Studies in the system Mn-O--The Mn 2 O 3 -Mn 3 O 4 and Mn 3 O 4 -MnO equilibria

As a first step in an investigation of phase relations in the system Mn-O, the equilibria 6Mn 2 O 3 = 4Mn 3 O 4 + O 2 and 2Mn 3 O 4 = 6MnO + O 2 have been studied in the temperature intervals 845 to 1029 degrees C. and 1248 to 1562 degrees C., respectively, and at O 2 partial pressures ranging from 0.21 to 1 atm. and from 10 (super -3.66) to 0.21 atm. respectively. The conditions for coexistence of 2 crystalline phases in stable univariant equilibria are expressed as follows: Mn 2 O 3 , Mn 3 O 4 : log p (sub O 2 = 8.05 - 10100 . 1/T; Mn 3 O 4 , MnO : log p (sub O 2 = 13.31 - 26000 . 1/T. Exploratory runs in the solidus temperature region for the composition range between MnO and Mn 3 O 4 indicate the presence of a eutectic at approximately 1540 degrees C. An explanation is offered for the poor agreement among previously published data on these equilibria.