Chapter 5 Diffusion

Question 1

diffusion

Answer 1

mass transport by atomic motion

Question 2

interdiffusion

Answer 2

Question 3

self diffusion

Answer 3

In pure metals self-diffusion occurs where there is no net mass transport, but atoms migrate in a random manner throughout the crystal. In alloys inter-diffusion takes place where the mass transport almost always occurs so as to minimize compositional differences.

Question 4

vacancy diffusion

Answer 4

an atom breaks its bonds and jumps into neighboring vacant site

Question 5

interstitial diffusion

Answer 5

solute atoms which are small enough to occupy interstitial sites diffuse by jumping from one interstitial site to another. The unit step here involves jump of the diffusing atom from one interstitial site to a neighboring site.

Question 6

case hardening

Answer 6

is a technique in which a metal surface is reinforced by the adding of a thin layer of another metal alloy that is more durable, increasing the object’s life.

Question 7

doping

Answer 7

In semiconductor production, doping is the intentional introduction of impurities into an intrinsic semiconductor for the purpose of modulating its electrical, optical and structural properties. The doped material is referred to as an extrinsic semiconductor

Question 8

how do we quantify the rate of diffusion

Answer 8

Question 9

steady-state diffusion

Answer 9

is an unchanging condition, system or physical process that remains the same even after transformation or change

Question 10

Answer 10

Question 11

if temperature increase the diffusion coefficient will _______?

Answer 11

if temperature increase the diffusion coefficient will increase

Question 12

diffusion and temperature equation

Answer 12

Question 13

Fick’s second law

Answer 13

the rate of accumulation (or depletion) of concentration within the volume as proportional to the local curvature of the concentration gradient.

Question 14

nonsteady state diffusion

Answer 14

concentration changes with both time and distance ( rate of change is time-dependent )

Question 15

non steady-state diffusion example 1

Answer 15

Question 16

non-steady state diffusion example 2

Answer 16

Question 17

example determining time to reach a conc level

Answer 17

Question 18

diffusion is faster for

Answer 18

• open crystal structures
• materials w/secondary bonding
• smaller diffusing atoms
• lower density materials

Question 19

diffusion is slower for

Answer 19

• closed packed structures
• materials w/ covalent bonding
• larger diffusing atoms
• higher density materials