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EMS430U - Materials Engineering > Chapter 1 - Introduction > Flashcards

Chapter 1 - Introduction Flashcards

1
Q

What materials properties are relevant to engineers?

A

Price and availability, mechanical properties like stress, tension, fatigue, strength and density, non mechanical properties like thermal optical magnectic and electrical properties, oxidation corrosion Friction and wear biocompatibiltiy

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2
Q

What is transmittance?

A

The optical ability of an object to transmit radiant energy, can be observed in Aluminium oxide single vs multi crystals where porosity causes light diffraction leading to more opaque in colour vs clear in single crystals where light can freely pass through.

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3
Q

How can materials be classifies

A

Metals, Polymers, Composites and Ceramics

Advanced classification include, biomaterials, smart materials, semi conductors and nano engineered materials

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4
Q

What are the structural properties of Metals

A

Orderly arrangement of atoms

Made up of one or more metallic elements and small amounts of non metallic

High density

Stiff

Strong

Ductile

Non localised electrons - Good electrical and heat conductors

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5
Q

What are the structural properties of Ceramics?

A

Compound between metallic and non metallic elements

Oxides, nitrides and carbides

Stiff and strong

Insulating to heat and electricity

Can be transparent, translucent or opaque

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6
Q

What are the structural properties of composites

A

Composed of two or more materials from other categories i.e polymer, metal, ceramic

Combination of properties that cannot be found in one individual material

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7
Q

What are the structural properties of polymers

A

Usually based on C, H, O, N

Chain like molecular structure with a backbone of carbon atoms

Low density but not as strong or stiff as ceramic and metals

Can be very ductile

High chemical resistance but low chemical stability

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8
Q

What are some examples of advanced materials

A

Semiconductors: Have characteristics intermediate to electrical conductors and insulators

Biomaterials: Biocompatible, nonviableimplanted in the body and functioning a reliable and safe way.

Smart Materials: Sensors, Actuator, these are materials that can detect changes in their environment and respond

Nano-engineered materials: Properties depend on size and are scaled in the nanometer

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9
Q

Describe the structures of materials in their different levels

A

Subatomic level : Electronic structure of individual atoms that defines iteration among atoms (interatomic bonding) involves electrons within the individual atoms, their energies and interactions with the nuclei.

Atomic level: Arrangement of atosms in materials ( different arrangement of the same ato can have different properties in.e carbon: graphite and diamond)

Microscopic structure: Arrangement of small grains of material that can be identified by microscopy.

Macroscopic Structure: Structural elements that can be viewed with the naked eyes

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10
Q

What are the length scales of structures?

A

Macrostructure { Greater than 1mm

Micro structure { Between 1micrometer and 1 mm

Molecular structure { Between 1 nanometer and 1 micrometer

Atomic structure { Less than 1 nano meter

angstrom = 1 Å = 10-10 m
nanometer = 1 nm = 10-9 m
micrometer = 1 μm = 10-6 m
millimeter = 1 mm = 10-3 m

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11
Q

T are the four components of material science?

A

Processing, structure, Properties and Performance

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12
Q

What can the structure of a material be described as?

A

The arrangement of its internal components.

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13
Q

What are important in materials selection

A

Deteriorations, Economics and conditions which it’ll be subjected to

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14
Q

What is atomic number (Z) and atomic mass (A).

What are isotopes and atomic weight s

A

Atomic Number (Z) is the number of protons available in the nucleus

Atomic mass (A) s the sum of the protons and neutrons in the nucleus measured in amu

Isotopes are members of the same element with different atomic masses

Atomic weight is the weighted average of the atomic masses of naturally occurring isotopes.

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15
Q

What is amu defined as being measured in

A

1/12 of the atomic mass of the most common isotope of carbon Carbon 12 (12^C)

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16
Q

What is the equation that links atomic number (Z) and atomic mass (A)

A

Z = A + N where N = amount of neutrons

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17
Q

How many molecules are in 1 mole of a substance and what is avogadros constant?

A

The one mole of any substance there are 6.022x10^23 atoms or molecules and this is also known as avogadros number

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18
Q

What is the equation for average Atomic Weight?

A

Am = Σi fim Aim

Sum of the (percentage/100 x atomic weight) weight for each isotope

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19
Q

What are the number of electrons present in the spdf shells of electrons

A

S = 2

P = 6

D = 10

F = 14

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20
Q

What are the two interatomic forces that bind atoms together? What is the equation for net force

A

Attractive (Fa) and repulsive forces (Fr)

Fn =Fa + Fr

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21
Q

Describe Ionic Bonding

A

Between compounds of metallic and non metallic elements
Metallic gives up valence electrons to non metallic
Both gain an electric charge
The attractive force is Columbia - between positive and negative ions

22
Q

Describe Covalent bonding

A

Materials whose items have small electronegativity or near in periodic table. There is an overlap in orbitals so elements share electrons
Usually non metals

23
Q

Metallic bonding

A

Metals and their alloys, valence electrons are not bound to any atom and drift trough the entire metal (sea of electrons)

24
Q

Describe van der waals bonding or secondary bonding

A

Weak Bonds present in all atoms arise from molecular or atomic dipoles

25
Q

Hydrogen bonding?

A

Between molecules that contain hydrogen as one of its costituents

26
Q

what is a crystalline material and describe it characteristics?

A

A crystalline material is one in which the atoms are situated in a repeating or periodic array over large atomic distance

atoms are packed in 3D arrays typical of metals ceramics and some polymers

27
Q

Describe the characteristics of non-crystalline materials/ amorphous materials

A
  • complex structures
    -complex structures
    -rapid cooling
28
Q

Why do dense structures have lower energy?

A
29
Q

What is a unit cell?

A

Smallest repetitive volume which contained the complete lattice pattern of a crystal. Parallelpipeds/prismx with 3 sets of parallel faces

30
Q

How can we stack metal atoms to minimise empty space?

A

3D structures

31
Q

What are the characteristics of metallic crystal structures and describe

A
  • densely packed
  • have the simplest crystal structure

They re densely packed because typically only one element is present so al atomic radii are the same
Metallic bonding is not directional
Nearest neighbour distance tens to be small to lower bond energy
Electron cloud shields cores from each other

32
Q

Describe simple cubic structure

A

Rare due to low packing density
Close packed directions are cube edges

33
Q

What is the atomic packing factor? APF

A

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

34
Q

Volume of a cube and volume of a sphere?

A

Sphere = 4/3pir^3

Cube = a^3

35
Q

How to calculate APF atomic packing factor of simple cubic structure?

A

Contains 8 corners x 1/8 = 1 unit cell/atom

APF = 1 x 4/3pi(0.5a)^3/a^3

36
Q

Describe a body centered cubic structure

A

Atoms touch each other along cube diagonals

Same as simple cubic structure except there is an atom in the middle of the structure

Coordination number = 8

37
Q

What is coordination number

A

The number of atoms that any single atom is touching

38
Q

How to calculate APF for a BCC Body centered cubic structure

A

2 atoms: 1 in center + 8 corners x 8

APF = 0.68

39
Q

Describe face centered cubic structure (FCC)

A

Coordination number = 12

Atoms touch each other along face diagonals

Atoms touch each other along face diagonals.

40
Q

How to calculate Atomic packing factor APF for FCC Face centered cubic structure?

A

4 atoms: 6 face x 8 corners x 1/8

APD = 0.74

41
Q

What is the stacking system for FCC stacking

A

ABCABC stacking sequence

2D projection

42
Q

What is the stacking sequence for hexagonal close packed structure (HCP) and Atomic Packing Factor

A

ABAB stacking sequence

3D projection/2D projection

Coordination number =12
APF = 0.74
C/a = 1.633
6 atoms unit cell

43
Q

How do you calculate theoretical density?

A

Mass of atoms in unit cell / volume of unit cell

P = nA/VcNa

Where n = no of atoms
A = atomic weight

Vc = volume of unit cell

NA avogadros number = 6.023 x10^23

44
Q

Define the trend of densities of materials and the reasoning behind it

A

Metals > ceramics > polymers

Metals have high density because of close packing due to metallic bonding and they have high atomic masses

Ceramics have less dense packing due to its lighter elements

Polymers have low packing density often amorphous structures and lighter elements

45
Q

What is polymorphism what does it depend on?

A

Two or more distinct crystal structures for the same material this usually depends on temperature and pressure

46
Q

what is the unit cel edge length for fac centered cube

A

A = 2R√2

47
Q

How to calculate number of unit cells?

A

N = Ni + Nf/2 + Nc/8

Where ni is the number interior atoms
Nf o of face atoms
Nc No of corner atoms

For hexagonal close packed structures N =i + Nf/2 +Nc/6

48
Q

what is the equation for unit cell edge length for body centered cubic

A

A = 4R/√3

49
Q

Calculate the volume of an FCC unit cell in terms of the atomic radius R.

A

a^2 + a^2 = (4R)2

a = 2R√2

V = a^3= (2R√2)^3 = 16R^3√2

50
Q

Rank in terms of deformability metals ceramic and polymers

A

polymers, metals ceramics

EMS430U - Materials Engineering (5 decks)

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