This article is about the Pyrex glass. For the programming language, see Pyrex programming language.

Pyrex is a brand name of borosilicate glass introduced by Corning Glass Works in 1924. Though borosilicates had been produced before, the name Pyrex is widely used as a synonym for the material. Corning spun off its kitchenware division in 1998, and the Pyrex brand is now owned by World Kitchen, Inc.

Note: Pyrex kitchen products produced by World Kitchen are no longer made from borosilicate glass,10-K filing, WKI Holding Co., Inc., 2004; p. 8. and their packaging indicates that they must never be used over a flame, on stove tops, under a broiler, or in a toaster oven.

Composition and physical characteristics

Fraction by weight

Element, (Atomic number), Fraction

B (5) 0.040064, O (8) 0.539562,

Na (11) 0.028191,

Al (13) 0.011644,

Si (14) 0.377220,

K (19) 0.003321.

Physical characteristics

Density (g/cm3) = 2.23000E+00;

Mean Excitation Energy (eV) = 134.000000

Manufacturing process

Pyrex is created by adding boron to the traditional glassmaker's "frit" of silicate sand, soda, and ground lime. Since Pyrex melts at a higher temperature than ordinary silicate glass, some new techniques were required to bring Pyrex into industrial production. Borrowing from the welding trade, new burners combining oxygen with natural gas were required.

Properties

• Borosilicate glass has a thermal expansion coefficient about one-third that of ordinary glass. This reduces material stresses caused by temperature gradients, thus making it more resistant to breaking.
• Pyrex begins to soften around 821 °C (1510 °F); at this temperature, the viscosity of type 7740 Pyrex is 10^7.6 poise.
• Pyrex is less dense than ordinary glass.
• When broken, Pyrex tends to crack into large pieces rather than shattering (it will snap rather than splinter).

Examples of usage

Caltech's famous 200-inch telescope mirror at Mount Palomar was cast by Corning during 1934–36 out of Pyrex, which expands and contracts less than ordinary glass. Modern, commercially-built reflector telescopes use pyrex glass for the primary and secondary mirrors.

Pyrex's refractory properties and physical strength make it ideal for use in laboratories, where it is used to make high-durability glass lab equipment, such as beakers and test tubes.

Glass cookware is another common usage; a Pyrex pie plate is almost the American standard pie dish. Pyrex measuring cups, which featured painted-on markings illustrating graduated measurements, are also widely used in American kitchens.

Aquarium heaters are sometimes made out of pyrex. Due to its high heat resistance, it can tolerate the great temperature differences between water and the nichrome heating element.

Specialty tobacco pipes, though commonly used for smoking marijuana, are made from Pyrex. The high heat resistance allows the pipe to tolerate a longer period of use.

Many high quality flashlights, such as those made by Surefire, use Pyrex for the lense. This allows for a higher percentage of light transmittance through the lense than compared to plastics and lower-quality glass.

External links

• Illustrated history of the Palomar observatory and its Pyrex mirror
• Shattering Pyrex report
• Pyrex official website
• Pyrex composition according by NIST
• NIST Homepage - Physics Laboratory

References