Supercooled water escaping metastability

The return of supercooled water to stable equilibrium condition is an irreversible process which takes place adiabatically [1]. In fact, the process is a very fast process and results in the formation of a liquid-solid mixture at the coexistence temperature. The solid phase grows up as a dendritic structure. It has been suggested that the formation of dendrites can promote the release of latent heat at the liquid solid interface [2]. The investigation of the dendrite formation by fast imaging, while simultaneously monitoring the local temperature, reveals the existence of two regimes. At supercooling temperature below 266.7 K the process arrives to completions in a very short time (<0.07 s), whereas at higher temperatures several seconds are needed for the system to reach equilibrium. The boundary between the two regions is very sharp (< 0.5 K), which suggests an abrupt transition. The slow process evolves following the same universal path, independently of the initial supercooling temperature. Even in the presence of a slow process, no heat flux to the thermostatic bath is revealed. Hence, on a scale involving the whole system, the process maintains its adiabatic character. The transition between the two processes is explained in terms of the balance between the local flux of the latent heat released by the growing crystal and the flux of heat between the equilibrated liquid at the melting temperature and its environment, still at the initial temperature. [1] see, e.g., F. Aliotta, P.V. Giaquinta, M. Pochylski, R.C. Ponterio, S. Prestipino, F. Saija, C. Vasi, J. Chem Phys. 138, 184504 (2013). [2] M.E. Glicksmann, A.O. Lupulescu, J. Cryst. Growth 264, 541-549 (2004).