Glass & its types

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Ceramic materials divide into three categories:
1.Glasses – melting & solidification processing
2.Traditional ceramics – particulate processing
3.New ceramics – particulate processing
Introduction of Ceramics
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3. Classification + Applications of Ceramics
Glasses Clay
products
Refractories Abrasives Cement Functional
ceramics
- optical
- composite
- reinforce
- containers/
- household
- wares
- bricks
- bricks for
high T
(furnaces)
- sandpaper
- cutting
wheel
- polishing
materials
- composites
- structural as
construction
- engine
- rotor
-valve
-bearing
- sensors
- windshield
Traditional or Classical
Ceramics
Advanced
Ceramics
- thermal
protection
materials
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Glass
 Glass is one of three basic types of ceramics. Glass is
distinguished by its amorphous (non crystalline) structure.
 Structure : Network formers
Molecules that link up with each other to form long chains and
networks. Hot glass cools, chains unable to organize into a
pattern. Solidification has short-range order only.
 Amorphous structure occurs by adding impurities (Na+,Mg2+,Ca2+, Al3+).
 Impurities: interfere with formation of crystalline structure
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Glass
 Raw Materials
1. Glass forming oxides: usually the dominant constituent
SiO2, B2O3, P2O5, etc.
2. Fluxes: reduce melting temperatures
Na2O, PbO, K2O, Li2O, etc.
3. Property modifiers: added to tailor chemical durability,
expansion, viscosity, etc.
CaO, Al2O3, etc.
4. Colorants: oxides with 3d, 4f electron structures; minor
additives (<1 wt%)
5. Fining agents: minor additives (<1 wt%) to help promote bubble
removal
As-, Sb-oxides, KNO3, NaNO3, NaCl, fluorides, sulfates
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6. What is Glass?
• Fusion of sand (SiO2), soda (Na2CO3) & lime (CaO)
that produces a transparent solid when cooled.
• A 3D network of atoms which lacks the repeated,
orderly arrangement typical of crystalline materials.
• Physical Properties: hard, elastic, brittle, non-
conductor of electricity, density, refractive index, etc.
• Chemical: resistant to all but fluorine and very strong
bases.

7. The primary uses for glass are in windows,
containers, light bulbs and eyewear.
• Borosilicate Glass (pyrex): 5% borax
(Na2B4O7) is added to resist breaking
when heated or cooled.
• Colored Glass: metal oxides or colloidal
iron (Fe) & sulfur (S) are added to change
its color.
• Lead Glass: Pb increases refractive index
& density
What Types of Glass Are There?

8. What Types of Glass Are There?
• Flat glass: made by a “float glass
process”; molten glass is floated on a
pool of tin while cooling. Commonly
found in doors and windows.
• Laminated glass: used in
windshields, two sheets of glass with
plastic between them.
• Tempered safety glass: used in car side
windows and designed to break into
tiny pieces; potassium (K) replaces
sodium (Na) on the surface.

9. • Each force causes a deformation that may leave a
visible mark or fracture the glass. This can be used to
determine the direction and amount of force.
• Glass acts initially as an elastic surface and bends
away when a force is applied. When the force
increases beyond its tensile strength, it cracks.
How Do Glass Windows Break?

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Glassmaking
1. The ingredients for glass are mixed, and along with a proportion of
cullet (broken glass), are added to a bath furnace, where they are
heated to about 1500 C and fused together.
2. Molten glass is fed as „gobs‟ to an automatic bottle or jar making
machine.
3. A hot gob is first made into a parison or blank shape (by either pressing
or blowing), which is then blown to the final bottle or jar shape. Surface
coatings (sc) may be applied while hot.
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4. The bottles or jars pass into a lehr (an annealing oven), where they
are first reheated to soften the glass to remove stresses, and then
cooled gradually to prevent stresses developing.
5. The bottles or jars are inspected and tested to meet quality
standards. Bottles not passing the quality checks are broken and
returned to the furnace as cullet. Cullet reduces the amount of
energy required to melt the glass ingredients.
6. Bottles passing inspection and testing are packed for dispatch to
where they will be filled, capped, and labeled.
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Shaping Processes in Glassmaking
 Shaping processes to fabricate these products can be
grouped into three categories:
1. Discrete processes for piece ware (bottles, jars,
plates, light bulbs)
2. Continuous processes for making flat glass (sheet
and plate glass) and tubing (laboratory ware,
fluorescent lights)
3. Fiber-making processes to produce fibers (for
insulation and fiber optics)
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Shaping of Piece Ware
 Ancient methods of hand-working glass included glass blowing.
 Handicraft methods are still used today for making glassware items of
high value in small quantities. However, most modern glass shaping
processes are highly mechanized technologies for producing discrete
pieces in high quantities.
 Piece Ware Shaping Processes
1. Spinning – similar to centrifugal casting of metals
2. Pressing – for mass production of flat products such as dishes, bake
ware, and TV tube faceplates
3. Press-and-blow – for production of wide-mouth containers such as
jars
4. Blow-and-blow - for production of smaller-mouth containers such as
beverage bottles and incandescent light bulbs
5. Casting – for large items such as large astronomical lenses that
must cool very slowly to avoid cracking.
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Spinning of funnel-shaped glass parts such as back sections of cathode
ray tubes for TVs and computer monitors:
(1) gob of glass dropped into mold; and
(2) rotation of mold to cause spreading of molten glass on mold surface
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Pressing of flat glass pieces:
(1) glass gob is fed into mold from furnace;
(2) pressing into shape by plunger; and
(3) plunger is retracted and finished product is removed (symbols v
and F indicate motion (velocity) and applied force)
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1. A gob of hot glass drops into the blank (parison) mould.
2. The mould is sealed shut by a „base‟ part and a plunger pushes the glass
into the mould (made from iron).
3. The glass is shaped into a „blank‟ and also pushed into the neck finish by
the plunger. This part of a jar or bottle is finished to its final shape at this
stage.
4. The blank shape (parison) is removed, rotated 180 , and transferred to
the blow (finishing) mould.
5. This mould is in two halves, made from fine-grain cast iron, and is highly
polished.
6. Air is blown into the hot parison to expand it tightly against the mould
walls.
7. The mould opens, the bottle is removed, annealed in the lehr, inspected
and tested, and shipped for filling.
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1. A gob of hot glass drops into the blank (parison) mould.
2. The end is sealed and a puff of air pushes glass into the neck (finish).
3. A puff of air from below pushes glass into the mould and shapes it into
a „blank‟ or parison, a thick-walled bottle looking vaguely like the final
bottle shape.
4. The blank shape (parison) is removed, rotated 180 , and transferred to
the blow (finishing) mould.
5. This mould is in two halves, made from fine-grain cast iron, and is
highly polished.
6. Air is blown into the hot parison to expand it tightly against the mould
walls.
7. The mould opens, the bottle is removed, annealed in the lehr, inspected
and tested, and shipped for filling.
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Casting
 If molten glass is sufficiently fluid, it can be poured into a
mold.
 Relatively massive objects, such as astronomical lenses
and mirrors, are made by this method.
 After cooling and solidifying, the piece must be finished by
lapping and polishing.
 Casting of glass is not often used except for special jobs.
 Smaller lenses are usually made by pressing.
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Shaping of Flat and Tubular Glass
 Processes for producing flat glass such as sheet and plate glass:
Rolling of Flat Plate
Starting glass from melting furnace is squeezed through
opposing rolls whose gap determines sheet thickness, followed
by grinding and polishing for parallelism and smoothness
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Float Process
Molten glass flows onto the surface of a molten tin bath,
where it spreads evenly across the surface, achieving a
uniform thickness and smoothness - no grinding or
polishing is needed.
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Danner Process
Molten glass flows around a rotating hollow mandrel
through which air is blown while the glass is drawn.
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23. Thanks
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