Phase Equilibria and Mutual Diffusion in Liquid Lithium-Sodium Alloys

Abstract

The shape of the liquid-liquid coexistence line in the phase diagram of a lithium-sodium system is determined using the gamma-ray attenuation technique. The measured coordinates of the critical point of the coexistence curve (critical temperature T_C = 576.8 ± 1.0 K; critical composition X_C= 35.9 ± 0.4 at. % Na) are in good agreement with the data in the literature. The critical exponent β for the coexistence curve is 0.34 ± 0.004 in the range 1 · 10⁻³ < (T_C—T)/T_C < 5 · 10⁻². Mutual diffusion in a Li-=Na melt of near-critical composition is studied at temperatures of 583 to 998 K using the same technique. The behaviour of the interdiffusion coefficient is found not to obey the Arrhenius law at temperatures below 700 K. Darken’s relation is used to estimate the temperature dependence of the long-wave limit S_CC(0) of the Bhatia-Thornton concentration-concentration correlation function.