Ppt

1. Solid solutions in metals:
Sugar+ water = Solute+ solvent
A solid solution forms when as the solute atoms are added to host material, the
crystal structure is maintained and no new structure is formed.
Primary solid solution
Secondary solid solution

2. • Impurities in solids:
• Pure solids are costly and hence impurities are
deliberately added to the solids so as to reduce
its properties
• A) without altering its appearance 7.5% Cu make
Ag stronger, harder and more durable , lowering
its cost.
• B) Zn is added to Cu== Brass
• C) alloy
• D) ceramic products

3. Rule of Solid Solubility

4. Hume-Rothery- empirical rules to predict solid
solubility
• For solid solubility exist b/t two elements, the following settlements
are always true:
• Atomic Size: the atomic radii of the two elements must be with in
15 % of each other.
• Crystal Structure: the type of crystal structure must be same.
• Chemical Valence: The valence of the two elements must differ by
no more than one.
• Electro negativity: It must be nearly equal if not, a compound may
be formed as a result of the difference in affinity for electrons.
• The more electropositive one element and the more
electronegative the other, the greater the likelihood that they will
form an intermetallic compound instead of a substitutional solid
solution.

5. Atomic Size
• Extensive substitutional solid solution occurs
only
• If the relative difference between the atomic
diameters (radii) of the two species is less
than 15%.
• If the difference > 15%, the solubility is
limited.
• Comparing the atomic radii of solids that form
solid solutions,

6. Crystal Structure Rule
• For appreciable solid solubility, the crystal
structures of the elements must be identical.
• Although the crystal structure remains un
changed
• However, the dimension of the unit crystal cell
changes progressively with addition of solutes.

7. Valency Rule
• A metal will dissolve a metal of higher valency
to a greater extent than one of lower valency.
• Or a solute of higher valency is more likely to
dissolve in a solvent of lower valency.
• The solute and solvent atoms should typically
have the same valence in order to achieve
maximum solubility

8. • E.g copper dissolve up to 38.3 atomic percent
Zinc
• But zinc dissolve only 2.8 atomic percent
copper

9. Electronegativity
• Chemical property that describes the ability of an atom
to attract electrons (or electron density) towards itself.
• An atom's electronegativity is affected by both its
atomic weight and the distance that its valence
electrons reside from the charged nucleus.
• The higher the associated electronegativity number,
the more an element or compound attracts electrons
towards it.
• The more electropositive one element and the more
electronegative the other, the greater the likelihood
that they will form an intermetallic compound instead
of a substitutional solid solution.

10. Electronegativity,
• It is not strictly an atomic property,
• But rather a property of an atom in a molecule
• The equivalent property of a free atom is its
electron affinity.
• The opposite of electronegativity is
electropositivity:
• A measure of an element's ability to donate
electrons.

11. Electro negativity
• Electro negativity: It must be nearly equal
• If not, a compound may be formed as a result
of the difference in affinity for electrons
• If electron affinity is the same for each
component, No compound will be formed and
the one phase region will be retained

12. The Electro negativity
Electronegativity difference close to 0 gives
maximum solubility.
• The more electropositive one element and the
more electronegative the other,
• The greater is the likelihood that they will form
an intermetallic compound instead of a
substitutional solid solution.
• Ordered intermetallic compounds are formed if
the components have very different
electronegativity.
•

14. • The compounds limits the amount of solid
solution that can occur between the
elements.
• The actual extent of solid solubility depends
on the stability of the intermediate phase
• The more stable the compound the less is the
extent of the primary phase field.
• E.g Mg2Pb in alloy of Mg with Pb

15. • The principle of the fourth rule is that
• The single solution becomes unstable with
regards to the compound, whose free energy
near its ideal composition will be lowest.
• The phase regions (compound plus solid
solution) then appear and the phase diagram
no longer contains the broad region of
complete solubility.

16. • The first three rules are based on the increase
in enthalpy due to distortion of the crystal
lattice,
• Disruption of crystal structure, in crude sense
unsaturated bonds.
• There distortion leads to appreciable positive
deviation and therefore limited mutual solid
solubility.

19. • Positive deviation of the enthalpy of mixing
and consequently limited solid solubility may
be predicted from known atomic properties.