Immiscibility in the Fe3O4-FeCr2O4 Spinel Binary

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A recent thermodynamic model of mixing in spinel binaries, based on changes in cation disordering (x) between tetrahedral and octahedral sites, is investigated for applicability to the Fe{sub 3}O{sub 4}-FeCr{sub 2}O{sub 4} system under conditions where incomplete mixing occurs. Poor agreement with measured consolute solution temperature and solvus is attributed to neglect of: (1) ordering of magnetic moments of cations in the tetrahedral sublattice antiparallel to the moments of those in the octahedral sublattice and (2) pair-wise electron hopping between octahedral site Fe{sup 3+} and Fe{sup 2+} ions. Disordering free energies ({Delta}G{sub D}), from which free energies of mixing are ... continued below

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1239 Kilobytes pages

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Ziemniak, S.E. & Castelli, R.A. March 20, 2003.

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This report is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided by UNT Libraries Government Documents Department to Digital Library, a digital repository hosted by the UNT Libraries. It has been viewed 47 times , with 5 in the last month . More information about this report can be viewed below.

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  • Lockheed Martin
    Publisher Info: Lockheed Martin Corporation, Schenectady, NY 12301 (United States)
    Place of Publication: Schenectady, New York

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Description

A recent thermodynamic model of mixing in spinel binaries, based on changes in cation disordering (x) between tetrahedral and octahedral sites, is investigated for applicability to the Fe{sub 3}O{sub 4}-FeCr{sub 2}O{sub 4} system under conditions where incomplete mixing occurs. Poor agreement with measured consolute solution temperature and solvus is attributed to neglect of: (1) ordering of magnetic moments of cations in the tetrahedral sublattice antiparallel to the moments of those in the octahedral sublattice and (2) pair-wise electron hopping between octahedral site Fe{sup 3+} and Fe{sup 2+} ions. Disordering free energies ({Delta}G{sub D}), from which free energies of mixing are calculated, are modeled by {Delta}G{sub D} = {alpha}{chi} + {beta}{chi}{sup 2} - T(S{sub c} + {chi}{sigma}{sub el} + {gamma}{chi}{sigma}{sup mag}) where the previously-neglected effects are accommodated by: (1) adding a non-configurational entropy term to provide coupling between cation disordering and magnetic ordering and (2) revising the configurational entropy (S{sub c}) analysis. Applying the constraint {alpha} = -(2/3){beta} and regressing the existing database for Fe{sup 2+} ion disorder in Fe{sub 3}O{sub 4} gives: {beta} = -31,020 {+-} 1050 J mol{sup -1}, {sigma}{sub el}/R = -0.730 {+-} 0.081 and {gamma}, the coupling parameter between cation disordering and magnetic ordering, = -0.664 {+-} 0.075. The revised mixing model predicts a consolute solution temperature (T{sub cs}) = 600 C and a solvus at 500 C of n = 0.05 and 0.70 for the Fe(Fe{sub 1-n}Cr{sub n}){sub 2}O{sub 4} spinel binary.

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1239 Kilobytes pages

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OSTI as DE00821371

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  • Other Information: PBD: 20 Mar 2003

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  • Report No.: LM-03K029
  • Grant Number: AC12-00SN39357
  • DOI: 10.2172/821371 | External Link
  • Office of Scientific & Technical Information Report Number: 821371
  • Archival Resource Key: ark:/67531/metadc740472

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  • March 20, 2003

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  • Oct. 18, 2015, 6:40 p.m.

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  • April 28, 2016, 8:51 p.m.

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Ziemniak, S.E. & Castelli, R.A. Immiscibility in the Fe3O4-FeCr2O4 Spinel Binary, report, March 20, 2003; Schenectady, New York. (digital.library.unt.edu/ark:/67531/metadc740472/: accessed September 22, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.