EMS 164- Homework 3 Solutions
1.
In a graphical representation show that diffusion occurs down the chemical potential
gradient in a diffusion couple made of two solid solutions with compositions within a
miscibility gap (class problem).
(Not graded)
Figure 2.1 in text book
2. In two clear schematics, show the octahedral and tetrahedral positions of interstitial
atoms in an fcc structure.
(10 points)
Octahedral sites in a fcc crystal
Total number of octahedrals: 12* ¼ +1= 4
octahedral sites in one fcc cubic structure.
(2 points for drawing fcc, 2 points for the octahedral
shape, 1 point for all the octahedral sites.)
Tetrahedral sites in a fcc crystal
Total number of tetrahedrals: 8*1= 8 tetrahedral sites
in one fcc cubic structure.
(2 points for drawing fcc, 2 points for the
tetrahedral shape, 1 point for all the tetrahedral sites.)
3. At a particular temperature, the diffusion coefficient for Pb in naturally occurring
ZrSiO
4
is
D
=
8.3
×
10
-
28
cm
2
s
. Find the value of the concentration gradient where the
flux of lead,
J
, is equal
J
=
5.0
×
10
-
30
g
cm
2
⋅
s
.
(10 points)
Ficks’ first law: J
B
= -D
B
* ∂C
B
⁄∂x (
2 points for equation)
Where D
B
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- Spring '10
- J.Groza
- Chemistry, Chemical bond, Cubic crystal system
-
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