TIME-DEPENDENCE OF TIP MORPHOLOGY DURING CELLULAR DENDRITIC ARRAYED GROWTH

Succinonitrile-1.9 wt pct acetone has been directionally solidified in 0.7 X 0.7-cm-square cross section pyrex ampoules in order to observe the cell/dendrite tip morphologies, not influenced by the ''wall effec ts,'' which are present during growth in the generally used thin (abou t 200 mu m) crucibles. The tips do not maintain a steady-state shape, as is generally assumed. Instead, they fluctuate within a shape envelo pe. The extent of fluctuation increases with decreasing growth speed, as the micro structure changes from the dendritic to cellular. The inf luence of natural convection has been examined by comparing these morp hologies with those grown, without convection, in the thin ampoules.