THE EFFECT OF FORCED-CONVECTION ON THE MELT GRADIENT AND GROWTH-RATE DURING THE BRIDGMAN AND GRADIENT FREEZE CRYSTAL-GROWTH OF SILVER-DOPED LEAD BROMIDE

The Bridgman and the gradient freeze growth of lead bromide doped with silver bromide has been studied in a partially transparent furnace both with and without vigorous forced convection. The forced convection was accomplished using coupled vibrational stirring, a vortex mixing technique. Growth rates for PbBr2 under static conditions were found to vary with the fraction of the melt solidified. This variation was from 0.13 to 5.8 times the rate predicted from the furnace gradient. This suggested that the temperature gradient varied during growth. Growth rates calculated from the temperature gradients measured at the crucible wall during growth closely matched the observed growth rate. The change in gradient under strong forced melt convection and its effect on the growth rate were also studied, and showed results similar to those found under static conditions.