Effect of Nb on the high-temperature sulfidation behavior of cobalt

Journal Article · Sat Apr 01 04:00:00 EST 1989 · Oxid. Met.; (United States)

DOI:https://doi.org/10.1007/BF00846687· OSTI ID:5846819

Gleeson, B; Douglass, D L; Gesmundo, F

The sulfidation behavior of Co-Nb alloys containing up to 30 wt.% Nb was studied in sulfur vapor at a pressure of 0.01 atm in the temperature range of 600-700/degree/C. Increasing niobium content decreased the sulfidation rate, following the parabolic rate law. An activation energy of 25.6 kcal/mole was obtained for Co-10Nb, Co-20Nb, and Co-25Nb, while a value of 20.5 kcal/mole was found for Co-30Nb. All were two-phase alloys, consisting of solid solution /alpha/-Co and the intermetallic compounds, NbCo/sub 3/. The two-phase alloys formed a rather thick outer layer of cobalt sulfides and a heterophasic inner layer that was complex. The inner layer always contained the mixed sulfide CoNb/sub 2/S/sub 4/ which, depending on the alloy composition, coexisted with cobalt sulfide, NbS/sub 2/, and/or NbCo/sub 3/ particles. Short-time sulfidations showed that the solid solution initially sulfidized rapidly to form nodules of cobalt sulfide, whereas the NbCo/sub 3/ phase formed a thin protective layer of NbS/sub 2/. The nodules grew laterally until they coalesced into the continuous, outer thick layer, while the NbS/sub 2/ completely or partially reacted with the cobalt sulfide to form CoNb/sub 2/S/sub 4/. Platinum markers were always found at the interface between the inner and outer scales, the location of the original metal surface.

• Research Organization: Univ. of California, Los Angeles (USA)
• OSTI ID: 5846819
• Journal Information: Oxid. Met.; (United States), Journal Name: Oxid. Met.; (United States) Vol. 31:3-4; ISSN OXMEA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102 -- Metals & Alloys-- Structure & Phase Studies
360105* -- Metals & Alloys-- Corrosion & Erosion
ACTIVATION ENERGY
ALLOYS
BACKSCATTERING
CHALCOGENIDES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COBALT ALLOYS
COBALT BASE ALLOYS
COBALT COMPOUNDS
COBALT SULFIDES
COHERENT SCATTERING
CORROSION
CORROSION RESISTANCE
CORROSIVE EFFECTS
CRYSTAL STRUCTURE
DIFFRACTION
DISPERSIONS
ELECTRONS
ELEMENTARY PARTICLES
ELEMENTS
ENERGY
FERMIONS
KINETICS
LEPTONS
MATERIALS TESTING
METALLURGICAL EFFECTS
METALS
MICROSCOPY
MICROSTRUCTURE
MIXTURES
NIOBIUM
NIOBIUM ALLOYS
NIOBIUM COMPOUNDS
NIOBIUM SULFIDES
NONMETALS
OPTICAL MICROSCOPY
QUANTITY RATIO
REACTION KINETICS
REFRACTORY METAL COMPOUNDS
SCALING
SCATTERING
SOLID SOLUTIONS
SOLUTIONS
SULFIDATION
SULFIDES
SULFUR
SULFUR COMPOUNDS
TESTING
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
X-RAY DIFFRACTION