Experimental study on floating-zone tube growth and comparison with computer simulation

Floating-zone (FZ) tube growth of NaNO3 was conducted to study the effect of process parameters and the feasibility of the process. Due to the effect of surface tension, the grown tube size was smaller than the feed. The size reduction became more significant with increasing zone length and decreasing feed tube size. The grown tube size was also sensitive to the pulling speed. Computer simulation was conducted for the experiments, and good agreement was found. In the present study, downward growth was not successful, and the difficulties were illustrated through computer simulation. In all casts, the observed melt/solid interfaces were very convex, and this could be explained through calculated thermocapillary convection. As compared with rod growth, tube growth was more difficult due to its poorer zone stability. Two failure modes of the zone were observed during crystal growth, and they were different from those observed in rod growth.