Abstract
In an attempt to understand the phenomena of solidification in zone refining, a simple eutectic-forming organic system (naphthalene-benzoic acid) has been subjected to normal freezing. Experimental results have been analyzed in two ways, by the rates of solidification and impurity profiles in the solid. It has been shown that the lowering rate (equal to the rate of solidification at steady state)must be selected so as to maintain a balance between the heat transfer rate in a liquid and that in a solid. An inclusion factor, defined as a volume fraction of the included liquid at an interface, has been introduced to explain the presence of impurity in the solid. Values of the inclusion factor have been obtained from the impurity concentration profiles in the solid and plotted against the lowering rates and the stirring rates of the liquid. The results showed that a good separation was achieved under the conditions of sufficiently small lowering rates and sufficient stirring of the liquid.
