Zerodur
Zerodur (manufacturer's spelling: ZERODUR®) is a glass-ceramic material from Schott AG , which is produced through controlled volume crystallization .
properties
Zerodur contains a crystalline phase and a residual glass phase, which determine the extraordinary characteristics of the material. These special features include an extremely low coefficient of expansion , good material homogeneity, chemical resistance, long-term stability and hardly any fluctuating mechanical properties.
Manufacturing
To manufacture Zerodur, parts made of glass are first reheated. At around 800 degrees Celsius, substances added to the glass melt form crystal nuclei on which tiny crystals (average size around 50 nanometers) grow as the temperature rises. These have the property of contracting when heated. They thus counteract the thermal expansion of pure glass. The art of this process, known as ceramization, consists in adjusting the ratio of crystal phase to glass phase in such a way that the resulting thermal expansion is minimal, and even zero in certain temperature ranges. This is the case when about 70 percent by weight of the melt is crystalline. The process of ceramization can take up to several months, depending on the size of the glass blank.
use
The material Zerodur is typically used as a substrate material for optical elements in astronomy, e.g. B. in comet probes, as a mirror carrier for modern large astronomical telescopes , such. B. the Very Large Telescope in Chile (four mirrors each 8.2 meters in diameter), the Keck Observatory in Hawaii (two mirrors each 10.0 meters in diameter), the GREGOR solar telescope or the Gran Telescopio Canarias on La Palma (one mirror 10.4 meters in diameter) as well as used in precision optics and precision measurement technology. Because of its excellent thermal properties, Zerodur is also used as a material for frames and supports for lithography and nano measuring machines. One example of this is the nanopositioning and measuring machine (NMM-1) from the Technical University of Ilmenau . For use in space travel, Zerodur is interesting because of the possible reduction in take-off weight compared to other mirror materials. In coordinate metrology, high-precision measuring machines sometimes use Zerodur scales with vapor-deposited longitudinal graduations made of chrome.
History and material variants
Zerodur was launched in 1968 . Ceran followed in 1971 , using Zerodur glass ceramic for "Ceran" hobs . Since then, the material has been expanded to include numerous material variants, e.g. B. "Zerodur K20". It is produced by thermal conversion of the semitransparent starting material Zerodur, is thermally highly stable and does not change over many heating cycles. "Zerodur K20" glass ceramic has a high long-term temperature stability of up to 850 degrees Celsius. The material can e.g. B. be used for mechanical and optical components in high-performance lasers or as mold material for use in hot molding (glass, plastic).
Web links
Individual evidence
- ↑ Source: 50 years of Schott in Mainz. Quarterly issues for culture, politics, economy and history. Special edition Mainz. 22nd year, 2002.
- ↑ Length measuring system with Zerodur graduation carriers. Retrieved September 26, 2019 .
- ^ Schott AG Zerodur