimen thickness during cyclic oxidation in air of steel Crofer 22 APU

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Figure 8

Calculated life times (8) for the three studied steels in air using kp-values of thick specimens i.e., 1mm for ZMG232 and 2mm for Crofer 22 APU and JS-3: (a) 800°C; and (b) 900°C

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Figure 9

Comparison of measured and calculated life times for the two studied commercial steels Crofer 22 APU and ZMG232 in air at 900°C taking the thickness dependence of kp into account (compare Fig. 6)

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Figure 10

Typical oxide scale morphology after breakaway oxidation of high-Cr steels, showing 0.5mm thick specimen (ZMG232) after 972h cyclic oxidation at 900°C in air

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