High-temperature sulfidation of Mo-50 Wt. % Re

Journal Article · Thu Jun 01 04:00:00 EDT 1989 · Oxidation of Metals; (USA)

DOI:https://doi.org/10.1007/BF00666467· OSTI ID:7108931

Wang, Ge; Douglass, D L ^[1]; Gesmundo, F ^[2]

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1. Univ. of California, Los Angeles (USA)
2. Universita di Genova (Italy)

Mo-50 Re was sulfidized over the range of 1,000-1,100{degree}C in sulfur vapor at pressures of 10{sup {minus}4} and 10{sup {minus}2} atm. The reaction kinetics followed the parabolic rate law with an activation energy of 55.4 kcal/mole for p{sub S{sub 2}} = 10{sup {minus}4} and 48.2 kcal/mole for p{sub S{sub 2}} = 10{sup {minus}2} atm. The pressure dependence varied between +1/4 to +1/6 for the slope of a plot of log K{sub p} vs log p{sub S{sub 2}}. The positive pressure dependence as well as the nature of surface markings suggest that inward diffusion of sulfur interstitials was the rate-controlling step. Sulfidation caused the formation of an external scale of MoS{sub 2} (rhombohedral form) with no evidence of rhenium sulfidation. The selective removal of molybdenum from the surface enabled a layer of the {chi}-phase, an intermetallic compound having the approximate formulae MoRe{sub 3}, to form a continuous layer beneath the MoS{sub 2} scale. The {chi}-phase-layer growth also followed the parabolic rate law. Analysis of the diffusional processes occurring in both the scale and the alloy substrate gave an expression for the ratio of the thickness of the scale and of the {chi}-phase as a function of the corresponding rate constants for the growth of each layer. Finally, the conditions required for the formation of the {chi}-phase layer between the outer scale and the alloy substrate were obtained in terms of the ratio between the diffusion coefficients of the two metals in the intermetallic compound.

• OSTI ID: 7108931
• Journal Information: Oxidation of Metals; (USA), Journal Name: Oxidation of Metals; (USA) Vol. 31:5-6; ISSN 0030-770X; 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
360202 -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
ACTIVATION ENERGY
ALLOYS
CHALCOGENIDES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COHERENT SCATTERING
CORROSION RESISTANCE
CORROSIVE EFFECTS
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DIFFRACTION
DIFFUSION
ELEMENTS
ENERGY
INTERMETALLIC COMPOUNDS
INTERSTITIALS
KINETICS
MATHEMATICAL MODELS
METALS
MICROSTRUCTURE
MOLYBDENUM
MOLYBDENUM ALLOYS
MOLYBDENUM COMPOUNDS
MOLYBDENUM SULFIDES
NONMETALS
PARTIAL PRESSURE
PHASE TRANSFORMATIONS
POINT DEFECTS
PRESSURE DEPENDENCE
REACTION KINETICS
REFRACTORY METAL COMPOUNDS
RHENIUM ALLOYS
SCALING
SCATTERING
SULFIDATION
SULFIDES
SULFUR
SULFUR COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
X-RAY DIFFRACTION