NET, IAS, State-SET (KSET, WBSET, MPSET, etc.), GATE, CUET, Olympiads etc.: Cement & Glass
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Portland Cement
The approximate composition of Portland cement is:
- Calcium oxide (CaO) - 62%
- Silica (SiO2) - 22%
- Alumina (Al2O3) - 7.5%
- Magnesia (MgO) - 2.5%
- Ferric oxide (Fe2O3) - 2.5%
The above compounds are provided by the two raw materials
(a) Limestone, (b) Clay
- Cement containing excess amount of lime cracks during setting while cement containing less amount of lime is weak in stength. Setting of cement is an exothermic process.
- A small amount of gypsum is added to slow down the setting of cement.
- Cement with excess of silica shows slow setting and that having an excess of alumina shows quick setting.
- Cement containing no iron is white but hard to burn.
Glass
- Ordinary glass is solid mixture of silica, sodium silicate and calcium silicate.
- Glass is a super cooled liquid hence; it has no definite crystal structure and melting point.
- We can say that glass is a mixture, not a compound.
Types of Class
Soft Glass
- It is soda lime silicate glass.
- It melts at low temperature. It is used in manufacturing of bottles, test tubes and glass of windows etc.
Hard Glass
- It is potash lime silicate.
- It melts at high temperature in comparison to soft glass and is used in manufacturing of flask, etc.
Flint Glass
- It is lead-potash silicate and is used in manufacturing of prism and lens of optical instruments.
Pyrex Glass
- It is a mixture of sodium aluminum borosilicate.
- It has high percentage of Silica, about 80% . It is used in manufacture of high quality equipment in laboratory because it does not melt at very high temperature.
Quartz Glass
- It is obtained from pure silica. It has a low coefficient of expansion and does not break even when plunged in water while red hot.
Ground Glass
- It is prepared by grinding ordinary sand (soft) glass by emery and turpentine oil.
Reinforced Glass
- It has a network of wires embedded in and does not shatter easily.
Safety Glass
- It is also known as Shatter Proof glass.
- It is prepared by placing a layer of transparent plastic glass (usually a sheet of vinyl acetate resin) between two layers of glass by means of a suitable adhesive.