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Oxide reduction and sintering of Fe–Cr alloy honeycombs

Published online by Cambridge University Press:  31 January 2011

Jason H. Nadler ,
Thomas H. Sanders Jr.  and
Robert F. Speyer
Jason H. Nadler
Affiliation:
School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332
Thomas H. Sanders Jr.
Affiliation:
School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332
Robert F. Speyer
Affiliation:
School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332
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Abstract

H2 reduction and densification of extruded Fe2O3–Cr2O3 mixtures with honeycomb geometry (0.3-mm wall thickness) were studied using dilatometry, x-ray diffraction, and scanning electron microscopy. Reduction of pure Fe2O3 heated at 5 °C/min was completed by approximately 525 °C. Two separate sintering steps ensued, well separated in temperature from reduction, one associated with elimination of pores between Fe agglomerates (750–900 °C), and the other associated with sintering of these agglomerates (995–1275 °C). With increasing Cr2O3 content, sintering was increasingly delayed until initiation of Cr2O3 reduction above 1000 °C. The α → γ iron phase transformations were consistent with the Fe–Cr phase diagram, but the γ → α transformations at higher temperatures deviated from the phase diagram because of the influence of impurities (Si, Ca) in the solid solution. Pure Cr2O3 honeycomb formed an approximately 35-μm-thick porous Cr coating that imposed a diffusion barrier to further reduction. The high vapor pressure of chromium prohibited compositions in excess of 25 wt.% Cr2O3 from full reduction and densification.

Type
Articles
Information
Journal of Materials Research , Volume 18 , Issue 8 , August 2003 , pp. 1787 - 1794
Copyright
Copyright © Materials Research Society 2003

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