Zerodur Explained

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^[1] and space applications,^[2] lithography machines for microchips and displays,^[3] and inertial measurements systems for navigation.^{[4] [5]}

In astronomy, it is used for mirror substrates in large telescopes such as the Hobby-Eberly Telescope,^[6] the Keck I and Keck II telescopes,^[7] the Gran Telescopio Canarias,^[8] the Devasthal Optical Telescope,^[9] the European Southern Observatory's 8.2 m Very Large Telescope,^[10] and the 39 m Extremely Large Telescope.^[11] It also has been used for the primary mirror of SOFIA's airborne telescope.^[12]

In space, it has been used for the imager in Meteosat Earth observation satellites,^[13] and for the optical bench in the LISA Pathfinder mission.^[14]

In microlithography, Zerodur is used in wafer steppers and scanner machines for precise and reproducible wafer positioning.^{[15] [16]} It is also used as a component in refractive optics for photolithography.^[17]

In inertial measurement units, Zerodur is used in ring laser gyroscopes.^[18]

Properties

Zerodur has both an amorphous (vitreous) component and a crystalline component. Its most important properties^[19] 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.^[20]
• High 3D homogeneity^[20] 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·m^1/2.^{[21] [22]}

Physical properties

• Dispersion: (n_F − n_C) = 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^[23]

History

Schott began developing glass-ceramics in the 1960s lead by Jürgen Petzoldt, in response to demand for low expansion glass ceramics for telescopes.

In 1966, Hans Elsässer, the founding director of the Max Planck Institute for Astronomy (MPIA), asked the company if it could produce large castings of almost 4 meters using low-expansion glass-ceramic for telescope mirror substrates. In 1969, the MPIA ordered a 3.6sigfig=2NaNsigfig=2 mirror blank, along with ten smaller mirror substrates. The mirrors were delivered by late 1975,^[24] and went into operation in 1984 in a telescope at the Calar Alto Observatory in Spain. Further orders for mirror blanks followed.^[25]

See also

• CorningWare
• Macor
• Ring laser gyroscope
• Sitall

References

1. Book: Döhring . Thorsten . Wenhan . Roland . Myung K. . Fan . Jiang . Geyl . Cho . Wu . Four decades of ZERODUR mirror substrates for astronomy . May 2019 . 4th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Large Mirrors and Telescopes . https://www.spiedigitallibrary.org/conference-proceedings-of-spie/7281/1/Four-decades-of-ZERODUR-mirror-substrates-for-astronomy/10.1117/12.831423.short . Proceedings of the SPIE . 7281 . 10.1117/12.831423 . 10 May 2024.
2. Carré . Antoine . May 2023 . Comprehensive review of the effects of ionizing radiations on the ZERODUR® glass ceramic . Journal of Astronomical Telescopes, Instruments, and Systems . 9 . 2 . 10.1117/1.JATIS.9.2.024005 . free .
3. News: September 29, 2023 . SCHOTT Strengthens Glass Substrate Portfolio . Printed Electronics Now.
4. Web site: Sokach . Stephen . ZERODUR: The Highly Technical Glass-Ceramic . 10 May 2024 . Tech Briefs. July 2020 .
5. Web site: Zerodur . 10 May 2024 . Mindrum Precision.
6. Web site: Hobby-Eberly Telescope McDonald Observatory . 2024-07-12 . mcdonaldobservatory.org.
7. Web site: A Mirror's Perfect Reflection . 10 May 2024 . W.M. Keck Observatory. 28 May 2010 .
8. Web site: Description of the GTC . 10 May 2024 . Gran Telescopio CANARIAS.
9. Web site: 3.6 m DOT Telescope . July 7, 2024 . ARIES.
10. Web site: Very Large Telescope . 10 May 2024 . ESO.
11. Web site: Mirrors and Optical Design . 10 May 2024 . ESO.
12. Krabbe . Alfred . Ramsey K. . Hans-Peter . Melugin . Roeser . June 2000 . SOFIA telescope . Proceedings, Airborne Telescope Systems . Airborne Telescope Systems . 4014 . 276 . 10.1117/12.389103 . 10 May 2024. astro-ph/0004253 . 2000SPIE.4014..276K .
13. Web site: MTG (Meteosat Third Generation) - eoPortal . 2024-07-12 . www.eoportal.org . en.
14. Web site: LISA Technology Package Optical Bench Interferometer During Calibration . 10 May 2024 . ESA.
15. Web site: Hartmann . Peter . SCHOTT – Ultra low expansion glass ceramic ZERODUR . 10 May 2024 . Max-Planck-Institut für Astronomie . 49.
16. Book: Jedamzik . Ralf . Optical Microlithography XXVII . Glass ceramic ZERODUR enabling nanometer precision . Kafai . Andreas . Lai . Erdmann . 2014 . Proceedings of the SPIE . 9052 . 90522I . 10.1117/12.2046352 . 2014SPIE.9052E..2IJ .
17. Mitra . Ina . September 2022 . ZERODUR: a glass-ceramic material enabling optical technologies . Optical Materials Express . 12 . 9 . 3563 . 10.1364/OME.460265 . 10 May 2024. free .
18. Pinckney . Linda R. . 2003 . Glass-Ceramics . Encyclopedia of Physical Science and Technology (Third Edition) . 807–816 . 10.1016/B0-12-227410-5/00293-3 . 978-0-12-227410-7 . 10 May 2024.
19. Web site: Technical Details ZERODUR®. schott.com. 6 September 2024.
20. Hartmann. Peter. Jedamzik . Ralf . Carré . Antoine . Krieg . Janina . Westerhoff . Thomas . Glass ceramic ZERODUR®: Even closer to zero thermal expansion: a review, part 2. Journal of Astronomical Telescopes, Instruments, and Systems . 24 March 2006 . 7 . 2 . 10.1117/1.JATIS.7.2.020902. free .
21. Web site: Viens . Michael J . April 1990 . Fracture Toughness and Crack Growth of Zerodur . 6 September 2024 . NASA Technical Memorandum 4185 . NASA.
22. Hartmann. P.. ZERODUR - Deterministic Approach for Strength Design. Optical Engineering. NASA. 18 December 2012. 51. 12. 124002. 10.1117/1.OE.51.12.124002. 2012OptEn..51l4002H. 120843972. PDF. 11 September 2013.
23. Senf. H. E Strassburger . H Rothenhausler . A study of Damage during Impact in Zerodur. J Phys IV France. 7. Colloque C3, Suppltment au Journal de Physique I11 d'aotit 1997. 1997. C3-1015-C3-1020. 10.1051/jp4:19973171. 31 August 2011.
24. Book: Pannhorst, Wolfgang . 1995 . Bach . Hans . Low Thermal Expansion Glass Ceramics . Springer . 107–121 . Chapter 4: Zerodur® - A Low Thermal Expansion Glass Ceramic for Optical Precision Applications . 3-540-58598-2.
25. Book: Lemke, Dietrich . Im Himmel über Heidelberg - 50 Jahre Max-Planck-Institut für Astronomie in Heidelberg (1969 – 2019) . 2019 . Berlin, Heidelberg . DE.