Chapter 5 - Diffusion

Question 1

case hardened

Answer 1

hardness and resistance to failure by fatigue has been enhanced by diffusing excess carbon or nitrogen into the outer surface layer

Question 2

diffusion

Answer 2

material transport by atomic motion

Question 3

diffusion couple

Answer 3

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

Question 4

interdiffusion or impurity diffusion

Answer 4

the process whereby atoms of one metal diffuse into another

Question 5

self-diffusion

Answer 5

when diffusion occurs in pure metals, or all atoms exchanging positions are of the same type

Question 6

conditions of diffusion (2)

Answer 6

1. 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

Question 7

vacancy diffusion

Answer 7

the interchange of an atom from a normal lattice position to an adjacent vacancy, necessitates the presence of vacancies

Question 8

interstitial diffusion

Answer 8

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

Question 9

diffusion flux

Answer 9

(J) the rate of mass transfer, how fast diffusion occurs

Question 10

steady-state diffusion

Answer 10

when diffusion flux does not change with time

Question 11

concentration profile

Answer 11

when concentration C is plotted versus position or distance

Question 12

concentration gradient

Answer 12

the slope at a point on the concentration profile

Question 13

diffusion coefficient

Answer 13

(D) the constant of proportionality

Question 14

Fick’s first law

Answer 14

J = -D * dC/dx, used for steady-state diffusion

Question 15

Fick’s second law

Answer 15

(Cx-Co)/(Cs-Co) = 1 - erf(x/(2sqrt(Dt))), used for nonsteady-state diffusion, erf is the gaussian error function

Question 16

carburizing

Answer 16

used to harden the surface of a steel above that of its interior, increases the surface concentration of carbon

Question 17

activation energy

Answer 17

(Qd) the energy required to produce the diffusive motion of one mole of atoms

Question 18

predeposition step

Answer 18

impurity atoms are diffused into the silicon (making of ICs)

Question 19

drive-in diffusion

Answer 19

higher temperature than the predeposition step, forms an oxide layer on the surface

Question 20

junction depth

Answer 20

(xj) represents the depth or value of x at which the diffusing impurity concentration is just equal to the background concentration of that impurity