Glass

G

Glass Fibers

It is possible to produce fibers that can be woven or felted like textile fiber by drawing out molten glass to diameters of a few ten-thousandths of an inch. Both long, continuous multifilament yarns and short-staple fibers 25 to 30 cm (10 to 12 in) long may be produced.

Woven into textile fabrics, glass fibers make excellent drapery and upholstery materials because of their chemical stability, strength, and resistance to fire and water. Glass fabrics alone, or in combination with resins, make excellent electrical insulation. By impregnating glass fibers with plastics, a composite fiberglass is formed that combines the strength and inertness of glass with the impact resistance of the plastic.

H

Miscellaneous Types of Glass

Glass bricks are hollow construction blocks with ribbed or patterned sides that can be laid in mortar and used for exterior walls or interior partitions.

Foam glass, used in floats or as insulation, is made by adding a foaming agent to finely ground glass and heating the mixture to the softening point. At that point the foaming agent releases a gas that produces a multitude of small bubbles within the glass.

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In the 1950s glass optical fibers (see Fiber Optics) were developed that have many uses in science, medicine, and industry. High-refractive-index glass fibers, laid parallel to one another and separated by thin layers of low-refractive-index glass, can be optically worked as a lens. Fiberscopes incorporating such bundles can transmit an image through acute angles, thus easing the examination of normally inaccessible sites. Such solid fiber-optics applications as magnifiers, minifiers, and faceplates also improve viewing. When used in conjunction with lasers, optical fibers are also proving important in the development of various communications systems (see Telephone). A new kind of glass called halide glass, discovered in the 1970s, may prove especially useful for this application. It is made of a halide, such as fluorine, combined with a heavy metal, such as zirconium, barium, or hafnium.

Laser glass is doped, or mixed, with several percent of neodymium oxide and is capable of emitting laser light if the glass is pumped and assembled in the proper device. It is considered a good laser source because of the relative ease with which large, homogenous specimens of the glass can be obtained for extremely high-powered generation.

Double-glazing cells are units in which two sheets of plate or window glass are sealed together at their edges, leaving an air space between. Various types of seals and spacing materials may be used in their construction. As windows they provide superior heat insulation and will not cloud over in moist air.

A method for making large glass structures without using high temperatures was developed in the 1980s at the University of Florida. Called the sol-gel technique, it mixes water with a chemical such as tetramethoxysilane to produce a silicon oxide polymer; a chemical additive slows down the condensation process and allows the polymer to build up uniformly. The method may prove useful for making large, complex shapes with specific properties.

I

Recycling Glass

Scrap glass taken from the glass manufacturing process, called cullet, has been internally recycled for years. The scrap glass is economical to use as a raw material because it melts at lower temperatures than other raw materials, thus saving fuel and operating costs.

Glass that is to be recycled must be relatively free from impurities and sorted by color. Glass containers such as bottles and jars are the most commonly recycled form of glass, and their colors are flint (clear), amber (brown), and green. Other types of glass, such as window glass, pottery, and cooking utensils, are considered contaminants because they have different compositions than glass used in containers. The recycled glass is melted in a furnace and formed into new products.

Glass containers make up 90 percent of the total recycled glass used in the United States. The recycling rate for glass in 2000 was about 23 percent. Other uses for recycled glass include glass art and decorative tiles. Cullet mixed with asphalt forms a paving material called glassphalt.