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(Academic) Queen Mary Uni > Materials Engineering (Week 1) > Flashcards

Materials Engineering (Week 1) Flashcards

1
Q

What Materials Properties are relevant to Engineers ?

An Economic Property (1)

A

Price and Availability

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2
Q

What Materials Properties are relevant to Engineers ?

Bulk Mechanical Properties (6)

A

Density
Stiffness (Modulus) and damping
Strength (many types)
Toughness
Fatigue
Creep

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3
Q

What Materials Properties are relevant to Engineers ?

Bulk non-mechanical properties (4)

A

Thermal properties
Optical properties
Magnetic properties
Electrical properties

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4
Q

What Materials Properties are relevant to Engineers ?

Surface properties (3)

A

Oxidation and corrosion
Friction and wear
Biocompatability

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5
Q

What Materials Properties are relevant to Engineers ?

Production properties (4)

A

Ease of manufacture
Fabrication,
joining,
finishing

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6
Q

What Materials Properties are relevant to Engineers ?

Aesthetic properties (3)

A

Appearance,
texture,
feel

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7
Q

Example: Optical properties

Transmittance:

A

Aluminum oxide may be transparent, translucent, or
opaque depending on the material structure.

-single crystal
-polycrystal: low porosity
-polycrystal: high porosity

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8
Q

Classification of Materials:

A

Metals
Polymers/plastics
Ceramics
Composites

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9
Q

Metals composition/examples:

A

Composed of one or more metallic elements (e.g. Fe, Al, Cr, Cu, Ti, Au, Ni) and small amounts of non-metallic elements (C, N, O)

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10
Q

Metals features (7):

A

Orderly arrangement of atoms
• High density, stiff, strong and ductile used in structural applications
• Nonlocalised electrons, good electrical conductors and
heat conductors

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11
Q

Ceramics, examples:

A

• Cement and concrete
• Glasses and silicates
• Alumina (Al203, emery,
sapphire)
• Silicon carbide (SiC)
• Silicon nitride (Si3N4)

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12
Q

Ceramics features: (11)

A

Compounds between metallic and non-metallic elements Frequently they are oxides nitrides and carbides
Stiff and strong (comparable to metals), but very brittle Typically insulating to heat and electricity
Can be transparent, translucent or opaque

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13
Q

Polymers examples:

A

• Polyethylene (PE), Polypropylene (PP)
• Polymethylmethacrylate (PMMA, Perspex) Nylon
• Polystyrene (PS)
• Polyurethane (PU)
• Polyvinylchloride (PVC)
• Rubbers

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14
Q

Polymers features: (6)

A

Many polymers are organic compounds based on C, H, O, N.

Usually consist of large chainlike molecular structures with a backbone of carbon atoms.

Low density, but not as strong or stiff as ceramics and metals

Can be very ductile, easily formed into complex shapes

High chemical resistance but low temperature stability.

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15
Q

Composites examples:

A

• Wood
• Bone
• Fibreglass
• Carbon-fibre re-inforced polymer

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16
Q

Composites features: (2)

A

• composed of two (or more) individual materials, which come from the other categories.

• combination of properties that is not displayed by any single material.

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17
Q

Advanced materials (4 examples):

A

Semiconductors Biomaterials
Smart materials
Nano-engineered materials

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18
Q

Advanced materials
Graphene example:

A

Graphene, one-atom-thick sheets of carbon, can carry electric charges far faster than currently used materials.
But it has proven difficult to make it behave as a semiconductor like silicon, or to attach “contacts” to the sheets.
A study in Nature Communications solves those problems by cooking up graphene from a material called silicon carbide.

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19
Q

Advanced materials
Zinc oxide nanorods example:

A

Zinc oxide nanorods are semiconducting and piezoelectric and can be used in energy harvesting devices, electronic components such as diodes, chemical sensors and bioimaging sensors.

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20
Q

The 4 structures of materials:

A

Subatomic level
Atomic level
Microscopic structure
Macroscopic structure

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21
Q

Subatomic level:

A

Electronic structure of individual atoms that defines interaction among atoms (interatomic bonding)

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22
Q

Atomic level

A

Arrangement of atoms in materials (for the same atoms can have different properties, e.g. two forms of carbon: graphite and diamond)

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23
Q

Microscopic level

A

Arrangement of small grains of material that can be identified by microscopy

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24
Q

Macroscopic level

A

Structural elements that may be viewed with the naked eye

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25
Q

Microstructures – Properties
(Length Scales)

A

macrostructure >1mm determines shape of object, macroscopic properties

microstructure
determines physico-chemical nature

molecular structure
determines physico-chemical nature

atomic structure
determines physico-chemical nature

~1 nm – 1 μm
1 nm – 1 μm
<1 nm

Generally NOT INTRINSIC – can be manipulated!!

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26
Q

Angstrom = 1A =

A

10^-10m

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27
Q

The Materials Selection Process (3 steps):

A
  1. Pick Application: Determine required Properties Properties: mechanical, electrical, thermal, magnetic, optical, deteriorative.
  2. Properties: Identify candidate Material(s) Material: structure, composition.

3.Material: Identify required Processing
Processing: changes structure and overall shape example: casting, sintering, vapor deposition, doping forming, joining, annealing.

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28
Q

How do you work out the atomic mass?

A

Atomic number (Z) and atomic mass (A)
– A ~ Z+N (N : number of neutrons)

29
Q

NA: Avogadro’s number

A

6.023 × 10^23

30
Q

1 amu/atom is the same as…

A

1 gram/mole

31
Q

Where do you find the electronegative and electropositive elements in the periodic table

A

Electropositive on the very left then becomes more and more electronegative as you move along towards the right end

32
Q

Name the three main bonding types

A

Ionic
Covalent
Metallic

33
Q

Also weaker (secondary) bonds, example…

A

van der Waals (dipole) hydrogen bonding

34
Q

Ionic (brief description): to do with electronegativity

A

Strong differences in electronegativity

35
Q

Covalent (brief description): to do with electronegativity

A

Small differences in electronegativity

36
Q

Metallic bonding (brief description) to do with valence electrons

A

Valence electrons unbound

37
Q

The properties of materials are
directly related to …

give examples

A

…their crystal
structure.

magnesium and beryllium
are brittle - gold is not

38
Q

what kind of structures tend to have lower
energies

A

dense, ordered packed structures

39
Q

Materials and Packing

Crystalline materials:

A

-atoms pack in periodic, 3D arrays, examples are metals, many ceramics and some polymers

40
Q

Materials and Packing

Non-crystalline materials:

A

atoms have no periodic packing

occurs for: complex structures, rapid cooling

41
Q

Another word for Noncrystalline

A

“Amorphous”

42
Q

Unit Cell:

A

smallest repetitive volume which
contains the complete lattice pattern of a crystal.

Unit cell are parallelpipeds or prisms with 3 sets
of parallel faces

The corners of the unit cell coincide with the centre of atoms.

43
Q

Metallic crystal structure:

A

-Tend to be densely packed

-Have the simplest crystal structures.

44
Q

Reasons for dense packing (Metallic Crystal Structures) :

A
  • Typically, only one element is present, so all atomic radii are the same.
  • Metallic bonding is not directional.
  • Nearest neighbour distances tend to be small in
    order to lower bond energy.
  • Electron cloud shields cores from each other
45
Q

What are the 4 Metallic Crystal Structures:

A

Simple Cubic Structure (SC)
Body Centered Cubic Structure (BCC)
Face Centered Cubic Structure (FCC)
Hexagonal Close-Packed Structure (HCP)

46
Q

Simple Cubic Structure (SC): (2)

A
  • Rare due to low packing density (only Po has this structure)
  • Close-packed directions are cube edges.
47
Q

Atomic Packing Factor (APF):

A

APF = Volume of atoms in unit cell /
Volume of unit cell

*assume hard spheres

48
Q

Simple Cubic Structure (SC): APF

A
  • APF for a simple cubic structure = 0.52
49
Q

Body Centered Cubic Structure (BCC)

A

Atoms touch each other along cube diagonals. –Note: All atoms are identical; the center atom is shaded differently only for ease of viewing.

50
Q

Body Centered Cubic Structure (BCC) examples

A

ex: Cr, W, Fe (α), Tantalum, Molybdenum

51
Q

APF for a body-centered cubic structure is…

A

0.68

52
Q

Face Centered Cubic Structure (FCC):

A

Atoms touch each other along face diagonals.
Note: All atoms are identical; the face-centered atoms are shaded differently only for ease of viewing.

53
Q

Face Centered Cubic Structure (FCC): examples

A

ex: Al, Cu, Au, Pb, Ni, Pt, Ag

54
Q

APF for a face-centered cubic structure is…

A

0.74
maximum achievable APF

55
Q

FCC Stacking Sequence:

A

ABCABC… Stacking Sequence

56
Q

Hexagonal Close-Packed Structure
(HCP): staking sequence

A

ABAB… Stacking Sequence

57
Q

Hexagonal Close-Packed Structure
(HCP): APF

A

APF = 0.74

58
Q

Hexagonal Close-Packed Structure
(HCP): examples

A

ex: Cd, Mg, Ti, Zn

59
Q

Theoretical Density, ρ

A

Density = ρ = Mass of Atoms in Unit Cell / Total Volume of Unit Cell

ρ = n A / Vc Na

where
n = number of atoms/unit cell
A = atomic weight
Vc = Volume of unit cell = a^3 for cubic
Na = Avogadro’s number = 6.023 x 10^23 atoms/mol

60
Q

Densities of Material Classes:

A

In general
ρ metals > ρ ceramics > ρ polymers

61
Q

In general, why does the following order exist:
ρ metals > ρ ceramics > ρ polymers

A

Metals have…
* close-packing
(metallic bonding)
* often large atomic masses

Ceramics have…
* less dense packing
* often lighter elements

Polymers have…
* low packing density
(often amorphous)
* lighter elements (C,H,O)

Composites have…
* intermediate values

62
Q

Polymorphism

A

Two or more distinct crystal structures for the same material (allotropy/polymorphism)

63
Q

Polymorphism examples (2):

A

Titanium: α, β-Ti
HCP α form at room temp.
BCC β form at 882 °C

Carbon
diamond, graphite
The prevailing crystal
structure depends on
temperature and
pressure.

64
Q

Atoms may assemble into … or
… structures.

A

crystalline
amorphous (An amorphous structure has no organization, and the atomic structure resembles that of a liquid)

65
Q

Common metallic crystal structures are …

A

FCC,
BCC,
HCP.

66
Q

Coordination number and atomic packing factor
are the same for which 2 crystal structures?

A

FCC and HCP crystal structures

67
Q

We can predict the density of a material, provided we know what?

A

the atomic weight, atomic radius, and crystal
geometry (e.g., FCC, BCC, HCP).

68
Q

What Materials Properties are relevant to Engineers ? (6)

A

-An economic properties
-Bulk mechanical properties
-Bulk non-mechanical properties
-Surface properties
-Production properties
-Aesthetic properties

(Academic) Queen Mary Uni (14 decks)

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