As a fundamental physical property of liquids, velocity of sound wave in liquids is very important and useful. Many thermophysical parameters may be derived from sound velocity, such as adiabatic bulk modulus, ratio of isobaric to isochoric heat capacities, Grüneisen gamma and so on. However, so far, there is little direct experimental information on macroscopic thermodynamic properties of liquids or melts under high pressure, especially the experimental technique to measure sound velocity of liquid has not been well established.

Recently, a breakthrough made by SONG Wei and LIU Yonggang from the Lab of the Earth’s Interior and Geofluid Geochemistry (LEIGG) at Institute of Geochemistry, Chinese Academy of Science (IGCAS) provided a new idea to enable the sound velocity measurements of liquid at high pressure and high temperature conditions.

Based on conventional large volume press and pulse-echo ultrasonic technique, they have overcome the difficulty in determining the length of liquid specimen under high pressure with a grooved ultra-hard reflector, and the sound velocity in liquid Na has been measured up to 2 GPa. The P-V data deduced from their sound velocity results through equation of state is in an excellent agreement with previous data determined by other method. This new experimental technique is convenient and ready for use, being expected to advance investigation on thermodynamic properties of liquid metals and other melts under high pressure.

Their work was supported by the National Natural Science Foundation of China (Grant No. 40974052), the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No.KZCX2-YW-Q08–3-4), and the Mutual Foundation of Huge Scientific Equipment of National Natural Science Foundation of China and Chinese Academy of Science (Grant No. 10979053). The paper about their work has been published on Review of Scientific Instruments 82, 086108 (2011).

(By LIU Yonggang)