Page 50 - Curriculum Visions Dynamic Book

is part of the recently developed “stealth” technology.
Ceramics and
optics
Most crystals
are transparent. However, when
they are in the
form of powders,
they are not transparent
because the
powders scatter
light. But as single crystals many are more transparent than glass.
Crystals of ceramics have been used
as superior forms of camera lenses. Many high- quality camera lenses are not made of glass but of the mineral fluorite. This produces clearer pictures, especially at high magnifications when used with zoom lenses.
Sapphire (crystalline aluminium oxide) is a very hard ceramic. A single industrially grown crystal can be cut into thin sheets and used where glass would get scratched and cause problems. One such application is the bar code window at supermarket checkouts. A single sheet of sapphire covers the reader window.
The very bright lights that are used in sports stadiums or in street lights are not enclosed in glass. Under high-temperature conditions glass would fail. Instead, a transparent ceramic of alumina (aluminium oxide) and magnesium oxide is used. It also goes into the “glass” bulb in a sodium discharge tube, the common amber- coloured light in most street lights and the mercury vapour lights in sports stadiums. These lights are not only bright, they are also several
(Above) This digital video camera uses a fluorite lens for sharpness of image.
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