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While materials such as "vaseline" Glass are also glass-ceramics, the term mainly refers to a mix of Lithium -, Silicon -, and Aluminium - Oxide s which yields an array of materials with interesting thermomechanical properties. The most commercially important of these have the distinction of being impervious to Thermal Shock . Originally developed for use in the Mirror s and mirror mounts of astronomical Telescope s, these materials have become known and entered the domestic market through its use in glass-ceramic Cooktops , as well as Cookware And Bakeware . ( 2004 )]] The crystalline component of thermal glass-ceramics, beta Spodumene , has a ''negative'' Coefficient Of Thermal Expansion , which contrasts with the positive coefficient of the glass. Adjusting the proportion of these two materials offers a wide range of possible coefficients in the finished composite. When an interface between materials will be subject to thermal Fatigue , glass-ceramics can be adjusted to match the coefficient of the material they will be bonded to. At a certain point, generally between 70% and 78% crystallinity, the two coefficients balance such that the glass-ceramic as a whole has a thermal expansion coefficient that is very close to zero. Glass-ceramic is a mechanically very strong material and can sustain repeated and quick temperature changes up to 800 - 1000 °C . At the same time, it has a very low Heat Conduction Coefficient and can be made nearly transparent (15-20% loss in a typical cooktop) for radiation in the Infrared Wavelength s. Today , there are two major types of electrical Stove s with cooktops made of glass-ceramic:
Some well-known brands of glass-ceramics are ''Ceran'' (cooktops), ''Zerodur'' (telescope mirrors), or ''Macor''. German manufacturer Schott has introduced Zerodur in 1968 , Ceran followed in 1971 . The same class of material is also used in Corningware dishes, which can be taken from the freezer directly to the oven with no risk of thermal shock. |
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