Page 8 - Curriculum Visions Dynamic Book

The ingredients of glass
In industry glass is mostly made by combining sand (silicon dioxide – SiO2), soda (sodium carbonate – Na2CO3), and lime (calcium oxide
– CaO). However, there are many special glasses that contain a wide variety of other materials.
The most bulky ingredient (usually sand)
is called a former. The material that makes
the former melt at a lower temperature (the
soda in this case) is called a flux. The material (for example, lime) that stops the glass from crumbling, forming crystals, or dissolving is called a stabilizer. They are all described in more detail below.
It is quite possible to make glass just by heating silica on its own to produce silica glass. But to do so, the temperature has to be raised
to over 1,700°C. The energy needed for this
is so high that pure silica glass is expensive. Nevertheless, cheaper glasses cannot match it for standing up to rapid temperature changes or for its low reactivity. It is also used to make some
(Above) The composition of glass is given by its chemistry. All of the material used to make glass are oxides. In this table they are shown by percentage weight.
(Below) Laboratories need silica glasses to perform experiments that involve intense heating.
Oxide ingredient in
Soda-lime glass
Silica (SiO2)
73.6
Soda (Na2CO3)
16.0
Lime (CaO)
5.2
Potash (K2O)
0.6
Magnesia (MgO)
3.6
Alumina (Al2O3)
1.0
Iron oxide (FeO)
–
Boric oxide (B2O3)
–
Lead oxide (PbO)
–
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