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The mysterious crystallization process: How does a liquid quietly turn into a solid?
In nature, the process of liquid turning into solid is not just a common physical change, but a process full of mystery and change. When the temperature of liquids drops below their freezing point, they begin to crystallize, a process that forms a crystalline solid. Therefore, understanding these processes is crucial to our understanding of how matter transitions from one state to another.
Most liquids will follow a certain structure during the crystallization process, which is a wonder of nature.
Basic principles of freezing
Freezing is one of the phase changes in which a liquid turns into a solid. This phenomenon occurs when a liquid cools below its freezing point. Although the melting and freezing points are the same for most substances, some substances, like agar, exhibit different solid-liquid transition temperatures. The melting point of agar is 85°C (185°F), while the freezing point of its crystals is between 32°C and 40°C (90°F and 104°F).
Two stages of crystallization process
The freezing process is usually achieved by the crystallization process, which includes two main events: nucleation and crystal growth.
Nucleation is the process by which molecules begin to assemble into clusters and arrange themselves in a crystal structure defined here, and subsequent crystal growth is the process by which the successfully formed initial structure continues to grow.
Super cooling phenomenon
In nature, crystallization of pure liquids usually begins at some lower temperature below its melting point because of the high activation energy of homogeneous nucleation. This process also shows that the temperature at which crystallization begins needs to be low enough to allow stable nucleation to occur. Heterogeneous nucleation may be triggered if there are irregularities, solid or gaseous impurities, or other nucleating species on the surface of the container.
Exothermic properties
The freezing process is usually exothermic, meaning heat is released as a liquid turns into a solid. Although the temperature of the substance does not rise during the freezing process under normal circumstances, this does not prevent the release of heat. Because during the freezing process, heat must be continuously removed from the liquid in order for the freezing process to continue.
The heat released is called latent heat and is nearly equal to the energy required to melt the same amount of solid.
Vitrification of amorphous materials
Some materials, such as glass and glycerin, can harden without crystallizing and are called amorphous solids. These amorphous materials do not have a specific freezing point, but instead exhibit constant changes in their physical properties over different temperature ranges. This process is called vitrification and is different from the traditional freezing process.
Freezing ability of organisms
Many organisms can survive conditions below the freezing point of water, primarily because they produce antifreeze to protect themselves from damage by ice crystals. Certain bacteria and plants are able to survive effectively at temperatures as low as −2°C, while certain animals, such as nematodes and amphibians, can survive severe freezing conditions.
Freezing technology in food preservation
Freezing is widely used for food preservation, which can effectively slow down food deterioration and the growth of microorganisms. With the advancement of technology, freezing can not only preserve the flavor and nutrients of food, but also improve the timeliness of food preservation, which makes freezing a commercially viable and economical method of food preservation.
Conclusion
In our lives, freezing not only affects the preservation of food, but also deeply reflects the mysterious process of material transformation. From crystallization to supercooling, from biological adaptation to economic applications, freezing phenomena provide us with countless topics worth exploring. The change from liquid to solid is not just a physical transformation, but more like a "magic". How many unknowns are left waiting for people to discover?
