Zerodur
Zerodur
Extremely durable glass-ceramic
Zerodur[2] is a lithium-aluminosilicate glass-ceramic[3] produced by Schott AG since 1968.[4] It has been used for a number of very large telescope mirrors including GTC, Keck I, Keck II,[5] and SOFIA, as well as some smaller telescopes (such as the GREGOR Solar Telescope). With its low coefficient of thermal expansion (CTE), it is suitable for producing mirrors that maintain acceptable figures in extremely cold environments, such as deep space.[6] Although it has advantages for applications requiring a coefficient of thermal expansion less than that of borosilicate glass, it remains very expensive as compared to borosilicate. The tight tolerance on CTE, ±0.007×10−6 K−1, allows for its use in high-precision applications.
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