Chapter 5: Diffusion

Question 1

Mass transport by atomic motion

Answer 1

Diffusion

Question 2

Diffusion of atoms of one metal into another metal

Answer 2

Interdiffusion

Question 3

Atomic migration in pure metals

Answer 3

Self-diffusion

Question 4

For vacancy diffusion, an atom must have sufficient——energy to break bonds with neighboring atoms and move to an adjacent vacancy.

-chemical
-vibrational
-electrical

Answer 4

Vibrational

Question 5

The number of atoms capable of diffusion——as the temperature increases.

-increases
-decreases
-remains unchanged

Answer 5

Increases

Question 6

A(n)——atom would diffuse by the interstitial mechanism because the atom is relatively small.

-iron
-copper
-carbon

Answer 6

Carbon

Question 7

The diffusion mechanism in which net atomic migration is from a lattice site to an adjacent vacancy.

Answer 7

Vacancy Diffusion

Question 8

A diffusion mechanism by which atomic motion is from interstitial site to interstitial site.

Answer 8

Interstitial Diffusion

Question 9

The quantity of mass diffusing through and perpendicular to a unit cross-sectional area of material per unit time.

Answer 9

Diffusion Flux (J)

Question 10

The diffusion flux is proportional to the concentration gradient. This relationship is used for steady-state diffusion situations.

Answer 10

Fick’s First Law

Question 11

The constant of proportionality between the diffusion flux and the concentration gradient in Fick’s first law. Its magnitude is indicative of the rate of atomic diffusion.

Answer 11

Diffusion Coefficient (D)

Question 12

The diffusion condition for which there is no net accumulation or depletion of diffusing species. The diffusion flux is independent of time.

Answer 12

Steady-state Diffusion

Question 13

The curve that results when the concentration of a chemical species is plotted versus position in a material

Answer 13

Concentration Profile

Question 14

The slope of the concentration profile at a specific position

Answer 14

Concentration gradient (dC/dx)

Question 15

The impetus behind a reaction, such as diffusion, grain growth, or a phase transformation. Usually attendant to the reaction is a reduction in some type of energy (e.g., free energy).

Answer 15

Driving force

Question 16

The ——indicates the rate at which atoms diffuse

• diffusion flux
• concentration gradient
• diffusion coefficient

Answer 16

Diffusion Coefficient

Question 17

The diffusion coefficient is influenced by——

• the diffusing species
• the host material
• both the diffusing species and the host material

Answer 17

Both the diffusing species and the host material

Question 18

What equation is this?

D=D0 exp (-(Qd)/RT)

Answer 18

Dependence of the diffusion coefficient on temperature
Where:
D0= a temperature-independent pre exponential (m^2/s)
Qd= the activation energy for diffusion (J/mol or eV/atom)
R= the gas constant, 8.31 J/molK or 8.62x10^-5 eV/atomK
T= absolute temperature

Question 19

An increase in temperature results in —— of the value of diffusion coefficient, D, for self-diffusion.

• no change
• a decrease
• an increase

Answer 19

An increase

Question 20

The activation energy for diffusion is represented by —— in the equation for the dependence of diffusion coefficient on temperature.

• D0
• Qd
• R

Answer 20

Qd

Question 21

For diffusion of magnesium (Mg) into aluminum (Al), the temperature-independent preexponential, D0, is equal to——.

• 130,000
• 6.5x10^-5
• 1.2x10^-4

Answer 21

1.2x10^-4

Question 22

The energy required to initiate a reaction, such as diffusion

Answer 22

Activation energy (Q)