Subject: The Liquid Range - A Question

From: Bernd R Eggen <[email-masked]>
Date: Thu, 2 May 1996 11:13:42 +0100 (BST)

Dear All,

I am puzzled about the liquid range for elements:

Element Melting Boiling     Liquid Range (all in K)

 H      14          20          6
 He      1           4          3 (only under pressure)
 Li    453        1620       1167
 Be   1550        3243       1693
 B    2573        3931       1358
 C    3800        5100       1300
 .
 .
 .
 Ga    303        2676       2373
 .
 .
 .
 W    3680        5930       2250
 Hg    234         629        395
 U    1405        4018       2613

There are some simple rules for the melting of
solids (Lindemann, 1910), which contain as parameters
Young's modulus, density and molecular mass of the
solid and gives fairly good results.

Tm = E/(2*rho) * M/R * b^2   (with b^2 = 1/50)

I guess similar rules may exist for the boiling
point (Tb) of liquids.

Ideally, if solids can be described with a potential
energy function with two main parameters controlling
the well-depth (eps) and curvature at the minimum (sig),
are there (approximate) expressions for Tm and Tb
in terms of eps and sig (and molecular mass M) ?

What determines the range of the liquid phase, say
for all elements that crystallise in the fcc & hcp
structure ? Why has Ga such a large liquid range ?
What is the nature of the chemical forces and is
there a parameter which would give clues about or
a good correlation for the liquid range?

Any comment would be greatly appreciated.
Please e-mail [email-masked] -

With best regards, Bernd Eggen.

-- 

Dr. Bernd R. Eggen,
Theoretical Chemistry,
The University of Sussex,
Falmer, Brighton, BN1 9QJ, UK.