Whether a metal will melt then boil (that is, solid --> liquid -->
vapor) or sublime (solid --> vapor) is dependent on the pressure at
which the phase change is taking place. A good starting point is Perry's
Chemical Engineers' Handbook or the CRC's Handbook of Chemistry and
Physics. In both one will find the melting points for metals as well as
the vapor pressure of many metals.

The metal will boil when the vapor pressure is greater than the
operating pressure. If this temperature is below the melting point of
the metal, it will sublime.

For example:
Chromium:
    mp = 1860 C
    vapor pressure 1850 C = 10 mm Hg (13.3 mBar)
    Therefore, chromium should sublime at pressures lower than about 15
mBar
Aluminum:
    mp = 660 C
    vapor pressure = melting point at below 10^-12 mBar (est.)
    will melt and boil (assuming the evaporator is running at about 10^-6
mBar)
Nickel:
    mp = 1453 C
    vapor pressure = melting point at about 2-3 x 10^-2 mBar (est.)
    Therefore, it may melt or it may sublime depending on your process
temperature

The downside, however, is that the references given don't list vapor
pressures below 1 mm Hg (= 1.3 mBar). One can extrapolate to lower
pressures using their values (as I did for nickel and aluminum) by
fitting the data to a line on a log-log plot. A quadratic works well.
This can be done in an spreadsheet program. It's not perfect, but it
works well for estimates.

Regards,

Chris

On Tuesday, January 29, 2002, at 04:53 AM, Yahong Yao wrote:

> Hello All,
>
> When metals are heated up, some change from solid to liquid then to
> vapor (for example, Au, Al, Ni...), and some change form solid to vapor
> directly (Cr).  I am wondering where I can find a list of such
> information for commonly used metals.  Thanks a lot.
>
> Yahong

--
Christopher F. Blanford
Inorganic Chemistry Laboratory, South Parks Road, Oxford, OX1 3QR, UK
Phone: (44)/(0)-1865-282603; Fax: (44)/(0)-1865-272690
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