Question

Can the number and type of defects be varied and controlled? How? Explain the exponential variation of the concentration of defects with temperature. Explain each term of the equation in terms of their physical significance

Answer 1

Q1.
Can the number and type of defects be varied and controlled? How?

The number and type of defects can be varied and controlled by following quantities,
(1) number of vacancy can be controlled by temperature, T.
(2) number of dislocations can be controlled by amount of plastic deformation.
(3) number of interstitial point ‘defects’ can be controlled by weight of material.

Q2.
Explain the exponential variation of the concentration of defects with temperature.

The equilibrium number of vacancies for a given quantity of material increases with temperature according

to the Arrhenius equation, Nv= N*exp(-Qv/k*T)
The Arrhenium equation is obtained from the calculation of Gibss free energy at equilibria, dG = -T*dS
The exponential term comes from the Boltzman's formula of entropy calculation, S =k*Ln(P)
Where P, is the number of configurations due to defects.

Q3.
Explain each term of the equation in terms of their physical significance
equation, Nv= N*exp(-Qv/k*T)
Nv = number of vacancy at equilibrium
N = Total number of atoms
Qv = Activation energy for the formation of vacancy
k= Boltzman's constant
T = temperature