Ch05 Notes
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Transcript of Ch05 Notes
9/10/2015
1
Diffusion (Chapter 5)
Substitutional Diffusion
Activation Energy ofSelf diffusion
ActivationEnergy toform aVacancy
ActivationEnergy tomove a vacancy
= +
Figure 4.35
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2
1/T
K
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Interstitial Diffusion mechanism
Interstitial atoms
Matrixatoms Figure 4.37
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4
Fick’s 1st Law
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5
Carburizing
C %
Figure 4.43 bCarbon Gradients In Carburized metals
(After “Metals handbook,” vol.2: “Heat Treating,” 8th ed, American Society of Metals, 1964, p.100)
dx
dcD
dx
d
dt
dC xx
Plane 1 Plane 2
Change of concentration of solute Atoms with change in time in different planes
Fick’s 2nd Law
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1
‐1
erf(z) z
0 0
0.1 0.08
0.2 0.17
0.3 0.26
0.4 0.37
0.5 0.47
0.6 0.58
0.7 0.72
0.8 0.90
0.9 1.16
1.0 infinity
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erf(z) z
0 0
0.1 0.08
0.2 0.17
0.3 0.26
0.4 0.37
0.5 0.47
0.6 0.58
0.7 0.72
0.8 0.90
0.9 1.16
1.0 infinity
The chemical O‐ethyl S‐[2‐(diisopropylamino)ethyl] methylphosphonothioate(C11H26NO2PS known as VX) has a molar mass of 267.37 g/mol and a diffusivity of 5.1 x 10‐12 m2 /s through low‐density polyethylene (LDPE). You happen to be at a chemical spill of VX and decide to cover yourself with a trash bag (made out of LDPE) for protection. You are accidently splashed by 0.0426g of VX, creating a 4cm diameter by 1mm thick spot on the outside of the your ad hoc personal protection suit. If the trash bag is 0.005 cm thick, how long do you have before the concentration on the inside of the bag becomes lethal at 19.04 mol/m3? If you need it, here is the erf table.
Effect of Temperature
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Diffusivity Data for Some Metals
Solute Solvent D0
(M2/S)
Q KJ/m
ol
Carbon FCC Iron 2 x 10-5 142
Carbon BCC Iron 22 x 10-5 122
Copper Aluminum 1.5 x 10-5 126
Copper Copper 2 x 10-5 197
Carbon HCP Titanium
51 x 10-5 182Figure 4.47
(After L.H. Van Vlack. “Elements of Materials Science and Engineering.” 5th ed., Addison-Wesley, 1985. P.137.)