Chapter 3 - Crystalline Solids

Question 1

crystalline material

Answer 1

atoms are situated in a repeating or periodic array over large atomic distances

Question 2

materials that form crystalline structures

Answer 2

all metals, many ceramic materials, certain polymers

Question 3

crystal structure

Answer 3

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

Question 4

atomic hard-sphere model

Answer 4

when atoms or ions are thought of as being solid spheres having well-defined diameters, where spheres touch one another

Question 5

lattice

Answer 5

three-dimensional array of points coinciding with atom positions

Question 6

unit cells

Answer 6

small repeats entities in crystal structures

Question 7

common crystal structures of metals (3)

Answer 7

face-centered cubic, body-centered cubic, hexagonal close-packed

Question 8

face-centered cubic crystal structure (FCC)

Answer 8

unit cell of cubic geometry with atoms located at each of the corners and the centers of all the cube faces, total of four whole atoms may be assigned to a given unit cell, ex: gold, silver, copper, aluminum, APF = 0.74

Question 9

Coordination number

Answer 9

the number of nearest-neighbor or touching atoms

Question 10

atomic packing factor (APF)

Answer 10

the sum of the sphere volumes of all atoms within a unit cell, divided by the unit cell volume, FCC: 0.74, BCC: 0.68, HCP: 0.74

Question 11

body-centered cubic crystal structure (BCC)

Answer 11

unit cell of cubic geometry with atoms located at each of the eight corners and a single atom at the cube center, two atoms are associated with each unit cell, ex: chromium, iron, tungsten, APF = 0.68

Question 12

hexagon close-packed crystal structure (HCP)

Answer 12

unit cell of hexagonal geometry, equivalent of six atoms are associated with each unit cell, ex: cadmium, magnesium, titanium, zinc, APF = 0.74

Question 13

polymorphism

Answer 13

when a metal or nonmetal has more than one crystal structure, often a change in density and other physical properties accompanies a polymorphic transformation

Question 14

allotropy

Answer 14

when polymorphism is founding elemental solids

Question 15

lattice parameters

Answer 15

aka interracial angles and acial lenghts

Question 16

crystal systems (7)

Answer 16

1. cubic
2. tetragonal
3. hexagonal
4. orthorhombic
5. rhombohedral
6. monoclinic
7. triclinic

Question 17

crystal system definition

Answer 17

the different possible combinations of lattice parameters

Question 18

cubic crystal structure

Answer 18

axial relationships: a = b = c

interaxial angles: α = β = γ = 90º

Question 19

hexagonal crystal structure

Answer 19

axial relationships: a = b ≠ c

interaxial angles: α = β = 90º, γ = 120º

Question 20

tetragonal crystal structure

Answer 20

axial relationships: a = b ≠ c

interaxial angles: α = β = γ = 90º

Question 21

rhombohedral (trigonal) crystal structure

Answer 21

axial relationships: a = b = c

interaxial angles: α = β = γ ≠ 90º

Question 22

orthorhombic crystal structure

Answer 22

axial relationships: a ≠ b ≠ c

interaxial angles: α = β = γ = 90º

Question 23

monoclinic crystal structure

Answer 23

axial relationships: a ≠ b ≠ c

interaxial angles: α = γ = 90º ≠ β

Question 24

triclinic crystal structure

Answer 24

axial relationships: a ≠ b ≠ c

interaxial angles: α ≠ β ≠ γ ≠ 90º

Question 25

crystallographic direction

Answer 25

a line between two points, or a vector

Question 26

miller-bravais

Answer 26

coordinate system with four axes, a1, a2, a3 are 120º apart from each other with z perpendicular to them

Question 27

linear density (LD)

Answer 27

number of atoms centered on direction vector divided by length of the direction vector

Question 28

planar density (PD)

Answer 28

number of atoms centered on plane divided by area of plane

Question 29

single crystal

Answer 29

when the periodic and repeated arrangement of atoms is perfect or extends throughout the entirety of the specimen without interruption, unit cells interlock the same way with the same orientation

Question 30

grains

Answer 30

small crystals

Question 31

polycrystalline

Answer 31

materials made up of a collection of grains

Question 32

grain boundary

Answer 32

the atoms mismatch where two grains meet

Question 33

anisotropy

Answer 33

the directionality of properties, associated with the variance of atomic or ionic spacing with crystallographic direction, function of the symmetry of the crystal structure

Question 34

isotropic

Answer 34

substances in which measured properties are independent of the direction of measurement

Question 35

diffraction

Answer 35

occurs when a wave encounters a series of regularly spaced obstacles that are capable of scattering the wave and have spacings that are comparable in magnitude to the wavelength

Question 36

diffractometer

Answer 36

apparatus used to determine the angles at which diffraction occurs for powdered specimens

Question 37

noncrystalline

Answer 37

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

Question 38

amorphous

Answer 38

without form, atomic structure resembles a liquid