Ships At Winter

Freezing is an exothermic process, meaning that as liquid changes into solid, heat is released. This is ten seen as counter-intuitive, since the temperature the material does not rise during freezing, except if the liquid was supercooled, but this can be understood since heat must be continually removed from the freezing liquid or the freezing process will stop. The energy released upon freezing is a latent heat, and is known as the enthalpy fusion and is exactly the same as the energy required to melt the same amount the solid.
Vitrification
Certain materials, such as glass or glycerol, may harden without crystallizing; these are called amorphous solids. Amorphous materials as well as some polymers do not have a true freezing point as there is no abrupt phase change at any specific temperature. Instead, there is a gradual change in their viscoelastic properties over a range temperatures. Such materials are characterized by a glass transition which occurs at a glass transition temperature which may be roughly defined as the "knee" point the material's density vs. temperature graph.