Supercooling is persistence of a phase below the equilibrium temperature where a lower-temperature phase becomes favorable. A liquid remaining unfrozen below its equilibrium melting temperature is the standard example.
Creating a crystal nucleus gains bulk free energy but costs interfacial energy. Small embryos can disappear, while one exceeding the critical size can grow; this nucleation barrier permits a metastable liquid. A surface or suspended inclusion can lower the barrier through heterogeneous nucleation, whereas homogeneous nucleation occurs within the bulk. Measured freezing onset consequently depends on droplet size, purity and waiting time. Growth releases latent heat and can temporarily warm the remaining material toward the coexistence temperature, separating the onset of nucleation from the later heat-removal problem.
Supercooling is a phenomenon where a liquid is cooled below its freezing point without it becoming solid. This occurs when a liquid is in a perfectly homogeneous state, meaning there are no impurities or surface defects to serve as nucleation sites for crystallization. Under these conditions, the molecules in the liquid can remain in a disordered, liquid state despite the temperature being below the typical freezing point.
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