HW4 DiffusionI Solutions

HW4 DiffusionI Solutions - HW4 Diffusion I 1. The following...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
HW4 Diffusion I 1. The following figure shows the self-diffusion coefficient as a function of reciprocal temperature for two hypothetical metals, A and B. a) Which metal has a larger activation energy for diffusion? metal A or metal B. Prove your assertion using an equation. Metal B has a larger activation energy for diffusion, because it has a steeper slope. Look at the relation in y- mx + b form, with “x” being 1/T (reciprocal temperature.) The slope, m, is equal to –Q/R. The slope is negative, so Q is positive (as it should be. A negative activation energy barrier makes no sense.) b) Calculate the activation energy for self-diffusion for metal B, using values from the graph. Be sure that you interpolate numbers properly on the logarithmic scale. To find the activation energy, we need the slope. You can calculate the slope by selecting two points on the line of interest. I have circled the points I selected with green and purple circles. = T R Q D D o 1 ln ln mR Q R Q m = =
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
HW4 Diffusion I Let the green point be point 1, and the purple point be point 2. Point 1: To find the x-coordinate of point 1, use a ruler: From 0.80 to the x-coordinate is 0.67 cm. From 0.80 to 0.90 is 3.16 cm. Therefore, the point’s x-coordinate is: The y-coordinate was conveniently chosen to be -13.00 Point 2: The x-coordinate is 0.44 cm to the left of 1.10 on the x-axis. This corresponds to an x-coordinate of: The y-coordinate was chosen to be something easy to read: -15.5 point 1 x1 = 0.82 y1 = -13.00 point 2 x2 = 1.09 y2 =-15.50 Our equation requires a natural log on the y-axis. We have a base 10 log. You can do the conversion with different methods. Since it is hard to remember all the logarithm rules, I’ll just convert to a regular number
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 11/28/2010 for the course MTE 209 taught by Professor Tanyafalten during the Fall '09 term at Cal Poly Pomona.

Page1 / 5

HW4 DiffusionI Solutions - HW4 Diffusion I 1. The following...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online