Solid‐Solid and Solid‐Vapor Reactions and a New Phase in the System Mn‐O

The univariant equilibrium pressure‐temperature curve along which β‐MnO 2 , Mn 2 O 3 , and O 2 are stable together has been determined up to a Po 2 of 200 atmospheres with a trace of water as a catalyst. The analogous curve for the assemblage Mn 2 O 3 , Mn 3 O 4 , and O 2 has also been determined. In both cases the experimental data differ considerably from the thermodynamic calculations. Interconversion studies of the γ, ρ, ɛ and ramsdellite phases indicate only that γ‐MnO, is probably not a poorly crystallized ramsdellite. A new phase probably containing mainly trivalent manganese has been obtained under a wide variety of conditions. The absence of any consistent X‐ray diffraction line shifts in either the MnO or Mn 3 O 4 phases when they were prepared with different stoichiometries raises some question regarding the extent of stable solid solution in these two phases in the system Mn‐O.