ACTIVITY COMPOSITION RELATIONS IN NIAL2O4-MNAL2O4 SOLID-SOLUTIONS AND STABILITIES OF NIAL2O4 AND MNAL2O4 AT 1300-DEGREES-C AND 1400-DEGREES-C


TIMUCIN M., MUAN A.

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, vol.75, no.6, pp.1399-1406, 1992 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 75 Issue: 6
  • Publication Date: 1992
  • Doi Number: 10.1111/j.1151-2916.1992.tb04200.x
  • Title of Journal : JOURNAL OF THE AMERICAN CERAMIC SOCIETY
  • Page Numbers: pp.1399-1406

Abstract

Activities of NiO were measured in the oxide and spinel solutions of the system MnO-NiO-Al2O3 at 1300-degrees and 1400-degrees-C with the aim of deriving information on the thermodynamic properties of the spinel phases. Synthetic samples in selected phase assemblages of the system were equilibrated with metallic nickel and a gas phase of known oxygen partial pressures at a total pressure of 1 atm. The data on NiO activities and directions of conjugation lines between coexisting oxide and spinel phases were used to establish the activity-composition relations in spinel solid solutions at 1300-degrees and 1400-degrees-C. The MnAl2O4-NiAl2O4 solid solutions exhibit considerable negative deviations from ideality at these temperatures. The free energy of formation of MnAl2O4 from its oxide components (MnO + Al2O3) at 1300-degrees and 1400-degrees-C is calculated to be -24.97 and -26.56 kJ . mol-1, respectively. The activities determined in the stoichiometric spinel solid solutions are more negative as compared with those predicted from cation distribution models.