Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Materials Science 1 > Structure & Crystalline Solids > Flashcards

Structure & Crystalline Solids Flashcards

You may prefer our related Brainscape-certified flashcards:
Biology 101 flashcards
1
Q

what are the two types of main structures of solid materials?

A

amorphous and crystalline

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what is the structure of a crystalline material?

A

they have atoms situated in a periodic array over large atomic distances

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

give some examples of materials that have crystalline structures?

A

metals and most ceramics

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what are amorphous materials?

A

materials that have no long range order, they are a non-repeating pattern (non crystalline) - these include glasses like silica, plastics and rapidly cooled metals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

how do crystalline structures form?

A

if we cool something down or if we precipitate something out of something

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

how do ice crystals form on lakes? (can be applied to any formation of crystal structure)

A
  • ‘nuclei’ form during solidification, each of which grows into crystals, nucleation - when the molecules/atoms are initially coming together
  • crystals grow and meet
  • eventually they cannot grow anymore and we form out solid crystal
  • these grains are separated by an amorphous grain boundary because the orientation of the crystals are all mismatched
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

how can we reveal the grain structure of a crystal?

A

use polishing and etching (using acids)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what type of atomic packing does a crystalline structure have?

A

dense, regular packing (tend to have lower bond energy than amorphous structures)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what type of atomic packing does an amorphous structure have?

A

non-dense, random packing (varying bonds lengths) - they tend to have larger bond energy and bond lengths compared to crystalline structures) - more reactive, less energy needs to be put in

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

how do we describe the arrangement of crystalline solids?

A

using the unit cell - the smallest repeating arrangement (basic building block)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what is the difference between the hard sphere model and the reduced sphere representation?

A

hard sphere model - atoms donated by hard, touching spheres

reduced sphere representation - reduced spheres

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what are the 4 main unit cells we find in metallic crystal structures?

A

SC - simple cubic
FCC - face centred cubic
BCC - body centred cubic
HCP - hexagonal close packed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

why do metallic crystalline structures tend to have dense packing?

A

due to non-directional bonding in metals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what is the simple cubic structure? (SC)

A
  • cubic unit cell

- very rare, only Po has this structure (polonium)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what does the coordination number refer to?

A

the no. of nearest neighbours or touching atoms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what is the coordination number of simple cubic structures?

A

6

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

how do we describe the packing?

A
  • using the atomic packing factor
  • we can expect values less than 1 because it is a ratio
  • APF = volume of atoms in unit cell / volume of unit cell (assuming hard sphere model)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what is the equation for the atomic packing factor?

A

(no. of atoms per unit cell ) x (4/3π(r)^3) / a^3

where r is written in terms of a (lattice parameter of a cubic cell)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what is the atomic packing factor (APF) for a simple cubic structure?

A

0.52 (has 8 x 1/8 atoms = 1 atom per unit cell)

r = 0.5a

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what is the face centred cubic structure (FCC)?

A
  • atoms located at each corner and the centre of each cube faces
  • some examples include copper, aluminium, silver, gold (ductile metals)
  • coordination number = 12
  • APF = 0.74 (has 8 x 1/8 atoms + 6 x 1/2 = 4 atoms per unit cell)
  • r = 2^0.5a / 4 (because then face diagonal of the cube is equal to 4r which is equal to root2xa)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what does ductility relate to in terms of crystal structure?

A

ductility (ease of plastic deformation) is linked to crystal structure and close packed planes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

how do slip systems work?

A

slip occurs on specific atomic planes and in specific crystallographic slip directions i.e slip systems

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

what are the slip planes?

A

they are the most close packed planes (note: only count different ones, ignore parallel)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

for the unit cell what is the order of directions?

A

(x, y, z) - helps us define a plane or a direction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

what is the equation for no. of slip systems?

A

no. of slip systems = slip directions x slip planes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

what is the body centred cubic structure (BCC)?

A
  • atoms located at each of the corners and the cube centre
  • some examples include chromium, α-iron, tungsten
  • coordination number = 8
  • APF = 0.68 (has 8 x 1/8 atoms + 1 = 2 atoms per unit cell)
  • r = 3^0.5a / 4 (because the central diagonal of the cube is equal to 4r which is equal to root3xa)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

what is the direction of the slip plane in FCC structure?

A

(1, 1, 1)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

how does the slip direction relate to the slip plane?

A

the slip plane is perpendicular to the slip direction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

how many slip systems does a FCC structure have and why?

A
  • 4 slip planes
  • 3 slip directions
    = 12 slip systems
    (found in ductile metas as there are many opportunities for planes to slide over each other)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

how many slip systems does a BCC structure have and why?

A
  • 6 slip planes
  • 2 slip directions
    = 12 slip systems
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

what is the direction of the slip plane in BCC structure?

A

(1, 1, 0)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

what is the hexagonal close packed structure (HCP)?

A
  • hexagonal unit cell
  • top and bottom faces of hexagonal cell consist of 6 atoms (a hexagon) with an atom in the centre
  • the middle plane consists of 3 atoms
  • some examples include magnesium, titanium, cadmium and zinc
  • least ductile metals (only 1 slip plane)
  • coordination number = 12 and APF = 0.74 like FCC
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

how many slip systems does a HCP structure have and why?

A
  • 1 slip plane
  • 3 slip directions
    = 3 slip systems
    (most brittle of the metals, but subtle difference between FCC structure)
34
Q

what is the direction of the slip plane in HCP structure?

A

(0, 0, 1)

35
Q

what type of structure is NaCl?

A

simple cubic

36
Q

what are some applications of perfect crystalline structures?

A
  • electronic and optical materials (Silicon wafers/chips)
  • high performance single crystal turbine blades
  • abrasive materials (synthetic diamond)
37
Q

what does anisotropic mean?

A

different in different directions - some crystals have direction properties, different properties in different directions

38
Q

what is an issue with manufacturing a silicon wafer (crystal)?

A

high embodied energy and cost of production (however we have a large elemental abundance of silicon) - silicon wafers are used in semi conductor devices

39
Q

what does the size of the crystal relate to?

A

the cooling rate:
large crystals = cooled slowly
small crystals = cooled quickly

40
Q

what are some similarities/differences between single VS poly-crystalline structures?

A

SINGLE:

  • properties vary with direction (anisotropic)
  • example: the stiffness of BCC iron

POLYCRYSTALS

  • has some regions of crystalline areas
  • properties may/may not vary with direction
  • if grains are randomly orientated: isotropic
  • if grains are textured: anisotropic
41
Q

general summary of crystalline materials…

A
  • atoms packed in periodic 3D arrays
  • typical of metals, many ceramics, some polymers
  • slow cooling
42
Q

general summary of non-crystalline (amorphous) materials…

A
  • atoms have no periodic packing
  • occurs for complex structures
  • rapid cooling
  • examples include glasses and some polymers
43
Q

what are defects in crystals?

A

areas in a crystal which aren’t perfect

44
Q

why are defects/imperfections in crystals important?

A

many of the important properties of materials are due to the presence of imperfections

45
Q

what are the 4 main types of defects?

A
  • point defects (0D)
  • line defects (1D)
  • area defects (2D)
  • volume defects (3D)
46
Q

what are some examples of point defects?

A
  • vacancy atoms
  • self interstitial atoms
  • substitutional atoms
47
Q

what are some examples of line defects?

A
  • dislocations
48
Q

what are some examples of area defects?

A
  • grain boundaries
49
Q

what are some examples of volume defects?

A
  • precipitates
  • cracks
  • porosity
50
Q

what is a vacancy atom in terms of point defects?

A

where an atom is missing creating a distortion of planes

51
Q

what are self interstitial atoms in terms of point defects?

A

where an extra atom is positioned between atomic sites creating a distortion of planes

52
Q

what are substitutional atoms in terms of point defects?

A

when one of the main atoms in the crystal is substituted with something else (note: you can get interstitial substitutional atoms such as small atoms that get added in which don’t disrupt the lattice)

53
Q

what are the conditions that make it likely for substitutions in the crystal to work?

A
  • the difference in atomic radii must be less than 15%
  • they must have similar electronegativities (close on the periodic table)
  • same crystal structure for pure metals (e.g gold and silver)
54
Q

what is a frenkel defect?

A

a special type of point defect where there is both a vacancy and an interstitial

55
Q

why are metals ductile?

A

the movement of dislocations

56
Q

what type of defect are dislocations?

A

line defects

57
Q

what are dislocations?

A

dislocations are one-dimensional defects around which atoms are misaligned

58
Q

what are the two types of dislocations?

A
  • edge dislocations

- screw dislocations

59
Q

what is an edge dislocation?

A

when an extra plane of atoms is inserted in a crystal structure

60
Q

what is a screw dislocation?

A

a spiral planar ramp resulting from shear deformation

61
Q

what is the burger’s vector?

A

a measure of lattice distortion (the amount the dislocation has shifted)

62
Q

how do dislocations move?

A
  • dislocations are mobile under an applied stress
  • incrementally breaking/re-making bonds
  • large numbers of dislocations move for plastic deformation to occur in metals and alloys (or will just fracture like a ceramic)
63
Q

in what material do dislocations move smoothly (think caterpillar)?

A

in metals because there is non-directional bonding, movement is hard in covalent and ionic ceramics and so there is no dislocation movement

64
Q

what is dislocation density?

A

total dislocation length per unit volume of material or the number of dislocations that intersect a unit area of a random section

65
Q

what does the dislocation density determine?

A

the strength of the material

66
Q

what does deformation do to the number of dislocations?

A

creates defects which increases the number of dislocations

67
Q

what is a grain boundary in terms of area defects?

A

they are 2D defects that are regions between crystals, they are the transitions from a lattice of one region to that of the other

68
Q

what does a high angle of misalignment mean for a dislocation?

A

harder to move compared to moving between a grain boundary with a smaller angle of misalignment

69
Q

some general info on grain boundaries…

A
  • they can vary considerably in size

for example grains can be large in diamond or silicon but very small (mm or less) in other things

70
Q

what does the size of the grains define?

A

the number of grain boundaries - if there are little grains there are going to be more grain boundaries than if you had larger grains, therefore depending on the solidification and the number of grain boundaries, this will effect the deformation

71
Q

what are precipitates in terms of volume defects?

A

you can grow 3D precipitates by heating up certain alumnium alloys (deliberate heat treatment) - they can help restrict the movement of dislocations

72
Q

what type of materials do cracks and damage effect?

A

brittle materials

73
Q

where do you come across porosity defects?

A

in ceramics and metals

74
Q

what do the defects in a solid effect?

A

the mechanical properties of that solid and defects are inevitable

75
Q

what is an example of a substitutional defect?

A

Cu in Ni

76
Q

what is an example of an interstitial defect?

A

C in Fe

77
Q

what is the difference between body centred cubic and body centred tetragonal?

A

in BCC, all the angles in the cube are 90 degrees and all the lengths of the cube are equal - in BCT, all the angles are 90 degrees but one out of the 3 lengths are slightly longer than the other (rectangular shape)

78
Q

why do more grain boundaries mean for the strength of a material and why?

A

more grain boundaries = harder for dislocations to move and harder to deform the material

79
Q

how many whole atoms are in a simple cubic unit cell?

A

1

80
Q

how many whole atoms are in a FCC unit cell?

A

4

81
Q

how many whole atoms are in a BCC unit cell?

A

2

Materials Science 1 (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions