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Transient state scale formation on Fe 32 Ni 20 Cr and Fe 20 Cr in H 2 ‐H 2 O‐H 2 S atmospheres
Author(s) -
Hussey R. J.,
Papaiacovou P.,
Grabke H. J.
Publication year - 1986
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.19860371103
Subject(s) - sulfidation , oxidizing agent , dissolution , quenching (fluorescence) , alloy , hydrogen , nickel , sulfide , bar (unit) , materials science , analytical chemistry (journal) , hydrogen sulfide , oxide , chemistry , metallurgy , sulfur , physics , organic chemistry , chromatography , quantum mechanics , meteorology , fluorescence
The transient state of simultaneous oxidation and sulfidation of Fe‐32 Ni‐20 Cr and Fe‐20 Cr was studied at 700°C for short time exposures in H 2 ‐H 2 O‐H 2 S. After heating the specimens in pure, dry hydrogen they were corroded by introduction of the oxidizing and sulfidizing atmosphere for 2, 4 or 15 min. After quenching the layer was investigated by SEM, AES, X‐ray and electron diffraction. Four different gas compositions were applied: pS 2 = 10 −12 bar and pO 2 = 10 −25 , 10 −26 , 10 −27 , 10 −28 bar, all within the thermodynamic stability range of Cr 2 O 3 . After the short time exposures oxides and sulfides were present on the surface, Cr 2 O 3 and Cr 3 S 4 had grown side by side and in case of the alloy Fe‐32 Ni‐20 Cr Fe‐ and Ni‐containing sulfides formed patches on top of the scale. The amount of sulfides was higher for the lower oxygen pressures. After a longer time exposure, 120 min, all sulfides had vanished. Simultaneous formation of oxides and sulfides occurs in the transient state during phase boundary reaction or transport control. Upon transition to diffusion control the sulfides vanish by dissolution into the alloy and reaction with the gas atmosphere. This is valid for low pS 2 where no iron and nickel sulfides are stable.