JNTU
JNTU B.Tech II METALLURGY AND MATERIAL SCIENCE Previous Question Paper (October - 2020 - R16)
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).
- Tetragonal: a = b ≠ c; α = β = γ = 90°. Example: White 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.
Copper has an atomic radius of 0.128 nm, and an atomic weight of 63.5 g/mol. Compute its theoretical density.
Answer
To calculate the theoretical density (ρ) of copper, we use the formula:
Where:
- n = 4 atoms/unit cell (Copper has an FCC structure).
- A = 63.5 g/mol (Atomic weight).
- V_c = Volume of the unit cell = (4R / √2)³, where R = 0.128 nm = 1.28 × 10⁻⁸ cm.
- N_A = 6.022 × 10²³ atoms/mol (Avogadro's number).
First, calculate V_c:
Now, calculate density:
Discuss different methods of determining the grain size.
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Discuss various methods of constructing the binary phase diagrams and explain the advantages and disadvantages of each method.
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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.
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Distinguish between the following:
Annealing and normalizing
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Austenite, Pearlite and Martensite.
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Distinguish between α, β and α+β titanium alloys with respect to composition, microstructure, properties and applications.
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Differentiate between the following:
Soda lime glass and fused silica
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Vycor and Pyrex glasses.
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What are clay – based ceramics? How are they made? Explain their limitations.
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