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Re: Melting under pressure, was Squeeky Snow.



Concerning Ludwik's comment:

The "melting under pressure" idea was discussed here several
winters ago. It was pointed out that pressure must be very
high to produce melting. I do not think that pressures
generated by shoes are sufficiently large.

At 18:10 12/21/00 -0500, David Bowman wrote:

/snip/ determine the melting point depression
with increasing pressure.
The value that I get is that the melting point
decreases with increasing pressure at rate of 7.5 mK/atm.

/snip/ So it appears that Ludwik is on solid ground
(rather than on thin ice, or rather than being all wet)
with his above claim.

David Bowman

The experimental data (at least as depicted in the phase diagram for
water in A Inst Phys HB McGraw-Hill) seems confirming:
the phase boundary beween water and Ice I though somewhat curved
is at most -11 degC per 1000 atm to the Ice II phase transition
at about 1940 atm., -21.5 degC (measured off the diagram).

I can only wonder why this information evokes for me all the
look and feel of the famous pronouncements that still echo in
our ears:
a calculation of the Earth's age based on a heat loss time series
(wasn't Kelvin's estimate less than 1Myr?)
and a calculation of the practical impossibility of heavier than
air flight. Each of these two eminently sensible evaluations
was defeated by an unexpected physical effect - radioactive
heating, and lift enhancement via curved foils.

If I walk with gritty leather soled shoes over polished
mild steel plate, I expect to leave scratches - but shock horror!
the plastic deformation needed for scratching mild steel is
around 1700 atm.(25000 psi)
Can my shoes really exert this sort of pressure?

Perhaps not the leather - but perhaps the imbedded gritty
asperities can - like the gritty asperities of well cooled snow?

:-)

brian whatcott <inet@intellisys.net> Altus OK
Eureka!