Thermodynamics on the Bi-Fe-Ti System and the Gibbs Energy of Bi9Ti8

Partial isothermal sections of the Bi-Fe-Ti system at 700 degrees C and 900 degrees C were constructed to investigate the reactivity of Fe with Bi-Ti liquid alloy. In the ternary system, three-phase equilibria such as liquid-Fe-Fe2Ti, liquid-Fe2Ti-Bi2FeTi4, and liquid-Bi9Ti8-Bi2FeTi4 were confirmed at both temperatures. The solubility of Fe in liquid Bi at these temperatures is negligibly small. On the other hand, it is notable that the solubility of Fe in liquid Bi containing Ti at 900 degrees C is much larger and reaches 2.3 mol pct. Then, we measured the electromotive force (emf) between Bi-20 mol pct Ti alloy and pure Ti at 700 degrees C in equimolar NaCl-KCl where 1 mol pct TiCl2 was added. From the result, the interaction parameter of the liquid phase in the Bi-Ti system and the standard molar Gibbs energies of formation of Bi9Ti8 and Bi2FeTi4 at 700 degrees C were estimated. (C) The Minerals, Metals & Materials Society and ASM International 2018