Civil Engineering Reference
In-Depth Information
In Belgium in 1907 the first glass was produced by machine. In 1959, float glass was
developed, for the first time giving a completely homogeneous surface without any irreg-
ularities.
Different proportions of raw materials can be used to make glass, but it usual-
ly consists of 59 per cent silicon dioxide in the form of quartz sand, 18 per cent
soda ash, 15 per cent dolomite, 11 per cent limestone, 3 per cent nephelin and 1
per cent sodium sulphate. The formula for the process is:
Na
2
CO
3
+ CaCO
3
+ SiO
2
= Na
2
O
CaO
6SiO
2
+ CO
2
(6)
This glass, based on natron, is the most common. Replacing the soda ash with
potash (K
2
CO
3
) gives a slightly harder glass. Lead glass is achieved by replacing
limestone in the potash glass with lead (Pb).
For glass that needs high translucency for ultraviolet light an important con-
stituent is phosphorous pentoxide (P
2
O
5
).
Fluorine compound agents decrease the viscosity and melting point of glass
mixtures, which can reduce the use of energy. Antimony trioxide (Sb
3
O
2
) can be
added to improve malleability, and arsenic trioxide (As
2
O
3
) acts as an oxidizing
agent to remove air bubbles from the molten glass. Both are added in a propor-
tion of about 1 per cent each. Stabilizers which increase the chemical resistance
are often used: CaO, MgO, Al
2
O
3
, PbO, BaO, ZnO and TiO
2
.
Coloured glass contains substances which include metal oxides of tin, gold,
iron, chrome, copper, cobalt, nickel and cadmium, mixed in at the molten stage
or laid on the completed sheet of glass electrolytically or as vapour.
Traditionally, coloured glass has been used for decoration. In modern coloured
glass the colouring is very sparse and it can be difficult to differentiate from
normal glass. Decorative qualities are less important than the ability of the
coloured glass sheet to absorb and/or reflect light and warmth. The aim is to
reduce the overheating of spaces or reduce heat loss. Products which achieve this
are usually known as energy glass, and have a high energy-saving potential.
There are two types: 'absorption glass', which is coloured or laminated with
coloured film, and 'reflection glass', which has a metal or metallic oxide applied
to it in the form of vapour. Early energy glass reduced the amount of light enter-
ing the building by up to 70 per cent; today's is much more translucent, but the
area of glass in a room may need to be increased to achieve adequate levels of
light.
Production of glass for windows
To produce good quality glass, good quality raw materials with no impurities
must be used. The ingredients are ground to a fine powder, mixed and smelted
down.
