Liquid supercooling phenomenon. The formation of ice is actually a crystallization process. If there are crystal nuclei (ice crystals) in raw water, water molecules of liquid below its standard melting point will form crystal structures around the crystal nuclei and attach to the ice crystals, so the process of ice formation can be carried out. But some water is too clean, without dust and impurities.

The container is very clean and smooth. Without such a crystal nucleus, ice crystals cannot form because there is nowhere to attach, so the liquid part on the temperature axis can extend all the time. Even if the temperature is below freezing point (0), water will remain liquid until uniform nucleation and crystallization occur.

You can see that this phenomenon illustrates three points:

1, this bottle of water is very uniform (very pure or even a real solution);

2. The cooling process is uniform and undisturbed;

3. The inside of the container is smooth.

Extended data:

Low temperature process of supercooled water;

Through theoretical and experimental research, it is found that the formation of new phase includes two processes: "nucleation" and "crystal growth". The phenomenon that the temperature of hypobaric liquid continues to drop to 440C without crystallization when it is cooled to 480C is called supercooling. The liquid state at this time is called supercooled state, also called metastable state. Metastable state is the precondition of liquid-solid phase transition.

The formation of new phase must go through the conditions of "supersaturation" or "supercooling". When the driving force in the phase transition process destroys the metastable state, the phase transition moves to the crystallization direction. The crystallization center is formed in metastable state. Under the above experimental conditions, there is no crystallization center provided by the outside world, so it is necessary to form spontaneous small molecular groups in metastable state to become crystallization centers.

This is the reason why the liquid-solid phase change did not crystallize when it was cooled to freezing point, but the temperature dropped to 440℃ and then rose to freezing point. If a heterogeneous crystallization center is provided to the liquid when metastable state occurs, a nuclear embryo will be produced on the heterogeneous crystallization center.

Therefore, when demonstrating the solidification experiment of crystal with hypo, when the temperature drops to 480C, a small amount of hypo is added to the liquid as the crystallization center, and the crystal can grow on this basis. At this time, the melting-solidification curve of hypo crystal is the same. But no heterogeneous crystallization center is provided for the liquid.

Baidu encyclopedia-supercooling phenomenon