Materials - Glass

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What are glass qualities?
Stiffness (structural), brittle (normal), strength in compression, variable tensile strength, hard but easily damaged, normal glass fractures with sharp surfaces, corrosion resistant
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What's formal glass definition?
Glass is inorganic product of fusion (melting) which has cooled to rigid solid without crystallisation
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What is glass structure?
SiO4 structure, Si has 4+ charge and O has 2-(tetrahedron)
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What is order of glass like?
Glass has short range order, long range disorder
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How do specific volume (V/M) and viscosity change as glass cools?
As temperature increases, glass becomes molten. From molten to glass specific vol decreases and viscosity increases
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Why is glass amorphous?
Viscosity increases as temp reduction increases viscosity inhibiting the formation of a cystalline solid
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What is effect of adding alkali oxides?
Addition of alkali oxide breaks up structure which is dominated by covalent bonds
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What does alkali additions mean for bonding?
Addition of alkali oxides leads to non-bridging oxygen atoms bonding. M2O can represent Na2O
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What does Q4 mean in bridging and how many bridges would Na2O:2SiO2 have?
Q4 means 4 bridging oxygen atoms. Na2O: 2SiO2 -> NaOSiO3/2 (3/2 non-bridging units to Si). Q3 units with 1 non-bridged oxygen atom (connected directly to Si)
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What are network formers and modifiers? How many Si atoms share oxygen?
2 Si share one oxygen. Addition of network modifiers like Na2O disrupts structure. Si/Al are network formers
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What are constituents of commercial glass?
Commercial glass has 70% SiO2, 12-16% Na2O (sodium oxide), less CaO, MgO, Al2O3
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What are constituents of borosilicate glass?
Borosilicate (pyrex glass), 80% SiO2, 12% B2O3...
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What are constituents of glass fibre ?
Glass fibre glass low alkali, 54% SiO2, <2% Na2O and K2O
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What are main glass components?
Glass forming oxides (SiO2, B2O3, PSO5), Fluxes to lower melting point (Na2O, K2O, Li2O, PbO), Property modifiers to affect chemical durability/expansion (CaO, Al2O3...), Colouring agents, Processing agents, (<1% weight to remove bubbles, As/Sb-oxide
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What are main things in processing agents?
As/Sb oxides, KNO3, NaNO3, NaCl, fluorides, sulphates etc
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What are microstructure properties of glass?
Homogeneous with no interface to scatter light, no mechanism against cracks with tension opening flaws
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What is Griffith equation?
Surface flaws lead to reduced strength. Griffith: fracture stress = K1C/ alpha* (pi*a)^0.5 where K1C = square root of 2*E*fracture energy (Pa m^0,5) and a is crack size
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What increases flaws and what reduces?
Abrasion introduces flaws. Polishing, (mechanical, flame, acid etching), reduces flaw size, increases strength and reduces strength standard deviation.
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What zones form in fracture?
Glass fracture forms mirror (smooth near crack), mist (small band, rougher), and hackle (large and irregularly oriented) zones
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What affects strength of glass? (static fatigue - tensile)
Strength of glass under load falls with time in static fatigue. Increasing rate of loading reduces time for water to diffuse to cracks and react, increasing strength. Greater temp and humidity makes strength of glass fall faster.
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What's reaction between SiO2 and water that reduces tensile strength?
Si-O-Si bonds stretched. Si-O-Si+H2O -> 2SIOH - crack growth mechanism
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What demand is there for float glass?
Float glass has Europe, North America and China as 75% of market, for windows etc. Demand affected by economic growth, legislation concerning safety and energy conservation etc
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What are materials in float glass?
80% fed to furnace, 20% cullet (recycled). Coloured glass materials : selenium, iron+cobalt oxides
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What is the first step of the float process? (ie - melting and the tin bath)
Batch formation, melting at 1600 degrees with water cooled stirrers to make melt homogeneous, then furnace pours glass over molten tin which spreads the glass and allows it to cool before ribbon drawn off bath
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What happens after glass is cooled and hardened?
Glass annealed to prevent stress, then inspected for flaws and cut up. 0.4-25 mm thick and 3m long
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What conditions are needed for tin bath?
Cooling occurs on tin bath, glass has lower density than tin so can float. Inert 95% N2 and 5% H2 atmosphere needed to prevent oxidation. Glass becomes even thickness with parallel surfaces. Glass solid enough at end to draw out
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How long can float factories last for?
11-15 years, continuously making glass.
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What can be added to glass to change colour in melting? (modified glass)
Tinted glass - Co and Ni make grey, FeO (ferrous oxide) - blue, Ferric iron (Fe2O3) - yellow, all combined make green
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What are online coatings? (modified glass)
Coated on the float - Chemical vapour deposition applies microscopically thin coating. Pilkington K Glass, Pilkington E advantage etc
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What is wired glass? (modified glass)
Wired glass made for fire resistance. Steel wire mesh sandwiched between ribbons of semi-molten glass to give a rough cast surface that may be polished
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What is specialty glass?
Optilam glass for shatter resistance and Pyroshield for fire proof
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What is laminated glass?
Laminated glass involves bonding 2 layers of glass with plasticised interlayer. Processed under controlled heat and pressure. No effects on light transmission. Absorbs 90% UV and used in homes/offices. Apple stores use on steps for grip
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What is glass fibre used for and how can glass be used in concrete?
Glass fibre used for composites/insulation. Recycled glass in concrete, or cement component (microfiller), or unbound aggregate (like sand) etc
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How is glass used to make worktops and tiles?
Polymer/resin bonded glass products made of 45% recycled glass bottles. They're crushed and bound with a solvent free resin, poured in a mould, and make worktops etc
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What glass makes decorative glass tiles? What types of paving can glass make?
Decorative glass tiles made from granular bottle glass - pressed and melted. Pavers, slips and tiles can be made from glass.
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Card 2

Front

What's formal glass definition?

Back

Glass is inorganic product of fusion (melting) which has cooled to rigid solid without crystallisation

Card 3

Front

What is glass structure?

Back

Preview of the front of card 3

Card 4

Front

What is order of glass like?

Back

Preview of the front of card 4

Card 5

Front

How do specific volume (V/M) and viscosity change as glass cools?

Back

Preview of the front of card 5
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