Filling-box process during solidification of a liquid hypoeutectic binary solution

Solidification of binary solutions often occurs in many industrial applications, including the casting of binary alloys. In this study we consider the effect of a side cooling wall on the development of double-diffusive convection during solidification of a hypoeutectic aqueous ammonium chloride (NH4Cl–H2O) solution. To study flow development during solidification of this solution, we used the shadowgraph technique, particle image velocimetry, and a thermochromic-liquid-crystal slurry. In addition, the transient temperature distribution within the test cell was measured by type-T thermocouples. The results of these experiments revealed that the filling-box process originated from the bottom of the test cell to the top. This process induced several double-diffusive layers and counterclockwise roll cells in the melt, mainly caused by double-diffusive convection. Consequently, the filling-box process may cause serious V-segregates and material defects in solidified ingots.