Glass Flashcards
When was the chrystal palace built?
1851
How large was chrystal palace?
1,848 ft long and 408 ft wide
What are the key properties of glass?
- transparent
- High stiffness (young’s modulus)
- Brittle (low toughness, associated with catastrophic failure)
- Reasonable strength in compression
- Relatively low strength in tension but highly variable
- Hard, but easily damaged
- Fractures to give sharp surfaces
- Excellent corrosion resistance
- Low leaching of contaminants
What is the definition of a glass?
An inorganic product of fusion (melting) which has cooled to a rigid condition without chrystallisation
What are the key characteristics of glass?
- Non-chrystalline amorphous material with no longer range repeated order
- Typically produced from the liquid state by continuous cooling
- Exhibit a glass transition temperature
- Can be formed from certain liquids provided cooling rate is sufficiently high
What is the basic building block for most commercial glasses?
The SIO4 tetrahedron (silica tetrahedron
What type of bonding is Si-O
Covalent
What is a the microstructre of glass like?
Short range order
Long range disorder
Does glass contain dislocations?
no
What structure does glass have?
the same amorphous strucure of a liquid phase
What happens to viscosity as temperature is reduced?
It increases
Why does glass cooling not chrystallise?
The material becomes solid before it can chrystallise (Slow vs abrupt cooling)
How many Si share each O in glass?
2
What happens when you add sodium to glass mixture
Disrupts the sturcture
Maintaind charge neutrality
What terms describe Si and Na?
Si is a glass former
Na is a network modifier
Name some of the raw materials used in the maufacture of glass
Silica sand (glass sand) Feldspathic sand (alumina sand) Sodium Carbonate (soda ash) Calcium carbonate (limestone) Magnesium Carbonite (dolomite) Feldspar Nepheline syenite Aplite Sandspar
What is the composition of commercial glass?
70-74% silica 12-16% sodium oxide 5-11% Calcium oxide 1-3% magnesium oxide 1-3% aluminium oxide
Name some types of special glass
Vitreous silica Alumina-silicate glass Alkali-barium silicate glass Technical glass Glass ceramic Optical glass Sealing glass
What do many special glasses contain?
Polymer layers and special coatings
What are the 5 main constituents of glass?
- Glass forming oxides
- Fluxes that reduce melting temperature
- property modifiers
- colouring (tinting) agents
- Processing agents
Give an example of a glass forming oxide
SiO2, B2O3, P2O5
Give an example of a flux
Na2O, PbO, K2O, Li2O
Give an example of a property modifier
CaO, Al2O3
Give an example of a colouring agent
Oxides with 3d, 4f electron structures; minor additives (<1 wt%)
Give an example of a processing agent
As-oxide, Sb-oxides, NaNO3, NaCL, fluorides, sulphates
What do property modifiers do?
Tailor chemical durability, expansion, viscosity, etc.
What does a processing agents do?
Help promote bubble removal
Minor effect on bulk properties
What is the microstructure of glass like?
Homogeneous with no interfaces to scatter light
No potential for dislocations to move
Surface cracks and defects have a high stress concentrating effect
Tensile strenght follows the same rules as ceramics
Obeys a hookean response to stress
What is the equation for K_1c of glass?
K_1c = sqrt(2Ey_i)
E = youngs modulus y_i = the fracture surface energy
What is the usual value for K_1c for glass
0.56 MPa m^1/2
What can be done to reduce surface flaws?
Polishing
What methods of polishing are there?
Mechanical
Flame
Acid etching
What are the 3 regions of fracture on glass?
- Smooth region near fracture orign (Mirror Zone)
- small band of rougher surface (Mist Zone)
- Large irregularly orientated faceted area (hackle zone)
What is the definition of static fatigue?
When a material under load decreases in strength over time
Does glass undergo static fatigue?
yes
Will a glass be more or less likely to fail if a load is rapidly applied?
less - as it undergoes static fatigue
What happens to glass tensile strength?
It is reduced when tested under water
Why is the tensile strength of glass reduced under water?
The Si-O-Si at the crack tip are more reactive to water
This results in a crack growth mechanism
This lengthens the critical crack length, reducing the ultimate fracture stress
What factors help cracks to grow in glass underwater?
Higher temperature and humidity
What is the global market for flat glass in 2023 worth?
134 billion USD
How is the flat glass market divided?
70% used in windows for buildings
10% for glazing product and in the automotive industry
20% used for furniture and other interior applications
Which areas make up 75% of the global glass market
Europe, China, North America
What are the four main companies that produce the majority of float glass and how much do they produce?
- Pilkington
- Saint-Gobain
- Asahi
- Guardian
Produce 61%
What increases demand for glass?
Economic growth
Legislation/ regulations concerning safety, noise atttenuation
Energy Conservation
What type of glass is growing more in the market?
Value added products
How much of glass is made using the float process?
95%
When was the float glass process inveneted and by whom?
1952
Sir Alastair Pilkington
How does the float glass process work?
Molten glass @ 1000 C poured from a furnace onto a large shallow bath of molten tin
What is the purpouse of the tin bath in float glass manufacture?
Forms a level surface as it floats
What controls the thickness of glass?
The speed at which the solidifying glass ribon is drawn off the tin bath
What is annealing?
The processing of slowly cooling hot glass objects after they have been formed
What do glass products emerge as after annealing?
A “fire” polished product with virtually parallel surface
How long will an average float plant operate for?
11 to 15 years
How many kilometers of glass do float plants make a year?
6000 km
What is the range of thicknesses and widths that glass can be produced in?
0.4 - 25mm thick
up to 3 m wide
Describe in detail the float process for making flat glass?
- Materials are weighed and mixed
- mix is melted in furnace
- Molten glass is floated on top of a bath of molten tin and starts to cool slowly
- Glass is slowly cooled in lehr to prevent build up of stress
- Glass is automatically inspected to detect flaws
- Glass is automatically cut to size
How much glass can be melted in a large furnace?
2,500 tonnes
What do the terms batch and cullet mean?
Batch = raw materials mixture Cullet = broken or refus glass added to new material to facilitate melting in making glass
What temperature is needed to melt raw materials?
1600 C
How is the heat in a glass furnace generated?
Gas or oil fired
What happens to waste heat in the furnace?
It is recovered and used to warm up incoming combustion air
How is the melt made homogeneous?
Water-cooled stirrers
How deep is the molten tin in the molten tin bath?
~50mm
What is the make up of the atmosphere next to the molten tin bath?
95 % nitrogen 5% hydrogen
What is the temperature of the glass at the end of the tin bath?
600 C
How much glass is produced every week worldwide?
800,000 tonnes
How many float glass plant are operational worldwide?
320
What is the purpouse of annealing?
to control the cooling so that the stress is removed
Engineer the surfaces so they both are in compression
What are the ingredients added to tint glass and what colour do they make?
Co and Ni make grey glass
Ferrous oxide makes blue tint
Ferric iron makes yellow tine
Combine them all and you get a green tint
Why are tints used in buildings and vehicles?
To control heat and light transmission
When is glass coated with tints and how?
Coated on line in the float as the ribbon is form
Chemical vapour deposition applies microscopically thin coating
How is wired glass made?
Through a rolling process
Steel wire mesh is sandwiched between seperate mribbons of glass in a semi-molten state
It is passed through consolidating rollers which also impress a pattern
Why do we make wire glass?
to improve fire resistance and make safety glazing
How is laminated glass made?
By bonding 2 or more layers of glass together using a special plasticized interlayer
Give an example of a special plasticised interlayer
Polyvinyl butryal (PVB)
Where is laminated glass used?
Homes and offices, construction, architectural and transport applications
What kind of glasses are used in structural aspects, e.g. apple store stairs?
3 layers of glass bonded by DuPont SentryGlas Plus ionoplast
Has 8mm of glass, bonding, 15mm of glass, another 8mm
How is recycled glass used in construction?
Sued as an aggregate in concrete
As a microfiller in cement
As an unbound aggregate
As and aggregate in bituminous materials
