1. Solid solutions occur when atoms of a solute dissolve into the crystal lattice of a solvent in the solid state. There are two main types of solid solutions: substitutional and interstitial. 2. In a substitutional solid solution, atoms of the solute substitute for atoms of the solvent in the lattice. This can be ordered, with solute and solvent atoms arranged in specific sites, or disordered. 3. In an interstitial solid solution, atoms of the solute occupy the spaces between atoms of the solvent in the lattice. This only occurs when the solute atom is much smaller than the solvent.

1. Solid Solutions
Prof. H. K. Khaira
Professor, Deptt. of MSME
M.A.N.I.T., Bhopal

2. Phases in Metals
• Phase: a state of matter that is uniform
throughout in chemical composition and
physical state. (Gibbs)
• It is a physically distinct and mechanically
separable mass of matter.

3. Phases in Metals
• The following phases may be present in
metals in solid state.
– 1. Solid solution
– 2. Intermetallic compound

4. Phases in Metals
• Solid solution - When in a solid, the atoms
of solute are present in the lattice of the
solvent, it is known as solid solution.
• Intermetallic compound – a compound formed
by two or more metals such as AlLi.

5. Solid solution
• When in a solid, the atoms of solute are present
in the lattice of the solvent, it is known as solid
solution.
• solid-state solution of one or more solutes in a
solvent.
• It is considered a solution rather than a
compound when the crystal structure of the
solvent remains unchanged by addition of the
solutes.

6. • The solid solutions can be of two types.
– 1. Substitutional solid solution
– 2. Interstitial solid solution

7. Substitutional solid solution
• When the atoms of solute substitute for
the atoms of the solvent in its lattice, the
solution is known as Substitutional solid
solution.
• The solute may incorporate into the
solvent crystal lattice substitutionally by
replacing a solvent particle in the lattice.

8. Substitutional solid solution
Substitutional solid solution
Substitutional
element replaces host atoms
in its lattice
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9. Substitutional solid solution
• Substitutional solid solutions can be of two
types
– 1. Ordered solid solution
– 2. Disordered solid solution

10. Ordered solid solution
• If the atoms of the solute occupy certain
preferred sites in the lattice of the solvent,
an ordered solid solution is formed. It may
ocure only at certain fixed ratios of the
solute and solvent atoms.
• In Cu – Au system, Cu atoms occupying
the face-centered sites and Au atoms
occupying the corner sites of the FCC unit
cell.

11. Ordered Substitutional solid solution
Ordered Substitutional solid solution
Substitutional
element replaces host atoms
in an orderly arrangement
e.g., Ni-Al, Al-(Li,Zr)
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12. Disordered solid solution
• If the atoms of the solute are present
randomly in the lattice of the solute, it is
known as disordered solid solution.
• Most of the solid solutions are disordered
solid solutions

13. Interstitial solid solution
• When the atoms of the solute occupy the
interstitial spaces in the lattice of the solvent, it is
known as Interstitial solid solution.
• If the size of the solute is less than 40% that of
solvent, interstitial solid solution may be formed.
• The solute may incorporate into the solvent
crystal lattice interstitially, by fitting into the
space between solvent particles.
• Only H, Li, Na and B form interstitial solid
solution.

14. Interstitial solid solution
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