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MSE 2090: Introduction to Materials Science
Chapter 5, Diffusion
Diffusion - how do atoms move through solids?
Diffusion mechanisms
¾
Vacancy diffusion
¾
Interstitial diffusion
¾
Impurities
The mathematics of diffusion
¾
Steady-state diffusion
(Fick’s first law)
¾
Nonsteady-State Diffusion
(Fick’s second law)
Factors that influence diffusion
¾
Diffusing species
¾
Host solid
¾
Temperature
¾
Microstructure
Chapter Outline
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MSE 2090: Introduction to Materials Science
Chapter 5, Diffusion
Diffusion is material transport by atomic motion
.
Inhomogeneous materials can become homogeneous by
diffusion. For an active diffusion to occur, the temperature
should be high enough to overcome energy barriers to
atomic motion.
What is diffusion?
results of an atomistic simulation of atomic mixing
homework project in MSE 4592/6270
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MSE 2090: Introduction to Materials Science
Chapter 5, Diffusion
Interdiffusion
(or impurity diffusion)
occurs in
response to a
concentration gradient
.
Self-diffusion
is diffusion in one-component material,
when all atoms that exchange positions are of the same
type.
Interdiffusion and Self-diffusion
Before
After
(Heat)
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MSE 2090: Introduction to Materials Science
Chapter 5, Diffusion
Vacancy diffusion mechanism
To jump from lattice site to lattice site, atoms need
energy to break bonds with neighbors, and to cause
the necessary lattice distortions during jump.
This
energy comes from the thermal energy of atomic
vibrations (E
av
~ k
B
T)
The direction of flow of atoms is opposite the vacancy
flow direction.
Diffusion Mechanisms (I)
Atom migration
Vacancy migration
After
Before

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