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Physics B > Properties of Material > Flashcards

Properties of Material Flashcards

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1
Q

How are different microstructures achieved

A

By different cooling rates and the way in which the solid is processed subsequently

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2
Q

How do solids form

A

When liquids cool and solidify

Or when a gas condenses

As the particles lose energy and their motion becomes slower, the pack closely together - the way in which those particles pack together will determine its microstructure

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3
Q

Describe Amorphous structures

A

Disordered and resemble the arrangement of particles in a liquid - no long-range order within their molecular structure

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4
Q

Describe Crystalline Structures

A

Ordered, they have long range order within their molecular structure

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5
Q

What happens to poly-crystalline as they solidify

A

They form crystals which grow towards each other and they meet at grain boundaries

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6
Q

What is the distance the human eye can distinguish two points between

A

0.2 mm given sufficient light, without the aid of any additional lenses

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7
Q

What is the limiting condition of resolution known as

A

Rayleigh’s Criterion

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8
Q

When are images said to be just resolved

A

When the central maximum of one image falls on the first minimum of another image

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9
Q

Formula for the minimum angular resolution for a circular aperture

A

Theta = 1.22 (wavelength of the light / diameter of the apature)

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10
Q

What is the resolution of a light microscope

A

200 nanometers

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11
Q

How do Scanning Electron Microscopes work (SEM)

A

Specimens are gold sputter coated and then mounted in a vacuum chamber

A fine beam of electrons is scanned across the surface

A detector picks up the backscattered electrons to form an image

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12
Q

How do Transmission Electron Microscopes work (TEM)

A

Hot filament produces the electrons

Anode accelerates electrons

Magnetic lenses deflect the electrons as they pass through the coil

Further magnetic lenses focus the electrons that pass through the sample onto a
fluorescent screen

Image formed on the screen

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13
Q

How do Scanning Tunelling Microscopes work (STM)

A

Scanning a very sharp metal wire tip over a surface

Apply an electrical voltage to the tip or sample

Image the surface at an extremely small scale - down to resolving individual atoms

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14
Q

Resolution of SEM

A

1-20 nm

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15
Q

Resolution of TEM

A

0.2 nm

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16
Q

Basic model of metallic structure

A

Positively charged metal ions surrounded by a sea of mobile delocalised electrons

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17
Q

What occupies the lattice points in the crystal lattice

A

Atoms, molecules or ions

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18
Q

Metal characteristic properties

A

High Young Modulus
Toughness
Malleability
Ductility
Lustrous
Good Thermal Conductors
Good Electrical Conductors

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19
Q

What is a co-ordination number

A

The number of atoms a given atom is formed

20
Q

Packing name for a co-ordination number of 4

A

Square Close Packing

21
Q

Packing name for a co-ordination number of 6

A

Hexagonal Close Packing

22
Q

What are dislocations

A

Type of defect in the crystal lattice
Areas where the atoms are out of position in the crystal lattice

23
Q

Where are dislocations generated

A

Generated and move when a stress is applied

24
Q

What does the motion of dislocation allow

A

Slip-Plastic Deformation to occur

25
Q

Movement of the edge dislocation

A

When a force is applied - dislocations move through the lattice structure

26
Q

Why are metals so malleable and ductile

A

Ease of movement of dislocations

27
Q

What do moving dislocations cause

A

Plastic deformation of the metal

28
Q

What is toughness

A

Ability of a material to absorb energy and plastically deform without fracturing

Amount of energy per unit volume that a material can absorb before rupturing

29
Q

Where can toughness be found

A

Area under a stress-strain curve

30
Q

Why are metals malleable

A

The bond between the atoms can be broken easily and reformed

Force binding the metals are non directional

31
Q

What does the ductility of a metal describe

A

Its ability to be drawn out into a wire

32
Q

What makes a metal ductile

A

The ability of the layers of atoms to slip past each other

33
Q

How can atoms slide over one another

A

Applying a force that makes the atoms in one of the planes slide past the atoms in an adjacent plane

34
Q

What does a band structure of a solid describe

A

Ranges of energy that an electron within the solid may have and ranges of energy called band gaps

35
Q

What is the conduction band

A

Band of electron orbitals that electrons can jump up into from the valence band when excited

36
Q

What happens when electrons are in the conduction band

A

They have enough energy to move freely in the material

This movement of electrons creates an electric current

37
Q

Band theory in solids

A

Atoms are packed closely together

For each original level there will be many levels

Spacing between the atoms varies - levels will also be altered by different amounts

Results in a band of extremely closed spaced levels corresponding to one particular level in the isolated atoms

Solids can be considered to have energy bands that are shared by all atoms

38
Q

Band theory of conductors, insulators and semiconductors

A

Electrical conductivity of a solid will depend on the spacing of its energy bands and the extent to which they are occupied by electrons

Electrons in the conduction band are able to move freely

If Electrons in the valence band are provided with some additional energy - they can move up into the conduction band

The fermi level is half the bandgap energy

In a conductor - the valence and conduction bands overlap - making it very easy for the valence electrons to move up into the conduction band

39
Q

Outermost electrons in a metal

A

Responsible for metallic bonding

Also the conduction electrons involved in the flow of electric current through the metal

Means there is no gap between the valence and conduction bands

There is a single band which is partially filled instead

40
Q

Band theory for insulators

A

The valence band is full and the conduction band is empty - therefore there are no available free electrons for the conduction of electrical current

Also a very wide energy gap between the two bands - a large electrical potential is for electrons to cross into the conduction band

41
Q

Thermal Conduction

A

Tight packing of atoms in a metal means that kinetic energy can be transferred from one atom to another both rapidly and efficiently

Dleocalised electrons can also collide with ions in the lattice

42
Q

Thermal insulators

A

The denser the material the closer its atoms are together

Means the transfer of energy of one atom to the next is more effective

Less dense materials are better insulators

43
Q

Band theory used to explain optical properties of metals

A

Metals are opaque

This is because incident radiation has frequencies within the visible range and this excites electrons into unoccupied energy states

Most of the absorbed radiation is remitted from the surface in the form of visible light of the same wavelength - which appears as reflected light

44
Q

What makes metal appear lustrous

A

A portion of the energy captured when the metal absorbs light is turned into thermal energy

Rest of the energy is re-radiated by the metal as reflected light

Free electrons are able to absorb energy

45
Q

What is the Fermi Level

A

The highest energy level that an electron can occupy at the absolute zero temperature - lies between the valence band and conduction band

46
Q
A

Physics B (6 decks)

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