Thermodynamic properties of Ti in Ag–Ti alloys

Abstract

The thermodynamic properties of Ti in Ag–Ti alloys at 1273 K were determined using an oxygen sensor employing ZrO 2 (2.14 wt% MgO) as the solid electrolyte. TiO was identified as the equilibrium phase in the interface reaction layer formed by the reaction of Ti with Al 2O 3 at 1273 K. From the standard Gibbs energy of formation of TiO and the equilibrium oxygen partial pressure measured by the oxygen sensor, the titanium activity relative to pure solid titanium was calculated. Silver and titanium showed positive deviation from ideal solution behavior. Increasing the titanium concentration of the melt reduced the activity coefficient of Ag. The activity coefficient of Ti at first decreased and then increased with increase in titanium concentration. From the relevant thermodynamic relations, the activity coefficient of titanium at infinite dilution in silver, γ Ti 0 , the self-interaction coefficient of Ti, ε Ti Ti , and the standard Gibbs energy of solution of Ti in liquid silver relative to a 1 wt% solution of Ti at 1273 K were determined to be 0.072, −42.578 and −67.987 KJ/mol, respectively. Integral and excess thermodynamic functions of mixing at 1273 K were also determined. Furthermore, the results were compared with values predicted by the Miedema model. It was found that the experimental enthalpies of mixing and excess Gibbs energy of Ti in the Ag melt are less exothermic than those predicted by the semiempirical theory of Miedema.