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# MSE Ch 5

### Atomic and Ionic movements in materials.

TermDefinition
In diffusion, the magnitude of flux depends on ___ and ___. the initial concentration, temperature
Diffusing C into Fe from the surface is called ___ or ___. carburizing, case hardening
Case hardening with nitrogen is called ___. nitriding
Name the 2 ways diffusion occurs. through interstitial sites or through defects
Is diffusion more difficult through defects or interstitial spaces? interstitial spaces
When diffusion occurs at a grain boundary it can cause the boundary to ___. move
Diffusion through crystals is usually through defects because ___. atoms are usually too large to fit in interstitial sites
T or F? Vacancies are always moving. True
Name the 3 types of diffusion. 1. volume, 2. grain boundary, 3. surface.
Name the 3 subtypes of volume diffusion. 1. interstitial, 2. vacancy, 3. dislocations.
Increasing the number of grains ___(increases/decreases) the grain boundary area and thus ___(increases/decreases) the rate of diffusion. increases, increases
Of the 3 types of diffusion, ___ difffusion is the most easily achieved. surface
The energy required to begin diffusion is called ___ and is noted with ___. activation energy, Q
___ diffusion requires the most energy and ___ requires the least. volume, surface
The Arrhenius equation for jump rate of atoms is ___. Jump rate = c_0*e^(-Q/RT)
In c_0*e^(-Q/RT), c_0 = ___. a constant for the material
Q is in ___ per ___. cal, mol
The Arrhenius equation for diffusivity is ___. D = D_0*e^(-Q/RT)
In D = D_0*e^(-Q/RT), D_0 = ___. a constant for the material
Fick's first law is for ___ diffusion and describes the ___ of atoms. steady state, flux
Fick's first law is defined by the equation ___. J = -D(∆c/∆x)
In J = -D(∆c/∆x), J = ___. flux of atoms
In J = -D(∆c/∆x), (∆c/∆x) = ___ and is in ___ units. the concentration gradient, (atoms/cm³∙cm)
In J = -D(∆c/∆x), ∆c = ___. It will always be a ___ (-,+) number. starting concentration minus ending concentration, (-)
In J = -D(∆c/∆x), ∆x = ___. the distance or depth of the desired concentration
Steady state diffusion is ___(common/rare) in solids. rare
All else being equal, D is higher in ___(FCC/BCC) structures because ___. BCC, there is more space
As the temperature of Fe is INCREASED it changes phase from ___ Fe to ___ Fe at about ___°C or ___°K. BCC, FCC, 912, 1185
Fick's second law describes ___, AKA ___. transient diffusion, non-steady state
Diffusion in solids is almost always ___. transient
One solution to Fick's second law when at the surface of a material is the equation ___. (c_s - c_x)/(c_s - c_0) = erf[x/s√(Dt)]
In (c_s - c_x)/(c_s - c_0) = erf[x/2√(Dt)], c_s = ___. the constant concentration of diffusing atoms at the surface
In (c_s - c_x)/(c_s - c_0) = erf[x/2√(Dt)], c_x = ___. the concentration of diffusing atoms at point x below the surface
In (c_s - c_x)/(c_s - c_0) = erf[x/2√(Dt)], c_0 = ___. the starting concentration of diffusing atoms IN THE MATERIAL BEFORE diffusion occurs
In (c_s - c_x)/(c_s - c_0) = erf[x/2√(Dt)], D = ___. diffusivity
In (c_s - c_x)/(c_s - c_0) = erf[x/2√(Dt)], t = ___. seconds
In (c_s - c_x)/(c_s - c_0) = erf[x/2√(Dt)], x/2√(Dt) = ___. the argument of the error function
erf can approach, but not reach or exceed ___. 1
Using an error function table, to find a value between the given values we must use a process called ___. linear interpolation
T or F? Using an error function table, the left column is equal to x. False. It is equal to x/2√(Dt).
erf is equal to the ratio of ___ divided by ___. (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)
What are the units for erf? None.
What are the units for the argument of the erf? None.
Created by: drjolley

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