Free growth of equiaxed crystals settling in undercooled NH4Cl-H2O melts

Recently theoretical works concerning the effect of convection on the growth of isolated dendrites have been compared with experiments on NH4Cl settling equiaxed crystals. It was inferred that more accurate theories were still needed to describe properly the equiaxed crystal growth in the presence of convection. Some new results have been obtained using the following experimental set-up: in a tube containing an undercooled solution of NH4Cl-H2O, settling NH4Cl equiaxed crystals have been filmed with a video camera so as to determine the evolution with time of their size and of their settling velocity. After a careful comparison of the experimental results with some calculations involving the choice of a stability constant, no major discrepancy has been found to prevent the application of the theories in question to moving equiaxed crystals. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.