Chp. 7 Vocab
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activation energy (Q)
The energy required to initiate a reaction, such as diffusion.
carburizing
The process by which the surface carbon concentration of a ferrous alloy is increased by diffusion from the surrounding environment.
concentration gradient
The slope of the concentration profile at a specific position.
concentration profile
The curve that results when the concentration of a chemical species is plotted versus position in a material.
diffusion
Mass transport by atomic motion.
diffusion coefficient (D)
The constant of proportionality between the diffusion flux and the concentration gradient in Fick’s first law. Its magnitude is indicative of the rate of atomic diffusion.
diffusion flux (J)
The quantity of mass diffusing through and perpendicular to a unit cross-sectional area of material per unit time.
driving force
The impetus behind a reaction, such as diffusion, grain growth, or a phase transformation.
Fick’s first law
The diffusion flux is proportional to the concentration gradient. This relationship is used for steady-state diffusion situations.
Fick’s second law
The time rate of change of concentration is proportional to the second derivative of concentration. Used in nonsteady-state diffusion situations.
interdiffusion
Diffusion of atoms of one metal into another metal.
interstitial diffusion
A diffusion mechanism in which an atom migrated from one insterstitial position to an empty adjacent one.
nonsteady-state diffusion
The diffusion condition for which there is some net accumulation or depletion of diffusing species. The diffusion flux is dependent on time.
steady-state diffusion
The diffusion condition for which there is no net accumulation or depletion of diffusing species. The diffusion flux is independent of time.
self-diffusion
Atomic migration in pure metals.
vacancy diffusion
The diffusion mechanism in which net atomic migration is from a lattice site to an adjacent vacancy.