Re: [Phys-l] Thermodynamics, P vs. T plot

[John Denker <jsd@av8n.com>]

On 11/23/2010 05:42 PM, Peter Schoch wrote:
> The question arose asking if anything has a transition line that is
> vertical or nearly vertical. I admitted to never having seen one, and
> did not think it was possible -- but I am unsure of that last point.
>
> What would a vertical, or nearly vertical, transition line have as a
> physical significance?  Any insights would be most welcome!

The physical significance is associated with the fact that
water expands when it freezes, which is associated with the
funky crystal structure of ice.

If you had something what was very slightly less funky, the
phase boundary would be vertical.  This would not cause even
the slightest difficulties, theoretical or otherwise.

FWIW the boundary between ice VII and ice VIII is very nearly
vertical on the P versus T plot (aka horizontal on the T 
versus P plot)
  http://www.benbest.com/cryonics/lessons.html