Solid Solution - Phase Rule - Ds Mam
Solid Solution - Phase Rule - Ds Mam
Solid Solution - Phase Rule - Ds Mam
(SOLID SOLUTIONS)
INTRODUCTION
• In many cases, cooling a molten solution does not result in the formation of a pure
crystal or in the formation of a compound, but a solid solution is obtained.
• The solid solution has the characteristic of a liquid solution in the sense that
particles of one component are distributed at random among the particles of the
other component. But the particles cannot move at random atmost they can
vibrate about fix positions.
• Here, we shall discuss only the substitutional solid solutions.
• This results when particles of one substance are replaced in their latest position by
atoms of another substance.
• In a true substitutional solid solutions, the replacement of atoms of one substance
by atoms of another substrate is at random.
• There is no order such as replacement of every second atom or every third atom.
Such a solid solution is formed by Nickel and copper.
Factors Influencing Substitution In Solid Solution
• The two metals should not have very much different first ionization
potentials.
• If the ionization potential values are widely different then crystals of
a compound of the metals are formed (intermetallic crystals).
Factors Influencing Substitution In Solid Solution
RATIO OF THE NUMBER OF ELECTRONS IN THE OUTER ORBITALS TO THE
NUMBER OF ATOMS IN THE MIXTURE
• If the atoms of two elements in the solid solution are approximately of the same size and if
the elements have similar first ionization potential the electron/atom ratio determines the
nature of the solid solution.
• For the Formation of substitutional solid solution ratio (e/A) of the two metals should be of
the order of 1.4.
PHASE DIAGRAMS FOR SOLID SOLUTIONS
• Since the two components are miscible
in solid and liquid phases.
• The maximum number of phases which
can exist at equilibrium would be only
two, and phase rule for such a system
will give the minimum number of
degree of freedom at constant pressure
as:
F = 3 ꟷ P = 3 ꟷ 2 = 1.
• Hence an invariant system is impossible
and there will be no singular point that
is discontinued such as eutectic point Fig 1: A continuous series of solid solution.
At point P’ a solid solution of A+B separates out
on the phase diagram. containing larger amount of B as shown by point Q.
PHASE DIAGRAMS FOR SOLID SOLUTIONS
1. Continuous series