The high-temperature corrosion behavior of Co-Nb alloys in mixed-gas atmospheres

Journal Article · Wed Apr 01 04:00:00 EST 1992 · Oxidation of Metals; (United States)

DOI:https://doi.org/10.1007/BF00665188· OSTI ID:7068776

Shing, C C; Douglass, D.L. Gesmundo, F. ^[1]

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

The corrosion of Co-Nb alloys containing up to 30wt.% Nb in H{sub 2}H{sub 2}S-H{sub 2}O gas mixtures was studied over the temperature range of 600-800 C. The gas composition falls in the stability region of cobalt sulfide and Nb{sub 2}O{sub 5} in the phase diagrams of the Co-O-S and Nb-O-S systems at all temperatures studied. Duplex scales, consisting of an outer layer of cobalt sulfide and a complex, heterophasic inner layer, were formed at all temperatures studied. In addition to cobalt sulfide and CoNb{sub 3}S{sub 6}, a small amount of NbO{sub 2} was found in the inner layer. The reason for the formation of NbO{sub 2} over that of Nb{sub 2}O{sub 5} in the scale is that the outer sulfide scale lowers the oxygen activity within the scale into the NbO{sub 2}-stability region. Two-stage kinetics were observed for all alloys, including an initial irregular stage usually followed by a steady-state parabolic stage. The steady-state parabolic rate constants decreased with increasing amounts of Nb, except for Co-20Nb corroded at 700 C. Nearly identical kinetics were observed for Co-20Nb corroded at 600 C. and 700 C. The presence of NbO{sub 2} particles leads only to a limited decrease of the available cross-section area for the outward-diffusing metal ions. The activation energies for all alloys are similar and are in agreement with those obtained in a study of the sulfidation of the same alloys. The primary corrosion mechanism involves an outward Co transport.

• OSTI ID: 7068776
• Journal Information: Oxidation of Metals; (United States), Journal Name: Oxidation of Metals; (United States) Vol. 37:3-4; 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 REACTION KINETICS
CHEMICAL REACTIONS
COAL GASIFICATION
COBALT ALLOYS
COBALT BASE ALLOYS
COBALT COMPOUNDS
COBALT SULFIDES
CORROSION
CORROSION RESISTANT ALLOYS
CORROSIVE EFFECTS
CRYSTAL STRUCTURE
DATA
DIAGRAMS
ELEMENTS
ENERGY
EXPERIMENTAL DATA
FLOWSHEETS
FLUIDS
GAS GENERATORS
GASES
GASIFICATION
HYDROGEN
HYDROGEN COMPOUNDS
HYDROGEN SULFIDES
INFORMATION
KINETICS
MASS TRANSFER
MICROSCOPY
MICROSTRUCTURE
MORPHOLOGY
NIOBIUM ALLOYS
NIOBIUM COMPOUNDS
NIOBIUM OXIDES
NIOBIUM SULFIDES
NONMETALS
NUMERICAL DATA
OPTICAL MICROSCOPY
OXIDATION
OXIDES
OXYGEN
OXYGEN COMPOUNDS
PARTIAL PRESSURE
PHASE DIAGRAMS
REACTION KINETICS
REFRACTORY METAL COMPOUNDS
SAMPLE PREPARATION
SULFIDATION
SULFIDES
SULFUR COMPOUNDS
TEMPERATURE RANGE
TEMPERATURE RANGE 0400-1000 K
TEMPERATURE RANGE 1000-4000 K
THERMOCHEMICAL PROCESSES
TRANSITION ELEMENT COMPOUNDS
VAPORS
WATER VAPOR
WEIGHT