Change of Ultrasonic Wave Velocity in Indium near the Melting Point

The ultrasonic wave velocity of indium was precisely measured in the temperature range from 120 to 183°C including the melting point. An ultrasonic pulse transmission method was used and the adopted sound frequency was 1 MHz. The melting point of the specimen was 156.4°C. The sound velocities were 2504 m/s in the solid phase just below the melting point and 2297 m/s in the liquid phase just above the melting point. The temperature coefficients of the sound velocity were 0.191 m/s·deg in the solid phase and 0.254 m/s·deg in the liquid phase. By combining the present results with existing data of thermal expansivity and specific heat, the elastic properties of indium at and around the melting temperature were reduced, and discussion was made on the obtained results.