Jawaharlal Nehru Technological University Hyderabad
Jawaharlal Nehru Technological University Hyderabad B.Tech II METALLURGY AND MATERIALS SCIENCE Previous Question Paper (October - 2020 - R15)
Answer any five questions. All questions carry equal marks.
Main
Describe lattice parameters for seven crystal systems with examples for each.
Answer
The seven crystal systems are defined by their lattice parameters, which consist of three edge lengths (a, b, c) and three interaxial angles (α, β, γ). The systems are:
- Cubic: a=b=c, α=β=γ=90°. Example: Copper (Cu), Iron (Fe).
- Tetragonal: a=b≠c, α=β=γ=90°. Example: Tin (Sn).
- Orthorhombic: a≠b≠c, α=β=γ=90°. Example: Orthorhombic Sulfur.
- Rhombohedral (Trigonal): a=b=c, α=β=γ≠90°. Example: Arsenic (As).
- Hexagonal: a=b≠c, α=β=90°, γ=120°. Example: Magnesium (Mg).
- Monoclinic: a≠b≠c, α=γ=90°≠β. Example: Monoclinic Sulfur.
- Triclinic: a≠b≠c, α≠β≠γ≠90°. Example: Potassium dichromate (K2Cr2O7).
Copper has an atomic radius of 0.128 nm, and an atomic weight of 63.5 g/mol. Compute its theoretical density.
Answer
Copper has an FCC crystal structure, which has an atomic packing factor of 4 atoms per unit cell. The theoretical density (ρ) is calculated using the formula:
Where n=4 (atoms per unit cell), A=63.5 g/mol, and N_A=6.022 × 10^23 atoms/mol. For FCC, the relationship between edge length (a) and atomic radius (R) is a = 2R√2.
- Calculate edge length: a = 2 × 0.128 nm × √2 = 0.3619 nm = 3.619 × 10^-8 cm.
- Calculate unit cell volume: V_c = a^3 = (3.619 × 10^-8 cm)^3 = 4.74 × 10^-23 cm^3.
- Calculate density: ρ = (4 atoms × 63.5 g/mol) / (4.74 × 10^-23 cm^3 × 6.022 × 10^23 atoms/mol).
- ρ = 254 / 28.54 = 8.89 g/cm^3.
The theoretical density of copper is 8.89 g/cm^3.
Discuss different methods of determining the grain size.
Answer
Sign in to view the complete answer paper.
Discuss various methods of constructing the binary phase diagrams and explain the advantages and disadvantages of each method.
Answer
Sign in to view the complete answer paper.
Draw TTT diagram for 0.4%C steel and explain the phase transformations that occur on cooling from austenite to room temperature under different cooling rates.
Answer
Sign in to view the complete answer paper.
Distinguish between the following:
a) Annealing and normalizing
b) Austenite, Pearlite and Martensite.
Answer
Sign in to view the complete answer paper.
Distinguish between α, β and α+β titanium alloys with respect to composition, microstructure, properties and applications.
Answer
Sign in to view the complete answer paper.
Differentiate between the following:
a) Soda lime glass and fused silica
b) Vycor and Pyrex glasses.
Answer
Sign in to view the complete answer paper.
What are clay – based ceramics? How are they made? Explain their limitations.
Answer
Sign in to view the complete answer paper.