Engineering Chemistry S Datta

19
Silicate Technology
INTRODUCTION
Glass and Pottery are the earliest products of man made chemical industry. Glass was
known to the ancient Egyptians 6000 years ago. Glass is an amorphous, transparent or
translucent, rigid super supercooled liquid of infinitely high viscosity comprising of metallic
silicates one of which is usually of an alkali metal. Ceramic products are made of clay which
are silicates, cement is also a mixture of silicates and other compounds. So, all these industries
fall under silicate technology.
Silicates are chemical compounds of silicon and oxygen with metals. Clay and soil are different
products. Clay must not be confused with soil. Soil is the thin outermost layer of the earth. Soil
is infact a mixture of clay, sand, humus (decayed vegetable matter) and various other minerals.
Clay is a mixture of variety of minerals like bentonite, kaolinite, hauoysite etc. Basically
most of these are hydrated silicates of aluminium. The structural pattern of silicates are
important in different ceramic products which have been shown in following figures: In a
silicate unit silicon atom is symmetrically surrounded by four oxygen atoms to form a tetrahedral
unit. These tetrahedral units remain joined in the silicates (see Fig. 19.1).
Chain silicates. These silicates are of two types viz., single chain silicates and double
chain silicates. Single chain silicates contain [(SiO 3
) n
] –2n ion as the primary unit (Fig. 19.1),
while double chain silicates contain [(Si 4
O 11
) n
] –6n as the primary unit (Fig. 19.2).
– –
– –
–
–
–
– – –
Fig. 19.1 Structure of [(SiO 3
) n
] –2n ion (single chain). e — Silicon atom, d — Oxygen atom.
– –
–
–
–
–
–
–
–
–
–
–
–
–
Fig. 19.2 Structure of [(Si 4
O 11
) n
] 6n– ion (double chain).
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