Activities of manganese in solid and liquid Fe--Mn alloys

By the application of solid state galvanic cells with (Y 2 O 3 )ThO 2 as electrolyte, activity of Mn in solid Fe--Mn alloys has been measured between 1050 to 1174K. The activity of manganese shows negative deviation from ideality for all compositions studied in the present investigation. Three-phase equilibrium involving Fe--Mn + MnAl 2 +2xO 4 +3x +alpha-Al 2 O 3 has been used to determine thermodynamic properties of liquid Fe--Mn alloys at 1823K. This method has elimated difficulties associated with finding suitable container material resistant to MnO at high temperature and has lowered the amount of dissolved oxygen in the molten alloy. The presence of n-type electronic conduction in (Y 2 O 3 )ThO 2 electrolyte does not significantly affect the measured values for activity of mangenese. The nature of interaction between atoms in solid and liquid alloys remains unaltered. Activities approach ideality with increase in temperature. The liquid solution behaviour is exactly described by a subregular solution model. The results obtained independently for solid and liquid alloys are consistent with the phase diagram for Fe--Mn system. 33 ref.--AA