Phase Equilibria in the ZrO₂–MgO–MnO_x System

Abstract

Phase equilibria were experimentally investigated in the MgO–MnOx and the ZrO2–MgO–MnOx systems for different oxygen partial pressures by powder X‐ray diffractometry, scanning electron microscopy, and differential thermal analysis. The formation of two compositionally and structurally different β‐spinel solid solutions was observed in the MgO–MnOx system in air in the temperature interval 1473–1713 K. Isothermal sections of the ZrO2–MgO–MnOx phase diagram were constructed for air conditions (bold-italicPboldObold2 = 0.21 bar) at 1913, 1813, 1713, 1613, and 1523 K. In addition, isothermal sections at 1913 and 1523 K were constructed for bold-italicPboldObold2 = 10−4 bar. The β‐spinel and halite phases of the MgO–MnOx system were found to dissolve up to 2 and 5 mol% ZrO2. A continuous c‐ZrO2 solid solution forms between the boundary ZrO2–MnOx and ZrO2–MgO systems. It stabilizes in the ZrO2–MgO–MnOx system down to at least 1613 K in air and down to 1506 K at bold-italicPboldObold2 = 10−4 bar.

Thermodynamics of the Mg‐Mn‐O system—modeling and heat capacity measurements

“…The compositions of the MgO‐MnO x system selected for heat capacity measurements and differential thermal analysis (DTA) were prepared and investigated in . Thus the same indexing of the samples is used in this study.…”

“…MgMnO 3 might require high pressure to form, whereas other reports that it can be formed at 1173 K in oxygen atmosphere at normal pressure . It should be noted that this phase was indicated by XRD in of some of the samples after calcinations at 873 K, that is, before the samples were equilibrated. After heat treatment at 1173 K for 7 days MgMnO 3 phase was not detected.…”

“…The phase diagram has been investigated in some studies . Riboud and Muan report the phases being present at different temperatures and composition.…”

“…have determined the stable phases at different compositions and oxygen partial pressures. In our previous paper we reported phase diagram data, including equilibria between halite and spinel as well as halite and liquid oxide.…”

“…To make the description compatible with previous works the ionic two‐sublattice liquid model will be used. An experimental study of the Mg‐Mn‐Zr‐O system, including some results for the Mg‐Mn‐O system, have been done within this study and is published by Pavlyuchkov et al …”