How to keep ice at it's solid state at 40degrees celcius? Help please
Ziad Rahayel
I am not sure I am posting to the right group for this!
I am looking for a way to keep ice/water in it's solid state at
temperatures up to 40degrees celcius. Any means to do this is welcome,
thermodynamics, chemical... Whatever.
Thank you very much
Ziad Rahayel
Joe
> I am looking for a way to keep ice/water in it's solid state at
> temperatures up to 40degrees celcius. Any means to do this is welcome,
> thermodynamics, chemical... Whatever.
David Hesselschwerdt replied:
> The solution that comes to my mind is to maintain the ice in a
> vacuum, although I don't know how feasible that is to your purpose
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It seems to me that vacuum, equilibrium thermodynamics and the
standard phase diagram are of little help:
>From the Clausius-Clapeyron equation,
delta T = (Tc(Vwater - Vice)/L) (delta P)
where the Vs are specific volumes and
other terms have their usual meanings.
For ice-water, the coefficient isabout - 8 mK per atmosphere.
The negative sign is your first problem:
because water expands on freezing, you have to lower
the pressure to raise the melting temperature. The other
problem is size: (Vwater - Vice) is relatively small,
~0.0001 m^3/kg. So the effect of P is much smaller for
freezing than it is for evaporation.
If the volumes are very small and you go to great lengths
to avoid surfactant and bubble contamination, you might be
able to get substantial negative pressures. After all, the
xylem vessels in tall trees can withstand negative pressures
of at least several atmospheres. I think that suctions
produced in bulk water in laboratories have exceeded
10 MPa without cavitation, but only for small volumes,
carefully prepared.
In our lab, we regularly have water at pressures of
< -10 MPa. The preparation is not especially difficult,
but the water is in layers between surfaces separated
by only several molecular diameters. This size is less
than the critical cavitation radius, and the surfaces
are very hydrophilic.
Yan, Z., Pope, J. and Wolfe, J. (1993) J. Chem. Soc.
Faraday Trans., 89, 2583-2588.
So I expect that you will only get a fraction of a degree
from delta P. You would need 5000 atmospheres suction to raise
the melting point to 40 C. In principle pure, solid ice
should support this as a tensile stress, but I suspect that
at the interface with your chamber you will have a layer
of water that might cavitate. The bulk modulus of water
is ~2 GPa so a hypothetical suction of 500 MPa would
cause an expansion of tens of %!
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Good news:
You can get a three degree increase easily: use D2O, not H2O.
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Related fictions:
i) Kurt Vonnegut's novel "Cat's Cradle" is based on a
fictional form of water that is solid at room temperature.
ii) There was a flurry of interest in artifactual
"polywater" with that property about 30 years ago. Its
interesting history is reported in
"Polywater" Felix Franks., MIT Press, 1981
Joe Wolfe, School of Physics, J.W...@unsw.edu.au
University of New South Wales, Sydney.