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·
Surfaces
have an energy per unit area, γ
, associated with them. The work required to increase the surface area
by dA is: dw
= γ
dA
·
The
surface or interfacial energy (tension) may be written in terms of the
Gibbs function, G, of the system.
·
For
an infinitesimal process, the change in the Gibbs function is given by:
dG
= - SdT + Vdp + γ dA
+ Σi
μidni
with:
T= temperature, p = pressure, A = surface area, µi = chemical
potential of species ni
·
For
a system under conditions of constant pressure, temperature, and composition:
γ
= (dG/ dA) p,T,n
·
For
Silver at 750 C the surface energy
is 1.14 Joules m-2, for copper at 1080 C the surface energy
is 1.43 Joules m-2, Al2 O3 at 1850 C has
a surface energy of 0. 91 Joules m-2, and for TiC at 1100 C
γis
1.19 Joules m-2. |
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