Modeling and ground based experiments on detached solidification

Steady-state detached solidification of InSb and water was calculated using the numerical solution of the Moving Meniscus Model. Detachment was predicted to occur in a sealed ampoule at zero gravity under proper conditions. For steady detachment, the freezing rate must exceed a critical value, Henry's constant of the dissolved gas must be below a critical value, the temperature of the top of the melt must be below a critical value, the contact angle of the melt on the ampoule wall must exceed a critical value, and the diffusion coefficient must exceed a critical value. Each critical value depends on the physical properties and the other operating conditions.; A simple approximate material balance solution also was obtained for the Moving Meniscus Model of detached solidification. At steady state the flux of dissolved gas toward the freezing interface must be equal to the sum of the flux into the freezing solid and that into the gap across the meniscus. Both the numerical and the material balance methods gave two solutions for some combinations of variables, with extremum values beyond which steady detachment was predicted to be impossible. When two gap widths are possible, the larger appears to be stable while the smaller is unstable with respect to the material balance.; The Vertical Bridgman-Stockbarger (VBS) apparatus was used to directionally solidify water on earth. Under some conditions, gas bubbles or gas tubes formed and were incorporated in the ice only at the ampoule wall, and not in the interior. Sometimes gas tubes grew periodically around the ampoule wall; this behavior seems not to have been reported before in the literature. Such growth is favored by a large contact angle of the water on the ampoule wall. There was an optimal range of freezing rates and an optimal range of the temperature difference between the heater and refrigerated bath for gas bubbles or tubes to grow on the ampoule wall. Increasing the concentration of dissolved gas yielded larger gas bubbles and tubes. Longer cylindrical gas tubes were produced when the ampoule was not rotated. Flow visualization studies showed that the convection patterns near the freezing interface were the reverse of those observed experimentally and theoretically in systems that do not display a maximum in liquid density near the freezing temperature.