GA Study Notes On Manufacturing of Glass : SSC CGL Tier-1 2017


Glass
Glass is an amorphous and transparent solid. It is also called supercooled liquid of silicates.It resembles a solid due to the great increase in its viscosity when it is cooled rapidly. It has a tendency to flow, though very slowly.That is why the glass windows and doors become slightly thicker at the bottom than at the top with the time.Chemically it is written as Na2O.CaO.6SiO2.

  • Raw material used for the formation of glass are sodium carbonate, calcium carbonate, and sand.
  • Finely powdered mixture known as batch, is mixed with cullet (broken glass pieces) and then fused in a tank furnace at 1673 K. After few hours, molten glass is obtained.
  • Molten glass is cooled slowly and uniformly. The process of slow and uniform cooling is known as annealing.
  • Annealing process strengthens the glass.
  • Different addition of metal oxides or metal salts before it is annealed may produce different coloured glasses.
Substance used
Colour of glass
Cuprous oxide
Red
Cupric oxide
Peacock blue
Potassium dichromate
Green or Greenish yellow
Ferrous oxide
Green
Ferric oxide
Brown
Manganese dioxide
Light pink, in excess black
Cobalt oxide
Blue
Gold chloride
Ruby
Cadmium
Yellow
Carbon
Amber colour
Types  of glasses, Properties, and Uses
  • Soft glass It is a mixture of sodium or calcium silicates. It is used in making window glass, mirrors and common glass wares etc.
  • Hard glass It is a mixture of potassium and calcium silicates. It is more resistant to the action of acids for making hard glass apparatus.
  • Flint glass It is mainly a mixture of sodium, potassium and lead silicates. It is used in making bulbs and optical instruments.
  • Quartz glass (Silica glass) It is used in the preparation of chemical apparatus and optical instrument.
  • Crookes glass It is used for making lenses for spectacles.
  • Photochromatic glass On exposure to bright light, photochromatic glass darkens temporarily. So, it is very useful as a Sun shield. The silver bromide in the glass reduces the intensity of bright light.
  • Safety glass The three layers are joined together by the action of heat and pressure. It does not break easily under impact and is used in the auto vehicle windshield.
  • Tempered glass It is a type of safety glass.It’s roughly four times stronger than single-thickness annealed glass due to a manufacturing process with cycles of rapid heating and cooling.Tempering puts the outer surfaces into compression and the inner surfaces into tension.
  • Laminated glass It’s formed from two pieces of glass bonded around a tough plastic interlayer made of polyvinyl butyral.Heat and pressure used in manufacturing make the lamination look like a single piece of optically clear glass. That’s why it works in car windshields and machinist’s safety goggles, as well as in windows, glass doors and skylights.
  • Optical glass It is used for making lenses for microscope, telescope, and spectacles.
  • Glass fibres used as insulating material in oven, refrigerator etc.
  • Optical fibres are extensively used in telecommunication surgical operations etc. Optical fibres can transmit images round corners.
  • Lead crystal glass Lead glass has a high refractive index. So, it is used for making expensive glassware.
  • Borosilicate glass Its components are silica, boric acid, aluminium oxide, potassium dioxide and sodium dioxide.Borosilicate glass is resistant to chemicals and shocks and has a very low expansion upon heating. This makes borosilicate fit for baking dishes, laboratory glassware, and pipelines.
  • Etching of glass Glass is attacked by hydrofluoric acid (HF), therefore it is used in the etching of glass.

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