Glass | Constituents Of Glass | Properties Of Glass | Types And Uses Of Glass

GLASS 

Glass may be defined as a hard, brittle and transparent or translucent material. Technically glass is any substance or combination of substances that has solidified from the liquid state without crystallisation.

 

Constituents of Glass

The main constituents of glass are silica, sodium or potassium carbonate, lime, manganese dioxide, cullet and colouring materials.

 

1. Silica

Silica is the principal constituent of glass. Silica alone when fused at a very high temperature would give a good glass on cooling. However, it is essential to add some quantity of alkaline materials along with lime to make the molten silica glass sufficiently viscous so as to get good workability and resistance against weathering agencies.

 

2. Sodium or Potassium Carbonate

It is an alkaline material that is also an essential component of glass. This is being added in a certain proportion so as to reduce the melting point of silica and to impart viscosity to the molten glass.

 

3. Lime

This is added in the form of chalk so as to impart durability to glass. In order to make the glass bright and shining, lead oxide is added in place of lime.

 

4. Manganese Oxide

This is added in a certain proportion so as to correct the colour of the glass due to the presence of iron in raw materials of glass.

 

5. Cullet

Cullet is the old broken glass of the same type as that is intended to be manufactured.

 

6. Colouring Substances

At the time of manufacturing a coloured glass, a suitable colouring substance is added at the fusion stage to provide the desired colour to the glass.

 Various Uses Of Glass In Construction

Properties of Glass

Properties of glass are mainly governed by the factors such as the composition of constituents, state of the surface, thermal treatment, dimensions of the object, etc. Glass has been popular and useful due to the following properties:

·       It has no sharp melting point and no definite crystalline structure.

·       It is capable to absorb, refract or transmit light.

·       At elevated temperatures acts as an excellent electrical insulator.

·       It can take up the high polish and can be used as a substitute for any costly gem.

·       It is not affected by air or water.

·       It can not be attacked by ordinary chemical agents.

·       It can be altered to meet certain requirements by changing fusibility, hardness, refractive power, etc.

·       It is transparent and translucent.

·       It is possible to weld pieces of glass by fusion.

·       It is affected by alkalis.

·       Based on advanced technology, it is possible to make glass lighter than cork or softer than cotton.

·       The only drawback is that it is brittle.

 

Types and Uses of Glass

 

1. Conventional Types

Based on composition and properties, the conventional glass may be classified as soda-lime or crown glass, flint glass, and Pyrex or heat-resistant glass.

 

Soda Lime or Crown Glass

The composition by weight, in general, is sand 75 parts, lime 12.5 parts, soda 12.5 parts, alumina 1 part and waste glass 50 parts. It can be easily fused at comparatively low temperatures. It is quite cheap and available in clean and clear state.

It is principally used for window glass, plate glass and container glass (such as bottles, tumblers, etc.).

 

Flint Glass

The composition of flint glass is sand 100 parts, lead 70 parts, potash 32 parts and waste glass 10 parts. It liquefies at a lower temperature compared to soda-lime glass and has better lustre. As the lead compounds are reduced easily, the glass must be melted in an oxidising atmosphere, etc.

It is used for tableware and for optical works. It has also a wide range of use as electric lamps, thermometers, electron tubes, laboratory apparatuses, containers for foods, etc.

 

Pyrex or Heat-resistant Glass

Both the above two glasses when subjected to sudden temperatures are not able to sustain because of large coefficients of thermal expansion. Only the basic oxides make them susceptible to chemical attack by water and acids. Elimination of the basic oxides and inclusion of boron oxide produce a glass that is very resistant to thermal shock and to attack by water and acids. The composition of material for such a glass by weight are silica 80 parts, boron oxide 14 parts, sodium oxide 4 parts, alumina 2 parts, with traces of potassium oxide, calcium oxide and magnesium oxide. In order to melt such as mixture, a very high temperature is required.

These glasses are called borosilicate glasses which are extensively used for cooking utensils and laboratory wares.

 

2. Special Types of Glasses

Special types of glasses are sheet glass, plate glass, float glass, wired glass, translucent glass, glass blocks, safety glass, bullet-proof glass, tinted glass, structural glass, etc.

 

Sheet Glass

This is mainly used for small panels of doors and windows. These glasses are to be free from blisters, scratches, waves, bubbles, etc. It is manufactured in thickness varying from 1.5–5 mm and sizes up to 1.5 m × 1 m.

 

Plate Glass

It is available in thickness varying from 3–32 mm. This type of glass is stronger and more transparent with very little waviness. It is generally used for large-sized panels such as waiting halls, shopping complexes, etc. There are three varieties of this type of glass, namely roughcast, rolled (or patterned) and polished glass. Generally, the polished variety is denoted as plate glass.

 

Flutted Glass

These are the glasses that have corrugations on one side of the plate glass. The other side is wavy but smooth. In this type, the light is admitted without the glare of the sun. It is used in situations where privacy without the obstruction of light is needed. Ribs may be in the horizontal or vertical directions. Horizontal ribs give more light in the middle and less at the sides. The upright ribs give more light at the sides and less in the middle. It is thus more ideal to use for skylight roofs and

 

Float Glass

This type of glass is prepared by passing the molten glass through a molten tin bath (float bath). Because the free-standing surface of the tin bath is very smooth, the float glass is of uniform thickness. It possesses excellent optical clarity and aesthetic appearance. Finally, it is annealed to relieve all the stress. This is mainly used for large-sized shop windows and facades of tall buildings.

 

Wired Glass

In this type of glass, wire-netting material is embedded during the time of manufacture. It has high resisting power compared to ordinary plate glass. Because of wire-netting, it does not fall into pieces when broken. It is used for fire-resisting doors and windows and for skylights and roofs.

 

Translucent Glass

This glass is also called obscured glass or frosted glass. In such glasses, a pattern or texture is imprinted on one or both faces. This prevents the image from being seen through. The textured side should face the inside of a place (to be made obscure) and the plane glass side should face the other side. This type of glasses is used for doors and windows of the bedroom, bathroom, lavatories, etc.

 

Bullet-proof Glass

This type of glass is prepared by following special techniques. Here, the glass is made of several layers of plate glass with alternate layers of vinyl resin plastics. Further, the inner layers are thicker than the outer layers. At the time of manufacturing, special care is taken for heating and cooling of layers. The thickness of this type of glasses varies from 15–75 mm. The special quality of the glass is that it will not allow bullets to pierce through it. It is used in a special type of car, bank counters, jewellery stores, etc.

 

Glass Blocks

These are glass units that consist of two halves fused together so as to form a hollow inside. These blocks provide insulators against heat, cold and noise. These blocks are used for constructing wall panels.

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