Dear students,
This assignment will get you to think about the concepts we learned under the topic of diffusion in solids. For Question 1, select the correct response to each sub questions and EXPLAIN IN A FEW SENTENCES WHY YOU SELECTED THIS ANSWER. For Question 2.1, work out the problem and please be neat. You can turn it in Isidore or you can turn in this sheet along with your answers. I will be great if you could turn it in Isidore!
Question 1:
1. Explain the effect of the following on the rate of diffusion and provide a brief explanation why each of these factors affect the rate of diffusion.
a. Mechanism of diffusion (what are the mechanisms and how do they affect diffusion)
b. Type of diffusion (what are the types and how do they affect diffusion)
c. Bond strength
d. Crystal structure
e. Temperature
2. Diffusion will occur fastest when
a. It occurs by grain boundary diffusion via the interstitial mechanism
b. It occurs by grain boundary diffusion via the vacancy mechanism
c. It occurs by surface diffusion via the interstitial mechanism
d. It occurs by surface diffusion via the vacancy mechanism
3. Diffusion is likely to occur faster in a material that has the following characteristics:
a. HCP crystal structure, ionic bonding at higher temperatures
b. FCC crystal structure, covalent bonding, lower temperatures
c. BCC crystal structure metallic bonding, higher temperatures
d. When it feels like it.
e. Which of the following is true about diffusion?
4. Diffusion is only affected by concentration differences and temperature
a. Interstitial diffusion requires the most activation energy
b. There are over 17 types of diffusion
c. Vacancy diffusion is strongly dependent on temperature
Question 2:
The diffusion coefficient for Cr+3 in Cr2O3 is 6E-15 cm2/s at 727°C and is 1 E -9 cm2/s at 1400°C. Determine the activation energy and the constant Do.
Without referring to actual data, can you predict whether the activation energy for diffusion of carbon in FCC iron will be higher or lower than that in BCC iron? Explain.