GLASS

GLASS

Definition Preparation Composition VARIETY Uses

DEFINITIONGlass 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

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 .

Potassium as K2Co3 . Calcium as lime stone, 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). Culets 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 ResistanceCaO, MgO, Al2O3, PbO, SrO, BaO, ZnO, ZrO

MANUFACTURING STEPS

Melting

Forming and Shaping

Annealing

Finishing

MELTING PROCESS1). Raw materials in proper proportions are mixed with

culets.

2).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

3).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.

FINISHINGFinishing is the last step in glass manufacturing. It involves following steps.

Cleaning.

Grinding.

Polishing.

Cutting.

Sand Blasting.

SODA LIME 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.

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

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.

It is common hard glass containing silica and boron with small amount of alumina and less alkaline solids.

ALUMINO-SILICATE GLASS The typical approximate

composition of this type of glass SiO2(55%), Al2O3(23%), MgO(090, 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 tube and certain domestic equipments.

99.5% VITREOSIL GLASS

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.

COLOURED GLASSAddition 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

FIBER 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

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….

GLASS GALLERY

IT IS CLEAR THAT GLASS PLAYS A VITAL ROLE IN OUR LIFE…GLASS COVERS A VERY LONG JOURNEY BEFORE IT COME TO US..AND IT’S REALLY HARD TO MAKE GLASS. SO BETTER WATCH BEFORE CRACKING ONE.

THE END

BY :-

JaideepAmanNehalKunal