Freezing Water More Complicated than Thought
Everyone is taught early on in school that water turns to ice at 32 F or 0 C, but, as with many things taught early on in school, this is not completely true. Researchers at the University of Utah have found water can reach -55 F or -48 C before it must freeze into ice. Though computer models had to be used to arrive at this absolute freezing temperature, liquid water has been found at -40 F in clouds and -42 F in experiments.
Whenever a material changes from a liquid to a solid it tries to form a crystalline structure and when something cools too quickly, the result is an amorphous structure, like that of glass. For these internal structures to form though, a seed must be present to grow from. Most water we encounter is filled with impurities that will act as seeds, but pure water requires the spontaneous formation of a structure within the liquid. This is only guaranteed to happen at -55 F (-48 C).
Above this temperature something called ‘intermediate ice’ forms. These are water molecules which have taken on a structure similar to that of pure ice, but not quite. Intermediate ice also forms when water is frozen so quickly as to create low-density amorphous ice.
Water, one of, if not the most important substance on Earth is also one of the weirdest. Just remember, as winter comes and you see ice and snow outside, to be thankful the impurities in the water you see means the temperature can be as high as a relatively balmy 32 F, or 0 C.