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IGNOU MPHE-25 (July 2024 – June 2025) Assignment Questions
PART A
1. a) Explain with diagram, how many identical points are created by a 3 roto-inversion operation. Among 3-fold rotation and 3 roto-inversion operation, which one has higher order? Why?
b) What are glassy alloys? Discuss their mechanical properties vis-à-vis normal metal alloys and ceramic oxide materials. State any four technological applications of glassy alloys.
c) What are solid solutions? Explain the rules (Hume-Rothery) governing the formation of substitutional solid solutions.
2. a) Explain with diagram the float zone method of crystal growth. State its advantages over the Czochralski method.
b) Calculate the mass of phosphorus required to make a silicon crystal with 1017 cm−3 doping density, if the initial melt load of silicon is 50 kg. The density of silicon in the melt is 2.5 g cm−3 and phosphorus has an atomic weight of 30.97u. Assume that the segregation coefficient k0=0.35 is constant throughout the growth process.
c) Describe the importance and cost advantages of powder metallurgy in materials processing.
d) What is epitaxial growth? What are the advantages of MBE growth technique? State its applications.
3. a) Explain with appropriate diagrams various point defects observed in solid crystals.
b) Calculate the equilibrium concentration of vacancies in a copper crystal at 1000 K. Given that melting point of copper is 1083C and enthalpy of vacancy formation in copper is 120 kJ per mole.
c) What is dislocation defect? Discuss its role in the crystal growth.
PART B
4. a) Based on the diffusion mechanisms involved explain why carbon atom diffusion is faster than nickel atom diffusion in iron lattice.
b) What are eutectic phase diagrams? With the help of a schematic diagram for a binary system explain the significance of eutectic point and liquidus, solidus & solvus curves.
c) Explain the Avrami and Johnson-Mehl models of computing phase transformation rates based on their assumptions and growth mechanisms.
5. a) Draw a typical stress-strain curve of a material. Define various mechanical strengths and indicate corresponding deformation regions on this plot.
b) What is meant by “thermal shock” experienced by the materials? How can it be reduced? State the expression for thermal shock resistance (TRS) explaining all the terms involved.
c) Define corrosion in case of materials. Discuss the five major factors affecting / promoting corrosion process.
6. a) Explain the phenomena of Colossal Magnetoresistance (CMR) and Giant Magnetoresistance (GMR). Give examples of materials where these effects are observed.
b) What are shape memory materials? Explain the phase transition hysteresis observed in NiTi alloy giving rise to shape memory phenomenon. Discuss any two applications of shape memory materials.
c) What is graphene? Describe the bonding in graphene. Explain the band structure of graphene on E-k diagram.
d) What is organic electronics? Explain the working of an organic diode.
