Solidification of Ga-Mg-Zn in a gas-filled drop tube: Experiments and modeling

Droplets of Ga24Mg36Zn40 were solidified in a 3 m, helium-filled drop tube. The solidified droplets contained uniformly distributed MgZn2 dendritic primary crystals, whose number was determined as a function of droplet size. A new model for the solidification in a gas-filled drop tube was developed. It allows introduction, stochastically in space and time, of multiple nuclei with interfering thermal fields. Using classical homogeneous nucleation kinetics, the model reproduces the size dependence of the number of primary crystals. The crystal-melt interfacial tension is estimated at 0.0008-0.002 J/m(2). This low value is attributed to the polytetrahedral structural similarity between the melt and the MgZn2 Frank-Kasper phase. The program is available upon request. (C) 2000 American Institute of Physics. [S0021-8979(00)10303-2].