Ch 5 Flashcards
Define diffusion
Mass transport by atomic motion
Define diffusion mechanisms
The atoms in a solid or not fixing position, but are able to move around because of vacancies and thermal vibrations
Why does diffusion increases with increasing temperature?
Vacancy concentration in the amplitude of thermal vibrations, both increase with increase in temperature
Define substitutional diffusion
Diffusion process for atoms on lattice sites is vacancy atom exchange
Define interstitial diffusion
No vacancies required for diffusion
(Most interstitial sites are vacant)
List the two diffusion mechanisms
Substitutional diffusion
Interstitial diffusion
Substitutional diffusion: extra of what is required
Extra energy
(The atoms must pass or a high energy position since the nearby atoms must spread apart)
Substitution diffusion: how is it activated?
Thoroughly activated process
Substitutional diffusion: what two things increased exponentially with temperature
Diffusion rate
Diffusion coefficient
Substitutional diffusion: what two things does activation energy depend on
The extra energy required to jump
The number of vacancies present
Substitutional versus interstitial diffusion:
Which has a lower activation energy and is much faster, particularly at low temp
Interstitial for both
Define steady state diffusion
(And it’s formula)
Diffusion it in a steady state concentration gradient obeys Fick’s First law
4 factors affecting diffusion/arrhenius equation
Type of species
Diffusion mechanism
Concentration gradient
Temperature
Formula for the rate of diffusion
Describe diffusion rates the bulk, the surface, and the grain boundary
Diffusion: what formula do we need to use when concentration changes with time
How can we nominally estimate how far an atom diffuses into a surface over time
