Thermochemistry of MgAl2O4‐Al8/3O4 Defect Spinels

ALEXANDRA NAVROTSKY, BARRY A. WECHSLER, KAREN GEISINGER, FRIEDRICH SEIFERT

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98 Scopus citations

Abstract

Solution calorimetry of MgAl2O4‐Al8/3O4 solid solutions was performed in a molten 2PbO · B2O3 solvent at 975 K. The results indicate small negative heats of mixing, relative to spinel standard states for both end‐members. These data were combined with information on the energetics of the α‐γ transition in Al2O3 and on the MgAl2O4‐Al8/3O4 (MgO‐Al2O3) subsolidus phase relations to estimate the partial molar entropy of mixing of γ‐Al8/3O4 in the solid solution. This entropy is much less positive than that calculated from several models for the configurational entropy of mixing of magnesium, aluminum, and vacancies on octahedral and/or tetrahedral sites. The data suggest a good deal of local order to be present in the solid solutions, consistent with negative enthalpies of mixing and entropies of mixing far less than ideal configurational values.

Original languageEnglish (US)
Pages (from-to)418-422
Number of pages5
JournalJournal of the American Ceramic Society
Volume69
Issue number5
DOIs
StatePublished - May 1986
Externally publishedYes

ASJC Scopus subject areas

  • Ceramics and Composites
  • Materials Chemistry

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