Chapter 12

Question 1

What is the bonding and bonding charactersrtics of Ceramics?

Answer 1

Ionic and Covelant Bonding.

% ionic character increases with difference in electronegaticity of atoms.

Question 2

What are the factors that determine the crystal structure?

Answer 2

Relative sizes of ions and the maintenance of charge neutrality (Net charge in ceramic should be zero)

Question 3

How do you form a more stable structure?

Answer 3

Maximize the # of oppositely charged ion neighbors.

Question 4

How does coordination number increase?

Answer 4

r_cation / r_anion (ratio of cations to anions in terms of radius)

Question 5

Which has a larger radius Anoins or Cations?

Answer 5

Anions

Question 6

What is the charge of an anion?

Answer 6

Negative

Question 7

What is the charge of an cation?

Answer 7

Positive

Question 8

What are characteristics of Oxide Structures for Ceramic materials?

Answer 8

1) Oxeygen anions larger than metal anions.
2) Close packed oxygen in a lattice (Usually FCC)
3) Cations fit into interstitial sites among oxegyn ions

Question 9

What are the Coordination # and structure for diffrent r_c/r_a?
1) < 0.155
2) 0.155 - 0.225
3) 0.225 - 0.414
4) 0.414 - 0.732
5) 0.732 -1.0

Answer 9

1) 2, Linear
2) 3, Traingular
3) 4, Tetrahedral (ZnS , Zinc Blend)
4) 6, Octahedral (NaCl, Sodium Chloride)
5) 8, Cubic (CsCl, Cesium Chloride, AX Structure)

Question 10

What are the most common coordination numbers for ceramics?

Answer 10

4,6,8

Question 11

When is Bond Hybridization possible?

Answer 11

When there is significant covelant bonding.

Question 12

What common compounds have NaCl structure?

Answer 12

MgO and FeO

Question 13

What are AX_2 Crystal Structures?

Answer 13

When the charge of the cation and anion are not the same.

Question 14

What is AX_3 crystal structure?

Answer 14

When there are two types of cations in a compound

Question 15

What are Silicate Ceramics?

Answer 15

Ceramics composed of oxegyn and silicon.

Question 16

What are characterstics of SiO_2?

Answer 16

Polymorphic (has more than one crystal structure) forms are quartz, crystobalite, and tridymite.
Bonds lead to a high melting temperature 1710 degrees Celsius.
Basic compund for glass.

Question 17

What are characteristics of layered Silicates?

Answer 17

Have negative charge that is blanced by adjacent plane rich positively charged cations.

Question 18

What is characterstic of Diamond?

Answer 18

Tetrahedral bonding of carbon (hardest material known, very high thermal conductivity). Used for cutting tools and medical devices.

Question 19

What are characteristics of graphite?

Answer 19

Parallel hexagonal arrays of carbon atoms, weak van derWaal’s forces between layers, planes slide easily over one another - good lubricant.

Question 20

Types of defects in ceramics?

Answer 20

Vacancies (exist for both cations and anions), Interstital (exist usually for only cations but can happen in anion as well), Frenkel defect, Shottky defect (a paired set of cation and anion vacanies)

Question 21

What are the two types of impurities in Ceramics?

Answer 21

Substitutional cation and Subsitutional anion impurity