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Materials > Ceramics > Flashcards

Ceramics Flashcards

1
Q

What is the definition of a ceramic?

A

Inorganic, non-metallic materials

They are typically crystalline, with some glassy phases

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2
Q

What compounds are ceramics made from? Give some examples

A 
Formed from compounds of metallic and non-metallic elements
e.g. 
aluminium and oxygen (alumina) (Al2O3)
Calcium and oxygen (CaO)
Silicon and Nitrogen
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3
Q

Give some examples of ceramic products

A

Clay products, whitewares, refractories, glass, abrasives

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4
Q

Where are ceramics used in civil engineering?

A

Bricks and glass

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5
Q

What are the general properties of ceramics?

A
  • High compressive strength, relatively low tensile strength
  • Low toughness/ brittle
  • Relatively high hardness
  • Good thermal and electrical insulators
  • very good durability under environmental conditions
  • Relatively low cost, despite thermal processing
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6
Q

What are the advantages of brick over stone?

A

Processing advantages out weigh higher energy costs
Lower application costs
Rerlatively low skill to install

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7
Q

How are traditional ceramics manufactured?

A

This applies to pottery, porcelain, tiles…

  • Moulded in plastic state
  • then fired (sintered or ‘burnt’)
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8
Q

What are the phases of tratditional ceramics (clays)?

A 
Glassy phate (melts and ''glues'' poly christalline multiphase body)
This is done through multiphase sintering
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9
Q

Clays are complex hydrated alumino silicates, give some examples

A

Kaolinite
Montmorrilonite

With silicates feldspar and quartz sand/ flint

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10
Q

What are the six categories of clays used in industry?

A 
Brick clay
bentonite
Common clay
Fire clay
Fuller's earth
kaolin
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11
Q

What is the size range of ceramic powders?

A

0.5 - 5 um

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12
Q

What makes up a clay?

A

Ceramic powder with water

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13
Q

What makes up most traditional ceramic materials?

A

A mixture of clays

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14
Q

What are the three phases of sintering?

A
  • initial green body
  • intermediate
  • final sintered body
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15
Q

What happens in liquid phase sintering?

A
  • Glassy phhase may melt and wet higher melting point consituents
  • Liquid draws the solid together by viscous flow and capillary pressure
  • Liquid phase may cool to a glass or chrystallise
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16
Q

If the liquid phase in ceramics cools to a glass what does it mean for the high temperature properties?

A

Poor, if it chrystallises, the thermal properties are improved

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17
Q

Give a range of temperatures for ceramics

A

850 C (tiles) to >1650 C for engineering ceramics

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18
Q

Give the names of 3 engineering ceramics

A

Silicon nitride
Silicon carbide
Zirconium oxides

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19
Q

Describe the microstructure of alumina

A

Large chrystalline particles with glassy phase in between, There are also microscopic holes

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20
Q

Describe typical ceramic microstructure

A

Chrystalline phases
Amorphous (glassy) phase
porosity

21
Q

Why are dislocations in ceramics so dangerous?

A

Dislocations in ceramic and glassy materials are not mobile

22
Q

What do pores and surface pores act as in ceramics?

A

Stress concentrators (Griffith flaws)

23
Q

What are the properties of ceramics?

A
  • High hardness
  • Low toughness (brittle)
  • Low tensile strength
  • High compressive strength
24
Q

What is Griffith’s equation?

A 
sigma_f = K_Ic/(alpha*sqrt(pi*a))
K_Ic = Fracture toughness
alpha = geometrical factor (~1)
a = size of the biggest crack under stress
25
Q

What does Griffith’s equation say about ceramics?

A

The strength is much less than expected as they have many flaws - this makes ceramics brittle

26
Q

What is the equation for the stress intensity factor?

A 
K1 = alpha*sigma*(sqrt(pi*a))
sigma = nominal stress
a = crack depth
alpha = the constant dependent on the crack and test piece geometry
27
Q

What does the stress intenisty factor K_1c describe?

A

The intesnity of the elastic crack tip stress field in a thick

28
Q

What is the effect of oversintering on the microstructure?

A

It opens up the pores - reducing the strength

29
Q

What is the general structure of ceramic processing technologies?

A
  1. Particle forming processes
  2. Powder pressing/ extrusion/ slip casting
  3. drying
  4. firing (sintering)
  5. ceramic product
30
Q

Give some examples of particle forming processes

A

Slurry formation
Moisture optimisation
spray drying

31
Q

Give some examples of powder pressing

A

Hot pressing
Uniaxial pressing
Isostatic pressing

32
Q

How does spray drying work?

A

Slurry is sprayed and dried to form agglomerated particles that flow

33
Q

How does slip-casting ceramics work?

A
  1. Slip is poured into mould
  2. Water absorbed
  3. Finished piece
34
Q

How does thin walled slip casting work?

A
  1. slip is poured into mould
  2. mould is drained
  3. top trimmed
  4. finished piece
35
Q

How does extrusion of ceramic bodies work?

A

A ram goes into a dummy block that pushes the wet ceramic in a container through a die, forming the final shape

36
Q

What ceramic products are made by extrusion?

A

Bricks and pipes

37
Q

What are Adobe bricks?

A

Unfired clay bricks

38
Q

Where are adobe blocks used?

A

Latin America, Africa, The Indian subcontinent

39
Q

When do Adobe bricks date back to?

A

8000 BC

40
Q

How many bricks are manufactured in the UK per annum?

A

2.7 billion

41
Q

How many bricks were made at peak production in the Uk and when?

A

10-12 billion (1930s)

42
Q

How are bricks manufactured?

A 
pressed at a high temperature
Clay helps act as a fuel during firing
Using coarse granular material from quarry
Extruded at very high rates
Then wire cut
43
Q

What are the benefits of masonry?

A

Durability

44
Q

What are the main destructive agents for bricks?

A 
Water
frost (Repeated freeze/ thaw cycles do most damage)
Temperature change
45
Q

What signs of wear do bricks exhibit?

A

Flaking, spalling and mortar joint crumbling

46
Q

What makes up the white efflorescence on bricks, and when does it occur?

A

Sodium, potassium and magnesium sulphates
Occurs in the early life of a bulding, after wet conditions
The deposit of salt solution on the surface of the water

47
Q

What causes Iron staining of bricks?

A

Occurs in wire bricks and those with high iron content
Iron salts migrate to the surface
It is cause by the saturation of immature bricks
Disappears with natural weathering

48
Q

What causes lime staining on bricks?

A

Free lime in mortar leaches
Occurs when work is left without being covered
Triggered by water - e.g. rain

Materials (13 decks)

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