1. business and industrial
2. chemicals industry
3. plastics and polymers

GLASS
Glass
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Definition
Preparation
Composition
Variety
Uses
Definition
Glass is an amorphous, hard, brittle, transparent or
translucent super cooled liquid of infinite viscosity,
having no definite melting point obtained by fusing a
mixture of a number of metallic silicates or borates of
Sodium, Potassium, Calcium, and Lead.
It possess no definite formula or crystalline structure.
• “An inorganic product of fusion which has cooled to a
rigid condition without crystallizing”
• Does not have a specific melting point
• Softens over a temperature range
Properties of glass
Glass is:
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Amorphous
Brittle
Transparent / Translucent
Good electrical insulator
Unaffected by air, water, acid or chemical reagents
except HF
• No definite crystal structure means glass has high
Compressive strength
• Can absorb, transmit and reflect light
Raw materials used in manufacturing glass
Raw Materials
• Sodium as Na2Co3 (used in soft glass).
• Potassium as K2Co3 (used in Hard Glass).
• Calcium as lime stone, chalk and lime.
• Lead as litharge, red lead (flint glass).
• Silica arc quartz, white sand and ignited flint.
• Zinc is zinc oxide (Heat and shock proof glass).
• Borates are borax, Boric acid (Heat and shock proof glass).
• Cullets or pieces of broken glass to increase fusibility.
Glass Components
• Formers – Network Formation
SiO2, B2O3, P2O5, GeO2, V2O5, As2O3, Sb2O5
• Fluxes – Softeners
Na2O, K2O, LiO, Al2O3, B2O3, Cs2O
• Stabilizers – Provide Chemical Resistance
CaO, MgO, Al2O3, PbO, SrO, BaO, ZnO, ZrO
Manufacturing steps

Melting

Forming and Shaping

Annealing

Finishing
Melting process
Raw materials in proper proportions are mixed with
cullets. It is finely powdered and intimate mixture called
batch is fused in furnace at high temperature of 1800°C
this charge melts and fuses into a viscous fluid.
CaCO3 + SiO2  CaSiO3 + CO2 
Na2CO3 + SiO2  Na2SiO3 + CO2
After removal of CO2 decolorizes like MnO2 are added to
remove traces of ferrous compounds and Carbon.
Heating is continued till clear molten mass is free from
bubbles is obtained and it is then cooled to about 800°C.
Forming, shaping, and annealing
• Forming and Shaping
The viscous mass obtained from melting is poured into
moulds to get different types of articles of desired shape by
either blowing or pressing between the rollers.
• Annealing
Glass articles are then allowed to cool gradually at room
temperature by passing through different chambers with
descending temperatures. This reduces the internal Strain
in the glass.
finishing
Finishing is the last step in glass manufacturing. It
involves following steps.

Cleaning

Grinding

Polishing

Cutting

Sand Blasting
Varieties of glass
Soda lime or soft
glass
Potash lime or hard
glass
Lead glass or flint
glass
Borosilicate or Pyrex
glass
Alumino- Silicate
glass
96% Silica glass
99.5% Silica
glass(Vitreosil)
Safety glass
Optical or Crook’s
glass
Poly-crystalline glass
Toughened glass
Colored glass
Wired Glass
Glass Wool
Fiber glass
Photosensitive
glass
Photo-chromic glass
Neutral glass
Laminated glass
Insulating glass
Sodalime or soft glass
• About 90% of all glass is soda-lime glass made with silica (sand),
Calcium carbonate and soda ash.
• The approximate composition is Na2CO3.CaO.6SiO2.
• They are low cost, resistant to water but not to acids.
• They can melt easily and hence can be hot worked.
• Uses:
Window glass, Electric bulbs, Plate glass, Bottles, Jars, cheaper table
wares, test tubes, reagent bottles etc
Potash lime or hard glass
• Potash lime glass is made with silica (sand), Calcium carbonate and
potassium carbonate.
• The approximate composition is K2CO3.CaO.6SiO2.
• They posses high melting point, fuse with difficulty and are less
acted upon by acids, alkaline and other solvents than ordinary glass.
• Uses:
These glasses are costlier than soda lime glass and are used for
chemical apparatus, combustion tubes and glassware which are used
for heating operations.
Lead glass or flint glass
• It is made up of lead oxide fluxed with silica and K2CO3
is used instead of sodium oxide.
• Its approximate composition is K2Co3.PbO.SiO2.
• To get dense optical glasses about 80% lead oxide is
used. Lead glasses has a lower softening temperature
than soda glass and higher refractive index and good
electrical properties. It is bright lustrous and possess
high specific gravity.
• Uses:
High quality table wares, optical lenses, neon sign
tubing, cathode ray tubes, electrical insulators, crystal
art objects or cut glass, Windows and Shields for
protection against X-rays and Gamma rays in medical
and atomic energy fields etc.
Borosilicate / pyrex / jena glass
• It is common hard glass containing
silica and boron with small amount of
alumina and less alkaline solids.
• It contains SiO2(80.5%), B2O3(13%),
Al2O3(03%), K2O(3%) and Na2O(0.5%).
These glass have low thermal coefficient
of expansion, and high chemical
resistance i.e..shock proof.
• Uses:
Industrially used for pipeline of
corrosive liquids, gauge glasses,
superior laboratory apparatus, kitchen
wares, chemical plants, television tubes,
electrical insulators etc.
Alumino-silicate glass
• The typical approximate composition
of this type of glass is SiO2(55%),
Al2O3(23%), MgO(09%), B2O3(07%),
CaO(05%) and Na2O, K2O(01%).
• This
type
of
glass
possess
exceptionally
high
softening
temperature.
• Uses:
It is used for high pressure mercury
discharge
tubes,
chemical
combustion tubes and certain
domestic equipments.
96% silica glass
• It contains 96% Silica, 03% B2O3 and traces of
other materials.
• It is translucent, the coefficient of thermal
expansion is very low hence it has high
resistance to thermal shock, have high chemical
resistance to corrosive agents and are corroded
only by Hydrofluoric acid, hot phosphoric acids
and concentrated alkaline solutions.
• Uses:
Used only where high temperature resistance is
required (800°C). They are used in construction
of chemical plants, laboratory crucibles,
induction furnace lining and electrical
insulators.
99.5% silica glass / vitreosil
• It contains pure silica heated to its
melting point. It is translucent, the
coefficient of thermal expansion is very
low hence it has high resistance to
thermal shock, have high chemical
resistance to corrosive agents.
• If Vitreosil glass is heated above its
melting point, it becomes transparent and
is known as clear silica glass.
• Uses:
They are used in construction of chemical
plants, laboratory crucibles, induction
furnace lining, electrical insulators and
heaters and have high light transmission
properties.
Safety glass
• It is made by fusing two to three flat
sheets of glass and in between them
alternate thin layer of vinyl plastic is
introduced. It is heated where both the
layers merge together and glass is
toughened.
• Uses:
It is used as wind shield in automobiles
and airplanes. On breaking it pieces does
not fly apart because of the presence of
the plastic layer in between the glass
layers.
Optical or crook’s glass
• It contains Phosphorus, PbCO3, silicates and Cerium oxide which
has the property to absorb harmful ultra-violet light. This glass is
given through homogeneity by heating it for a prolonged period of
time. These glasses have low melting point and are relatively soft.
• Uses:
They are used for making optical lenses.
Poly-crystalline glass
• It is new type of glass which is produced by adding
nucleating agents to a conventional glass batch and
then shaped into desired form. It is then subjected to
heating where nucleating agents forms large number
of micro crystallites. It is not ductile. It exhibits high
strength and considerable hardness.
• Uses:
For making specialized articles.
Toughened glass
• It is made by dipping articles still hot in
an oil bath, so that chilling takes place.
This results in outer layer of articles
shrink and acquire a state of
compression while inner layer are in
state of tension. Such glass is more
elastic to mechanical and thermal shock.
It breaks into a fine powder.
• Uses:
For making window shields of fast
moving vehicles, windows of furnace and
automatic opening doors.
Coloured glass
Addition of transition metal compounds to glass gives color to the glass. They
are outlined below.
Yellow: Ferric Salts
Green: Ferrous and Chromium
salts
Purple: Magnese dioxide salt
Red: Nickel and cuprous salts
Cu2O
Lemon Yellow: Cadmium
sulphide
Fluorescent greenish yellow:
Uranium oxide
Blue: Cobalt Salts, CuO
Greenish Blue Color:
Copper Sulphate
Brown: Iron
Opaque milky white: Cryolite
of Calcium phosphate
Ruby : Auric Chloride
Wired glass
• Wired glass does not fall apart into splinters when it breaks and is fire
resistant. It is made by fusing wire in between the two glass layers.
Uses:
For making fire resistant doors, roofs, skylights and windows
Fibre glass
• It is transformed into a fine thread of filament and has got a high
tensile strength.
Uses:
Found extensive use for the manufacture of fabric, reinforcing
plastics and production of thermal insulation materials etc
Photosensitive glass
• These are glasses by which a
colored picture may be developed
by exposing the glass to black
and white negative in ultra violet
light.
The
appropriate
proportions of potash-alumina
glass, mixed with LiSO3, cerium
and Silver salts have also been
used as photosensitive glass.
• Uses:
Photographic development
Glass wool
• Glass wool consists of tiny fibers
formed by action of steam jets on
dripping molten glass down from
very fine hole.
• Uses:
Heat Insulation, for filtration of
Corrosive
chemicals,
sound
insulation etc
Photo-chromic glass
• The three dimensional silicate network
contains large no. of microscopic
particles of silver halide which on
exposure to light produce color.
• Uses:
In making tinted car glasses and
goggles.
Neutral glass
• These glasses are highly resistant to chemical attacks and they are
specialized soda lime glass where alkali has been replaced by alumina,
boron oxide and zinc oxide.
• Uses:
Making Syringes, Injection Ampoules and vials etc.
Laminated glass
• The sheets of glass fiber or glass wool are soaked in a solution of
thermosetting plastic like phenol formaldehyde resin and placed one above
the other and then cured under heat or pressure. It is strong as steel. Non
flammable and insulating. In bullet resistant glass vinyl resins are added in
alternate layers.
• Uses:
Shatter, shock and Bullet proof Glass
Insulating glass
• Two or more plates of glass are filled with dehydrated air and the
edges are sealed air-tightly.
• Uses:
Provides thermal insulating and so houses remain cool in summer
and warm in winter.
Fracture / failure of glass
• Glass does not have crystal lattice structure hence it breaks. Fracture
is caused by small imperfections, flaws and irregularity on the
surface of the glass. Flaws are very fine cracks cause concentration
of stress and the crack proceeds quickly causing a fracture.
THE END