Abstract:The isoactivity of [Y] of samples was obtained in multiple-hole graphite crucibles by controlling the oxygen potential through the reaction 2[Y]+3CO=Y₂O₃+3C. The activity interaction coefficients between Y and Sn, Zn, Pb alloying elements were determined as follows by using conjugate gradient method of solving ill-conditioned equations: for the Cu-Y-Sn sysytem, e_Y^Sn=1.544, γ_Y^Sn=-0.280, γ_Y^Sn,Y=-1.005, e_Sn^Y=2.060, γ_Sn^Y=-1.528, ε_Sn^Y=ε_Y^Sn=662.5; for the Cu-Y-Zn system, e_Y^Zn=0.062, γ_Y^Zn=-0.445, γ_Y^Zn,Y=0.169, e_Zn^Y=0.047, γ_Zn^Y=0.142, ε_Y^Zn=ε_Zn^Y=14.7, for the Cu-Y-Pb system, e_Y^Pb=-0.183, γ_Y^Pb=-0.100, γ_Y^Pb,Y=0.119, e_Pb^Y=-0.432, γ_Pb^Y=0.315, ε_Pb^Y=ε_Y^Pb=-139.5, the equilibrium products for Cu-Y-M (M=Sn, Zn, Pb) systems were identified as Y₂O₃ at 1200℃. The equilibrium constant of reaction 3[O]+2[Y]=Y₂O₃ is 3.3×10¹⁹, the standard free energy of formation of Y₂O₃ in liquid Cu is -550.53 kJ/mol.

Key words:     isoactivity    activity interaction coefficient    Cu-Y-Sn, Cu-Y-Zn, Cu-Y-Pb