Minimum Temperature of Supercooled Water

name         Hannah
status       other
grade        other
location     N/A

Question -   Is it possible for water to reach -20 Celsius or 
colder without freezing? Is there a minimum temperature that 
water supercools and if yes, what would that be?
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   This is not such an easy question to answer definitively, 
because water below 0 C. is unstable, so anything that provides a 
growth site starts supercooled water to turn to ice. This could be 
a dust particle, or even a random fluctuation in the density of the 
water itself. The lowest temperature that has been observed is 
about -40 C. However, this is not an absolute lower limit "in 
principle". What happens is this. As the temperature decreases, the 
viscosity of water increases dramatically -- it becomes more like 
syrup or honey so the water molecules cannot move around quickly 
enough to form crystals. This behavior also depends upon the 
pressure applied to the water. Under the right conditions (and 
luck) water can be cooled to form a glassy state, which is unstable 
energetically, but cannot release the energy because the water 
molecules are "frozen" in place.
   You can demonstrate this effect using glycerin instead of water. 
The melting point of glycerin is 14 C., but almost no one has seen 
crystalline glycerin because its viscosity increases so much as the 
temperature is reduced below its melting point. You may also have 
seen another example without realizing it. If you leave a jar of 
honey on the shelf for a long time you frequently see that it 
"crystallizes". What is going on is the sugar in "fresh" honey is 
supercooled below its melting temperature, but with age it 
sometimes begins to form crystals that are seen easily.
    For a more in-depth study you can go to: 

https://dspace.mit.edu/handle/1721.1/34440

Vince Calder
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