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## #1 2014-05-12 19:55:23

Agnishom
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From: The Complex Plane
Registered: 2011-01-29
Posts: 18,823
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### Material Science Questions

1.a) What is coordination number? Show that the minimum ction to anion rdius rtio for the co-ordination no. 4 is 0.225.

b)Explain the unit cell structure of diamond and calculate its density and packaging efficiency. Lattice parameter for diamond can be taken as 3.57 Amstrong.

2. a) State and deduce Fick's second law of diffussililon.

3. a) For a fibre reinforced composite, derive the expression for critical length of the fibre.

b) Explain the stress-strain curve for a fibre reinforced composite under longitudinal loading.

c) For a fibre reinforced composite material, the modulus ratio is 42 and fibre contributes 32% of the cross-sectional area. What percentage of longitudinal force is taken by the fibre?

4. a) Define an intrinsic semiconductor. Using an energy bond diagram, show how electrons and electron holes are created in pairs in intrinsic silicon. - Explain

b) The electrical resistivity of pure silicon is 2.3 * 10^3 Ohm Metre at room temperature 300 Kelvin. Calculate its electrical conductivity at 200 Degree Celsius. Assume that the Eg of silicon is 1.1 electronVolt; K=8.62*10^-5 electronVolt/Kelvin

c) How does the energy-band model explain the poor electrical conductivity of an insulator such as prue diamond?

5. a) Distinguish between traditional and Engineering Ceramic materials and give examples of each.

b) C[sub]d[/sub]S[sub]e[/sub] has the Zinc blende crystal structure. Calculate the density of C[sub]d[/sub]S[sub]e[/sub]
Ionic Radii are C[sup]2+[/sup][sub]d[/sub]=0.102 nanometer and S[sup]-2[/sup][sub]e[/sub]=0.191 nanometer. Atomic weight of C[sub]d[/sub] and S[sub]e[/sub] are 112.40 and 78.96 g/mol

c) Define the glass transition temperature. Name two glass forming oxides.

6. a) Differentiate between addition and condensation polymerisation.

c) Write the structural formulas and uses for the mers of the following:
i) PS ii) PE iii) PVC

7. b) Describe n-type extrinsic silicon semiconductor.

c) Explain why the electrical conductivity of intrinsic silicon and germanium increases with increasing temperature.

8. Write short notes on:
i) Vander Waal's Bond
ii) Dispersion strengthened Composite
iii) Diffusion Flux
iv) Piezoelectricity
v) Rectifier Diode
vi) Dielectric Strength
vii) Glass for mining oxides
viii) Polymeric Alloys

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## #2 2014-05-13 07:58:11

ShivamS
Member
Registered: 2011-02-07
Posts: 3,629

### Re: Material Science Questions

1. I was looking for a good diagram online and found this full solution - 12.2 on: http://140.116.81.56/1002aero/am%20ch%2 … 20soln.pdf

2. a) Look at the first two pages of: http://www.eng.utah.edu/~lzang/images/lecture-4.pdf

4. a) An intrinsic semiconductor (some people call it an undoped semiconductor or i-type semiconductor) is a pure semiconductor without any substantial dopant.

b) In an insulator, such as pure diamond, the electrons are tightly bound in covalent or ionic bonds. The energy-band model theorizes that these bound electrons fill a lower valence band which is separated by a large energy gap,

, from an empty outer conduction band. A large potential is thus necessary for an electron to overcome the gap. In the case of pure diamond, approximately 6 to 7
are required to free an electron for conduction.

6. a) Addition polymer is formed when the monomer units are repeatedly added to form long chains and no elimination of any by-product takes place. For example, Polythene.

Condensation polymer is formed when two or more monomer units react together and elimination of simple compounds such as

, ROH takes place. For example, Nylon (6, 6) is a condensation polymer obtained from hexamethylene diamine and adipic acid.

c)

Last edited by ShivamS (2014-05-13 08:25:25)

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## #3 2014-05-13 10:33:05

Agnishom
Real Member
From: The Complex Plane
Registered: 2011-01-29
Posts: 18,823
Website

### Re: Material Science Questions

Polysaccharides and protiens are condensation polymers too. The formation of the glycosidic linkages and the polypeptide chains involve the loss of water.

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
'You have made another human being happy. There is no greater accomplishment.' -bobbym

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