To determine the thermodynamic properties of the MgO-BO_1.5 binary system, the following reaction was used:

MO_n(in slag)+nC(gr.)=M(in liquid copper)+nCO (g)

where MO_n represents MgO or BO_1.5.
The activity coefficients of boron and magnesium in liquid copper were first determined by equilibrating pure liquid B₂O₃ or pure solid MgO with liquid copper under controlled CO partial pressure in a graphite crucible at 1723K:

ln γ_B=0.82+2.81x_B, ln γ_Mg=-1.22 (x_B≤0.106, x_Mg≤0.0013)

The themodynamic properties of MgO and BO_1.5 in MgO-BO_1.5 binary slag at 1723K were determined as a function of composition by equilibrating the MgO-BO_1.5 slag with liquid copper under CO atmosphere. In addition, the interaction parameter (ε_Mg^B) in the Cu-B-Mg alloy was determined to be -100 at 1723K.