ME311
MATERIALS ENGINEERING
SPRING 2012
HOMEWORK #5
DUE DATE: March 8, before class
PROBLEM 1:
You are given the task of purchasing a Microscope with the highest resolution possible.
Among the instruments shown in the Table below, which microscope would you select?
What is the best resolution for each radiation used? Assume the numerical aperture of the
lens, NA=1.
Microscope
Radiation Used
A
Xrays
B
Ultraviolet
C
Green Light
D
Electrons
E
Red Light
PROBLEM 2:
The diffusivity of lithium in silicon is 10
5
cm
2
/sec at 1376 K and 10
6
cm
2
/sec at 968 K.
What are the values for the enthalpy and the preexponential term for diffusion of lithium
in silicon?
Hint:
Using the expression that relates the Diffusion coefficient with temperature, first
remove the exponential terms to obtain an equation of a straight line. Subsequently, use a
graphical form to answer the above questions.
PROBLEM 3:
Consider a diffusion couple setup between pure tungsten and a tungsten alloy containing
1 at% thorium. After several minutes of exposure at 2000 C, a transition zone of 0.01 cm
thickness is established. What is the flux of thorium atoms at this time if the pre
exponential term (D
o
) has a value of 1 cm
2
/s and the activation enthalpy for diffusion has
a value of 120,000 cal/mole?
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview.
Sign up
to
access the rest of the document.
 Spring '08
 MEYERS
 Orders of magnitude, exponential terms

Click to edit the document details