#### 3.D.2.b. Fusion Curve

Consider now the coexistence curve between
the solid and liquid phases.

This is depicted as the fusion curve AB in
Fig.3.4.

Note that the fusion curve does not
terminate.

It can have either positive or negative
slope, as depicted with a solid and dotted line in Fig.3.4, respectively.

The relevant Clausius-Clapeyron equation is

(
dP
dT
)
coex
=
Δ
h
sl
TΔ
v
sl
(3.17)

where
Δ
h
sl
>0
is the molar latent heat of fusion. Hence, the sign of
Δ
v
sl
=
v
l
−
v
s
determines that of the slope of the fusion
curve. A well known example of a fusion
curve that has a negative slope is that between ice and water.