The Hysteresis Phenomena of Flow Patterns due to Thermal and Solutal Marangoni Convections in a Liquid Bridge under Zero Gravity

The floating zone (FZ) method is one of the growth techniques used to grow single crystal materials. FZ growth is achieved in a containerless environment (without a crucible) by the movement of a molten zone of a solid rod, which forms a free-standing liquid bridge between two solid sections. However, the surface tension along the free surface of the molten zone varies due to temperature and concentration gradients, and in turn gives rise to Marangoni convection in the melt. It is therefore essential for the growth of high quality crystals by FZ to have a better understanding and precise control of the Marangoni convection occurring in the melt [1-3]. From this point of view, the role of thermal Marangoni convection in the FZ system has been investigated numerically and experimentally [4-7] using a half-zone liquid bridge. The Thermal Marangoni convection in liquid bridge of low Prandtl number fluids becomes oscillatory via two-step flow transitions. The first transition occurs from axisymmetric steady to a 3-D steady flow, and then at a larger temperature difference, the second transition to an oscillatory flow takes place. A stability map of thermal Marangoni convection was proposed by Imaishi et al. [4]. In the growth of alloys such as SixGe1-x, it was shown that it is necessary to consider not only the thermal Marangoni convection but also the solutal Marangoni convection due to surface tension differences of the components of the alloy [8-13]. The flow transformation with the increase or decrease in the Marangoni number is accompanied by the hysteresis phenomena [14]. In this study, the hysteresis phenomenon of flow patterns due to thermal and solutal Marangoni convections in a liquid bridge under zero gravity was numerically simulated.