This document discusses the properties of liquid and solid phases of metals. It notes that while solids and gases can be easily classified, liquids have many unknown properties. X-ray diffraction has shown that liquids have short-lived ordered atomic structures similar to solids. There is only a small difference in bonding between solids and liquids. The document also examines how the free energy of solids, liquids, and gases varies with temperature and pressure, and discusses the melting point, boiling point, and triple point of phase changes.

1. SOLIDIFICATION OF METALS

2. LIQUID PHASE
 Solids and gases are on two different
extremes of classification and can be
classified easily while many properties of
liquid are unknown.
 E.g. the solids are considered as the most
ordered state and gas as the most
disordered state but liquid has an
intermediate entropy which is not completely
studied like other properties of liquid.

3. CONT. …
 There is a small difference in bonding of solid
and liquid as the change of liquid from solid
gives a density change of 2-6%
 Further the latent heat of fusion during
melting is 1/25 to 1/40 as compare to its
latent heat of vaporization.
 All of these thing lead to a conclusion that
solid and liquid have the same bonding.

4. CONT. …
 X-ray diffraction also confirmed this by
showing that liquid has a short lived group of
atoms having ordered structure like solids
and having same coordination num. like
solids.
 Due to many defects in liquids the ordered
structure is not long lived.
 Due to high mobility of liquid atoms the
diffusion in liquid is high just below its melting
point as compare to solids just above the
M.P.

5. CONT. …
 The high diffusion is also due to defects in
liquids.
 The liquid phase is an ever changing phase with
changing structure and properties with time.
 A difference in solid and liquid is the diffusion in
solid is by vacancy mechanism and will not
change the structure but in liquids the diffusion
due to defects will continuously change its
structure.

6. CONT. ….
 The liquid phases of most metals are similar
in their properties as compare to metals in
solid states having different properties.
 The properties of liquid metal depends upon
the structural defects than the nature of
bonding which is contrary to solids.
 The solid phase has the least entropy and
internal energy contrary to liquid while liquid
has an intermediate between the two.

7. CONT. ….
 The free energy of gas falls more rapidly,
next of liquids and in the last of solids but this
varies with pressure.
 From the figure if we consider the 3 points aa
, bb & cc and draw the curves of solid , liquid
and gas showing the relation between free
energy and temperature at constant
pressure.

9. CONSIDER THE ISOBAR AA…

10. ISOBAR AA…
 This shows that below Tm the solid phase
has lowest free energy and at Tm the internal
energy of liquid start to decrease which
become more stable until Tb and after that
gas is stable.
 By figure the Tm is point on which liquid and
solid curve meets and Tb is point on which
liquid and gas meet.

12. ISOBAR BB…
 It passes through the triple point on which all
the 3 phases coexist and below this point the
only stable phase is solid and after this the
only stable phase is the gaseous phase.

14. ISOBAR CC…
 This lies below the triple point and the curve
also shows that the free energy of liquid is
greater than the solid and gas thus it will not
exist.
 A point exist where the solid is transformed
to gas this is the temperature of sublimation.