Cryogenic vials...really necessary?

Peter pxpst2 at vms.cis.pitt.delet.edu
Fri Oct 10 08:45:01 EST 1997


In article <61l1om$cn2$1 at infa.central.susx.ac.uk>,
bapn4 at central.susx.ac.uk (Martin Goodson) wrote:
 
> now could you explain how the direct phase transition from vapour to solid
> occurs (sublimation) at atmospheric pressure?
> 
Sublimation as defined by Linus Pauling is " the complete process of
evaporation of a crystal and the recondensation of a gas directly as a
crystal without passing through the liquid state."

Although a vacuum will greatly increase this process it is not at all
required unless you want to perform the sublimation at room temperature
which is called Lyophilization.  The fact that it the process is occuring
in a freezer your solution will remain frozen and so that is the only
process that can occur.  Evaporation is defined as the process of liquid
water to the gas phase and in the freezer there is no liquid state.
> 
> 
> this is true: there will be a slight difference in humidity between the
> coils and the tube but i suspect that this will so small to be
> insignificant. There will not be much water vapour above ice at -80C.

This is true the gradient is indeed small and this is why others have
noted that the time scale I gave is way off.  I would suspect that the
peaple that have repied and said that they have gotten much longer storage
than 12 months are storing their samples in a Non Frost Free Freezers.  A
Frost Free freezer is designed to remove the ice crystals from the
condensor coil.  At home this little feature is  one of the factors that
causes freezer burn to meats.  :) 
> 
Peter



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