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CIVE40007 – Materials > Ceramics > Flashcards

Ceramics Flashcards

1
Q

What is an Ashby diagram?

A

Is a scatter plot used to showcase properties of different materials.

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2
Q

What is embodied energy in materials?

A

The total energy consumed during all processes of the material’s life cycle.
- Used in mining, extraction, transportation, processing and manufacturing

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3
Q

What are two sources of raw material?

A
  • Mining and quarrying
  • Agriculture
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4
Q

What is concretes embodied energy like compared to other materials?

A

Concrete is a low-energy material relative to other materials like low-carbon steel and silicon.

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5
Q

How cna ceramics be defined?

A

Ceramics can be defined as inorganic, non-metallic materials.

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6
Q

What are some properties of ceramics?

A

Typically crystalline, with some glassy phase

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7
Q

What elements are ceramics formed from?

A
  • Silicon and nitrogen
  • Calcium and oxygen
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8
Q

What is included in the ceramic industry?

A

Clay products → roofing tiles

Whitewares → Dinnerware

Refractories → Brick and monolithic products

Glass → Flat glass

Abrasives → Natural and synthetic, diamond

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9
Q

What are the general properties of ceramics?

A
  • High compressive strength
  • Tensile strength is relatively low
  • Low toughness/brittle materials
    – no significant mechanisms to stop cracks from propagating
  • Relatively high hardness (some are very hard)
  • Relatively low cost, despite the need for thermal processing
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10
Q

What are the key points to do with using stone in construction?

A
  • Stone of various types: lowest energy and carbon dioxide emissions
  • Needs a combination of cheap and skilled labor
  • High energy input during construction
  • Property limitations on design and use
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11
Q

What are the advantages of brick over stone?

A
  • Lower application costs
  • Relatively low skill
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12
Q

What is involved in ceramic manufacturing?

A
  • Sintering
  • Clays moulded on a plastic state and fired
  • Glassy phases which melts and ‘glues’ together a complex polycrystalline multiphase body
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13
Q

What are the six categories of clay materials used in industry?

A
  • Brick clay
  • Bentonite
  • Common clay
  • Fire clay
  • Fuller’s earth
  • Kaolin
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14
Q

What is the structure of clay?

A
  • Silica in the middle and four oxygens bonds
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15
Q

What is waters role in the clay platelet structure?

A

Polar water molecules acts as a lubricant between layers and make clay slippery

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16
Q

What are usually the saize of ceramic powders?

A

Ceramic powders are typically in the size range of 0.5 - 5.0 µm

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17
Q

What is clay?

A

Clays are weathered minerals of sizes 0.5 - 5.0 µm mixed with water

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18
Q

What are traditional ceramic materials made from?

A

mixtures of clays

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19
Q

What optimises sintering?

A

Engineering ceramic powders are synthesized

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20
Q

What is a green body?

A
  • Used for raw pre mature ceramics
  • An object whose main constituent is weakly bound clay material
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21
Q

What temperatures are used for sintering?

A

Sintering temperatures vary from 850°C for tiles to >1650°C for engineering ceramics

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22
Q

What are the key features of the ceramic microstructure alumina?

A
  • Crystals of aluminium oxide
  • 96% alumina with MgO, CaO and SiO_2
  • Thermally etched surface
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23
Q

What does the ceramic microstructure usually consist of?

A
  • Crystalline phases
  • Amorphous (glassy) phase - helps in the sintering process
  • Porosity - cannot get out of material
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24
Q

What are dislocations?

A
  • Dislocations contribute to plastic deformation under high temperatures or stress
  • Dislocations in crystalline and glassy materials are not mobile → brittle materials cannot move to overcome applied stresses
25
Q

What is the roles of pores and surface flaws?

A
  • act as stress concentrators
26
Q

What is a disadvantages of ceramics?

A

No stress relieving mechanism to inhibit crack propagation

27
Q

Where are the flaws in brittle materials?

A

Flaw in the middle, stress at defect is higher

28
Q

What does amplification depend on?

A

Amplification depends on orientation, geometry, and dimensions.

29
Q

What is tensile frcture stress controlled by?

A

Controlled by defects present either from fabrication or surface damage

30
Q

What is griffiths equation?

A

tensile fracture stress = fracture toughness/geometrical factorsqrt(pia)

31
Q

What does griffiths calculation show?

A

Explains why a brittle material strength is much lower than expected

32
Q

What does the stress intensity factor describe?

A

Describes the intensity of the elastic crack tip stress field in a thick, deeply cracked specimen loaded perpendicular to the crack plane.

33
Q

What is the stress intensity factor equation?

A

K_1 = α σ (πa)1/2
- a is the crack depth
- α is a constant
- σ is the nominal stress

34
Q

What happens to the properties as the microstructure changes?

A

Changes

35
Q

What does sintering lead to?

A

Causes shrinkage to occur

36
Q

What happens if sintering temps increase?

A
  • Density increase and so does shrinkage
37
Q

What are the steps in producing ceramics?

A
  1. Particle forming processes
  2. Slurry formation, moisture optimisation, spray drying
  3. Powder pressing/ extrusion/ slip casting
  4. Drying
  5. Firing(sintering)
  6. Ceramic product
38
Q

What are the 3 types of pressing?

A
  • Hot pressing
  • Uniaxial pressing
  • Isostatic pressing
39
Q

What is involved in spray drying of ceramic powders?

A
  • Slurry is sprayed and dried to form agglomerated particles that flow
  • Packs much better
40
Q

What moulds are used for slip casting?

A

Porous gypsum moulds

41
Q

How does slip-casting work?

A
  • Mix particles in slurry form → mill in a solution
  • Pour slip into the cavity
  • Pour the water out of the slurry and leave a residue of powder inside the mould
  • Sinter
42
Q

What are the stages of cermaic products in terms of its structure?

A
  • Granular powder
  • Compacted green body
  • Ceramic component
43
Q

What are adobe mud blocks?

A
  • Adobe mud blocks are one of the oldest and most widely used building materials
  • Use of these sun-dried blocks dates back to 8000 B.C
  • Very common in Latin America, Africa and India
44
Q

How many bricks are manufactured in the UK currently?

A

2.7 billion bricks currently manufactured in the UK per annum

45
Q

Whats involved in the manufacture of bricks?

A
  • Extraction of clay
  • Varies in color
  • Extruded bricks and wire cut
  • Fired for about 7 days at max temp 1100˚C
46
Q

What are detsructive agents affecting masonry?

A
  • Water
  • Frost
  • Temperature change
47
Q

What happens when brick work absorbs water?

A

Interact with mortar

48
Q

What can bricks surfaces suffer from?

A

Brick surfaces may suffer from flaking or spalling and mortar joints will crumble when frost failure occurs

49
Q

What does most damage to masonry?

A
  • Repeated freeze/thaw cycles do most damage.
50
Q

What is effloresence on bricks?

A
  • Occurs during early life of a building, after wet conditions
  • Usually composed of sodium, potassium, and magnesium sulfates
  • White powdery substance
51
Q

How does efflorensence occur?

A
  • Salts in brickwork are dissolved by water
  • As the wall dries the salt solution becomes more concentrated
  • They deposit on the surface as white discoloration
52
Q

What is iron staining of bricks?

A

Clays have high iron content and under certain conditions can migrate out and can oxidise to form brown stain

53
Q

How does iron staining occur?

A

Iron staining is caused by the saturation of immature bricks

54
Q

How can you get rid of iron staining?

A

It disappears with natural weathering, but this can take many years

55
Q

What is lime staining?

A

Free lime present in mortar leaches out and leaves lime staining

56
Q

How does lime staining occur?

A
  • Occurs when work left without being covered
  • Exposure to rain triggers the process
  • White deposit forms where water removes lime from cement
57
Q

Sintered ceramics are typically characterised by…

A

The presence of crystalline phases

58
Q

What are some properties of the microstructure of ceramics?

A
  • high hardness, low toughness
  • low tensile strength, high compressive strength

CIVE40007 – Materials (16 decks)

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