Glass is an amorphous, hard, brittle, transparent or translucent material made by fusing sand with soda, lime, and other ingredients at high temperatures. It has no definite melting point or structural formula. Glass is classified as soft or hard, with soft glass being more widely used for windows and containers due to its lower melting point and resistance to water and acids, while hard glass is used for chemical apparatus and heat-resistant items. The manufacturing process involves melting raw materials at high heat, forming the molten glass into shapes, annealing to slowly cool the glass to reduce breakage, and finishing steps like polishing.

1. GLASS

2. Introduction
• Glass: it is an amorphous, hard, brittle,
transparent, or translucent, super cooled
liquid of infinite viscosity, obtained by fusing a
mixture of metallic silicates, most commonly
of Na,K,Ca. and Pb
• It has no sharp melting point and definite
structural formula

3.  It may be represented as xR2O.yMO.6SiO2,
where
R is an atom of an monovalent alkali metal
like Na,K,, etc,
M is an atom of a bivalent metal like
Ca,Pb,,Zn, etc.,x and y are whole numbers
In some glasses, SiO2is replaced by Al2O3.B2O3.P2O5, etc.
General formula of ordinary glass or soda-lime glass
is Na2O.CaO.SiO2

4. Properties of Glass:
 It is amorphous and it has no definite
melting point
It can absorb and reflect light
It is a good insulator of electricity
It is effected by Alkalis

5. It is not affected by Air, Water and acid however
it reacts with HF to form SiF4
Types of Glass
 Glasses are classified into two types:
1.Soft Glass (soda-lime glass)
2.Hard Glass(potash-lime glass)

6. Soft Glass (soda-lime glass):
• Structural formula of soft glass is
Na2O.CaO.6SiO2
• Sodium carbonate, calcium carbonate, silica
are raw materials for the preparation of soft
glass
• They are resistant to water and melt easily
• However they are easily attacked by acids

7. Uses
• They are widely used as window glasses,
electric bulbs, plate-glasses, bottles, jars,
building blocks, and cheaper table wares
where high temperature-resistance and
chemical stability are not required.

8. Hard Glass (Potash-Lime Glass)
• Composition of Hard-Lime glass is
K2O.CaO.6SiO2
• Silica, Potassium carbonate and sodium
carbonate are raw materials for preparation of
hard glass.
• They have high melting points and less acted
by alkalis, acids.

9. USES
• These glasses (costlier than soda-lime glasses)
are used for chemical apparatus, combustion
tubes, etc., which are to be used for heating
purposes

10. Manufacturing Steps:
• 1.Melting
• 2.Forming and Shaping
• 3.Annealing
• 4.Finishing

11. Melting
• : Raw marerials, in proper proportions(e.g
sand, soda, ash and limetone for common
glass) are mixed with refinely added cullets
called as “batch” are heated in open hearth
furnace in which heat is produced by burning
of producer gas.At high temperatures like
1800oC glass starts melting

12. Reaction involved in manufacturing of soft glass:
• CaCO3+SiO2  CaSiO3 + CO2
• Na2CO3 +SiO2  Na2SiO3 + CO2
When all the carbon dioxide has escaped out of
the molten mass , decolorizes (such as MnO2 or
nitre) are added to do away with ferrous
compounds and carbon , if present. If a coloured
glass is desired , the colouring salts are added at
this stage. Heating is continued, till the molten
mass is free from bubbles and glass- balls and
then cooled to about 8000C.

13. Colors-coloring salts
• Yellow- ferric salt
• Green- ferrous and chromium salts
• Blue- cobalt salts
• Purple-manganesedioxide
• Red- nickel salts or Cu2O
• Fluorescent greenish- yellow- uranium oxide
• Opaque milky white- Cryolite(Na3AlF3) or
calcium phosphate.

14. Forming:
• molten glass is then worked into articles of
desired shapes by either blowing or moulding
or pressing between rollers.

15. Glassblowing

16. Annealing:
• Glass, being insulator cannot be cooled rapidly
because if it is cooled rapidly the superficial
layer cools down and the inner layer remains
in expanded state which may cause breakage
of glass.
• Due to this reason glass is passed through
different zones of decreasing temperature and
this process is known as annealing.

17. Finishing
• All glass articles, after annealing, are
subjected to finishing processes such as
cleaning, grinding, polishing, cutting, sand-
blasting, etc.