PHOTOACOUSTIC MEASUREMENTS OF PHASE-TRANSITIONS IN SN-BI ALLOYS

In pure Sn specimens, the temperature dependence of photoacoustic signals shows remarkable change only in the immediate vicinity of the melting point, whereas in Sn-Bi alloys, such remarkable change occurs in the wide temperature range between the solidus and the liquidus. The frequency dependences of photoacoustic signals have also been measured in the frequency range from 1 Hz to 200 kHz. It is found that the dispersion of the photoacoustic anomaly at the melting of Sn changes remarkably by the addition of Bi. This result strongly suggests that the interface becomes irregular as the composition of Bi increases.