Void formation in unidirectional solidification

Visual and photographic observations of unidirectional solidification of liquids that shrink by about 10%% is reported. The liquid is contained in a constant-volume (sealed) cylindrical cell. To estimate the effect of gravity, cooling is provided from above or below. For degassed liquids, when solidified from below, it is observed that the shrinkage is accommodated at the top (like a cavity). However, when solidified from above, the shrinkage is accommodated by formation of voids and worms filled with vapor. The effect of dissolved gases is also investigated. It is observed that dissolved gases tend to distribute the voids for both solidification from below and above. Hence, dissolved gases may be used to control the location of shrinkage voids. Some discussions and predictions are made regarding the location of voids formed under zero gravity.