Determination of the two-melt phase boundary and study of the binary diffusion in liquid Bi–Ga system with a miscibility gap

New data on the shape of the two-melt phase boundary of the bismuth–gallium system with a miscibility gap have been obtained by a γ-ray attenuation technique. According to the measurements the coordinates of the critical point of the liquid–liquid coexistence curve are: critical temperature TC=532.3±1.5 K; critical composition NC=29.5±0.3 at.% Bi. In an extended range around TC the critical exponent β of the coexistence curve equals 0.310±0.005, which agrees closely with non-classical value calculated by the method of high-temperature series expansions. Kinetics of homogenisation of the Bi–Ga melt of near-critical composition have been investigated over the temperature range from 570 to 1225 K using the same technique. The temperature dependence of the coefficient of binary diffusion D derived from these measurement has been found to obey the Arrhenius equation: D(T)=1.67×10−3exp[−27175/RT], cm2 s−1, for the concentration range 20–40 at.% Bi.