The sulphidation of copper-rich Cu-Ag alloys in H-2-H2S at 550-750 degreesC

Citation
P. Castello et al., The sulphidation of copper-rich Cu-Ag alloys in H-2-H2S at 550-750 degreesC, CORROS SCI, 41(5), 1999, pp. 919-939
Citations number
43
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Material Science & Engineering
Journal title
CORROSION SCIENCE
ISSN journal
0010-938X → ACNP
Volume
41
Issue
5
Year of publication
1999
Pages
919 - 939
Database
ISI
SICI code
0010-938X(199905)41:5<919:TSOCCA>2.0.ZU;2-E
Abstract
The sulphidation of two copper-silver alloys containing 5 and 10 wt.% silve r (Cu-5Ag and Cu-10Ag, respectively) was investigated over the temperature range 550-750 degrees C in H-2/H2S mixtures under sulphur pressures below t he dissociation of Ag2S. External scales, composed mainly of cuprous sulphi de, often containing some (Cu,Ag)(2-x)S islands, formed on both alloys. The corrosion kinetics were significantly affected by the detachment of the ou ter scales at temperature, as a consequence of the significant volume incre ase due to sulphidation. After scale detachment, sulphidation proceeded thr ough a dissociative transport of sulphur in voids between the outer sulphid e layer and the alloy substrate, yielding an abrupt decrease of the corrosi on rate in all cases and modifying the composition of the reaction products in the case of Cu-10Ag. An increase of the volume fraction of the silver-r ich solid solution in the subscale region with respect to the original allo y was observed in all cases. The silver islands coalesced to a continuous s ubscale layer only in the sulphidation of Cu-5Ag at 650 and 750 degrees whe reas, in all the other cases, they remained as particles in a Cu2S matrix. The peculiar corrosion behaviour of these alloys is attributed to the low s olubility of silver in copper. (C) 1999 Elsevier Science Ltd. All rights re served.