From: "Paul F. Dietz" <dietz@interaccess.com>
Newsgroups: sci.space.policy
Subject: Re: (Feasibility of colonizing the Moon) Re: Yours, Mine or Ours: Who, 
	   Owns the Moon?
Date: Fri, 04 Feb 2000 19:59:45 -0600

BrianF5070 wrote:

> If you want to maintain liquid ore, you will have to pressurize the structure
> above the point at which the boiling point is greater than the triple point.
> You are probably only talking about a few to perhaps a hundred millibar, but
> you _will_ need that pressure.

The pressure given above is too high.  Some liquids have extremely low
vapor pressures (some do not).   Those that do typically melt at low
temperature but boil at high temperature.  Some elements that have
very low vapor pressures at their melting points (approx., in torr):

  Gallium    (essentially zero; too low to measure)
  Tin        (less than 1e-11 torr)
  Indium     (less than 1e-11 torr)
  Lithium    1e-10
  Bismuth    2e-10
  Lanthanum  3e-10
  Aluminum   2e-9
  Lead       3e-9
  Uranium    1e-8
  Sodium     1e-7
  Mercury    2e-6

(The low vapor pressure of lithium near its melting point has led
to the proposal of coating the first wall of magnetic fusion
reactors with a thin flowing layer of the liquid to prevent
sputtering damage.)

For some common metals, the vapor pressures at melting are
(again, approx., in torr):

  Chromium   5
  Magnesium  2
  Manganese  1
  Zinc       1e-1
  Iron       2e-2
  Titanium   3e-3
  Nickel     2e-3
  Copper     3e-4


Melting points can be lowered in mixtures of more than one element,
which should reduce the vapor pressure of the liquid metal.  The
vapor pressure is typically exponential in -c/T for some constant c,
so even small reductions in melting point have a large effect on
the vapor pressure.

On the other hand, for many elements the vapor pressure of the
*oxide* may be higher than that of the pure element.  Often
this oxide will be partially reduced; for example silica when
intensely heated will produce silicon monoxide and oxygen.

Perhaps this should be followed up to sci.space.tech?

	Paul