Material Science Engineering Answers

A steel shaft ABCD having a total length of 1.5 m is made of three lengths AB , BC and CD each 0.5 m long. AB and BC are solid shaft having diameter 50 and 75 mm respectively , CD is hollow with outside and inside diameters 75 and 50 mm respectively . when an axial torque of 5 kNm is transmitted from one end of the shaft to the other , the total angle of twist is 1.2° , Determine the maximum shear stress and modulus of rigidity of the material.

13. What is the purpose of the epi layer on the silicom？(   )

 a. The epi layer is used to form the gate of the transistor.

b. The epi layer provides a low defect crystal structure.

c. The epi layer has already been doped with n-type dopant to serve as the n-well.

d. The epi layer provides isolation between metal layers.

A.        What is meant by the term: atomic structure?

B.       State Pauli's Exclusion principle

C.          Write the electronic configuration for the following:

         Neon [Ne - 10]

Argon [Ar - 18]

D.  Sodium chloride (NaCl) exhibits predominantly ionic bonding. The [Na - 11]+ and [Cl — 17]- ions have electron structures that are identical to which two inert gases?

E. Clearly show that the atomic packing factor of face-centred cubic structure is 0.74.

Calculate the radius of a barium atom, given that Ba has a BCC crystal structure, a density of 3.6.g/cm³ and an atomic weight of 137 g/mol.

List the THREE (3) classification ofthe imperfections and THREE (3) defects in solids.

D.                Which properties of material would you need to consider if you required materials which were:

Capable of being bent into a fixed shape, iii. Capable Of not fracturing when small cracks are present, iv. Not easily broken

v. Act as electrical insulator vi. A good conductor of heat vii. Capable of being used as the lining for a tank storing acid.

E.                 List the TWO (2) applications of the following materials:

i. Plain Carbon steel 0.3 % Carbon ii. Medium Carbon Steel 0.7 Carbon iii. High Carbon Steel 0.9 — 1.5% Carbon iv. Stainless steel Cast Iron vi. Wrought iron

B.                 What is heat treatment?

C.                 Define and explain the processes of the following heat treatment process.

i.       Hardening ii. Tempering iii. Case hardening iv. Age hardening

D.                List the mechanical properties of the following materials and give TWO (2) engineering applications for each.

i.       Glass

Wood iii. Metal

Polymers

E.                 What is heat treatment and list TI--IREE (3) quenching media.

Ouestion 5

A.                Describe THREE (3) applications where tensile strength is primarily factor in material selection. What material would you select for what application and state why?

B.                 Copper has the atomic radius of Oa 128 nm, an FCC crystal structure and an atomic weight of 63.5 g/mol. Calculate the following:

i.       Cell edge length ii.      Vc - Unit cell volume iii.   Vs — Sphere volume iv.          Density,

v.       APF - Atomic Pack Factor via    Write the Avagador's Number

c.         Briefly explain what the factors that caused imperfection in solids are.

A. Make a sketch of the unit cell in a point model form of the following and writer the occupancy numbers and the Coordination numbers:

i. BCC — Body Centred Cubic ii. FCC - Face Centred Cubic iii. HCP - Hexagonal Close Pack