The corrosion behavior of Co-Mo alloys in H sub 2 -H sub 2 O-H sub 2 S environments

Journal Article · Mon Jun 01 04:00:00 EDT 1992 · Oxidation of Metals; (United States)

DOI:https://doi.org/10.1007/BF00666629· OSTI ID:7019010

Shing, C C; Douglas, D L ^[1]; Gesmundo, F ^[2]

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1. Univ. of California, Los Angeles (United States)
2. Univ. di Genova (Italy)

The corrosion behavior of Co alloyed with up to 40 wt.%Mo alloys was studied in H{sub 2}-H{sub 2}O-H{sub 2}S gas mixtures over the temperature range between 600 C. and 900 C. The parabolic rate constants for corrosion decreased with increasing amounts of Mo. The compositions of all gas atmospheres fall in the sulfide(s) stability region of the ternary M-O-S phase diagrams at all temperatures investigated. All the corrosion scales were composed of sulfides, while no oxide was detected. The sulfide scales formed were duplex at all temperatures except at 900 C. The outer layer consisted primarily of cobalt sulfide, while the inner layer was complex and heterophasic, the phases formed being highly composition dependent. MoS{sub 2} predominated in the inner layer for all alloys. However, a metallic Mo layer was formed in the innermost layer of Co-40Mo. Activation energies were different for all alloys, increasing with increasing Mo content. Identical kinetics were observed for Co-30Mo corroded at 700-800 C. A Chevrel-phase Co{sub 1.62}Mo{sub 6}S{sub 8} was present in scales formed on the samples exhibiting the temperature-independent kinetics. A possible model in which Co{sub 1.62}Mo{sub 6}S{sub 8} forms preferentially in H{sub 2}-containing mixed gas is suggested. Alloys corroded at 900 C. formed a lamellar-structure scale which contained Co and CoMo{sub 2}S{sub 4} layers perpendicular to the alloy surface. A eutectoid decomposition of an unknown Co-Mo sulfide may be responsible for the presence of the lamellar structure.

• OSTI ID: 7019010
• Journal Information: Oxidation of Metals; (United States), Journal Name: Oxidation of Metals; (United States) Vol. 37:5-6; ISSN 0030-770X; ISSN OXMEA
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
010404 -- Coal
Lignite
& Peat-- Gasification
36 MATERIALS SCIENCE
360105* -- Metals & Alloys-- Corrosion & Erosion
ACTIVATION ENERGY
ALLOYS
CHALCOGENIDES
CHEMICAL ANALYSIS
CHEMICAL COMPOSITION
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHROMIUM ALLOYS
CHROMIUM BASE ALLOYS
CHROMIUM COMPOUNDS
CHROMIUM SULFIDES
COAL GASIFICATION
COHERENT SCATTERING
CORROSION
CORROSION PRODUCTS
CORROSIVE EFFECTS
DATA
DIAGRAMS
DIFFRACTION
ELECTRON MICROPROBE ANALYSIS
ELECTRON MICROSCOPY
ELEMENTS
ENERGY
EXPERIMENTAL DATA
FLUIDS
GASES
GASIFICATION
HYDROGEN
HYDROGEN COMPOUNDS
HYDROGEN SULFIDES
INFORMATION
KINETICS
MICROANALYSIS
MICROSCOPY
MOLYBDENUM ALLOYS
MOLYBDENUM COMPOUNDS
MOLYBDENUM SULFIDES
NONDESTRUCTIVE ANALYSIS
NONMETALS
NUMERICAL DATA
OXYGEN
PARTIAL PRESSURE
PHASE DIAGRAMS
PHASE STUDIES
QUANTITY RATIO
REACTION KINETICS
REFRACTORY METAL COMPOUNDS
SCANNING ELECTRON MICROSCOPY
SCATTERING
SPECTROSCOPY
SULFIDATION
SULFIDES
SULFUR
SULFUR COMPOUNDS
TEMPERATURE RANGE
TEMPERATURE RANGE 0400-1000 K
TEMPERATURE RANGE 1000-4000 K
THERMOCHEMICAL PROCESSES
TRANSITION ELEMENT COMPOUNDS
VAPORS
WATER VAPOR
X-RAY DIFFRACTION
X-RAY SPECTROSCOPY