Material Science - short answer questions from AMIE exams

Name two important ceramic insulators with their properties.

• Porcelain is the most frequently used material for insulators. Insulators are made of wet, processed porcelain. The fundamental materials used are a mixture of feldspar (35%), china clay (28%), flint (25%), ball clay (10%), and talc (2%).
• Toughened glass is also frequently used for insulators. The melted glass is poured into a mould to form the shell. Dipping into hot and cold baths cools the shells.
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Write the scientific names of the following polymers with one of their typical use: Teflon, ABS.

• Teflon: PTFE (polytetrafluoroethylene)
• ABS: Acrylonitrile - Butadiene - Styrene
• Teflon-PTFE is a Polytetrafluoroethylene used in GoreTex and nonstick cookware, and also as a high-frequency, high-temperature dielectric/insulator for electrical wires and coaxial cables. 
• ABS is an ideal material wherever superlative surface quality, colour fastness and lustre are required. ABS is a two-phase polymer blend. A continuous phase of styrene-acrylonitrile copolymer (SAN) gives the materials rigidity, hardness and heat resistance. The toughness of ABS is the result of sub microscopically fine polybutadiene rubber particles uniformly distributed in the SAN matrix.

State the basic structural units of PMMA and Nylon 6,6 elaborating their properties.

PMMA: Polymethyl methacrylate

where 1 stands for H, 2 stands for H, 3 stands for CH3 and 4 stands for 

Nylon 6/6: The polar C=O groups bond to the next chain through hydrogen bridges. This bonding favours a matching of adjacent molecules and leads to more complete crystallinity, than in polyethene. Within crystals, the molecules are not kinked and coiled.

What is E-Glass? Where it is commonly used?

E-glass is fibre reinforced glasses, designed originally for electrical applications. They are most commonly calcium alumino borosilicate glasses that contain no Na+ ions.

What is Alnico?

Alnico is a family of iron alloys which in addition to iron are composed primarily of aluminium (Al), nickel (Ni), and cobalt (Co), hence the acronym al-ni-co. They also include copper, and sometimes titanium. Alnico alloys are ferromagnetic and are used to make permanent magnets.

Name two soft magnetic materials.

Pure iron, Silicon ferrite

Which of the following materials is shown in the figure. 

1. the most ductile
2. the most brittle
3. the strongest
4. the stiffest

The answer is given below

1. Material C
2. Material B
3. Material A
4. Material A

Which of the following materials is the most ductile?

• 80 - 20 brass; (50% elongation)
• 70 - 30 brass;(70% elongation)
• 60 - 40 brass;(40% elongation)

The most ductile material is the one with the largest percentage elongation, i.e. the 70 - 30.

What are the two forms which carbon can take in cast iron and which type of iron does it produce?

• Cementite - producing ‘white’ iron
• Graphite - producing ‘grey’ iron.

State whether low, medium or high carbon steel should be used for the following applications:

1. heat-treated pin
2. welded bracket
3. guillotine blades
4. forgings.

Answer is

1. Medium
2. Low
3. High
4. Medium or low.

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