DENDRITIC SOLIDIFICATION OF RARE-GASES

Rare gases form simple liquids and thus they can be used as model subs tances to study the dendritic solidification of metals and the develop ment of spatial structures at conditions far from equilibrium. The gro wth of rare gas dendrites into a volume of about 100 cm3 supercooled m elt was investigated using capillary injection technique. Tip growth v elocity 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 be en measured in the supercooling range 0.005 < DELTAT < 0.3 K. The prop erties of rare gas dendrites are compared with data of succinonitrile. The data hold the scaling laws, which are based on the assumption tha t thermal diffusion is the only mechanism of heat transport during den dritic solidification. The data of Kr and Xe do not confirm quantitati ve predictions of Ivantsov theory, nor the assumption v(tip)R2 = const . The experiment shows that the volume solidification rate increases w ith supercooling. The dendrites do not have the shape of a rotational paraboloid. The measurement of the volume of dendrites is done by mean s of the technique of Archimedes. We find that the volume of a dendrit e increases with L3, where L is an overall dimension of the dendrite.