Unstable flow and solidification speed due to the interaction of thermocapillary and solutocapillary forces in directional solidification

During floating zone growth from a melt with a surface active impurity with segregation coefficient k(eff) < 1, solutocapillary forces arise which counteract thermocapillary ones. A hydrodynamic instability of the surface-tension-driven flow (Marangoni effect) due to these counteracting forces has been found experimentally and its mechanism is discussed in this paper. In contrast to the well-known passive growth oscillations due to hydrodynamic instabilities in the melt, growth and remelting of the crystal actively participate in this instability.