Thermal analysis of float-zone traveling solvent crystal growth of LaB6

We analyze the thermal regime of float-zone traveling solvent crystal growth of LaB6. We construct a one-dimensional analytical approximation of the process taking into account relevant phase diagram, phase transition kinetics, and the effects of natural and Marangoni convection. We show that convection plays a crucial role in the formation of the thermal and mass transfer regimes of the process. First, convection strongly inhibits the temperature inside the melt. Second, convection inhibits even more strongly the mass transfer resistance of the molten zone and the temperature difference between the dissolution and solidification interface. Natural convection depends strongly on the molten zone height so that increase of the molten zone leads to a strong decrease in the temperature difference between solid/liquid interfaces. The action of Marangoni convection on the heat and mass transfer is shown to be considerably stronger; however, its influence does not depend strongly on the molten zone dimensions. It is shown that only the action of Marangoni convection can enhance mass transport between the dissolution and solidification interfaces to a rate sufficient to implement the growth of LaB6 at a pulling rate of 1 cm/h. (C) 1996 American Institute of Physics.