V. D. Aleksandrov, S. A. Frolova.
ABSTRACT
Based on the thermograms of heating and cooling various substances, the phenomenon of explosive crystallization of supercooled liquids is analyzed. As evidence of the phenomenon of explosive crystallization, the corresponding thermograms are given in coordinates of temperature – time for tellurium, bismuth, water, and acetic acid. On the schematic cooling curve, various structural transformations occurring in the liquid phase, as well as solidification stages are shown: the formation of crystal nuclei, their coagulation and subsequent isothermal crystallization. Explosive crystallization at the second stage is characterized by a rapid rise in temperature from the region of supercooling to the melting temperature with rates exceeding the cooling rate (i.e., heat removal) by two to three orders of magnitude. An attempt is made to explain the phenomenon of explosive crystallization from the standpoint of the known principles of the cluster-coagulation crystallization model and the theory of chain reactions. The calculations established that the critical sizes of the crystal nuclei are comparable with the sizes of the unit cells of the corresponding crystal lattices, and the work of their formation is comparable with the energies of intermolecular bonds. Based on calculations of the heat released during nucleation, as well as interfacial surface energy released during coagulation of crystal nuclei, it has been hypothesized that crystal-like clusters and stable crystal nuclei can serve as the “building” material for crystal growth. It is shown that during the formation of nuclei and their coagulation, the released energy is equivalent to quanta of electromagnetic radiation, which is capable of activating the appearance of new centers of crystallization, reproduction and coagulation of nuclei. Calculations showed that during coagulation of many nuclei, sufficient energy is released to quickly heat the substance from the supercooling region to the melting temperature. By analogy with the well-known diagram of thermal explosion, a similar diagram of the dependence of heat release and heat removal on time for the explosive crystallization process is constructed and analyzed. The critical values of the onset of the explosive process and the cooling rate of the liquid phase are found. The final stage of equilibrium crystallization after explosive is estimated.
KEY WORDS:
overheating; hypothermia; clusters embryos; coagulation; exploding crystallization.
DOI: 10.31857/S023501062006002X