Direct observation of time-temperature-transformation curves for crystallization of ice from solutions by a homogeneous mechanism

Emulsified samples of aqueous solutions of lithium chloride have been rapidly cooled to temperatures in the vicinity of the "homogeneous nucleation temperature" T_g and observed isothermally in a differential calorimeter to identify the time delay before the maximum crystallization rate (detected by the release of the heat of crystallization) is achieved. The locus of the times t_p to reach the maximum rate at different temperatures has the classic form of the time-temperature-transformation (TTT) curve described in theories of homogeneous nucleation and growth. The displacement of this TTT curve to longer times and lower temperatures can be observed by increasing the solution concentration. The results correlate well with much longer time observations made recently with electrical conductivity studies of thin bulk samples near their glass transition temperatures.