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Material Science
Chapter 5
14
Mechanical Engineering
Undergraduate 3
10/14/2012

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Term
Diffusion
Definition
This is the phenomenon of material transport by atomic motion.
Term
Diffusion couple
Definition
This is how diffusion takes place; by joining bars of two different metals together so that there is intimate contact between the two faces.
Term
Interdiffusion / Impurity Diffusion
Definition
The process whereby atoms of one metal diffuse into another
Term
Self-diffusion
Definition
Diffusion occurs for pure metals but all atoms exchanging positions are of the same type
Term
Vacancy diffusion
Definition
One mechanism involves the interchange of an atom from a normal lattice position to an adjacent lattice site or vacancy.
Term
Interstitial diffusion
Definition
Host or substitutional impurity atoms rarely form interstitials and do not normally diffuse via this mechanism.
Term
Diffusion Flux
Definition
Rate of Mass Transfer; (J) defined as the mass of equivalent, the number of atoms
Term
Steady-State Diffusion
Definition
If the diffusion flux does not change with time, a steady-state condition exits.
Term
Concentration Profile
Definition
When concentration C is plotted versus position (or distance) within the solid x, the resulting curve is this.
Term
Concentration Gradient
Definition
The slope at a particular point on this curve (concentration profile)
Term
Diffusion Coefficient
Definition
The Constant of proportionality D this is expressed in square meters per second.
Term
Diffusion Flux (equation) or Fick's first law
Definition
J = M / At
Term
Driving force
Definition
This is used in the context of what compels a reaction to occur. According to the Fick's first law.
Term
What is the driving force in Fick's first law?
Definition
The Concentration gradient
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