MODULE 2

Question 1

is one in which the atoms are situated in a repeating or periodic array over large atomic distances—that is, long-range order exists, such that upon solidification, the atoms
will position themselves in a repetitive three-dimensional pattern, in which each atom is bonded
to its nearest neighbor atoms.

Answer 1

Crystalline material

Question 2

-do not crystallize and the long-range atomic order is absent.

Answer 2

Non-crystalline/Amorphous Material

Question 3

the manner in which atoms, ions, or molecules are spatially arranged.

Answer 3

Crystal structure

Question 4

where spheres representing nearest-neighbor atoms touch one
another.

Answer 4

Atomic hard-sphere model

Question 5

means a three-dimensional array of points coinciding with atom positions (or
sphere centers).

Answer 5

Lattice

Question 6

small groups of atoms form a repetitive pattern.

Answer 6

UNIT CELLS

Question 7

are parallelepipeds or prisms having three sets of parallel faces; one is drawn within the
aggregate of spheres which in this case happens to be a cube.

Answer 7

UNIT CELLS

Question 8

is the basic structural unit or building block of the crystal structure and defines the crystal
structure by virtue of its geometry and the atom positions within.

Answer 8

UNIT CELLS

Question 9

What are three of the simple crystal strcutures found in metals?

Answer 9

1. face-centered cubic,
2. body centered cubic, and
3. hexagonal close-packed.

Question 10

The crystal structure found for many metals has a unit cell of cubic geometry, with atoms
located at each of the corners and the centers of all the cube faces.

Answer 10

face-centered cubic,

Question 11

the cube edge length a and the atomic radius R are related through of a fCC is

Answer 11

a = 2R√2

Question 12

Numbers of atoms per unit cell in FCC can be calculated using

Answer 12

N = Ni +Nf/2+Nc/8

Question 13

each atom has the same number of nearest-neighbor or touching atoms

Answer 13

coordination number

Question 14

What is the coordination number of FCC?

Answer 14

12

Question 15

is the sum of the sphere volumes of all atoms within a unit cell (assuming the atomic hard-sphere model) divided by the unit cell volume—that is,

Answer 15

Atomic packing factor (APF)

Question 16

Equation of APF

Answer 16

volume of atoms in a unit cell/Total unit cell volume

Question 17

Another common metallic crystal structure also has a cubic unit cell with atoms located at
all eight corners and a single atom at the cube center.

Answer 17

body-centered cubic
(BCC) crystal structure.

Question 18

Center and corner atoms touch one another along cube diagonals, and unit cell length a
and atomic radius R are related through

Answer 18

a =4R√3

Question 19

Number of atoms in FCC?

Answer 19

4

Question 20

NUMBER OF ATOMS IN BCC?

Answer 20

2

Question 21

coordination number for bcc?

Answer 21

8

Question 22

BCC atom packing factor

Answer 22

0.68

Question 23

FCC atom packing factor

Answer 23

0.74

Question 24

It is also possible to have a unit cell that consists of atoms situated only at the corners of a cube.

Answer 24

simple cubic (SC) crystal structure;

Question 25

The only simple-cubic element is

Answer 25

polonium,

Question 26

The top and bottom faces of the unit cell consist of six atoms that form regular hexagons and
surround a single atom in the center.

Answer 26

The Hexagonal Close-Packed Crystal Structure

Question 27

In order to compute the number of atoms per unit cell for the HCP crystal structure,

Answer 27

N = Ni +Nf/2+Nc/6

Question 28

number of atoms of hexagonal is?

Answer 28

6

Question 29

FCC Unit Cell Volume

Answer 29

16R3√2

Question 30

THEORETICAL DENSITY COMPUTATION

Answer 30

ρ =nA/(Vc xNa)

Question 31

when the periodic and repeated arrangement of atoms is perfect or extends throughout the entirety of the specimen without interruption,

Answer 31

single crystal.

Question 32

Most crystalline solids are composed of a collection of many small crystals or grains;

Answer 32

polycrystalline.

Question 33

Also, there exists some atomic mismatch within the region
where two grains meet; this area,

Answer 33

grain boundary.

Question 34

It lack a systematic and regular
arrangement of atoms over relatively large atomic distances.

Answer 34

noncrystalline solids

Question 35

meaning of amorphous?

Answer 35

“without form”

Question 36

The simplest of the point defects is

Answer 36

vacancy,

Question 37

The equilibrium number of vacancies Ny for a given quantity of material (usually per meter cubed) depends on and increases with temperature according to

Answer 37

Nv = N exp(−Qv/kt)

Question 38

The
value of k is

Answer 38

1.38 × 10−23 J/atom∙K, or 8.62 × 10−5
eV/atom∙K

Question 39

is an atom from the crystal that is crowded into an interstitial
site

Answer 39

self-interstitial

Question 40

small void space that under ordinary circumstances is not occupied.

Answer 40

interstitial site

Question 41

is the element or compound that is present in the greatest amount; on occasion,

Answer 41

Solvent

Question 42

used to denote an element or compound present in a minor concentration.

Answer 42

Solute

Question 43

is a linear or one-dimensional defect around which some of the atoms are misaligned.

Answer 43

dislocation

Question 44

it is a linear defect that centers on the line that is defined along the end of the extra
half-plane of atoms.

Answer 44

edge dislocation;

Question 45

being formed by a shear stress that is applied to produce the distortion shown in Figure, the upper front region of the crystal is shifted one atomic distance to the right relative
to the bottom portion.

Answer 45

screw dislocation,

Question 46

are boundaries that have two dimensions and normally separate
regions of the materials that have different crystal structures and/or crystallographic orientations.

Answer 46

Interfacial defects

Question 47

Within the boundary region, which is probably just several atom distances wide, there is some
atomic mismatch in a transition from the crystalline orientation of one grain to that of an adjacent
one.

Answer 47

grain boundary

Question 48

Surface atoms are not bonded to the maximum number of nearest neighbors and are
therefore in a higher energy state than the atoms at interior positions.

Answer 48

External Surfaces

Question 49

exist in multiphase materials, in which a different phase exists on each
side of the boundary; furthermore, each of the constituent phases has its own distinctive physical
and/or chemical characteristics.

Answer 49

Phase boundaries

Question 50

is a special type of grain boundary across which there is a specific mirror
lattice symmetry; that is, atoms on one side of the boundary are located in mirror image positions
to those of the atoms on the other side

Answer 50

twin boundary

Question 51

are defects in 3-dimensions. These include pores,
cracks, foreign inclusions and other phases.

Answer 51

BULK OR VOLUME DEFECTS

Question 52

Most dislocations found in crystalline materials are probably neither pure edge nor pure
screw but exhibit components of both types; these are termed

Answer 52

mixed dislocations

Question 53

The magnitude and direction of the lattice distortion associated with a dislocation are
expressed in terms

Answer 53

a Burgers vector