Radial segregation due to weak convection in a floating zone

The influence of weak convection, caused by surface tension forces, on radi al dopant segregation occurring in crystals grown under microgravity condit ions is studied numerically. The geometry considered corresponds to a float ing-zone configuration with partially coated melt surfaces consisting of sm all evenly distributed spots of free surfaces. In order to distinguish dopa nt distribution due to weak convection clearly from distribution due to dif fusion the spots only cover one quarter of the periphery. Thus, surface ten sion-driven convection is allowed only over one quarter of the floating-zon e configuration resulting in an asymmetric dopant distribution. The percent age of free surfaces present is varied in order to alter the Marangoni flow rates. The maximum dopant concentration due to radial segregation is plott ed as a function of a certain convection level. The results of the present numerical study are supposed to be used to design corresponding space exper iments launched at the end of the year 2000. (C) 2000 Elsevier Science B.V. All rights reserved.