Material Science Engineering Answers

The % live bacteria due to sterilization follows an exponential relation such as % live = 30 exp (-0.01 T). T is the temperature in oC. What should be the temperature to achieve just less than 5% live bacteria?

The percentage of microorganisms remaining vs. exposure time to autoclave sterilization process follows % = 70-t*2. The percentage of microorganisms remaining vs. exposure time to dry heat sterilization process follows % = 80-t*5. At what time both the methods are equally efficient?

If the densities are 7.9 and 4.0 gm/cc, what is the average density?

15 mm dia SS (Young’s modulus = 200 Gpa) rod is coated with HA (Young’s modulus = 300 Gpa). What should be the coating thickness (in mm) so that the Young’s modulus of the composite is 209 Gpa (use mixture rule)?

the following data were recorded during the tensile test of a 14-mm diameter mild steel rod. the gauge length was 50-mm, at fracture the elongation between the gauge was 4-mm and the minimum diameter was 11.3-mm. plot a convectional stress strain curve for mild steel

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.