Chapter 5 - Diffusion Flashcards
case hardened
hardness and resistance to failure by fatigue has been enhanced by diffusing excess carbon or nitrogen into the outer surface layer
diffusion
material transport by atomic motion
diffusion couple
formed by joining two bars of different metals together so that there is intimate contact between the two faces, the couple is heated for extended periods and then cooled
interdiffusion or impurity diffusion
the process whereby atoms of one metal diffuse into another
self-diffusion
when diffusion occurs in pure metals, or all atoms exchanging positions are of the same type
conditions of diffusion (2)
- there must be an empty adjacent site
2. the atom must have sufficient energy to break bonds with its nearest atoms and then cause some lattice distortion
vacancy diffusion
the interchange of an atom from a normal lattice position to an adjacent vacancy, necessitates the presence of vacancies
interstitial diffusion
when atoms migrate from an interstitial position to a neighboring one that is empty, found for inter diffusion of impurities, occurs more rapidly in metals than vacancy diffusion occurs
diffusion flux
(J) the rate of mass transfer, how fast diffusion occurs
steady-state diffusion
when diffusion flux does not change with time
concentration profile
when concentration C is plotted versus position or distance
concentration gradient
the slope at a point on the concentration profile
diffusion coefficient
(D) the constant of proportionality
Fick’s first law
J = -D * dC/dx, used for steady-state diffusion
Fick’s second law
(Cx-Co)/(Cs-Co) = 1 - erf(x/(2sqrt(Dt))), used for nonsteady-state diffusion, erf is the gaussian error function
carburizing
used to harden the surface of a steel above that of its interior, increases the surface concentration of carbon
activation energy
(Qd) the energy required to produce the diffusive motion of one mole of atoms
predeposition step
impurity atoms are diffused into the silicon (making of ICs)
drive-in diffusion
higher temperature than the predeposition step, forms an oxide layer on the surface
junction depth
(xj) represents the depth or value of x at which the diffusing impurity concentration is just equal to the background concentration of that impurity
