Introduction

A glass is an inorganic nonmetallic material that does not have a crystalline structure.  Such materials are said to be amorphous.  Typical glasses range from the soda-lime silicate glass in soda bottles to the extremely high purity silica glass for optical fibers.

The main constituent of Glass is Silicon dioxide.  The most common form of silica used in glassmaking has always been sand.

Sand by itself can be fused to produce glass but the temperature at which this can be achieved is about 1700° C.  Adding other chemicals to sand can considerably reduce the temperature of the fusion. The addition of sodium carbonate (Na2O), known as soda ash, in a quantity to produce a fused mixture of 75% silica (SiO2) and 25% of sodium oxide (Na2O), will reduce the temperature of fusion to about 800° C.   However, a glass of this composition is water soluble and is known as water glass. In order to give the glass stability, other chemicals like calcium oxide (CaO) and magnesium oxide (MgO) are needed.  The raw materials used for introducing CaO and MgO are their carbonates CaCO3 (limestone) and MgCO3 (dolomite), which when subjected to high temperatures give off carbon dioxide leaving the oxides in the glass.

Borosilicate glass:

Borosilicate glasses are composed mainly of silica (70-80%) and boric oxide (7-13%) with smaller amounts of the alkalis (sodium and potassium oxides) and aluminum oxide. They are characterized by the relatively low alkali content and consequently have good chemical durability and thermal shock resistance.  Thus they are permanently suitable for process plants in the chemical industry, for laboratory apparatus, for various high intensity lighting applications and asglass fibers for textile and plastic reinforcement.  In the home they are familiar in the form of ovenware and other heat-resisting ware e.g Pyrex.

Properties