1. SOLID SOLUTION
.

2. WHAT?
A solid solution is a single phase which exists over a
range of chemical compositions.
Some minerals are able to tolerate a wide and varied
chemistry, whereas others permit only limited chemical
deviation from their ideal chemical formulae.
In many cases, the extent of solid solution is a strong
function of temperature, with solid solution being
favoured at high temperatures and unmixing and/or
ordering favoured at low temperatures.

3. TYPES?
Substitutional solid solution:
Chemical variation is achieved
simply by substituting one type of
atom in the structure by another.

4. EXAMPLE
A good example of a solid solution is the Cu-Ni system,
for which the phase diagram is shown below.
Both metals are completely soluble in each other.
The α phase is a substitutional solid solution.
This occurs because both the Cu and Ni form face
centered cubic structures, and have similar atomic radii,
electronegativity's and valences.
Copper and nickel show very different physical
properties in their pure states, and the α phase provides
a continuous change between the extremes.

6. CONT. ….
The diameter of Cu atoms is 2.551 Ȧ and
that of Ni is 2.487Ȧ
The difference is only 2% and slight
distortion is produced in the lattice thus in
all proportions of Cu and Ni they crystallize
as F.c.c

7. TYPES?
Interstitial solid solution:
Chemical variation is achieved by
adding atoms or ions to sites in the
structure that are not normally
occupied.

8. EXAMPLE?
Solubility of carbon in b.c.c. iron (ferrite) below
723*C.
Due to the difference in size of carbon and
interstitial spaces work is done in order to
introduce the interstitial atom in to the crystal.
This work is shown by Wc and if number of C
atom is by nc then internal energy will be Wcnc.

10. CONT.….
Intrinsic entropy: each interstitial atom
increase the entropy of crystal that is
called intrinsic entropy.
It also affects the normal modes of
vibration and as the solute atom enters
the lattice make them more random and
irregular.

11. CONT. ….
Physical significance of Wc:
The main two sources of carbon are cementite
and graphite.
The activation energy for the trasfer of 1 mole of
C from cementite-Ferrite is 9700 cal/mol and
that for Graphite-ferrite is 14800 cal/mol. Thus
greater work is done to take a carbon 4rm
graphite and place it in ferrite.

12. CONT. …..
The solubility of C in ferrite is low if
Fe is in equilibrium with graphite
because a greater energy is required to
remove an atom 4rm graphite and place
it in iron.
The solubility of C is v.small in ferrite,
at 723*C it is only 0.02 %.

14. FACTORS AFFECTING THE SOLID
SOLUTION
Size of solute and solvent.
Relative positions of elements in
electromotive series.
Both the components (pure metals)
have same valence and crystallize in
same lattice form.