EIT Materials Science 1 — Questions and Answers
Question 1: What is the coordination number for an atom in a face-centered cubic (FCC) crystal structure?
- 6
- 8
- 12 (Correct answer)
- 14
Correct answer: 12
In an FCC structure, each atom is surrounded by 12 nearest neighbors, giving a coordination number of 12.
Question 2: Which of the following crystal structures has the highest atomic packing factor (APF)?
- Simple cubic (SC)
- Body-centered cubic (BCC)
- Face-centered cubic (FCC) (Correct answer)
- Diamond cubic
Correct answer: Face-centered cubic (FCC)
FCC has an APF of 0.74, which is the highest among the listed structures (BCC = 0.68, SC = 0.52, diamond = 0.34).
Question 3: At what temperature does the eutectoid reaction occur in the iron-carbon phase diagram?
- 727°C (Correct answer)
- 912°C
- 1148°C
- 1394°C
Correct answer: 727°C
The eutectoid reaction (austenite → ferrite + cementite) occurs at 727°C and 0.76 wt% C, producing pearlite.
Question 4: What is the eutectoid composition in the iron-carbon phase diagram?
- 0.022 wt% C
- 0.76 wt% C (Correct answer)
- 2.14 wt% C
- 4.30 wt% C
Correct answer: 0.76 wt% C
The eutectoid point occurs at 0.76 wt% C, where austenite transforms directly to pearlite (ferrite + cementite) at 727°C.
Question 5: What type of point defect involves a missing atom at a lattice site?
- Interstitial
- Vacancy (Correct answer)
- Substitutional impurity
- Edge dislocation
Correct answer: Vacancy
A vacancy is a point defect where an atom is absent from its regular lattice position.
Question 6: Fick's First Law of diffusion states that flux J equals:
- -D(dC/dx) (Correct answer)
- D(dC/dt)
- D(d²C/dx²)
- C/D
Correct answer: -D(dC/dx)
Fick's First Law is J = -D(dC/dx), where flux is proportional to the negative concentration gradient and the diffusion coefficient D.
Question 7: The primary distinction between steel and cast iron in the Fe-C phase diagram is:
- Steel contains less than 2.14 wt% C; cast iron contains 2.14–6.70 wt% C (Correct answer)
- Steel contains less than 0.76 wt% C; cast iron contains more than 0.76 wt% C
- Steel contains less than 1.0 wt% C; cast iron contains 1.0–4.3 wt% C
- Steel contains less than 4.3 wt% C; cast iron contains more than 4.3 wt% C
Correct answer: Steel contains less than 2.14 wt% C; cast iron contains 2.14–6.70 wt% C
The eutectic point at 2.14 wt% C divides the Fe-C system: alloys below 2.14 wt% C are steels, and those above are cast irons.
EIT Materials Science 1
What is the coordination number for an atom in a face-centered cubic (FCC) crystal structure?