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.

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.

In space, it has been used for the primary mirror of SOFIA’s telescope, for the imager in Meteosat Earth observation satellites, and for the optical bench in the LISA Pathfinder mission.

In microlithography, Zerodur is used in wafer steppers and scanner machines for precise and reproducible wafer positioning. It is also used as a mirror substrate material in refractive optics for EUV lithography.

In inertial measurement units, Zerodur is used in ring laser gyroscopes.

Properties
Zerodur has both an amorphous (vitreous) component and a crystalline component. Its most important properties are:
 * The material exhibits a particularly low thermal expansion, with a mean value of 0 ± 0.007×10−6 K−1 within the temperature range of 0 to 50 °C.
 * High 3D homogeneity with few inclusions, bubbles and internal stria.
 * Hardness similar to that of borosilicate glass.
 * High affinity for coatings.
 * Low helium permeability.
 * Non-porous.
 * Good chemical stability.
 * Fracture toughness approximately 0.9 MPa·m1/2.

Physical properties

 * Dispersion: (nF − nC) = 0.00967
 * Density: 2.53 g/cm3 at 25 °C
 * Young's modulus: 9.1 Pa
 * Poisson ratio: 0.24
 * Specific heat capacity at 25 °C: 0.196 cal/(g·K) = 0.82 J/(g·K)
 * Coefficient of thermal expansion (20 °C to 300 °C) : 0.05 ± 0.10/K
 * Thermal conductivity: at 20 °C: 1.46 W/(m·K)
 * Maximum application temperature: 600 °C
 * Impact resistance behavior is substantially similar to other glass