Ch5

Question 1

Diffusion

Answer 1

Mass/material transport by atomic motion

Question 2

Mechanisms of diffusion of gases/liquids

Answer 2

random (Brownian) motion

Question 3

Mechanisms of diffusion of solids

Answer 3

vacancy diffusion or interstitial diffusion

Question 4

Case Hardening

Answer 4

Diffuse carbon atoms into the host
iron atoms at the surface

Question 5

Result of Case Hardening?

Answer 5

The presence of C
atoms makes iron (steel) harder

Question 6

Self-diffusion

Answer 6

In an elemental solid, atoms migrating from one position to the other

Question 7

Interdiffusion

Answer 7

In an alloy, atoms tend to migrate from regions of high concentration to regions of low concentration

Question 8

What are the two types of diffusion mechanisms?

Answer 8

1. Vacancy
2. Interstitial

Question 9

What is the driving force behind diffusion?

Answer 9

Concentration gradient
Thermal energy

Question 10

Flick’s 1st Law

Answer 10

1. Rate of diffusion independent of time
2. Flux proportional to concentration gradient

Question 11

Flick’s 2nd Law

Answer 11

1. The concentration of diffusing species is a function of both time
   and position C = C(x,t)
2. Define boundary conditions

Question 12

Flick’s 1st Law deals with

Answer 12

steady-state diffusion

Question 13

Flick’s 2nd Law deals with

Answer 13

non-steady-state diffusion

Question 14

Expanding D formula. What is D?

Answer 14

diffusion coefficient [m^2/s]

Question 15

Expanding D formula. What is D_o?

Answer 15

pre-exponential [m/s^2]

Question 16

Expanding D formula. What is Q_d?

Answer 16

activation energy [J/mol or eV/atom]

Question 17

Expanding D formula. What is R?

Answer 17

gas constant [J/mol-K]

Question 18

Expanding D formula. What is T?

Answer 18

absolute temperature [K]