Chapter 12

Question 1

ceramics

Answer 1

means “burnt stuff,” indicating that desirable properties of these materials are normally achieved through a high-temperature heat treatment process called firing

Question 2

cation

Answer 2

• metallic ionsare

- positively charged because they have given up their valence electrons to the nonmetallic ions

Question 3

anion

Answer 3

negatively charged

Question 4

rock salt crystal structure

Answer 4

• most common AX crystal structure
• coordination number for both cations and anions is 6
• two interpenetrating FCC lattices—one composed of the cations, the other of anions

Question 5

cesium chloride crystal structure

Answer 5

• coordination number is 8

- anions are located at each of the corners of a cube, whereas the cube center is a single cation

Question 6

zinc blende or sphalerite structure

Answer 6

• coordination number is 4

- all ions are tetrahedrally coordinated

Question 7

tetrahedral position

Answer 7

four atoms (three in one plane, and a single one in the adjacent plane) surround one type

Question 8

octahedral position

Answer 8

six ion spheres, three in each of the two planes

Question 9

silicates

Answer 9

• materials composed primarily of silicon and oxygen, the two most abundant elements in Earth’s crust
• not considered ionic

Question 10

silicon dioxide or silica (SiO2)

Answer 10

• most simple silicate material

- material is electrically neutral and all atoms have stable electronic structures

Question 11

fused silica or vitreous silica

Answer 11

silica made to exist as a noncrystalline solid or glass having a high degree of atomic randomness, which is characteristic of the liquid

Question 12

network formers

Answer 12

other oxides that form glassy structures

Question 13

network modifiers

Answer 13

oxides that do not form polyhedral networks, their cations are incorporated within and modify the SiO4-4 network

Question 14

intermediates

Answer 14

other oxides, such as TiO2 and Al2O3 although not network formers, substitute for silicon and become part of and stabilize the network

Question 15

carbon

Answer 15

exists in two allotropic forms—diamond and graphite—as well as in the amorphous state

Question 16

diamond

Answer 16

metastable carbon polymorph at room temperature and atmospheric pressure

Question 17

graphite

Answer 17

• another polymorph of carbon

- furthermore, it is a stable polymorph at ambient temperature and pressure

Question 18

delocalized

Answer 18

does not belong to a specific atom or bond

Question 19

defect structure

Answer 19

designate the types and concentrations of atomic defects in ceramics

Question 20

electroneutrality

Answer 20

state that exists when there are equal numbers of positive and negative charges from the ions

Question 21

Frenkel defect

Answer 21

• type of defect involves a cation–vacancy and a cation–interstitial pair
• defect where cation leaves its normal position and moves into an interstitial site

Question 22

Schottky defect

Answer 22

• type of defect found in AX materials & involves a cation vacancy–anion vacancy pair
• removing one cation and one anion from the interior of the crystal and then placing them both at an external surface

Question 23

stoichiometry

Answer 23

state for ionic compounds wherein there is the exact

ratio of cations to anions as predicted by the chemical formula

Question 24

stress raisers

Answer 24

points at which the magnitude of an applied tensile stress is amplified and no mechanism such as plastic deformation exists to slow down or divert such cracks

Question 25

static fatigue or delayed fracture

Answer 25

fracture of ceramic materials will occur by the slow | propagation of cracks, when stresses are static in nature

Question 26

mirror region

Answer 26

crack surface formed during initial stage of propagation, usually smooth and flat

Question 27

mist region

Answer 27

crack surface formed during second stage of propagation, faint annular region just outside the mirror region

Question 28

hackle region

Answer 28

crack surface formed during third stage of propagation, composed of a set of striations or lines that radiate away from the crack source in the direction of crack propagation

Question 29

Wallner lines

Answer 29

arc shaped and provide information regarding stress distributions and directions of crack propagation

Question 30

viscous flow

Answer 30

the rate of deformation is proportional to the applied stress

Question 31

viscosity

Answer 31

measure of a noncrystalline material’s resistance to deformation

Question 32

porosity

Answer 32

subsequent to compaction or forming of these powder particles into the desired shape, pores or void spaces exist between the powder particles

Question 33

hardness tests for ceramics

Answer 33

- Vickers and Knoop techniques | - use indenters having pyramidal shapes

Question 34

creep

Answer 34

occurs at higher temperature in ceramics