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Materials > Structure of Crystalline Solid Chpt 3 > Flashcards

Structure of Crystalline Solid Chpt 3 Flashcards

1
Q

What is the structure of Crystalline materials

A

atoms pack in periodic arrays

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2
Q

What type of materials are typical to have crystalline structures?

A

metals, many ceramics, some polymers

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3
Q

What’s the structure of a noncrystalline material

A

atoms have no periodic packing

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4
Q

Where do you find noncrystalline materials?

A

complex structures, rapid cooling

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5
Q

Whats another word for noncrystalline?

A

Amorphous

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6
Q

What’s the correlation between density packing and energy?

A

dense, regular packed (compact) structures tend to have lower bonding energy

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7
Q

What’s a unit cell

A

basic repeating unit of crystalline materials

Repeating unit cells to form entire crystal

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8
Q

What’s lattice

A

atomic arrangements in crystalline solids that can be described with respect to a network of lines

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9
Q

What are lattice sites

A

the intersections of lines of unit cells in crystalline solids

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10
Q

What are the three characteristics of a lattice cell

A

lattice parameters: how many sides

axial length: length of each axix

interaxial angle: angle between each axis

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11
Q

describe the relationship between unit cells and atoms

A

an atom can share multiple unit cells

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12
Q

Why do Metallic Crystal Structures have dense packing?

A

metallic bonding is not directional, the nearest neighbor distance tends to be small in order to lower bond energy, and typically since only one element is present, all atomic radii are the same

They have simple structures

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13
Q

Do metallic crystal structures have dense or non-dense packing?

A

Dense

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14
Q

What are the four structures of metallic crystals

A

simple cubic (SC), Body-Centered Cubic (BCC), Face-Centered Cubic (FCC), Hexagonal Closed-Packed (HCP)

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15
Q

What is SC and describe it

A

Simple Cubic, arrangement of hard spheres in each (8) corner.

each corner of the unit cell is defined by a lattice point at which an atom can be found in the crystal

each of the 8 corners of the unit cell contain an identical particle

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16
Q

What is APF

A

Atomic packing factor

APF= Vol. of atoms in unit cell / vol. of unit cell

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17
Q

Whats the volume of a sphere

A

4/3pi(r)^3

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18
Q

What is the APF of a SC structure

A

(1*4/3pi(0.5d)^3) / d^3

d = length of a side

closed-packed directions contains:
8*1/8 = 1 atom/unit cell

0.52

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19
Q

What is BCC?

A

Body-Centered Cubic

contains 9 atoms, all identical, 8 in each corner of the unit cell (they say this is the atomic centers in the unit cell), and one in the center

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20
Q

What’s the APF of a BCC structure?

A

radius is 4r because you have 1/8 circles in corners and an atom in center with radius of that circle, so diameter of 2. from one corner to the other, it’s 4r. r = (sqrt(3)/4) * a

https://www.youtube.com/watch?v=ceOOxa1A6-A

of atoms: (one atom with all 8 components in each corner and another in the center)

APF = 2 * 4/3 pi (sqrt(3)a/4)^3 / a^3

0.68

21
Q

What is FCC?

A

Faced-Centered Cubic structure

1/8 sphere in each corner, half a sphere on each face of the cube cell

22
Q

How many lattice points in a FCC structure?

A

14 identical points.

23
Q

What elements have the FCC structure?

A

Cu, Al, Ag, Au

24
Q

Whats the APF of FCC structure?

A

on one face, its diagonal = sqrt(2)a = 4r

r = sqrt(2) / 4

https://www.youtube.com/watch?v=ceOOxa1A6-A

4 atoms per unit cell

APF = 4 * 4/3 pi (sqrt(2)a / 4)^3 / a^3

0.74

25
Q

What is HCP?

A

Hexagonal closed-packed structure

6 atoms form the regular hexagon, they surround 3 inside, 1 on top and bottom, and 2 on the corners (top and bottom)

26
Q

What crystals commonly have HCP?

A

metallic crystals, Cd, Mg, Zn, Ti

27
Q

Whats APF of HCP structure?

A

C is the length radius, a is length of a side of the hexagon,

Ideal ratio of two lattice parameters a, and c: c/a = 1.633

0.74 (same as FCC)

28
Q

How are FCC and HCP crystal structures made

A

may be generated by stacking of close-packed planes

29
Q

Look at infographic of all crystalline structures

A
30
Q

What is a coordination number?

A

the number of nearest neighbors (of lattice points)

https://www.chemistrylearner.com/coordination-number.html

31
Q

What are the coordination numbers of BCC FCC and HCP?

A

Body-centered cubic has 8

Face-centered cubic has 12

Hexagonal close-packed has 12

32
Q

How to find the theoretical density of Crystalline Materials

A

density (p) = n A / V_c N_a

n = atoms per unit cell

A = atomic weight (g/mol)

V_c = volume per unit cell (cm^3/unit cell)

N_a = Avogadro’s number (6.023 x 10^23 atoms/mol)

33
Q

how to write point coordinates

A

Px = qa
Py = rb
Pz = sc

34
Q

How does the packing of atoms in FCC and HCP look like?

A

HCP: ABABAB

FFC: ABCABCABC

A biggest, then B then c

A inbetween b and c

closed packed planes: FCC(111) planes ABC and HCP(0001) planes AB have APF of 0.74

35
Q

What are the axial angles in the hexagonal system?

A

90 and 120 degrees

36
Q

LEARN HOW TO DO DIRECTION PLANE AND POINTS

A
37
Q

What is Linear density? Planar density?

A

LD = # atoms centered on direction vector /
length of direction vector

PD = # atoms centered on a plane / A of plane

38
Q

KNOW HOW TO DO LINEAR AND PLANAR DENSITY

A
39
Q

What are single crystals?

A

perfect unit cells arrangment in same orientation.

40
Q

Que es Polycrystalline Materials

A

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many crystalline grains, not aligned with each other

41
Q

What is the area where crystalline grains meet?

A

the grain boundary

42
Q

Anisotropy what izzz

A

the directionality of properties. refers to the varience of atomic spacing with crystallographic direction.

like triclinic structures, highly anisotropic

43
Q

What is isotropic

A

substances where the measured properties are independent of direction of measurement

44
Q

What does having different directions in a crystal mean

A

different packing.

45
Q

What is a packing characteristic of FCC

A

cells are more separated along the edges than along the face diagonal

46
Q

KNOW HOW TO DO XRAY DIFFRACTION CRYSTALLINE IDETIFICATION AND STRUCTURE ANALYSIS

A
47
Q

How are x-ray beams used in material science

A

its shot towards an object, some of it will be absorbed, transmitted and scattered

the scattering pattern gives us info on electron density distribution and therefore position of atoms

48
Q

wide angle vs small angle x-ray scattering

A

wide angle: study small-scale structure (<1nm)

small angle: study large-scale feature (1-100nm)

Materials (8 decks)

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