Glass Flashcards
Why did they used to have lead-framed windows?
Leaded windows because the squares were as big as they could cast
What buildings use stained glass windows?
Cathedrals
What is the glass feature in the British museum?
Glass ceiling
What is example of structural glass?
Stairway, e.g., used in apple stores
What are the key properties of glass?
- High stiffness (High Young’s Modulus)
- Low toughness → associated with catastrophic failure
- Weak in tension unless made into small fibers → held in a matrix cementitious or polymer
- Easily damaged
- Excellent corrosions
- Low leaching of contaminants
What are the properties of specific types of composite glass?
- High tensile strength
- Low thermal conductivity
- Heat resistant (fire protection)
- Provide noise control
- Decorative/photographic
- High impact
What are characterisitics of glasses?
- Amorphous, non-crystalline, with no long range repeated order
- Produced from liquid state by continuous cooling
- Inorganic product of fusion
What is the structure of glass?
- SiO_4 tetrahedron is the basic building block for most commercial glasses
- Covalent and strong bonds
What is crystalline silica composed of?
- Quartz
- Planes of atoms and it is a regular array
- Short range order
What temps do you need for fusion to occur?
- 1800˚C
Why is sodium carbonate added to sand?
Sodium carbonate added to lower the temp
Glass topic
Why are lead, flint and iron added to the mixture?
Added to absorb infrared radiation
What happens on melting the raw material?
- Specific volume does not have an abrupt transition at a fixed temp
- Retains amorphous structure of liquid phases
What does the viscosity vs temperature curve show?
- Viscosity increased
- Viscosity inhibits ability to form a crystalline solid
- Soda-lime glass is workable at much better temp, lower viscosity
What happens when you add alkali oxides in glass?
- Break up structure
- Disorder due to a distribution of bond distances and angles
What elements make up the microstructure of glass?
- Sodium network modifier
- Silica glass former
- Aluminium network former
- Calcium network modifier
What is the structure of alkali silicate glasses?
- Additional charge of sodium means only 3 bonds so spare oxygen makes charge neutral
- Ionic non-bridging oxygens formed when alkali added like sodium
- Glassy and amorphous
What are the raw materials used in making glass?
- Silica Sand
- Feldspathic sand
- Sodium carbonate → produce soda ash
- Calcium carbonate
Whats the compositon of commercial glass?
- 70%-74% - SiO_2
- 12% -16% - Na_2O
What do special glasses contain?
Special glasses contain polymer layers or special coating
What are the different types of glass components?
- Glassing forming oxides:
- usually the dominant compositional constituent - Fluxes that reduce melting temp
- Property modifiers:
- added to tailor chemical durability, expansion, viscosity, etc - Coloring (tinting) agents:
- Processing agents :
- minor additives to help promote bubble removal
What element helps to remove bubbles from glass?
As-oxide → remove bubbles
How much of minor additives need to be added to help promote bubble removal?
Less than 1.0%
What are the physical properties of the microstructure?
- Homogenous, with no interfaces with the material to scatter light
- No mechanism to stop cracks propagating in normal glass
- Surface cracks and defects have a high stress-concentrating effect
How can your reduce surface flaws?
Polishing
How are surface flaws introduced?
Surface flaws introduced by abrasion with hard materials
Where is the highest tensile stress in the rod?
At the point closest to the fixed end
What role do flaws play within the material?
- Reduce strength
- Act as stress concentrators
How can one heal flaws?
- Flame polished by moving the flame up and down the length of the rod.
What is glass sensitive to?
Surface flaws
What happens when you break a glass rod?
You can see different regions of the crack
What are the different zones of fracture in glass?
Mirror, mist and hackle
What is the smooth region near the fracture zone?
Mirror zone
What is the small band of rougher surface?
Mist zone
What is the large irregularly oriented faceted area?
The hackle zone
How does static fatigue occur?
Comes from a reaction between air moisture and crack in high stress region
What happens to glass due to static fatigue?
- Glass tensile strength is reduced
- Breaks bonds and cracks slowly become longer
What areas of the world make up 75% of the market in the flat glass industry?
Europe, China and North America
What is the demand for flat glass driven by?
Demand is driven by economic growth and legislation/regulations concerning safety, noise attenuation and the need for energy conservation
What is the glass manufacturing process?
- Raw materials
- Batch formation
- Melting - form the glass happens on molten tin
- Cooling - formed into the shape
- Forming
- Annealing
- Quality control
- Packaging
What is involved in annealing?
Taking the stresses out
How long will a standard float plant operate?
11 to 15 years
How much glass do float plants make a day?
7000 tonnes
How much glass do float plants make a year?
Makes around 6000 kilometres of glass
What happens in the float process?
- Molten glass is formed at approximately 1600˚C and is poured continuously from a furnace onto a large shallow bath of molten tin
Why is tin used for the float process?
- Tin has the right properties
How can the thickness of glass be controlled?
Thickness controlled by speed of pouring
How long can glass melting last for?
Can last 50 hours
How is the furnace operated?
Furnace is gas or oil fired
How can the melt be made homogenous?
Water-cooled stirrers
Why is glass scored?
Glass is scored so it can be snapped to specific sizes
What is the depth of the molten tin?
50 mm
Why is the atmosphere in the furnace inert?
To prevent oxidation of the tin
What happens to the imperfection in glass mixture?
They are melted in the molten tin bath
What temperature does glass reach at the end of the tin bath?
600˚C
True or false glass is a high carbon material?
True
Where does annealing take place?
Annealing in an insulated chamber known as a lehr
How does the glass move through the lehr?
On rollers
How can you toughen glass?
For toughened glass quench it from both sides
How can you modify glass?
- Tint it
- Coat it
- Wire glass
When do you tint and give an example of what’s added to make tints?
- Extra ingredients added to the raw materials at the melting stage
- Co and Ni tint glass grey
What is coated glass? Give an example.
- Glass can be coated on-line in the float process as the ribbon of glass is formed
- Chemical vapour deposition applies microscopically thin coating
What is wired glass?
- Wired glass is made by a rolling process
- Steel wire mesh sandwiched between separate ribbons of glass (semi-molten)
What are examples of speciality glasses?
- Gorilla Glass
- Optilam
- Pyroshield
How is laminated glas produced?
Laminated glass produced by bonding two or more layers of glass together using a special plasticized interlayer
What conditions is laminated glass processed under?
Processed under controlled heat and pressure conditions
What are the typical components of structural glass?
3 layers of glass bonded by (1st) DuPont and (2nd) SentryGlas Plus ionoplast
What are the uses of glass in construction?
- Flat glass
- Laminated glass
- Glass blocks
- Glass fibre
- Recycled glass
- Lightweight glass aggregate
- Waste encapsulation
What is decorative cement-bonded glass concrete?
The process involves integrating recycled glass chips into the concrete mix and replacing a part or all of the traditional aggregate.
What are polymer/resin bonded glass products?
- 95% recycled glass bottles
- Bound together with a solvent-free resin
- Poured into mould
What is polymer/resion bonded glass used for?
Worktops, tiles, flooring
How are decorative glass tiles formed?
- Can also be granualr bottles and they are pressed and partly melted
What are pavers used for?
Pavers are often used for paving outdoor areas
What are slips used for?
Slips are thin layers applied to a surface
What are tiles used for?
Tiles can be used for a variety of surfaces, such as floors and walls.
What are pavers composed of?
- 50% CRT glass
- 97% recycled glass
