The sulfidation of two-phase Fe-Cu alloys in H-2-H2S mixtures at 500-700 degrees C

Citation
P. Castello et al., The sulfidation of two-phase Fe-Cu alloys in H-2-H2S mixtures at 500-700 degrees C, OXID METAL, 52(5-6), 1999, pp. 403-426
Citations number
49
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Metallurgy
Journal title
OXIDATION OF METALS
ISSN journal
0030-770X → ACNP
Volume
52
Issue
5-6
Year of publication
1999
Pages
403 - 426
Database
ISI
SICI code
0030-770X(199912)52:5-6<403:TSOTFA>2.0.ZU;2-#
Abstract
The sulfidation behavior of three two-phase Fe-Cu alloys containing 25, 50, and 75 wt.% copper has been investigated in H-2-H2S mixtures at 500-700 de grees C under gas-phase sulfur pressures, which is significantly above thos e for the dissociation of both FeS and Cu2S. In all cases, the three alloys sulfidized more slowly than both pure metals under the same conditions. At all temperatures, Fe-25Cu showed the slowest growth rates, whereas Fe-50Cu sulfidized more rapidly than the other two alloys. However, the kinetics c urves for the three alloys tended to over lap, particularly at the higher t emperatures. The scales were complex and contained an outer layer composed of a mixture of two different Cu-Fe double sulfides, Cu5FeS4 and CuFeS2, pl us an inner zone containing a mixture of metallic iron with the double sulf ide Cu5FeS4 formed by complete sulfidation of the copper-rich phase anti pa rtial sulfidation of the iron-rick phase. This region also contained large voids, possibly because of outward diffusion of metal cations, whereas the iron-rich islands were mainly unattacked. The depth of intrenal attack incr eased with increasing temperature and/or iron content. Finally, particles o f almost pure copper metal, probably formed during cooling from the reactio n temperature,,were present at the scale-subscale interface, as inclusions in the scale and as whiskers producing out of the external scale surface.