Chapter 5 (Diffusion)

Question 1

what are rates governed by

Answer 1

activation energies

Question 2

define the activation energy

Answer 2

the extra energy required to overcome the energy barrier to allow for movement of atoms

Question 3

what is inter-diffusion

Answer 3

migration of atoms from [high] to [low]

Question 4

what is self diffusion

Answer 4

migration of atoms within a single elemental solid

Question 5

what is substitutional diffusion

Answer 5

solute atoms exchange places with solvent atoms using vacancies

Question 6

interstitial diffusion

Answer 6

when smaller atoms diffuse between the larger ones in spaces called the interstices

Question 7

name 2 processes which use diffusion

Answer 7

1. case hardening

2. doping

Question 8

what is steady state diffusion

Answer 8

when the concentration doesn’t change with time

Question 9

what is non-steady state diffusion

Answer 9

when the concentration changes with both time and distance

Question 10

what type of energy supplies activation energy?

Answer 10

heat energy

Question 11

which is more rapid and why, insterstitial or vacancy diffusion?

Answer 11

interstitial diffusion because no vacancies are required so they can move readily, the atoms are generally smaller so they are more mobile

Question 12

with an increase in temperature, what will happen to the diffusion coefficient

Answer 12

it will increase exponentially