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

Abstract

Abstract The thermodynamics of Ti in Cu–Ti alloy at 1423 K was determined by means of an oxygen sensor employing ZrO 2 (2.14wt%MgO) as the solid electrolyte. Ti 2 O was the equilibrium phase in the interfacial reaction layer formed by the reaction of Ti with Al 2 O 3 . 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, γ Ti 0 , self-interaction coefficient e Ti Ti , and the standard Gibbs free energy of solution of Ti in copper relative to 1wt% Ti, Δ G 0 (Ti in Cu melt) at 1423 K were measured in the present study being γ Ti 0 = 0.200, e Ti Ti =4.828 and Δ G 0 (Ti in Cu melt) =−70.179 kJ/mol respectively. The thermodynamic functions of mixing and excess were determined at 1423 K, respectively, Δ G Cu−Ti X =Δ H Cu−Ti M =−19.17 X Ti +33.07 X Ti 2 (kJ/mol) ( X Ti ≤0.0325), and Δ G Cu−Ti M =−0.093−78.67 X Ti +344.9 X Ti 2 (kJ/mol) (X Ti ≤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.