Glass
Glass is commonly used in products such as windows, light bulbs, housewares such as
drinking glasses, chemical containers, beverage and beer containers, and decorative items
(see Figure 17.2). The composition of the glass depends on its application. The most widely
used form of glass is soda-lime-silica glass. The materials used in making soda-lime-silica
glass include sand (silicon dioxide), limestone (calcium carbonate), and soda ash (sodium
carbonate). Other materials are added to create desired characteristics for specific applica-
tions. For example, bottle glass contains approximately 2% aluminum oxide, and glass sheets
contain about 4% magnesium oxide. Metallic oxides are also added to give glass various
colors. For example, silver oxide gives glass a yellowish stain, and copper oxide gives glass
its blueish, greenish color, the degree depending on the amount added to the composition
of the glass. Optical glasses have very specific chemical compositions and are quite expensive.
The composition of optical glass will influence its refractive index and its light-dispersion
properties. Glass that is made completely from silica (silicon dioxide) has properties that
are sought after by many industries, such as fiber optics, but it is quite expensive to manu-
facture because the sand has to be heated to temperatures exceeding 1700C. Silica glass
has a low coefficient of thermal expansion, high electrical resistivity, and high transparency
to ultraviolet light. Because silica glass has a low coefficient of thermal expansion, it can be
used in high-temperature applications. Ordinary glass has a relatively high coefficient of
thermal expansion; therefore, when its temperature is changed suddenly, it could break eas-
ily due to thermal stresses developed by the temperature rise. Cookware glass contains boric
oxide and aluminum oxide to reduce its coefficient of thermal expansion.Fiber Glass Silica glass fibers are commonly used today in fiber optics, that branch of science
that deals with transmitting data, voice, and images through thin glass or plastic fibers. Every
day, copper wires are being replaced by transparent glass fibers in telecommunication to connect
computers together in networks. The glass fibers typically have an outer diameter of 0.0125 mm
(12 micron) with an inner transmitting core diameter of 0.01 mm (10 micron). Infrared
light signals in the wavelength ranges of 0.8 to 0.9 m or 1.3 to 1.6 m are generated by
light-emitting diodes or semiconductor lasers and travel through the inner core of glass fiber.17.3 Some Common Solid Engineering Materials 569
■Figure 17.2
Examples of glass products.Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).圀圀圀⸀夀䄀娀䐀䄀一倀刀䔀匀匀⸀䌀伀䴀圀圀圀⸀夀䄀娀䐀䄀一倀刀䔀匀匀⸀䌀伀䴀