Test 3. Chapter 12

Question 1

ceramic bonding?

Answer 1

• mostly ionic, some covalent

- % ionic character increase with difference in electronegativity

Question 2

ceramic bonding depends on what?

Answer 2

bonding

large vs small ionic bond character

Question 3

define coordination number

Answer 3

maximize the number of nearest oppositely charged neighbors

Question 4

what is charge neutrality

Answer 4

net charge in the structure should be zero

Question 5

coordination number increases with ???

Answer 5

rcation/ranion

Question 6

AX-type crystal structures include, _____________-

Answer 6

NaCl, Cs,Cl, and zinc blende

Question 7

AX2 crystal structure includes

Answer 7

UO2, ThO2, ZrO2, CeO2, fluorite

Question 8

why are ceramics more brittle than metals?

Answer 8

slippage along planes

• in ionic solids this slippage is very difficult
• too much energy needed to move one anion past another anion

Question 9

How can you measure elastic modulus

Answer 9

Room T behavior is usually elastic, with brittle failure.

Question 10

why is 3 point bend testing often used?

Answer 10

tensile tests are difficult for brittle materials

Question 11

most common elements on earth are _____________?

Answer 11

Si, O

Question 12

silicate ceramics

Answer 12

crystobalite

They are so small that the they have unusually unit structure. They share oxygen atoms

Crystalline SiO2 (silica) structures are quartz,
crystobalite, & tridymite

• The strong Si-O bond leads to a strong, high melting
material (1710ºC)

Question 13

armorphous silica

Answer 13

done have organized patter for the way we assemble the basic structure together

not enough atoms to cancel out the charge of the oxygen atoms so now you have HYDROGEN atoms added

Silica gels - amorphous SiO2

– Si4+ and O2- not in well-ordered
lattice

– Charge balanced by H+
(to form
OH-
) at “dangling” bonds
• very high surface area > 200 m2
/g

– SiO2
is quite stable, therefore
unreactive
• makes good catalyst support

Question 14

define silica glass

Answer 14

a dense form of amorphous silica

• has Na+ ions to correct charge inbalance. “counter cations”

– Borosilicate glass is the pyrex glass used
in labs
• better temperature stability & less brittle than sodium
glass

Question 15

silicates

Answer 15

Combine SiO4
4- tetrahedra by having them share
corners, edges, or faces

Cations such as Ca2+, Mg2+, & Al3+ act to
neutralize & provide ionic bonding

Question 16

layered silicates

Answer 16

– SiO4 tetrahedra connected
together to form 2-D plane

• (Si2O5)2-
• So need cations to balance charge

Question 17

carbon forms

Answer 17

amorphous/olycrystalline-surface area ca 1000m^2/g

Question 18

what are different forms for diamond? and describe?

Answer 18

– tetrahedral carbon
• hard – no good slip planes
• brittle – can cut it

– large diamonds – jewelry

– small diamonds
• often man made - used for
cutting tools and polishing
– diamond films (artificial)
• hard surface coat 

– tools,
medical devices, etc.

Question 19

carbon forms - graphite

Answer 19

• layer structure-aromatic layers
• weak van der waals forcer between layers
• planes slip easily, good lubricant

Question 20

carbon forms- fullerenes and nanotubes

Answer 20

• fullerenes or carbon nanotubes
• wrap the graphite sheet by curving into ball or tube
• buckminister fullerness

Question 21

what are some defects in ceramic structures?

Answer 21

frenkel defect- a cation is out of place ( a pair of cation vacancy +cation interstitial_

shottky defect- a pair set of cations and anion vacancy

Question 22

impurities must also satisfy __________= electroneutrailty

Answer 22

charge valance

Question 23

ceramic materials have _________ and __________ bonding

Answer 23

covalent and ionic bonding

Question 24

structures based on :

Answer 24

CHARGE NEUTRALITY

maximizing # of nearest oppositely charged neighbors

Question 25

structures may be predicted based on:

Answer 25

ratio of the cation and anion radi

Question 26

defects ?????//

Answer 26

must have preserved charge neutrality

have a concentration that varies exponentially w/T

Question 27

room T mechanical response is elastic, but fracture is brittle negligible deformation

-elevated T creep properties are generally superior to those of metals (and polymers)

Answer 27

general