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The Effect Of The Crystal Orientation Of The Formation Of The Oxygen-Deficient Magnetite

Published online by Cambridge University Press:  15 February 2011

Y. Wada ,
T. Togawa ,
H. Kato ,
M. Tsuji  and
Y. Tamaura
Y. Wada
Affiliation:
Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, 152, Japan
T. Togawa
Affiliation:
Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, 152, Japan
H. Kato
Affiliation:
Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, 152, Japan
M. Tsuji
Affiliation:
Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, 152, Japan
Y. Tamaura
Affiliation:
Department of Chemistry, Research Center for Carbon Recycling & Utilization
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Abstract

An oxygen-deficient magnetite (Fe3O4–8) has been found to form by passing H2 gas through magnetite powder at 300°C with its spinel structure retained. The oxygen-deficient magnetite is a metastable phase in the transformation of magnetite into α-Fe. The lattice constant of the oxygen-deficient magnetite enlarged to 0.8407nm in the maximum value which is substantially larger than that of the stoichiometric magnetite (a0=0.8396nm). The formation mechanism of the oxygen-deficient magnetite was studied at 300°C using two specimens of magnetite powders with developed orientations on the (111) and (100) planes. These are referred to as (111)- and (100)-magnetite, respectively. The formation of α-Fe was suppressed over the crystal of (111)-magnetite, where wUstite and oxygen-deficient magnetite were formed while keeping the f.c.c. arrangement of the oxygen ions in the solid. On the other hand, over the (100)-magnetite, the formation of a-Fe was enhanced. It is considered that, on the (111)- magnetite, the Fe2+ ion formed by H2-reduction on the surface can move into interstices of the f.c.c. lattice of bulk to form the oxygen deficient state. This will come from the fact that the Fe2+ ion on the surface is so strongly supported with three Fe-O bondings that the Fe2+ ions cannot readily diffuse on the surface when the surface oxygen ions are removed on the (111)- magnetite.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 344: Symposium I – Materials and Processes for Environmental Protection , 1994 , 45
Copyright
Copyright © Materials Research Society 1994

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