For the diffusion data given below, answer the following questions; a.) Which pr
ID: 1429395 • Letter: F
Question
For the diffusion data given below, answer the following questions;
a.) Which process has the higher activation energy: i.) the diffusion of C in BCC Fe or ii.) the diffusion of Fe in BCC Fe. What is the graphical basis of your argument?
b.) From the limited data here would you expect that the grain boundaries in a polycrystal constitute overall a faster or a slower diffusive path? Why?
c.) What is the activation energy for the diffusion of Cu in Cu?
For the diffusion data given below, answer the following questions; Which process has the higher activation energy: the diffusion of C in BCC Fe or ii.) the diffusion of Fe. What is the graphical basis of your argument? From the limited data here would you expect that the grain boundaries in a polycrystal constitute overall a faster or a slower diffusive path? Why? What is the activation energy for the diffusion of Cu in Cu?Explanation / Answer
a) the diffusion of Fe in BCC Fe has higher activation energy .
During a diffusion jump, the interstitial atom moves from one octahedral site to another. Midway between these two sites, it is surrounded by four atoms all at equal distances from the foreign atom. The four atoms form a tetrahedron with the foreign atom at the center. This tetrahedral site has a barrier to the motion of the interstitial atom. The tetrahedral configuration is the activated state for the jump, and the system must acquire an activation energy to overcome the energy barrier.
b) Slower diffusive path . The diffusing atoms jumps from one interstitial to neighboring interstitial site in executing a unit step. The neighbouring site is usually vacant in dilute solutions. The activation energy is simply the energy barrier along the path from one interstitial to next.
A substitutional atom jumps from a regular site into a neighbouring vacant site in executing the unit step. In addition to the probability of an atom crossing the activation barrier along the path, the probability of the neighbouring site being vacant has to be considered.
c) The apparent activation energy for recrystallization during self-annealing of 1.5-µm-thick electroplated copper films was determined using constant-heating-rate scans in a differential scanning calorimeter. The apparent-activation energy was measured to be 0.62 eV/atom