Question 1

In diffusion, the magnitude of flux depends on ___ and ___.

Accepted Answer

the initial concentration, temperature

Question 2

Diffusing C into Fe from the surface is called ___ or ___.

Accepted Answer

carburizing, case hardening

Question 3

Case hardening with nitrogen is called ___.

Accepted Answer

nitriding

Question 4

Name the 2 ways diffusion occurs.

Accepted Answer

through interstitial sites or through defects

Question 5

Is diffusion more difficult through defects or interstitial spaces?

Accepted Answer

interstitial spaces

Question 6

When diffusion occurs at a grain boundary it can cause the boundary to ___.

Accepted Answer

move

Question 7

Diffusion through crystals is usually through defects because ___.

Accepted Answer

atoms are usually too large to fit in interstitial sites

Question 8

T or F? Vacancies are always moving.

Accepted Answer

True

Question 9

Name the 3 types of diffusion.

Accepted Answer

1. volume, 2. grain boundary, 3. surface.

Question 10

Name the 3 subtypes of volume diffusion.

Accepted Answer

1. interstitial, 2. vacancy, 3. dislocations.

Question 11

Increasing the number of grains ___(increases/decreases) the grain boundary area and thus ___(increases/decreases) the rate of diffusion.

Accepted Answer

increases, increases

Question 12

Of the 3 types of diffusion, ___ difffusion is the most easily achieved.

Accepted Answer

surface

Question 13

The energy required to begin diffusion is called ___ and is noted with ___.

Accepted Answer

activation energy, Q

Question 14

___ diffusion requires the most energy and ___ requires the least.

Accepted Answer

volume, surface

Question 15

The Arrhenius equation for jump rate of atoms is ___.

Accepted Answer

Jump rate = c_0*e^(-Q/RT)

Question 16

In c_0*e^(-Q/RT), c_0 = ___.

Accepted Answer

a constant for the material

Question 17

Q is in ___ per ___.

Accepted Answer

cal, mol

Question 18

The Arrhenius equation for diffusivity is ___.

Accepted Answer

D = D_0*e^(-Q/RT)

Question 19

In D = D_0*e^(-Q/RT), D_0 = ___.

Accepted Answer

a constant for the material

Question 20

Fick's first law is for ___ diffusion and describes the ___ of atoms.

Accepted Answer

steady state, flux

Question 21

Fick's first law is defined by the equation ___.

Accepted Answer

J = -D(∆c/∆x)

Question 22

In J = -D(∆c/∆x), J = ___.

Accepted Answer

flux of atoms

Question 23

In J = -D(∆c/∆x), (∆c/∆x) = ___ and is in ___ units.

Accepted Answer

the concentration gradient, (atoms/cm³∙cm)

Question 24

In J = -D(∆c/∆x), ∆c = ___. It will always be a ___ (-,+) number.

Accepted Answer

starting concentration minus ending concentration, (-)

Question 25

In J = -D(∆c/∆x), ∆x = ___.

Accepted Answer

the distance or depth of the desired concentration

Question 26

Steady state diffusion is ___(common/rare) in solids.

Accepted Answer

rare

Question 27

All else being equal, D is higher in ___(FCC/BCC) structures because ___.

Accepted Answer

BCC, there is more space

Question 28

As the temperature of Fe is INCREASED it changes phase from ___ Fe to ___ Fe at about  ___°C or ___°K.

Accepted Answer

BCC, FCC, 912, 1185

Question 29

Fick's second law describes ___, AKA ___.

Accepted Answer

transient diffusion, non-steady state

Question 30

Diffusion in solids is almost always ___.

Accepted Answer

transient

Question 31

One solution to Fick's second law when at the surface of a material is the equation ___.

Accepted Answer

(c_s - c_x)/(c_s - c_0) = erf[x/s√(Dt)]

Question 32

In (c_s - c_x)/(c_s - c_0) = erf[x/2√(Dt)], c_s = ___.

Accepted Answer

the constant concentration of diffusing atoms at the surface

Question 33

In (c_s - c_x)/(c_s - c_0) = erf[x/2√(Dt)], c_x = ___.

Accepted Answer

the concentration of diffusing atoms at point x below the surface

Question 34

In (c_s - c_x)/(c_s - c_0) = erf[x/2√(Dt)], c_0 = ___.

Accepted Answer

the starting concentration of diffusing atoms IN THE MATERIAL BEFORE diffusion occurs

Question 35

In (c_s - c_x)/(c_s - c_0) = erf[x/2√(Dt)], D = ___.

Accepted Answer

diffusivity

Question 36

In (c_s - c_x)/(c_s - c_0) = erf[x/2√(Dt)], t = ___.

Accepted Answer

seconds

Question 37

In (c_s - c_x)/(c_s - c_0) = erf[x/2√(Dt)], x/2√(Dt) = ___.

Accepted Answer

the argument of the error function

Question 38

erf can approach, but not reach or exceed ___.

Accepted Answer

1

Question 39

Using an error function table, to find a value between the given values we must use a process called ___.

Accepted Answer

linear interpolation

Question 40

T or F? Using an error function table, the left column is equal to x.

Accepted Answer

False. It is equal to x/2√(Dt).

Question 41

erf is equal to the ratio of ___ divided by ___.

Accepted Answer

(starting surface concentration of diffusing atoms) - (concentration at location x AFTER diffusion occurs), (starting surface concentration of diffusing atoms) - (concentration of diffusing atoms already at location x BEFORE diffusion)

Question 42

What are the units for erf?

Accepted Answer

None.

Question 43

What are the units for the argument of the erf?

Accepted Answer

None.

MSE Ch 5

Atomic and Ionic movements in materials.

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