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First Year Eng > Materials Final > Flashcards

Materials Final Flashcards

1
Q

Even though Silicon is an intrinsic semiconductor, how can it be made into an extrinsic semiconductor?

A

By intentionally adding a small number of impurities (doping)
-Doping an element of different valance into the Si

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2
Q

If a material is amorphous, it can be characterized as having:

A

An atomic structure without long-range order

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3
Q

A thermoplastic polymer is best described as being compromised of:

A

Covalently bonded, long-chain molecules held together by van der Waal’s forces with or without long range order

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4
Q

What is the most important physical characteristic that influences the elastic properties of a material?

A

Bond strength

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5
Q

As it refers to polymers, the term cross linking means:

A

The formation of covalent bonds between polymer chains

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6
Q

Although the density can vary widely within any class of materials, the density of a metal is generally greater than the density of a ceramic because:

A

-atoms are more closely packed in metals than in ceramics
-ceramics are usually a mixture of metal atoms and lighter, non-metallic elements

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7
Q

The bulk modulus of a material is used to characterize:

A

The resistance of a material to volume change during hydrostatic loading

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8
Q

As it refers to the atomic structure of a crystalline material, what is a “line” defect?

A

An edge dislocation

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9
Q

The Burgers vector of a dislocation:

A

Has a magnitude equal to the shear displacement caused by the motion of the dislocation

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10
Q

Plastic deformation increases the yield strength of a metal because:

A

The number of entangled dislocations increases

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11
Q

Brass (a Cu-Zn alloy) is stronger than pure copper. This is because:

A

The zinc atoms distort the copper lattice

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12
Q

Is the following statement true? The structure of a thermoset is a 3-D network of covalently bonded molecules

A

True

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13
Q

Is the following statement true? The Young’s modulus of a thermostat is generally higher than a thermoplastic polymer

A

True

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14
Q

Crystalline ceramics do not experience significant plastic deformation because:

A

-the stress required to move dislocations is greater than the fracture stress
-the ionic bonds are too strong
-Small flaws in the material act as stress concentrators, causing fracture before plastic deformation can occur

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15
Q

The vulcanizing process is used to:

A

Create cross-links in elastomers

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16
Q

The specific heat Cp of a material is equal to:

A

The energy required to raise the temperature of a unit mass of the material by one degree

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17
Q

Metals typically have a higher value of fracture toughness than ceramics because:

A

Metals plastically deform

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18
Q

The basic result obtained from a creep test is a plot with which two parameters:

A

Strain and time

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19
Q

Creep deformation becomes an important consideration at which homologous temperature?

A

0.4

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20
Q

How many atoms are in a simple cubic?

A

1 atom

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21
Q

How many atoms are in a face centred cubic unit cell?

A

4 atoms

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22
Q

How many atoms are in a body-centred cubic unit cell?

A

2 atoms

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23
Q

The number of independent close-packed directions in a close-packed plane of atoms is:

A

3

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24
Q

What is the definition of a nanoparticle?

A

A structure with at least 1 dimension less than 1 micrometer

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25
Q

What are examples of nanoparticles?

A

-Sphere-like particles
-Rod-like particles
-Tube-like particles

26
Q

List the first unique property of nanoparticles

A

-Large surface to volume ratio

27
Q

List the second unique property of nanoparticles

A

-High percentage of atoms/molecules on the surface

28
Q

List the third unique property of nanoparticles

A

-Surface forces are very important, while bulk forces are not as important

29
Q

List the fourth unique property of nanoparticles

A

-Metal nanoparticles have unique light scattering properties and exhibit plasmon resonance

30
Q

List the fifth unique property of nanoparticles

A

-Semiconductor nanoparticles may exhibit confined energy states in their electronic band structure

31
Q

List the sixth unique property of nanoparticles

A

-Can have unique chemical and physical properties

32
Q

List the seventh unique property of nanoparticles

A

-Same size scale as many biological structures

33
Q

What range of atoms do molecules have?

A

1-10

34
Q

What range of atoms do nanoparticles have?

A

100-100,000

35
Q

What range of atoms do bulk materials have?

A

greater than 1 000 000

36
Q

Which one has lower a melting point? Nanoparticles or bulk materials

A

Nanoparticles

37
Q

What is a Carbon Nanotube?

A

a tubular form of carbon with diameter as small as 1 nm

38
Q

What are the types of Carbon Nanotubes (CNT)?

A

-Single Wall CNT
-Multiple Wall CNT

39
Q

True or False? CNT have very high current carrying capacity

A

-true

40
Q

What is a graphene?

A

Can be described as a one atom thick layer of carbon (graphite)

41
Q

Which is stronger? Graphene or structure steel? By how much?

A

Graphene is 200 times stronger than the structure steel

42
Q

What is the Pauli exclusion principle?

A

Two electrons of opposite spin per orbital

43
Q

How is the “sea of electrons” in metallic bonding formed?

A

In metals, the valance band and the conduction band overlap

44
Q

Define Band Gap Energy (EG)

A

The energy that must be applied to a non-metal to force a valance electron to break its inter atomic bonds and begin to move to conduct electricity

45
Q

What is Fermi energy (EF)?

A

The energy of the most energetic electron when only the lowest energy levels are filled

46
Q

What happens when voltage is less than the Band Gap Energy?

A

Electricity isn’t conducted

47
Q

What happens when voltage is greater than the Band Gap Energy?

A

Electricity is conducted

48
Q

What are examples of materials that are intrinsic semiconductors?

A

-Sillicon
-Germanium

49
Q

What are intrinsic semiconductors?

A

-Their valance bands and conduction bands do not overlap, but their energy gaps are small
-So even at room temperature, some electrons have enough thermal energy to enter the conduction band
-When electrons move onto the conduction band, they leave a hole behind in the valance band that moves in the opposite direction

50
Q

What is the major difference between intrinsic and extrinsic semiconductors?

A

-Intrinsic semi conductors are sensitive to temperature and its more difficult to accurately control their conductivity
-Extrinsic semi conductors have constant conductivity over a wide temperature range

51
Q

How do we create extrinsic semiconductors?

A

-By intentionally adding a small number of impurities (doping)

52
Q

What are most electrical devices made of?

A

Extrinsic semiconductors

53
Q

What happens if you add a n-type into a semiconductor?

A

Introduces extra electrons into the crystal lattice

54
Q

What happens if you add a p-type into a semiconductor?

A

Creates “holes” in the crystal lattice

55
Q

What is extrinsic semi conduction?

A

When donor electron in an n-type semi conductor dominate conductivity

56
Q

What is donor exhaustion?

A

When all donor electrons are in the conduction band as the temperature increases
-conductivity is constant

57
Q

How do p-type semiconductors work?

A

-The holes that are created are filled by other valance electrons in the valance band
-This movement requires less energy than the Band Gap energy

58
Q

How can we control the conductivity in a material?

A

-By changing the number of carriers
-Influencing the mobility

59
Q

What is drift velocity?

A

The average electron velocity in the direction of the force imposed by the applied field

60
Q

What is mobility of an electron

A

Indication of the frequency of scattering events

61
Q

What is corrosion?

A

The deterioration of a materials by chemical reactions with its environment

62
Q

What is an oxidation reaction?

A

A reaction where a chemical species produces free electrons

First Year Eng (23 decks)

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