Ceramics

Question 1

What is an Ashby diagram?

Answer 1

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

Question 2

What is embodied energy in materials?

Answer 2

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

Question 3

What are two sources of raw material?

Answer 3

• Mining and quarrying
• Agriculture

Question 4

What is concretes embodied energy like compared to other materials?

Answer 4

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

Question 5

How cna ceramics be defined?

Answer 5

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

Question 6

What are some properties of ceramics?

Answer 6

Typically crystalline, with some glassy phase

Question 7

What elements are ceramics formed from?

Answer 7

• Silicon and nitrogen
• Calcium and oxygen

Question 8

What is included in the ceramic industry?

Answer 8

Clay products → roofing tiles

Whitewares → Dinnerware

Refractories → Brick and monolithic products

Glass → Flat glass

Abrasives → Natural and synthetic, diamond

Question 9

What are the general properties of ceramics?

Answer 9

• 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

Question 10

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

Answer 10

• 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

Question 11

What are the advantages of brick over stone?

Answer 11

• Lower application costs
• Relatively low skill

Question 12

What is involved in ceramic manufacturing?

Answer 12

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

Question 13

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

Answer 13

• Brick clay
• Bentonite
• Common clay
• Fire clay
• Fuller’s earth
• Kaolin

Question 14

What is the structure of clay?

Answer 14

• Silica in the middle and four oxygens bonds

Question 15

What is waters role in the clay platelet structure?

Answer 15

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

Question 16

What are usually the saize of ceramic powders?

Answer 16

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

Question 17

What is clay?

Answer 17

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

Question 18

What are traditional ceramic materials made from?

Answer 18

mixtures of clays

Question 19

What optimises sintering?

Answer 19

Engineering ceramic powders are synthesized

Question 20

What is a green body?

Answer 20

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

Question 21

What temperatures are used for sintering?

Answer 21

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

Question 22

What are the key features of the ceramic microstructure alumina?

Answer 22

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

Question 23

What does the ceramic microstructure usually consist of?

Answer 23

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

Question 24

What are dislocations?

Answer 24

• 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

Question 25

What is the roles of pores and surface flaws?

Answer 25

- act as stress concentrators

Question 26

What is a disadvantages of ceramics?

Answer 26

No stress relieving mechanism to inhibit crack propagation

Question 27

Where are the flaws in brittle materials?

Answer 27

Flaw in the middle, stress at defect is higher

Question 28

What does amplification depend on?

Answer 28

Amplification depends on orientation, geometry, and dimensions.

Question 29

What is tensile frcture stress controlled by?

Answer 29

Controlled by defects present either from fabrication or surface damage

Question 30

What is griffiths equation?

Answer 30

tensile fracture stress = fracture toughness/geometrical factor*sqrt(pi*a)

Question 31

What does griffiths calculation show?

Answer 31

Explains why a brittle material strength is much lower than expected

Question 32

What does the stress intensity factor describe?

Answer 32

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

Question 33

What is the stress intensity factor equation?

Answer 33

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

Question 34

What happens to the properties as the microstructure changes?

Answer 34

Changes

Question 35

What does sintering lead to?

Answer 35

Causes shrinkage to occur

Question 36

What happens if sintering temps increase?

Answer 36

- Density increase and so does shrinkage

Question 37

What are the steps in producing ceramics?

Answer 37

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

Question 38

What are the 3 types of pressing?

Answer 38

- Hot pressing - Uniaxial pressing - Isostatic pressing

Question 39

What is involved in spray drying of ceramic powders?

Answer 39

- Slurry is sprayed and dried to form agglomerated particles that flow - Packs much better

Question 40

What moulds are used for slip casting?

Answer 40

Porous gypsum moulds

Question 41

How does slip-casting work?

Answer 41

- 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

Question 42

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

Answer 42

- Granular powder - Compacted green body - Ceramic component

Question 43

What are adobe mud blocks?

Answer 43

- 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

Question 44

How many bricks are manufactured in the UK currently?

Answer 44

2.7 billion bricks currently manufactured in the UK per annum

Question 45

Whats involved in the manufacture of bricks?

Answer 45

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

Question 46

What are detsructive agents affecting masonry?

Answer 46

- Water - Frost - Temperature change

Question 47

What happens when brick work absorbs water?

Answer 47

Interact with mortar

Question 48

What can bricks surfaces suffer from?

Answer 48

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

Question 49

What does most damage to masonry?

Answer 49

- Repeated freeze/thaw cycles do most damage.

Question 50

What is effloresence on bricks?

Answer 50

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

Question 51

How does efflorensence occur?

Answer 51

- 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

Question 52

What is iron staining of bricks?

Answer 52

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

Question 53

How does iron staining occur?

Answer 53

Iron staining is caused by the saturation of immature bricks

Question 54

How can you get rid of iron staining?

Answer 54

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

Question 55

What is lime staining?

Answer 55

Free lime present in mortar leaches out and leaves lime staining

Question 56

How does lime staining occur?

Answer 56

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

Question 57

Sintered ceramics are typically characterised by...

Answer 57

The presence of crystalline phases

Question 58

What are some properties of the microstructure of ceramics?

Answer 58

- high hardness, low toughness - low tensile strength, high compressive strength