Chapter 5 - Diffusion Flashcards
What is diffusion?
Material transport by atomic motion
What is a diffusion couple?
When two bars of different metals are joined, heated together, and cooled, where some of the metal atoms have transferred bars
What is the process by which atoms of metals diffuse into another called?
Interdiffusion /Impurity diffusion
Can interdiffusion occur with pure metals of the same type?
This is self-diffusion
What is vacancy diffusion?
An atom swaps from a normal lattice position to a vacancy
What is interstitial diffusion?
Atoms swapping from its original interstitial spot to a new one
What does Fick’s First Law describe?
The rate at which mass is transferred (diffusion flux)
In the equation for Fick’s first law, why is the diffusion constant negative?
The concentration moves from a higher amount to lower (negative slope)
What is a driving force?
The force that compels a reaction to occur
Why are there two equations for Fick’s First Law?
J = M/(At) is dependent on time
J = -D[(C2-C1)/(x2-x1)] is not
Which diffusion method is more rapid?
Interstitial is faster than vacancy
What is the driving force for Fick’s First Law?
The concentration gradient
What does Fick’s Second Law describe?
The diffusion flux for a non-steadystate diffusion
What is steady-state diffusion?
There is no net accumulation of diffusing species
What is nonsteady-state diffusion?
The diffusion flux and concentration gradient vary over time
