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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
Microstructures – Properties (Length Scales)
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!!
26
Angstrom = 1A =
10^-10m
27
The Materials Selection Process (3 steps):
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.
28
How do you work out the atomic mass?
Atomic number (Z) and atomic mass (A) – A ~ Z+N (N : number of neutrons)
29
NA: Avogadro’s number
6.023 × 10^23
30
1 amu/atom is the same as…
1 gram/mole
31
Where do you find the electronegative and electropositive elements in the periodic table
Electropositive on the very left then becomes more and more electronegative as you move along towards the right end
32
Name the three main bonding types
Ionic Covalent Metallic
33
Also weaker (secondary) bonds, example…
van der Waals (dipole) hydrogen bonding
34
Ionic (brief description): to do with electronegativity
Strong differences in electronegativity
35
Covalent (brief description): to do with electronegativity
Small differences in electronegativity
36
Metallic bonding (brief description) to do with valence electrons
Valence electrons unbound
37
The properties of materials are directly related to ... give examples
...their crystal structure. magnesium and beryllium are brittle - gold is not
38
what kind of structures tend to have lower energies
dense, ordered packed structures
39
Materials and Packing Crystalline materials:
-atoms pack in periodic, 3D arrays, examples are metals, many ceramics and some polymers
40
Materials and Packing Non-crystalline materials:
atoms have no periodic packing occurs for: complex structures, rapid cooling
41
Another word for Noncrystalline
"Amorphous"
42
Unit Cell:
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
Metallic crystal structure:
-Tend to be densely packed -Have the simplest crystal structures.
44
Reasons for dense packing (Metallic Crystal Structures) :
- 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
What are the 4 Metallic Crystal Structures:
Simple Cubic Structure (SC) Body Centered Cubic Structure (BCC) Face Centered Cubic Structure (FCC) Hexagonal Close-Packed Structure (HCP)
46
Simple Cubic Structure (SC): (2)
* Rare due to low packing density (only Po has this structure) * Close-packed directions are cube edges.
47
Atomic Packing Factor (APF):
APF = Volume of atoms in unit cell / Volume of unit cell *assume hard spheres
48
Simple Cubic Structure (SC): APF
* APF for a simple cubic structure = 0.52
49
Body Centered Cubic Structure (BCC)
Atoms touch each other along cube diagonals. --Note: All atoms are identical; the center atom is shaded differently only for ease of viewing.
50
Body Centered Cubic Structure (BCC) examples
ex: Cr, W, Fe (α), Tantalum, Molybdenum
51
APF for a body-centered cubic structure is...
0.68
52
Face Centered Cubic Structure (FCC):
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
Face Centered Cubic Structure (FCC): examples
ex: Al, Cu, Au, Pb, Ni, Pt, Ag
54
APF for a face-centered cubic structure is...
0.74 maximum achievable APF
55
FCC Stacking Sequence:
ABCABC... Stacking Sequence
56
Hexagonal Close-Packed Structure (HCP): staking sequence
ABAB... Stacking Sequence
57
Hexagonal Close-Packed Structure (HCP): APF
APF = 0.74
58
Hexagonal Close-Packed Structure (HCP): examples
ex: Cd, Mg, Ti, Zn
59
Theoretical Density, ρ
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
Densities of Material Classes:
In general ρ metals > ρ ceramics > ρ polymers
61
In general, why does the following order exist: ρ metals > ρ ceramics > ρ polymers
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
Polymorphism
Two or more distinct crystal structures for the same material (allotropy/polymorphism)
63
Polymorphism examples (2):
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
Atoms may assemble into ... or ... structures.
crystalline amorphous (An amorphous structure has no organization, and the atomic structure resembles that of a liquid)
65
Common metallic crystal structures are ...
FCC, BCC, HCP.
66
Coordination number and atomic packing factor are the same for which 2 crystal structures?
FCC and HCP crystal structures
67
We can predict the density of a material, provided we know what?
the atomic weight, atomic radius, and crystal geometry (e.g., FCC, BCC, HCP).
68
What Materials Properties are relevant to Engineers ? (6)
-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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