Materials - Ceramics

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What is embodied energy?
All the energy consumed by the processes associated with production of a development.
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What is a lifecycle analysis?
Study of impacts of production, use, and disposal of product. To analyse environmental impact
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What are ceramics? What order do they have?
Inorganic non-metallic materials, formed between compounds of metallic and non metallic materials (eg alumina, Al2O3), crystalline with glassy phase
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What are industry needs for ceramics?
Clay products - bricks, sewer pipes, roofing tiles. Whitewares. Refractories = brick and monolithic products, glass - flat glass and glass fibres for insulation, abrasives - diamond, garnet etc
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How has demand for brick changed?
Brick production, delivery, and stock have decreased from the 1950s until now
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What are qualities of ceramics?
High compressive strength, low tensile strength. Brittle (low toughness), hard, thermal and electrical insulators, durability and low cost
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What are advantages and disadvantages of working with stone? (consider stone wall)
Stone construction is low energy and CO2 emissions, needs cheap and skilled labour. Dry stone walls demand highly skilled labour, have energy intensive construction and the right materials aren't always available
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Why is brick better than stone?
Bricks have processing advantages although also higher energy costs. Application costs and skill requirements lower
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How is clay constructed?
Similar method to 2000 years ago. Clays moulded in plastic state then fired (sintered or burnt).
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What's liquid phase sintering in clay?
Clay consists of a glassy phase which melts and glues together a polycrystalline multiphase body. Liquid phase sintering
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What's a trickier name for clays?
Clays are complex hydrates aluminosilicates, (Kaolinite, feldspar, quartz)
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What is clay made from?
Clays are minerals rich in alumina, silica, and water. Wet clays are plastic, when heated become hard. Clay made from fine materials: flakes, fibres, hollow tubes. May contain iron oxide, silica, rock fragments
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What clays are used in industry?
Brick clay, bentonite, common clay, fire clay, Fuller's earth, kaolin
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What is clay structure?
Silicate tetrahedron sheet (-ve) followed by metallic octahedron (+ve). They are layered with interlayers
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Why is clay slippery?
Polar water molecules with positive charge on one side and negative on the other form layers between clay molecules (platelets) in expanded clay
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What is the size of ceramic powder molecules?
Ceramic powders are 0.5-5 micrometres. Clays are weathered minerals mixed with water. Ceramics are made from clay mixtures.
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What is liquid phase sintering?
Glassy phase melts and wets higher melting point constituents. Liquid draws solid together by viscous flow, driven by capillary pressure. Liquid phase may cool to a glass or crystallise. Temperatures vary from 850 degrees for tiles to 1650
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What temperature do engineering ceramics need to be sintered at?
Engineering ceramics such as silicon nitride/carbide need sintering at 1650 degrees
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What's difference between normal and high purity alumina?
Alumina has 250 micrometre grain size. High purity alumina inhibits grain growth with MgO and is more orderly
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Why are ceramics brittle?
Ceramics have crystalline phases, glassy phases, and porosity. Dislocations aren't mobile so brittle. Pores and surface flaws (Griffith flaws) stress concentrators - no relieving mechanism for cracks.
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What are qualities of ceramics?
High hardness and compressive strength, low toughness and tensile strength. Oxidised - chemical durability.
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What happens to stresses at microcracks?
Applied stress is amplified at micro-cracks, amplification relies on geometry.
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What is Griffith's equation?
Fracture stress = K1C/ α *(pi*a)^0.5 where K1C is fracture toughness, alpha is geometric factor which tends to 1, and a is size of biggest crack.
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What is effect of sintering temperature on properties?
Density and shrinkage increase while water absorption decreases
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What's process of making ceramics?
Slurry formation of water and clay, moisture optimisation, spray drying with atomiser makes agglomerated particles. Powder pressing/extusion/slip casting occurs, then drying, firing, and product
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What's extrusion?
Use ram to force billet through die-extrusion. Used for pipes and bricks
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What is uniaxial pressing?
Putting clay under high pressures to produce solid result, compacted
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What is slip casting?
Pour slip (liquid ceramic) in mould. Water is then absorbed.
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What are adobe unfired bricks?
They're mud blocks, one of the oldest and most widely used building materials. Used across Latin America, Africa, Asia, Middle East etc
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Compare modern and conventional brick making?
Conventional brick making had colour and property variance. Modern brick making presses them at high pressure, extrudes bricks and does wire cuts at higher pressure. In modern gas-fired tunnel kilns, clay is heated for 7 days up to 1100 deg
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How do freeze-thaw cycles affect ceramics?
Freeze-thaw cycles can occur from water absorption. Brick surfaces then crack/spall while mortar joints crumble
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Is there a correlation between frost resistance, strength, and water absorption?
No simple correlation between frost resistance, strength, and water absorption
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What's efflorescence?
White discolouration - occurs from sodium/potassium/magnesium sulphates leaching out of bricks due to water.
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What's iron staining?
Iron staining - occurs in wire cut bricks or bricks with clays containing iron. Iron salts migrate to surface and oxidise, turning surface brown. Due to saturation. Disappears after weathering for years
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What's lime staining?
White deposit forms where water removes lime from mortar
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Other cards in this set

Card 2

Front

What is a lifecycle analysis?

Back

Study of impacts of production, use, and disposal of product. To analyse environmental impact

Card 3

Front

What are ceramics? What order do they have?

Back

Preview of the front of card 3

Card 4

Front

What are industry needs for ceramics?

Back

Preview of the front of card 4

Card 5

Front

How has demand for brick changed?

Back

Preview of the front of card 5
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