Borosilicate is more a utility than a luxury type of glass. Although lacking the sparkle of soda-lime or crystal glass, this technical glass has still made a huge and unparalleled contribution to technology and our lives over the last 100 years. As the name implies, borosilicate glasses, the third major glass group, are composed mainly of silica (70–80 per cent) and boric oxide (7–13 per cent) with smaller amounts of the alkalis (sodium and potassium oxides) and aluminium oxide. The reason it is such an important glass is because of two of its main attributes, which are its high chemical resistance and its ability to withstand large changes in temperature.
Invented by Otto Schott, who went on to found Schott Glass, one of the giants of glass production, borosilicate glass is the material behind the global consumer brand Pyrex®, which was developed by the equally important US-based glass company Corning Glass in 1915. One of the most significant inventions of the twentieth century has to be the incandescent light bulb. Invented by Thomas Eddison in 1879, the lightbulb was only able to be mass-produced because of the invention of a ribbon forming machine, which was capable of producing the light in vast numbers, and because of the invention of a glass that was able to withstand the temperature variation between the inside of the lightbulb and the often freezing outside temperature. The ability of borosilicate glass to withstand thermal shock is what distinguishes it from the more common soda-lime glass.
Image: Arik Levy candleholder
Key features
•High thermal-shock resistance
•Less dense that soda-lime glass
•Stronger than soda-lime glass
•High resistance to chemicals, exceeding that of most metals even when exposed at 100ºC (212ºF) for long periods of time
•Low coefficient of expansion: this means virtually no stress takes place in the glass when, for example, boiling water is poured into it
Sources
Widely available in various forms, including semi-finished sheets and tubes for lampworking.
Cost
More expensive than soda-lime glass.
Sustainability issues
Exposure to water and acids only results in the leaching out of very small amounts of mainly univalent ions from the glass. The resultant, very thin, layer of silica with few pores that is formed on the surface inhibits further attack.
Production
It is a popular material within the low-production scales of some designers as it borrows the production methods of laboratoryware. In these applications it can be formed without expensive tooling to produce multiples of the same shape. Often this process starts from a tube of glass and it is worked on a lathe. However, it can also be produced in high volume mass-production. Its comparative strength means that it has a greater potential for creating beautifully thin-walled, skeletal forms. Soda-lime glass is the nearest alternative to borosilicate glass. However, for more versatile production and greater ability to play with forms, then high clarity plastics, such as some copolyesters, polycarbonates, acrylics and certain types of styrenes or ionomer resins, are a good alternative. For thermal shock resistance, advanced ceramics are also worth exploring.
Typical applications
It is heavily used in the chemical industry for laboratory apparatus, pharmaceutical containers, high-intensity lighting applications and as glass fibres for textile and plastic reinforcement. In the home it is familiar in the form of ovenware and other heat-resistant ware, and is possibly better known under the trade name Pyrex®.
Derivatives
Glass fibre Optical glass fibre.
| + | – |
|
–Low production costs –High chemical resistance –High thermal-shock resistance –Comparatively strong |
–Does not have the sparkle of some other glasses –Comparatively expensive |