Three phase equilibria for activity determinations: system Co--Mn

Abstract

A solid state e.m.f. cell with yttria-doped thoria as the electrolyte and a mixture of Cr + Cr₂O₃ as the reference electrode, was employed for the measurement of the activity of manganese in the Co--Mn system at 1760 deg K, for 0.3 > X_Mn > 0.05. The liquid alloy was contained in an alumina crucible and saturated with MnAl₂+2xO₄+3x . The cell can be represented by Pt, W, (Co--Mn) + MnAl₂+2xO₄+3x+ Al₂O₃ /ThO₂ --Y₂O₃ /Cr + Cr₂O₃ , Pt. The activity of manganese shows negative deviations from Raoult's law. The activities in the Co--Mn system are intermediate between those in the Fe--Mn and Ni--Mn systems. The Gibbs' energies of mixing in these systems follow the trends given by Miedema's model.