Chapter 12

Question 1

What is a Frenkel defect?

Answer 1

A defect consisting of a cation-vacancy and cation-interstitial pair.

Question 2

What is a Schottky defect?

Answer 2

A defect consisting of a cation-vacancy and anion-vacancy pair.

Question 3

What is an anion?

Answer 3

A negatively charged ion.

Question 4

What is a cation?

Answer 4

A positively charged ion.

Question 5

What is a defect structure?

Answer 5

Relating to the kinds and concentrations of vacancies and interstitials in a ceramic compound.

Question 6

What is electroneutrality?

Answer 6

The state of having exactly the same numbers of positive and negative electrical charges (ionic and electronic)—that is, of being electrically neutral.

Question 7

What is flexural strength?

Answer 7

Stress at fracture from a bend (or flexure) test.

Question 8

What is an octahedral position?

Answer 8

Where there are 6 nearest-neighbor atoms.

Question 9

What is stoichiometry?

Answer 9

For ionic compounds, the state of having exactly the ratio of cations to anions specified by the chemical formula.

Question 10

What is a tetrahedral position?

Answer 10

Where there are 4 nearest-neighbor atoms.

Question 11

What is viscosity?

Answer 11

The ratio of the magnitude of an applied shear stress to the velocity gradient that it produces—that is, a measure of a noncrystalline material’s resistance to permanent deformation.

Question 12

What is the most common type of mixed bonding in ceramics?

Answer 12

Covalent-Ionic bonding.

Question 13

What are oxide structures?

Answer 13

• The oxygen anions are larger than metal cations
• Close-packed oxygen in a lattice (usually FCC)
• Cations fit into interstitial sites among oxygen ions

Question 14

What are the factors that determine crystal structure?

Answer 14

1. Relative sizes of ions (maximize the number of opposite charged neighbors for stability)
2. Maintenance of charge neutrality (net charge = 0)

Question 15

What is the relationship between coordination number (nearest-neighbor) and ionic radii?

Answer 15

The coordination number increases as rcation/ranion increases.

Question 16

What are the five types of stable atomic structures?

Answer 16

• Linear (2 nn) [0 - 0.155]
• Triangular (3 nn) [0.155 - 0.225]
• Tetrahedtral (4 nn) [0.225 - 0.414]
• Octahedral (6 nn) [0.414 - 0.732]
• Cubic (8 nn) [0.732 - 1]

Question 17

What are 5 common ceramic crystal structures?

Answer 17

• Rock salt (sodium chloride)
• Cesium chloride
• Zinc blende (sphalerite)
• Fluorite
• Perovskite

Question 18

What are the 3 AX structure types?

Answer 18

• Rock salt (sodium chloride)
• Cesium chloride
• Zinc blende (sphalerite)

Question 19

What is the AX2 structure type?

Answer 19

• Fluorite

Question 20

What is the ABX3 structure type?

Answer 20

• Perovskite

Question 21

What are the characteristics of rock salt (sodium chloride)?

Answer 21

• AX
• FCC
• 6 cations 6 anions

Question 22

What are the characteristics of cesium chloride?

Answer 22

• AX
• Simple cubic
• 8 cations 8 anions

Question 23

What are the characteristics of zinc blende (sphalerite)?

Answer 23

• AX
• FCC
• 4 cations 4 anions

Question 24

What are the characteristics of fluorite?

Answer 24

• AX2
• Simple cubic
• 8 cations 4 anions

Question 25

What are the characteristics of perovskite?

Answer 25

- ABX3 - FCC - 12/6 cations 6 anions

Question 26

How is density calculated for ceramics?

Answer 26

(number of formula units*(ΣAc + ΣAa))/(unit cell volume*avogadro's)

Question 27

What are silicate ceramics?

Answer 27

- Have tetrahedral shapes - SiO2 polymorphic forms are quartz, cristobalite, and tridymite - Strong Si-O bonds result in high melting temps

Question 28

What are silicates?

Answer 28

- Bonding of adjacent SiO44- by sharing of common corners, edges, or faces - Cations within maintain charge neutrality and ionically bond SiO44- to each other

Question 29

What is the structure of glass?

Answer 29

Glass is noncrystalline (amorphous) that has impurity cations

Question 30

What are layered silicates?

Answer 30

- SiO4 tetrahedra connected together to form a 2-D plane - Net negative charge associated with each unit - Negative charge is balanced by an adjacent plane rich in cations - Adjacent sheets bonded by van der Waal's Ex: clays, mica, talc

Question 31

What are the 3 polymorphic forms of carbon?

Answer 31

- Diamond - Graphite - Fullerenes or carbon nanotubes

Question 32

What are the characteristics of diamond?

Answer 32

- Tetrahedral - Hardest material with high thermal conductivity - Large single crystals are gemstones - Small crystals are used for cutting/grinding - Thin films are used as surface coatings

Question 33

What are the characteristics of graphite?

Answer 33

- Layered structure of hexagonal arrays of carbon - van der Waa's forces between layers - Good lubricant since planes slide easily

Question 34

What are the characteristics of fullerenes/nanotubes?

Answer 34

- Single layers of graphene - Fullerenes are soccerball shaped made up of hexagons and pentagons - Nanotubes are carbon tubes

Question 35

What are the types of point defects in ceramics?

Answer 35

1. Vacancies (small holes) for both cations and anions 2. Intersitials (inserts) for just cations

Question 36

How is electroneutrality maintained when impurities are present?

Answer 36

If there is a substitutional cation impurity, there will be a cation vacancy to balance the charge. The same goes for anions

Question 37

Why are ceramics more brittle than metals?

Answer 37

Dislocation motion is difficult in ionic solids - Few slip systems - Resistance to the motion of ions of like charge

Question 38

What do flexural tests measure?

Answer 38

Room temperature mechanical behavior, 3-point bending test is often used

Question 39

What is the room temperature behavior of ceramics?

Answer 39

Elastic with brittle failure

Question 40

What are the Hume-Rothery rules?

Answer 40

a) similar atomic sizes (within <15%) b) the same crystal structures c) similar electronegativity d) similar valence systems