Surface behaviour and undercooling in the liquid Ga-Bi binary system detected by optical second harmonic generation

• 来源期刊: 中国物理（英文版）
• 关键词: surface phase transition second harmonic generation liquid(solid)/vapour interface Ga-Bi binary alloy undercooling
• 年，卷（期）: 2003,（3）
• 页码范围: 315-321
• 页数: 7页
• 语种: 英文

摘要

We employ an optical second harmonic generation(SHG) technique to investigate the surfeace behaviours at the liquid(solid)/vapour interface of the Ga-Bi binary metallic system. In a heating and cooling cycle between 280℃ and room temperature, there is no change of the SH-intensity in the heating process, whereas there exists an abrupt and abnormal change of the SH-intensity in the cooling process. It is interesting to find that a macroscopic Bi-rich solid layer is floating on the surface of the Ga-rich liquid phase just below the monotectic temperature (222℃±2℃) in the cooling process, in spite of the Bi-rich phase being heavier than the Ga-rich phase. On the other hand, different undercooling behaviours are observed at the surface and in the bulk. The behaviours of surface solidification and surface melting are different from those in the bulk.