Interface control mechanisms in horizontal zone-melting with slow rotation

Using slow rotation to control the interfaces in horizontal zone-melting (H ZM) is a widely adopted method for organic materials, i.e., the Pfann-Mille r technique. A short and nearly axisymmetric zone can be achieved easily ev en with a rotation rate of only 1 or 2 rpm. However, the melt convection mi ght not be the crucial mechanism for such a control. Through flow and inter face visualization during NZM of succinonitrile, the role of the slow rotat ion was investigated. Three-dimensional numerical simulation was further pe rformed to illustrate the key mechanisms for determining the zone shape. Be sides the good agreement between the simulation and the experiments, we fou nd that the heat of fusion released or absorbed during the rotational regro wth and remelting played a crucial role, and it could not be ignored in the simulation. (C) 2000 Elsevier Science B.V. All rights reserved.