Chapter 5- diffusion

Vocabulary flashcards based on lecture notes about Diffusion in Materials.

Diffusion

The movement of atoms within a material to eliminate concentration differences and produce a uniform composition.

Atom Movement

Atoms may move from one normal lattice to occupy a nearby vacancy.

Arrhenius Equation

An equation that relates the rate of atomic movement to temperature and thermal energy.

Vacancy Diffusion (subby)

Motion of a host or substitutional atom.

Interstitial Diffusion

Movement of an atom from one interstitial site to another.

Activation Energy

Energy that must be supplied to force an atom to its new position during diffusion.

Flux (J)

The rate at which atoms diffuse in a material, defined as the number of atoms passing through a plane of unit area per unit time.

Fick’s First Law

Explains the net flux of atoms in diffusion: J = -D(dc/dx).

D

The diffusion coefficient.

dc/dx

The concentration gradient (atoms/cm4).

Atomic Packing Factor (APF)

Diffusion occurs more slowly in materials with higher atomic packing factors.

Volume Diffusion

Atoms move through the crystal from one lattice or interstitial site to another in X, Y, and Z axes.

Grain Boundary Diffusion

Atoms move along the grain boundaries, interfaces, and surfaces in the materials.

Surface Diffusion

Atoms move on the surface because there is less constraint on the diffusing atoms at the surface.

Fick's Second Law

Describes non-steady state diffusion where the flux and concentration gradient vary with time.

Solution to Fick's Second Law

Used to determine the concentration profile of a diffusing species under non-steady state conditions.