Ultrasonic Velocities in Molten Bismuth, Tin, and a 50-at.% Alloy under Pressures up to 8.5 kbar

Abstract

Ultrasonic velocities in the melts of bismuth, tin, and a 50-at.% alloy of the two have been determined up to 8.5 kbar using pulse-echo techniques. For bismuth melt, one region exhibits increases in velocity with increasing temperature up to about 7.7 kbar, and from melting to the 270\ifmmode^\circ\else\textdegree\fi{}C isotherm. The temperature behavior of the velocity goes through a maximum around the 275\ifmmode^\circ\else\textdegree\fi{}C isotherm; and in the second region the velocity increases, but much less slowly, with increasing temperature. This behavior is related to a change in the liquid structure. Both regions show a normal increase in velocity with increasing pressure. Molten tin exhibits a normal decrease in velocity with increasing temperature over the range studied, and no structural changes in the liquid state were indicated. The 50-at.% alloy showed normal temperature behavior of the velocity over the limited pressure-temperature domain of 160-180\ifmmode^\circ\else\textdegree\fi{}C and up to 2.5 kbar, and an anomalous pressure and temperature behavior of the velocity above 2.5 kbar. The possibility of structural changes in the liquid state, under pressure, and the increase in velocity with increasing temperature shown by molten bismuth lead to the conclusion that the completely molten state per se need not necessarily yield a decrease in velocity with increasing temperature.