Use of microgravity to interpret dendritic growth kinetics at small supercoolings

The Isothermal Dendritic Growth Experiment (IDGE), first performed in low-earth orbit in March of 1994 showed variation in the growth data beyond that due to measurement uncertainties, and a significant deviation from predictions of diffusive transport theory with boundary conditions at infinity. Recently, two models described in the J. Crystal Growth suggested modifications from the Ivantsov model to describe the heat transfer of a dendrite growing into a supercooled melt. One model, by Sekerka et al. [J. Crystal Growth 154 (1995) 370], describes how convection resulting from the residual micro-accelerations present on orbit could enhance the heat transfer. Another, by Pines et al. [J. Crystal Growth 167 (1996) 383], describes the observed differences as a thermal boundary layer effect arising from the proximity of the growth chamber wall to the dendrite. Recent in-situ telemetry of dendrite ima of the IDGE in March 1996 showed no correlation between the variations in the crystal growth velocities and the quasi-static microgravity environment.