Observation of morphological instability during directional soldification in a rotational field

• Main Authors: Yang, Ya-Wen, 楊雅雯
• Other Authors: Lan, Chung-Wen
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/40988046119401423308

碩士 === 國立臺灣大學 === 化學工程學研究所 === 89 === During directional solidification of an alloy, the control of interface morphology is crucial to the quality of growth control. For a non-dilute alloy, the deep interface depression or pit formation, due to buoyancy flow, often accelerates the instability. Therefore, the control of melt flow is important to reduce the local solute accumulation and thus enhance the morphology stability. In this thesis, we set up a directional solidification system on a rotation table. High purity SCN was prepared by vacuum distillation. Ethanol was used as a solute to reveal the morphology instability during solidification. We also set up a rotation system to investigate the effect of rotation about growth axis. It was found that rotation about the growth axis at high speed reverses solute distribution and enhances interface stability. However, if the rotation speed is not high enough, due to the poor mixing of solute. The morphological instability occurs much earlier than that of no rotation.