Pyrex

From The UCSC Wikipedia Trust Project

Pyrex is a brand name of borosilicate glass introduced by Corning Glass Works in 1915. 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 as World Kitchen, Inc. However, Corning retained the Pyrex brand name, licensing it to World Kitchen and other companies that produce Pyrex-branded cookware.

Note: Pyrex kitchen products produced by World Kitchen are no longer made from borosilicate glass,^[1] but from Soda-lime glass and their packaging indicates that they must never be used over a flame, on stove tops, under a broiler, or in a toaster oven.

1 Composition and physical characteristics
2 Manufacturing process
3 Properties
4 Safety issues
5 Examples of usage
6 See also
7 References
8 External links

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 = 2.23 g/cm³
Mean Excitation Energy = 134.0 eV

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. ^[2]
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).

Safety issues

Pyrex, while more resistant to thermal shock than other types of glass, should never be subject to drastic or uneven temperature changes, such as when taken from the oven and placed on the stove elements (an excellent heat conductor) to cool, or immersed in cold water when hot. This can crack or shatter the dish.Template:Fact

However, recent reports suggest that due to the change in manufacturing,^[1] notwithstanding the claims made for Pyrex, the glassware can shatter violently and unexpectedly, even when used in accordance with manufacturers instructions.^[3] Claims have been made of severe personal injury during these events. The tendency to break into large pieces, rather than shatter like normal glass, can produce large cutting edges capable of causing serious injury. Some reports have suggested that older Pyrex was not as susceptible to these problems as currently produced Pyrex. It is unknown whether this has anything to do with the recent change in ownership and location of manufacture of the Pyrex brand.

Examples of usage

Caltech's famous 200-inch telescope mirror at Mount Palomar was cast by Corning during 1934 – 1936 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.

Most glassware used in laboratories is made of Pyrex, due partly to how little it warps when exposed to heat hence its ability to provide accurate measurements of volume over time.

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.

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

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