Page 195 - Materials Chemistry, Second Edition

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Sustainable Industrial Design and Waste Management
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New glass is made from a mixture of four main ingredients: sand, soda ash,
limestone, and other additives. These additives include iron for color (brown
or green), chromium and cobalt for color (green and blue respectively), lead
to alter the refractive index, alumina for durability, and boron to improve
the thermal options.
Glass can be divided into different types according to composition
and use:

• Container glass such as bottles and jars.
• Flat glass such as glass flat plates, automotive windscreens, and
mirrors.
• Fiberglass: Two types of fiberglass can be produced, continuous
and/or short fibers. Blanket fiberglass can be produced from contin-
ues fibers. The main applications are glass reinforced plastic (GRP),
glass reinforced cements (GRC), and blanket fiber material used for
insulation.
• Domestic glass such as domestic houseware, e.g. glasses and
ornaments.
• Special glass such as cathode ray tubes as used in television, med-
ical, and computer screens.

Glass manufacturing/recycled processes
The glass market has eight main categories, and within each category indi-
vidual classes might exist. The eight categories are:

• Bottle applications.
• Building materials such as doors, windows, etc.
• Concrete applications in terms of concrete additives or aggregates.
• Industrial mineral uses such as sandblasting.
• Insulation applications such as fiberglass insulation.
• Paving applications as aggregate.
• Remelt applications such as art glass.
• Miscellaneous applications such as abrasive material, ceramic glaz-
ing, designer clothes, etc.

In all categories, a glass melt is prepared from silica sand and other raw
materials such as lime, dolomite, soda, and cullet (broken glass). The use of
recycled glass is increasing everywhere. It reduces the consumption of both
raw materials and energy but necessitates extensive sorting and cleaning
prior to batch treatment to remove impurities.
Glass used for new bottles and containers must be sorted by color and
must not contain contaminants such as dirt, rocks, ceramics, etc. These
materials, known as refractory materials, have higher melting temperatures
than container glass and form a solid inclusion in the finished product.