Thermodynamic evaluation of Cu–Li phase diagram from EMF measurements and DTA study

Abstract

Two experimental techniques were used in investigations of the Cu–Li system. An electrochemical concentration cell method was applied in measurements of activities of Li in Cu–Li alloys while DTA measurements were performed for liquidus and solidus determination. Activity measurements were conducted using electrochemical cells with the liquid LiCl–LiF and LiCl–KCl electrolyte in the concentration range from X Li = 0.05 –0.7 for 20 alloys and at temperatures between 633 K (360 ∘C) and 923 K (650 ∘C). DTA experiments were performed by derivatograph Q-1500 (Paulik–Paulik–Erdey system) for 17 alloys with concentration changing from X Li = 0.18 to 0.975. The analyses of temperature dependencies of the electromotive force (EMF) for different concentrations of Cu–Li alloys indicated the existence of a new Cu 2Li 3 entropy-stabilized intermetallic phase. Using all available DTA literature data of Pastorello [S. Pastorello, Gazz. Chim. Ital. 60 (1930) 988–992] and Klemm and Volavšek [W. Klemm, B. Volavšek, Z. Anorg. Chem. 296 (1958) 184–187] and those from EMF and DTA measurements of this work the optimization and calculation of the Cu–Li system were performed. Finally, the thermodynamic properties of the fcc-(Cu), Cu 2Li 3 intermetallic phase and the liquid phase were established together with a new proposed phase diagram of the Cu–Li system. The heat of formation of Cu 2Li 3 compound established during the optimization of Cu–Li system is tentative and it should be experimentally confirmed or corrected in future investigations.