Chemical stratification and solidification in a differentially heated melt

Horizontal directional solidification of Ga-5%mass In was investigated with real-time radioscopic density visualization. A method to quantify the indium stratification from radioscopic images was developed. It was found experimentally that significant indium stratification developed in the melt-phase, with an average vertical indium concentration gradient of 0.09% mass/mm when the volume fraction of solid reached 0.5. Such a large gradient is justified only by a two-phase particulate melt and not by a liquid solution. Validation of the quantitative results was obtained through a heat transfer model for solidification developed from the observed solid-liquid interface morphology and position. Under a set of reasonable assumptions, the calculated interfaces agree well with observed ones, both in morphology and in position. Factors influencing the morphology of the interface are discussed in detail. The agreement of the conductive model with experiments ascertains that at rather large horizontal temperature gradients the melt is in a conductive mode while common CFD codes may predict convection. © 2002 Elsevier Science B.V. All rights reserved.