Zerodur

Zerodur is a lithium-aluminosilicate glass-ceramic manufactured by Schott AG. Zerodur has a near zero coefficient of thermal expansion (CTE), and is used for high-precision applications in telescope optics, microlithography machines and inertial navigation systems.

Manufacturing process

Zerodur is produced in a two-step process involving melting and ceramization. Depending on the size of the blanks, each step can take several months.

First, raw materials including main components of lithium oxide (Li2O), alumina (Al2O3), and silica (SiO2) are melted at high temperatures of around 1600 °C, poured into molds, and annealed in a controlled cooling process that relieves internal stresses that develop during forming.

Then the glass undergoes a ceramization process involving controlled volume crystallization, which creates high-quartz nano-crystallites of 30 nm to 50 nm. The negative CTE of the crystals compensates for the positive CTE of the residual glass matrix, which gives Zerodur its near zero thermal expansion.

Applications

The main applications for Zerodur include telescope optics in astronomy and space applications, lithography machines for microchips and displays, and inertial measurements systems for navigation.

In astronomy, it is used for mirror substrates in large telescopes such as the Hobby-Eberly Telescope, the Keck I and Keck II telescopes, the Gran Telescopio Canarias, the Devasthal Optical Telescope, the European Southern Observatory's 8.2 m Very Large Telescope, and the 39 m Extremely Large Telescope.

It also has been used for the primary mirror of SOFIA's airborne telescope.

ASA (AstroSysteme Austria) also produces some telescopes with Zerodur.