Evaporation is a phase transition from the liquid phase to gas phase that occurs at temperatures below the boiling temperature at a given pressure. Evaporation usually occurs on the surface. Evaporation may occur when the partial pressure of vapor of a substance is less than the equilibrium vapour pressure.
Boiling is a phase transition from the liquid phase to gas phase that occurs at or above the boiling temperature. Boiling, as opposed to evaporation, occurs below the surface. Boiling occurs when the equilibrium vapour pressure of the substance is greater than or equal to the environmental pressure. For this reason, boiling point varies with the pressure of the environment.
Sublimation is a direct phase transition from the solid phase to the gas phase, skipping the intermediate liquid phase.
The term vaporization has also been used to refer to the physical destruction of an object that is exposed to intense heat. As noted in discussions of the effects of nuclear weapons, this includes the vaporization of human bodies by the 1945 atomic bombings of Hiroshima and Nagasaki and the vaporization of the uninhabited Marshall Island of Elugelab in the 1952 Ivy Mike thermonuclear test.
A flux of so many gamma ray, x-ray, ultraviolet and heat photons strikes matter in a such brief amount of time (a great number of high-energy photons, some overlapping in the same physical space) that all molecules lose their atomic bonds and "fly apart". All nuclei lose their electron shells and become positively-charged ions, in turn emitting photons of a slightly lower energy than they had absorbed. All such matter becomes a gas of nuclei and electrons which rise into the air due to their high temperature or bond to each other as they cool.
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