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Enthalpies of formation of Fe-Ni monosulfide solid solutions

Amir H. Tavakoli and Alexandra Navrotsky
Enthalpies of formation of Fe-Ni monosulfide solid solutions
American Mineralogist (August 2013) 98 (8-9): 1508-1515


Binary and ternary sulfides in the Fe-Ni-S system are of major fundamental and practical interest in environmental, geological, and planetary science. Despite extensive thermodynamic modeling of phase equilibria, the enthalpies of formation of solid solutions in this system have not been measured directly as functions of both nickel/iron and metal/sulfur ratios. This communication reports enthalpies of formation of Fe-Ni monosulfide solid solutions [mss = (Fe (sub 1-x) Ni (sub x) ) (sub 1-z) S, 0 < or = x < or = 1; 0.875 < or = 1-z < or = 1] quenched from 750 degrees C, representing disordered structural states. Measurements were performed on three series of solid solutions using oxidative solution calorimetry in molten sodium molybdate solvent at 702 degrees C. The measured enthalpies of formation of Ni (sub 1-z) S solid solutions from elements are consistent with prior data reported for a few compositions. The enthalpies of formation of ternary compositions, (Fe (sub 1-x) Ni (sub x) ) (sub 1-z) S, are reported for the first time. Within their uncertainties, the enthalpies of formation of the solid solutions, quenched from high temperature, with respect to the end-members (enthalpies of mixing) at 25 degrees C are zero. An experimentally derived equation is proposed for the calculation of enthalpies of formation of all high-temperature monosulfide solid solutions in the Fe-Ni-S system. The thermodynamic stabilization of these disordered solid solutions arises not from energetic terms but from the configurational entropy.

ISSN: 0003-004X
EISSN: 1945-3027
Serial Title: American Mineralogist
Serial Volume: 98
Serial Issue: 8-9
Title: Enthalpies of formation of Fe-Ni monosulfide solid solutions
Affiliation: University of California at Davis, Peter A. Rock Thermochemistry Laboratory, Davis, CA, United States
Pages: 1508-1515
Published: 201308
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 51
Accession Number: 2013-073832
Categories: General geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 6 tables
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201344
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