Abstract:The iso-activity of [Y] of samples reached in multiple-hole-graphite crucibles by controlling the oxygen potential through the reaction 2[Y]＋3CO=Y₂O₃＋3C. Combining conjugate gradient method of solving ill-conditioned equations, the activity interaction coefficients betweer Y and Al, Si, Ti, Fe alloying elements were determined. The equilibrium constant of the reaction Z[Y]＋3[O]=Y₂O₃ and the standard free energy of formation of Y₂O₃ in liquid Cu were obtained at 1200℃.

Key words: iso-activity interaction coefficient; Cu-Y-M(M=Al; Si; Ti; Fe)