notes 12 (Structure & Properties of Cermamics) Flashcards Preview

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Flashcards in notes 12 (Structure & Properties of Cermamics) Deck (29)
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1
Q

what are ceramics

A

Inoganic non-metallic materials. typically compounds of metallic and non-metallic elements

2
Q

what bonding is found in Ceramics

A

Ionic or Covalent or a combination of both

3
Q

List some properties of Ceramics

A
  1. Hard & Brittle, aka low toughness and ductility)
  2. Good electrical and thermal insulators
  3. high melting points and good chemical stability
4
Q

what does the coordination reflect in ceramics

A

the ratio of the sizes of the ions

5
Q

what are the 2 factors which determine crystal structure of ceramics

A
  1. relative sizes of ions(the more tightly compacted, the more stable)
  2. the maintenance of charge neutrality
6
Q

what is the coordination number?

A

the number of adjacent atoms surround a reference atom without overlap of electron orbitals

7
Q

what can be said about silicates?

A
  1. maintain charge neutrality

2. ionically bond (SiO4)4- to one another

8
Q

glass structure

A

glass is amorphous(non-crystalline)

9
Q

describe Carbon

A

it is Polymorphic: diamond;graphite;fullerness

10
Q

Diamond characteristics(5)

A
  • strong covalent bonds
  • hardest known material
  • very low electrical conductivity
  • very high thermal conductivity
  • optically transparent
11
Q

Graphite properties (5)

A
  • in-plane covalent bonding
  • gives easy interplanar cleavage
  • high electrical conductivity i the plane
  • good strength
  • low thermal expansion
12
Q

Types of point defects in ceramics

A

vacancies: can exist for both cations and anions
Interstitials: can exist for cations
Frenkel defect: a cation vacancy-cation interstitial pair
shottky defect: a paired set of cation and anion vacancies

13
Q

why do interstitial vacancies not exist for anions

A

because anions are relatively large compared to the interstitial sites

14
Q

Mechanical Properties of ceramics

A
  1. brittle
  2. tensile strengths are very low
  3. compressive strengths are very high
  4. High HARDNESS
  5. the strength is typically dictated by defects/flaws
15
Q

what can be said about ionic crystals with respect to their slip systems

A

they have very few slip systems and charge neutrality problems

16
Q

Do ceramics have plastics deformation?

A

NO, unless at very high temperatures

17
Q

what is a flexural test?

A

measurement of elastics modulus or flexural strength

18
Q

how doe non crystalline ceramics deform

A

by viscous flow, like liquids

19
Q

what is affected by pores in ceramics

A

the stiffness, the flexural strength

20
Q

which is usually smaller in size: cations or anions

A

cations

21
Q

true or false, the larges the atoms size, the more atoms you can pack around it

A

true

22
Q

for like sized atoms, what is the coordintation number

A

12

23
Q

list the coordination number for the following cation-anion ratios:

A
2-linear
3-triangular
4-tetrahedral
6-octahedral
7-cubic
24
Q

what is particular about the anitfluorite structure:

A

the positions of cations and anions are reversed

25
Q

silica is polymorphic; which materials can it form

A

quartz, crystobalite, tridymite

26
Q

In layered silicates, how are adjacent layers bonded together

A

van der waals forces

27
Q

what is the structure of Fullerness

A

Hollow spherical cluster of 60 carbon atoms

28
Q

what is the elastic behaviour like (graphically) for ceramics

A

linear

29
Q

if a ceramic contains pres, what property would this affect?

A

Stiffness and Flexural strength