Thermodynamics of Ti in Cu–Ti alloy investigated by the EMF method

The thermodynamics of Ti in Cu–Ti alloy at 1423 K was determined by means of an oxygen sensor employing ZrO2(2.14wt%MgO) as the solid electrolyte. Ti2O was the equilibrium phase in the interfacial reaction layer formed by the reaction of Ti with Al2O3. Activities of titanium and copper relative to pure solid state were investigated, and both Cu and Ti in the system showed negative deviation from Raoult’s law. The increment of Ti concentration increased the activity coefficient of Ti and reduced the activity coefficient of copper. The activity coefficient of titanium in infinite dilution copper, γTi0, self-interaction coefficient εTiTi, and the standard Gibbs free energy of solution of Ti in copper relative to 1wt% Ti, ΔG0(Ti in Cu melt) at 1423 K were measured in the present study being γTi0= 0.200, εTiTi=4.828 and ΔG0(Ti in Cu melt)=−70.179 kJ/mol respectively. The thermodynamic functions of mixing and excess were determined at 1423 K, respectively, ΔGCu−TiX=ΔHCu−TiM=−19.17XTi+33.07XTi2 (kJ/mol) (XTi≤0.0325), and ΔGCu−TiM=−0.093−78.67XTi+344.9XTi2(kJ/mol) (XTi≤0.0325). The limiting partial enthalpy of solution of supercooled liquid Ti in copper at 1373 K was found to be −11.97 kJ/mol according to regular solution method.