Freezing

Most liquids freeze by crystallization, formation of crystalline solid from the uniform liquid.

Some of the ways by which crystals form are precipitating from a solution, freezing, or more rarely deposition directly from a gas.

For example, agar displays a hysteresis in its melting point and freezing point. In spite of the second law of thermodynamics, crystallization of pure liquids usually begins at a lower temperature than the melting point, due to high activation energy of homogeneous nucleation.

For most substances, melting and freezing points are approximately equal.

Most liquids freeze by crystallization, formation of crystalline solid from the uniform liquid.

The process of crystal formation via mechanisms of crystal growth is called crystallization or solidification.

Crystallization consists of two major events, nucleation and crystal growth.

Note that in a typical solidification or crystallization process, the thermodynamic driving force is dictated by the degree of supercooling.

The energy released upon freezing is a latent heat, and is known as the enthalpy of fusion and is exactly the same as the energy required to melt the same amount of the solid.

Latent heat is associated with the change of phase of atmospheric or ocean water, vaporization, condensation, freezing or melting, whereas sensible heat is energy transferred that is evident in change of the temperature of the atmosphere or ocean, or ice, without those phase changes, though it is associated with changes of pressure and volume.

Most living organisms accumulate cryoprotectants such as anti-nucleating proteins, polyols, and glucose to protect themselves against frost damage by sharp ice crystals.

A cryoprotectant is a substance used to protect biological tissue from freezing damage (i.e. that due to ice formation).

Such materials are characterized by a glass transition that occurs at a glass transition temperature, which may be roughly defined as the "knee" point of the material's density vs. temperature graph.

This transition is in contrast to the freezing or crystallization transition, which is a first-order phase transition in the Ehrenfest classification and involves discontinuities in thermodynamic and dynamic properties such as volume, energy, and viscosity.

Most living organisms accumulate cryoprotectants such as anti-nucleating proteins, polyols, and glucose to protect themselves against frost damage by sharp ice crystals.

Frost is a thin layer of ice on a solid surface, which forms from water vapor in an above freezing atmosphere coming in contact with a solid surface whose temperature is below freezing, and resulting in a phase change from water vapor (a gas) to ice (a solid) as the water vapor reaches the freezing point.

The nematode Haemonchus contortus can survive 44 weeks frozen at liquid nitrogen temperatures.

As a cryogenic fluid that rapidly freezes living tissue, its handling and storage require Thermal insulation.

See cryobiology for a full discussion.

This usually requires the addition of substances which protect the cells during freezing and thawing (cryoprotectants), 3) preservation of organs under hypothermic conditions for transplantation, 4) lyophilization (freeze-drying) of pharmaceuticals, 5) cryosurgery, a (minimally) invasive approach for the destruction of unhealthy tissue using cryogenic gases/fluids, and 6) physics of supercooling, ice nucleation/growth and mechanical engineering aspects of heat transfer during cooling and warming, as applied to biological systems.

Human gametes and 2-, 4- and 8-cell embryos can survive freezing and are viable for up to 10 years, a process known as cryopreservation.

Water-bears (Tardigrada), microscopic multicellular organisms, can survive freezing by replacing most of their internal water with the sugar trehalose, preventing it from crystallization that otherwise damages cell membranes.

Freezing is a common method of food preservation that slows both food decay and the growth of micro-organisms.

Freezing is also one of the most commonly used processes, both commercially and domestically, for preserving a very wide range of foods, including prepared foods that would not have required freezing in their unprepared state.

The Mpemba effect is a process in which hot water can freeze faster than cold water.

Continuous solidification of the melt is progressed on a liquid/solid interface positioned under the crucible.

Freezing is a phase transition where a liquid turns into a solid when its temperature is lowered below its freezing point.

Freezing is a phase transition where a liquid turns into a solid when its temperature is lowered below its freezing point.

Freezing is a phase transition where a liquid turns into a solid when its temperature is lowered below its freezing point.

Freezing is a phase transition where a liquid turns into a solid when its temperature is lowered below its freezing point.

In accordance with the internationally established definition, freezing means the solidification phase change of a liquid or the liquid content of a substance, usually due to cooling.

For example, agar displays a hysteresis in its melting point and freezing point.

For example, agar displays a hysteresis in its melting point and freezing point.

Crystallization consists of two major events, nucleation and crystal growth. In spite of the second law of thermodynamics, crystallization of pure liquids usually begins at a lower temperature than the melting point, due to high activation energy of homogeneous nucleation.

Nucleation is the step wherein the molecules start to gather into clusters, on the nanometer scale, arranging in a defined and periodic manner that defines the crystal structure.

Nucleation is the step wherein the molecules start to gather into clusters, on the nanometer scale, arranging in a defined and periodic manner that defines the crystal structure.

In spite of the second law of thermodynamics, crystallization of pure liquids usually begins at a lower temperature than the melting point, due to high activation energy of homogeneous nucleation.