an inorganic product of fusion that has cooledan inorganic product of fusion that has cooled
to a rigid condition without crystallizingto a rigid condition without crystallizing
When glass is cooled from the hot molten state,When glass is cooled from the hot molten state,
it gradually increases in viscosity withoutit gradually increases in viscosity without
crystallization over a wide temperature range,crystallization over a wide temperature range,
until it assumes its characteristic hard, brittleuntil it assumes its characteristic hard, brittle
form. Cooling is controlled to preventform. Cooling is controlled to prevent
crystallization, or high strain.crystallization, or high strain.
Glass, chemically, is actually more like a liquid,Glass, chemically, is actually more like a liquid,
but at room temperature it is so viscous orbut at room temperature it is so viscous or
'sticky' it looks and feels like a solid. At higher'sticky' it looks and feels like a solid. At higher
temperatures glass gradually becomes softer andtemperatures glass gradually becomes softer and
more like a liquid. It is this latter property whichmore like a liquid. It is this latter property which
allows glass to be poured, blown, pressed andallows glass to be poured, blown, pressed and
moulded into such a variety of shapes.moulded into such a variety of shapes.
Glass technology has evolved for 6,000 yearsGlass technology has evolved for 6,000 years
A most important development in glass technologyA most important development in glass technology
was the use of a blow pipewas the use of a blow pipe
The first glass was coloured because of the presenceThe first glass was coloured because of the presence
of various impurities such as oxides of iron andof various impurities such as oxides of iron and
chromium. Virtually colourless glass was first madechromium. Virtually colourless glass was first made
some 1,500 years ago.some 1,500 years ago.
Today many products of glass are made in fullyToday many products of glass are made in fully
automatic processing linesautomatic processing lines
Although glass is one of the oldest materials, itsAlthough glass is one of the oldest materials, its
properties are unique and not yet fully understood.properties are unique and not yet fully understood.
Glasses is one of three basic types of ceramics. Glass is an amorphous
(non-crystalline) solid material which is often transparent has widespread
partical, technological, and decorative usage in things like window panes,
tableware, and optoelectronics.
The most familiar, histrocially the oldest, types of glasses are based on the
chemical compound silica (silicon dioxide), the primary constituent of sand,
which is familiar from use as window glass and in glass bottles.
Actually glasses are extremely cooled liquid.
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.
Raw Materials To Making Glass
Silica sandSilica sand
Soda ashSoda ash
Lime stoneLime stone
Feldspathic materialsFeldspathic materials
Lead oxideLead oxide
Boric acidBoric acid
Crushed glassCrushed glass
Raw Materials To Making Glass
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,
CaO, Al2O3, etc.
4. Colorants: oxides with 3d, 4f electron structures; minor additives (<1
5. Fining agents: minor additives (<1 wt%) to help promote bubble
As-, Sb-oxides, KNO3, NaNO3, NaCl, fluorides, sulfates
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+
Impurities: interfere with formation of crystalline structure
TYPES OF GLASSES
It is mainly used where temperature resistance is
required. They can be used at temperatures upto
about 900 C. They have a very low co-efficient
of thermal expansion and have a high resistance
to thermal shock. Silica glass is also named as
It have some part of silica replaced by boron
oxide. This provides some desirable properties.
Borosilicate glass have not workability with high
sterngth, high, high chemical stability, high
electrical resistance and low thermal expansion.
It is used in high tension insulators, kitchenware,
telescope mirror, laboratory glass ware, industrial
instrument glass. One type of trade name is
lead glass also known as FLINT GLASSES.
These glasses have low melting point, good hot
workability, high electrical resistance and high
refractive indices. It is used as optical glass, art
and jewellery glass, thermometer tubing,
fluorecent lamps, television tube, window and
shields for protection from x-ray padition, table
It have good hot workability. It is also melt at
low temperature . These glasses are used as
window glass, chemical apparatures, breakers,
test tubes etc.
Some Other Types of Glasses
Various substanmces are added to get coloured
Various nucleating agents like sodium fluoride,
phosphorous pentoxide, titanium oxide or
vanadium oxide are added to glass melt to get
recrystallised glass. This glass also known as
POLYCRYSTALLING GLASS. This glass
process high hardness and impact strength and
better thermal conductivity.
It is also known as glass fibre. The material is in the
form of fibres produced from glass. The fibres are
produced from molten glass by drawing the material
through dies giving fibre of 2 to 10 micron in diameter.
The fibres are not brittle and have high tensile strength.
They are non flammable, chemically inactive, poor
conductor of sound and non- conductive to heat and
electricity. Fibres are used to produce composite
materials by mixing them with synthetic rasins.
They are produced from molten glass by
forcing the material through some vents by
centrifugal force. It gives short fibres at about 10
microns. This process is also known as
CROWN PROCESS. Glass wools are used as
It is produced by introducing innumerable air
cells in molten glass. It has low density and can
float in water . It can be cut into suitable sizes
and used for heat insulations.
General properties of glasses
High hardness / Brittle
Low density compared to high strength
Low thermal expansion coefficient
Low heat / electrical conductivity
High melting point
Good chemical resistance / Chemical inert
Wide range of optical transmission
Thin film transistors (TFT)
Optical memory devices
Electro photographic application
X-ray image sensors
Eu-doped optical fiber
DVD (digital video/versatile disc)
Hard cover made from ta-C