Experiments on surface tension driven flow in floating zone melting

Abstract

Surface tension driven flow in a NaNO 3 floating zone has been observed. It is comparable to natural convection and probably also important in many crystal growth techniques with a free melt surface. In experiments, related to floating zones, temperature oscillations have been found to be induced by oscillations of the surface tension driven flow which might be instable at higher driving forces. The frequency of these oscillations is proportional to the average temperature gradient imposed upon the free surface. This dependence might be used to identify oscillations of this kind. Surface tension driven flow induced by the concentration gradient of a surface-active impurity has been observed to be not negligible. A further mechanism for growth instability is discussed, which is based on surface tension gradients due to the concentration gradient of a surface-active impurity in front of a growing crystal.