Dendritic aggregates of ice and brine formed upon freezing of aqueous solutions have been studied. Chlorides of sodium, potassium, lithium and hydrogen were used as solutes; structures produced on freezing of binary, ternary and quaternary solutions were examined. Effects of freezing rate, solute concentration, solute diffusivity, mixing of solutions and magnetic fields are reported.
The spacing between ice platelets or dendrites was found experimentally to be proportional to the square root of the freezing time when the freezing rate was constant from beginning to end of solidification. During unidirectional freezing from a constant temperature chill, the solution at each location is subjected to a spectrum of freezing rates; dendrite spacing increases linearly with distance from the chill surface and it is inversely proportional to the square root of the maximum freezing rate.
In binary solutions dendrite spacing increases linearly with solute concentration; above a critical solute concentration ice platelets develop side branches. Application of an external magnetic field has an effect similar to increasing concentration. At a given solute concentration, spacing between ice dendrites increases linearly with solute diffusivity.
In ternary and quaternary solutions dendrite spacing is a function of the concentrations and diffusivities of each of the constituent solutes.