Defect and transport properties of nonstoichiometric cobaltous sulfide

Journal Article · Mon Apr 01 00:00:00 EST 1991 · Oxidation of Metals; (United States)

DOI:https://doi.org/10.1007/BF00738287· OSTI ID:6069569

Danielewski, M; Mrowec, S; Wojtowicz, A ^[1]

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1. Academy of Mining and Metallurgy, Cracow (Poland)

A very high defect concentration in a number of common-metal sulfides is considered to be the main reason for the rapid degradation of high-temperature alloys, including cobalt-base superalloys, in sulfur-containing atmospheres. Deviations from stoichiometry and chemical diffusion in cobaltous sulfide, Co{sub 1{minus}y}S, have been studied as a function of temperature (923-1,073 K) and sulfur activity (1-10{sup 3} Pa) using a thermogravimetric technique. It has been shown that in agreement with Libowitz's model, the unusual dependence of nonstoichiometry in Co{sub 1{minus}y}S on equilibrium sulfur pressure and temperature may be interpreted in terms of repulsive interaction of cation vacancies in this compound. The chemical diffusion coefficient has been found to be essentially pressure-independent and can be described as a function of temperature by the equation: {tilde D} = 0.29 exp({minus}110 {plus minus} 8.4 kJ/mol)/RT. Recalculation of these results shows that the mobility of cation vacancies in cobaltous sulfide decreases with an increase in their concentrations, probably due to the site-blocking effect. The self-diffusion coefficient of cobalt in Co{sub 1{minus}y}S, calculated from defect-diffusion coefficients and nonstoichiometry data, has been found to be very weakly dependent on sulfur activity, and its pressure and temperature dependence can be described by the following empirical equation: D{sub Co} = 8.9 {times} 10{sup {minus}4} p{sub s{sub 2}}{sup 1/20} exp({minus}93.6 {plus minus} 7.5 kJ/mol)/RT.

• OSTI ID: 6069569
• Journal Information: Oxidation of Metals; (United States), Vol. 35:3-4; ISSN 0030-770X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
COBALT
SELF-DIFFUSION
COBALT BASE ALLOYS
SULFIDATION
COBALT SULFIDES
ATOM TRANSPORT
ACTIVATION ENERGY
CRYSTAL DEFECTS
EQUATIONS
EXPERIMENTAL DATA
PHASE DIAGRAMS
PRESSURE DEPENDENCE
STOICHIOMETRY
TEMPERATURE DEPENDENCE
THERMAL GRAVIMETRIC ANALYSIS
VACANCIES
ALLOYS
CHALCOGENIDES
CHEMICAL ANALYSIS
CHEMICAL REACTIONS
COBALT ALLOYS
COBALT COMPOUNDS
CRYSTAL STRUCTURE
DATA
DIAGRAMS
DIFFUSION
ELEMENTS
ENERGY
GRAVIMETRIC ANALYSIS
INFORMATION
METALS
NEUTRAL-PARTICLE TRANSPORT
NUMERICAL DATA
POINT DEFECTS
QUANTITATIVE CHEMICAL ANALYSIS
RADIATION TRANSPORT
SULFIDES
SULFUR COMPOUNDS
THERMAL ANALYSIS
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
360105* - Metals & Alloys- Corrosion & Erosion
360102 - Metals & Alloys- Structure & Phase Studies