DENDRITIC SOLIDIFICATION OF RARE-GASES

Rare gases form simple liquids and thus they can be used as model substances to study the dendritic solidification of metals and the development of spatial structures at conditions far from equilibrium. The growth of rare gas dendrites into a volume of about 100 cm3 supercooled melt was investigated using capillary injection technique. Tip growth velocity v(tip), tip radius R, the secondary arm spacing S(tip) and the volume of the whole dendrite V of krypton and xenon dendrites have been measured in the supercooling range 0.005 < DELTAT < 0.3 K. The properties of rare gas dendrites are compared with data of succinonitrile. The data hold the scaling laws, which are based on the assumption that thermal diffusion is the only mechanism of heat transport during dendritic solidification. The data of Kr and Xe do not confirm quantitative predictions of Ivantsov theory, nor the assumption v(tip)R2 = const. The experiment shows that the volume solidification rate increases with supercooling. The dendrites do not have the shape of a rotational paraboloid. The measurement of the volume of dendrites is done by means of the technique of Archimedes. We find that the volume of a dendrite increases with L3, where L is an overall dimension of the dendrite.