1. C diffuses interstially in Fe whereas Cr would mainly diffuse in Fe through v
ID: 702861 • Letter: 1
Question
1. C diffuses interstially in Fe whereas Cr would mainly diffuse in Fe through vacancy diffusion. Therefore, the activation energy for C diffusion in Fe is _________________ than that of Cr in Fe at a given temperature.
a. Higher
b. Lower
c. Same
2. If you want to diffuse C into Fe to a thickness of 0.1 mm at 1027 C, how long would have to run you diffusion process at that temperature? (give answer in seconds)
3. A bar which contains a uniform concentration of 5 atomic percent Cr has its surface coated with pure Cr. When the bar is exposed to high temperature, at a point within the original bar but near the surface, the concentration of the Cr will generally ______________ with time.
a. Higher
b. Lower
c. Same
Explanation / Answer
Ans 1 : b) lower
The interstitial diffusion is faster and hence more efficient than the vacancy diffusion. It is because , in the interstitial diffusion , the binding of interstitials with the surrounding atoms of the substance is weaker and then there are always less vacancy sites as compared to interstitial sites , so the activation energy of C diffusion tends to be lower than Cr.
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