GLASS
Ø Glass
is an amorphous (non-crystalline) solid material that exhibits a glass
transition.
Ø The
first true glass was made in coastal north Syria, Mesopotamia or Ancient Egypt.
Ø The
earliest known glass objects, of the mid third millennium BCE, were BEADS,
perhaps initially created as accidental by-products of metal-working (slags) or
during the production of faience, a pre-glass vitreous material made by a
process similar to glazing.[
Ø The
most familiar type of glass, used for centuries in windows and drinking
vessels, is soda-lime glass that Composed of about 75% silica (SiO2)
plus sodium oxide (Na2O) from soda ash, lime (CaO), and several
minor additives.
Characteristics:
- † transparent
- † water proof
- † it breaks easily
- † it allows light to pass through
- † it's not flexible
†
transparent to visible wavelengths of light
has the ability to refract, reflect,
and transmit light following geometrical optics, without scattering it.
Glass Production involves two main methods:
- The Float Glass process- which produces sheet glass.
- Glass blowing- produces bottles and other containers.
The following is a list of the
more common types of silicate glasses, and their ingredients, properties, and
applications:
Fused
silica glass, vitreous silica glass: silica (SiO2). Has very low thermal
expansion, is very hard and resists high temperatures (1000–1500 °C). It is also the most resistant against
weathering (alkali ions leaching out of the glass, while staining it). It is
used for high temperature applications such as furnace tubes, melting
crucibles, etc.
Soda-lime-silica
glass, window glass: silica 72% + sodium oxide (Na2O) 14.2% + magnesia
(MgO) 2.5% + lime (CaO) 10.0% + alumina (Al2O3) 0.6%.
Is transparent, easily formed and most
suitable for window glass. It has a high thermal expansion and poor resistance
to heat (500–600 °C). Used for windows, containers, light bulbs, tableware.
Sodium
borosilicate glass, Pyrex: silica 81% + boric oxide (B2O3) 12% + soda
(Na2O) 4.5% + alumina (Al2O3) 2.0%. Stands heat expansion much better than
window glass.
Used for chemical glassware, cooking
glass, car head lamps, etc. Borosilicate glasses (e.g. Pyrex) have as main
constituents silica and boron oxide.
They are commonly used for reagent bottles, optical components and household
cookware.
Lead-oxide
glass, crystal glass: silica 59% + soda (Na2O) 2.0% + lead oxide (PbO) 25%
+ potassium oxide (K2O) 12% + alumina 0.4% + zinc oxide (ZnO) 1.5%. Has a high refractive index, making the look
of glassware more brilliant (crystal glass). It also has a high elasticity,
making glassware 'ring'. It is also more workable in the factory, but cannot
stand heating very well.
Aluminosilicate
glass: silica 57% + alumina 16% + boric oxide (B2O3) 4.0% + barium oxide
(BaO) 6.0% + magnesia 7.0% + lime 10%. Extensively used for fiberglass, used
for making glass-reinforced plastics (boats, fishing rods, etc.). Also for
halogen bulb glass.
Oxide
glass: alumina 90% + germanium oxide (GeO2) 10%. Extremely clear glass,
used for fiber-optic wave guides in communication networks. Light loses only 5%
of its intensity through 1 km of glass fiber.
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"Glass".Wikipedia: The free Encyclopedia.Wikipedia Foundation Inc. 30 september 2013. Web. 6 October 2013.<http://en.wikipedia.org/wiki/Glass
