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CHEE380 > Uhhh ignore > Flashcards

Uhhh ignore Flashcards

1
Q

Aufbau Principles

A

electrons occupy orbitals of increasing energy

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2
Q

Hund’s Rule

A

electrons occupy all degenerate orbitals before putting 2 electrons in the same orbital

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3
Q

Pauli Exclusion Principle

A

No 2 electrons can have same set of 4 quantum #s

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4
Q

Primary bonds

A
  • Ionic bond
  • Covalent bond
  • Metallic bond: atomic orbitals combine to form delocalized electron cloud shared by many atoms
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5
Q

Secondary bonds

A
  • Van Der Waals: weak bonding induced by fluctuating/permanent molecular dipoles
  • Hydrogen bonding: bonding between protons and available electron pair
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6
Q

Effects of bonding on melting temperature

A
  • Tm larger if bond energy larger
  • Tm is depth of potential energy curve
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7
Q

Effects of bonding energy on modulus of elasticity

A
  • E is larger if bonding energy is larger
  • E is related to curvature at unstretched length
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8
Q

Effects of bonding energy on coefficient of thermal expansion

A
  • It’s larger if bonding energy is smaller
  • Thermal expansion is mean interatomic distance which increases with thermal energy
  • Related to symmetry of potential structure
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9
Q

Melting temperature hardness relationship

A
  • Materials with high Tm are harder
  • Hardness is resistance of surface to plastic deformation and is influenced by height of total force curve (bonding energy)
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10
Q

Ionic + covalent bonds in ceramics leads to…

A
  • Large bond energy
  • Large Tm
  • Large E
  • Small thermal expansion coefficient
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11
Q

Metallic bonds in metals leads to…

A
  • Variable bond energy
  • Moderate Tm
  • Moderate E
  • Moderate thermal expansion coefficient
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12
Q

Covalent + secondary bonds in polymers leads to…

A
  • Directional properties
  • Secondary bonding dominates
  • Small Tm
  • Small E
  • Large thermal expansion coefficient
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13
Q

Valence band

A

Has highest energy electrons at 0 degrees K

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14
Q

Conduction band

A

Next band at energy > valence band

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15
Q

Fermi energy

A
  • At 0 degrees K all electrons have energy smaller or equal to Fermi energy
  • Energy where probability of occupancy is 50% for any T>0K
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16
Q

Movement of electrons in conductors

A

Energy needed is very small to move in a conduction region and become a free electron

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17
Q

Movement of electrons in insulators

A

Large energy band gap exists between full valence band + conduction region

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18
Q

Movement of electrons in semi-conductors

A

Same as insulators w/small band gap

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19
Q

Consequences of imperfections in a crystal

A
  • Resistance of pure metals near absolute 0 temperature is very small
  • Resistance increases with T
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20
Q

What happens when normal atoms are replaced with impurity atoms?

A
  • Local strains are produced that scatter electrons
  • Resistance increases even at absolute 0 temperatures
  • Very good conductors must be pure
  • Bad conductors are usually alloys
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21
Q

Does metal deformed by work hardening have lower or higher resistivity than the same metal in the stabilized state?

A

Higher

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22
Q

Intrinsic semiconductors

A
  • Fermi energy is in the middle of the band gap
  • Area above gap ~ # electrons in conduction
  • Area below gap ~ # missing electrons in valence band (AKA holes in valence band)
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23
Q

Extrinsic semiconductors

A
  • Fermi energy position changes according to doping
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24
Q

n-type extrinsic semiconductors

A
  • Surplus of 1 electron for each atom added which goes easily to conduction band so required energy is small
  • Have higher fermi levels than p types
  • Happens when you add phosphorus to silicon
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25
Q

p-type extrinsic semiconductors

A
  • Missing 1 electron for each atom added creating a hole
  • Hole easily goes to valence band so required energy is small
  • Happens when you add boron to silicon
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26
Q

Transistor

A
  • Constituted of 3 semiconductor sections
  • Current can flow between emitter + collector only if potential applied at base
  • Applied in amplifiers + electronic switches
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27
Q

Peltier effect

A
  • When current forced through bi-metal junction, electron going from point A to B gains energy at interface so energy taken from material (cooling effect)
  • When electron goes from B to A it loses energy at interface –> heating effect
  • When electron goes from p to n type it gains energy and energy taken from material so cooling effect (from lower to higher Fermi energy)
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28
Q

Amorphous

A
  • Non-dense + random packing
  • Solids w/out long range order/crystallinity
  • When fast solidification doesn’t allow time to organize crystal structure the result is liquid like appearance
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29
Q

Crystalline

A
  • Dense + regular packing
  • Have lower energy than amorphous solids
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30
Q

Single crystal

A

Imply long range orders

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31
Q

Polycrystals

A

Imply several crystals packed together

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32
Q

Metallic crystal structures

A
  • Densely packed
  • Simplest crystal structures
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33
Q

Why are metallic crystal structures densely packed?

A
  • Only 1 element present so all atomic radii are same
  • Metallic bonding non-directional
  • Nearest neighbour distances are small in order to lower bond energy
  • Electron cloud shields cores from each other
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34
Q

Unit cell

A

Smallest repetitive volume which contains complete pattern of crystal

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35
Q

Atomic packing factor

A

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

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36
Q

Coordination number

A

of first touching neighbours in hard sphere model

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37
Q

Simple cubic structure

A
  • 1 atom/unit cell
  • CN = 6
  • a = 2R
  • APF = 0.52
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38
Q

Body centred cubic structure

A
  • 2 atoms/cell
  • CN = 8
  • APF = 0.68
  • a = 4R/sqrt(3)
39
Q

Face centred cubic structure

A
  • a = 2Rsqrt(2)
  • CN = 12
  • APF = 0.74
  • 4 atoms/unit cell
  • Atoms touch along diagonal - close-packed direction
40
Q

Hexagonal close packed structure

A
  • 6 atoms/unit cell
  • APF = 0.74
  • CN = 12
41
Q

2 types of voids in FCC

A
  • Octahedral void (CN = 6) + 4/unit cell
  • Tetrahedral void (CN=4) + 8/unit cell
42
Q

Polymorphism

A

When metals + non-metals have >1 crystal structure

43
Q

Anisotropy in single crystals

A

Properties vary w/direction

44
Q

Anisotropy in polycrystals

A
  • Properties may/may not vary w/direction
  • If grains randomly oriented then isotropic. If grains oriented then anisotropic
45
Q

Transitions in crystalline solids

A
  • Before/after melting: atomic vibration increases w/T + volume expansion
  • At melting: crystal formation + high APF + sudden volume decrease
46
Q

Poisson ratio of 0.5

A

No volume change with strain

47
Q

Poisson ratio of 0

A

No lateral strain with axial strain

48
Q

Negative Poisson ratio

A

Positive lateral strain with positive axial strain

49
Q

Ductility

A
  • Measure of degree of plastic deformation that has been sustained at fracture
  • If fracture strain less than 5% then brittle
50
Q

Resilience

A

Capacity of material to absorb energy when deformed elastically

51
Q

Modulus of resilience

A

Strain energy / unit volume required to stress a material to the point of yielding

52
Q

Toughness

A

Capacity of material to absorb energy up to point of fracture

53
Q

Hardness test

A
  • Initial stress is high + plastic deformation occurs
  • As point goes in stress decreases + equilibrium reached
  • Shallower mark = harder material
54
Q

Ceramics

A
  • Brittle - elastic deformation until point of fracture
55
Q

Polymers

A

Can be brittle, plastic or elastic depending on structure

56
Q

Activation polarization

A
  • Activation energy required to have electrons transferred from electrode into analyte
  • Overvoltage is driving force for rxn
57
Q

Concentration polarization

A
  • Rxn rate limited by diffusion in solution
  • Affects cathode only
58
Q

Passive region

A

Oxide layer formed on surface which prevents passage of current

59
Q

Transpassive

A

Potential high enough to break oxide layer

60
Q

6 forms of corrosion

A
  • Uniform
  • Galvanic
  • Stress
  • Crevice
  • Pitting
  • Intergranular
61
Q

Uniform attack

A

Homogenous corrosion over whole surface

62
Q

Galvanic corrosion

A

Occurs when 2 metals/alloys having diff composition are electrically coupled while being exposed to electrolyte

63
Q

How to avoid Galvanic corrosion?

A
  • Choose metals close in galvanic series (low EMF potential)
  • Avoid unfavourable anode-cathode area ratios (have large anode)
  • Electrical insulation
  • Connect to more anodic metal
64
Q

Crevice corrosion

A

Occurs due to concentration diffs in ions + occurs in low concentration region

65
Q

Pitting

A

Concentration difference driven like crevice corrosion but corrosion pit forms as deep well driven by gravity

66
Q

Intergranular corrosion

A

Occurs at grain boundaries when metals are heated

67
Q

Selective leaching

A

1 element of alloy is selectively removed by corrosion process

68
Q

Erosion-corrosion

A

Occurs from combined chemical attack + mechanical abrasion from fluid motion - removes protective layer

69
Q

Stress corrosion

A
  • Metals which normally resist corrosive environment may corrode when stress applied in addition to corrosive environment
  • Small cracks form + propagate in direction perpendicular to stress - stress need not be externally applied
70
Q

Hydrogen embrittlement

A

Reduction in ductility + tensile strength that occurs when atomic hydrogen penetrates structure of the material

71
Q

P-B ratio

A

Used to determine whether you have good conformal oxide coating

72
Q

If P-B ration < 1?

A

Oxide takes less volume than metal

73
Q

If P-B ratio = 1?

A

Oxide takes same volume as metal

74
Q

If P-B ratio > 1?

A

Oxide takes greater volume than metal

75
Q

Kinetics of oxides on well-adhering films

A
  • Oxide growth limited by ionic diffusion as described by Fick’s law
  • Parabolic growth kinetics
76
Q

Kinetics of oxides on porous films

A
  • Growth is linear
  • P-B ratio < 1 or > 2
77
Q

Kinetics of thin oxides growing close to room temperature

A

Logarithmic growth kinetics

78
Q

Safety factor equation

A

Sigma_w = sigma_y/N

79
Q

Effect of depth of bond force curve on elastic modulus

A

Slope of bond force is proportional to E because when you have a steeper slope you need more force to get the same interatomic distance

80
Q

Thermal electromotive force

A
  • Potential diff of 2 metals subject to same temp
  • Diff in potential due to diff in resistivity + can be related to temp input
  • Use thermocouple to measure
81
Q

Linear defects / dislocations

A

1-D defects around which atoms are misaligned

82
Q

Edge dislocation

A
  • Extra half-plane of atoms inserted in crystal structure
  • Burger’s vector is perpendicular to dislocation line
83
Q

Screw dislocation

A
  • Spiral planar ramp resulting from shear deformation
  • Burger’s vector is parallel to dislocation line
84
Q

Equiaxed grains

A
  • Same size in all directions
  • Form due to rapid cooling near wall
85
Q

Why do dislocations preferentially move in the [1 1 1] plane of FCC instead of the [1 0 0] plane?

A

Smaller b so less energy needed for motion

86
Q

Grain boundaries

A
  • Regions between single crystals that mark the transition from lattice of 1 region to that of the other
  • Slightly disordered + low density inside leading to high mobility, high diffusivity + high chem reactivity
87
Q

Columnar grains

A
  • Elongated grains
  • Occur in area w/less undercooling
88
Q

Does a large number of boundaries + defects produce a softer or harder material?

A

Harder

89
Q

Do small grains make a stronger or weaker material?

A

Stronger because dislocations are stopped by grain boundaries

90
Q

Is the total interfacial energy greater for fine or for large grains?

A

For fine grains because the boundary area/unit volume is smaller for large grains

91
Q

At high temperatures what happens to grains?

A

They grow in size to minimize interfacial energy - large grains eat small grains

92
Q

Do large grains have larger or smaller CN’s than small grains?

A

Larger

93
Q

Diode

A
  • p-n rectifier junction
  • Current only flows in 1 direction

CHEE380 (6 decks)

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