ConceptCheck5 - increases with increasing temperature...

Info icon This preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
120 Concept Check 5.1 Question: Rank the magnitudes of the diffusion coefficients from greatest to least for the following systems: N in Fe at 700 ° C Cr in Fe at 700 ° C N in Fe at 900 ° C Cr in Fe at 900 ° C Now justify this ranking. ( Note: Both Fe and Cr have the BCC crystal structure, and the atomic radii for Fe, Cr, and N are 0.124, 0.125, and 0.065 nm, respectively. You may also want to refer to Section 4.3 .) Answer: The diffusion coefficient magnitude ranking is as follows: N in Fe at 900 ° C; D N (900) N in Fe at 700 ° C; D N (700) Cr in Fe at 900 ° C; D Cr (900) Cr in Fe at 700 ° C; D Cr (700) Nitrogen is an interstitial impurity in Fe (on the basis of its atomic radius), whereas Cr is a substitutional impurity. Since interstitial diffusion occurs more rapidly than substitutional impurity diffusion, D N > D Cr . Also, inasmuch as the magnitude of the diffusion coefficient
Image of page 1

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

View Full Document Right Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: increases with increasing temperature, D (900) > D (700). Concept Check 5.2 Question: Consider the self-diffusion of two hypothetical metals A and B. On a schematic graph of ln D versus 1/T, plot (and label) lines for both metals given that D (A) > D (B) and also that Q d (A) > Q d (B). Answer: The schematic ln D versus 1/ T plot with lines for metals A and B is shown below. As explained in the previous section, the intercept with the vertical axis is equal to ln D . As shown in this plot, the intercept for metal A is greater than for metal B inasmuch as D (A) > D (B) [alternatively ln D (A) > ln D (B)]. In addition, the slope of the line is equal to – Q d /R . The two lines in the plot have been constructed such that negative slope for metal A is greater than for metal B, inasmuch as Q d (A) > Q d (B)...
View Full Document

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern