View source for Zerodur

{{Short description|Extremely durable glass-ceramic}}

[[File:ELT secondary mirror blank successfully cast.jpg|thumb|300px|Opening of the [[European Extremely Large Telescope|ELT]] secondary mirror Zerodur blank mold containing the glass at first annealing at the [[Schott AG]] 4-meter blank annealing facility in Mainz, Germany.<ref>{{cite web|title=Secondary Mirror of ELT Successfully Cast - Largest convex mirror blank ever created|url=http://www.eso.org/public/news/eso1715/|website=www.eso.org|access-date=22 May 2017}}</ref>]]<nowiki> </nowiki>'''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|telescope optics]], [[Microlithography|microlithography machines]] and [[Inertial navigation system|inertial navigation systems]].

== Manufacturing process ==

Zerodur is produced in a two-step process involving [[melting]] and [[ceramization]]. Depending of the size of the blanks, each step can take several months.<ref name="techbriefs">{{cite web |last1=Sokach |first1=Stephen |title=ZERODUR: The Highly Technical Glass-Ceramic |url=https://www.techbriefs.com/component/content/article/37188-zerodur |website=techbriefs.com |access-date=13 February 2025}}</ref>

First, raw materials including main components of [[lithium oxide]] (Li<sub>2</sub>O), [[Aluminium oxide|alumina]] (Al<sub>2</sub>O<sub>3</sub>), and [[Silicon dioxide|silica]] (SiO<sub>2</sub>) are melted at high temperatures of around 1600&nbsp;°C, poured into molds, and annealed in a controlled cooling process that relieves internal stresses that develop during forming.<ref name="glassonweb">{{cite web |title=Glass-ceramic production is fit for the future |url=https://www.glassonweb.com/news/glass-ceramic-production-fit-future |website=GlassOnWeb |date=23 February 2017 |access-date=13 February 2025}}</ref><ref name="perkin-elmer">{{cite web |last1=Gardopee |first1=George J. |last2=Shen |first2=Da-Wun |title=Lightweight Zerodur Mirror Technology |url=https://apps.dtic.mil/sti/tr/pdf/ADA123538.pdf |publisher=The Perkin-Elmer Corporation |date=October 1982 |access-date=13 February 2025}}</ref>
Then the glass undergoes a ceramization process involved controlled volume [[crystallization]], which creates high-quartz [[Nanocrystalline material|nano-crystallites]] of 30nm to 50nm.<ref name="techbriefs" /> The negative CTE of the crystals compensates for the positive CTE of the residual glass matrix, which gives Zerodur its near zero thermal expansion.<ref name="perkin-elmer" />
==Applications==
[[File:KeckObservatory20071013.jpg|right|thumb|252x252px|The [[Keck II]] Telescope showing the segmented primary mirror made of Zerodur]]

The main applications for Zerodur include telescope optics in astronomy<ref>{{cite book |last1=Döhring |first1=Thorsten |editor-first1=Wenhan |editor-first2=Roland |editor-first3=Myung K. |editor-first4=Fan |editor-last1=Jiang |editor-last2=Geyl |editor-last3=Cho |editor-last4=Wu |chapter=Four decades of ZERODUR mirror substrates for astronomy |date=May 2019 |title=4th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Large Mirrors and Telescopes |chapter-url=https://www.spiedigitallibrary.org/conference-proceedings-of-spie/7281/1/Four-decades-of-ZERODUR-mirror-substrates-for-astronomy/10.1117/12.831423.short |series=Proceedings of the SPIE |volume=7281 |doi=10.1117/12.831423 |access-date=10 May 2024}}</ref> and space applications,<ref>{{cite journal |last1=Carré |first1=Antoine |date=May 2023 |title=Comprehensive review of the effects of ionizing radiations on the ZERODUR® glass ceramic |journal=Journal of Astronomical Telescopes, Instruments, and Systems |volume=9 |issue=2 |doi=10.1117/1.JATIS.9.2.024005 |doi-access=free }}</ref> lithography machines for microchips and displays,<ref>{{cite news |date=September 29, 2023 |title=SCHOTT Strengthens Glass Substrate Portfolio |url=https://www.printedelectronicsnow.com/contents/view_breaking-news/2023-09-29/schott-strengthens-glass-substrate-portfolio/ |publisher=Printed Electronics Now}}</ref> and [[Inertial measurement unit|inertial measurements systems]] for navigation.<ref>{{cite web |last1=Sokach |first1=Stephen |title=ZERODUR: The Highly Technical Glass-Ceramic |url=https://www.techbriefs.com/component/content/article/37188-zerodur |access-date=10 May 2024 |website=Tech Briefs|date=July 2020 }}</ref><ref>{{cite web |title=Zerodur |url=https://www.mindrum.com/glass/zerodur/ |access-date=10 May 2024 |website=Mindrum Precision}}</ref>

In astronomy, it is used for mirror substrates in [[large telescopes]] such as the [[Hobby–Eberly Telescope|Hobby-Eberly Telescope]],<ref>{{Cite web |title=Hobby-Eberly Telescope {{!}} McDonald Observatory |url=https://mcdonaldobservatory.org/research/telescopes/HET |access-date=2024-07-12 |website=mcdonaldobservatory.org}}</ref> the [[W. M. Keck Observatory|Keck I and Keck II telescopes]],<ref>{{cite web |title=A Mirror's Perfect Reflection |url=https://www.keckobservatory.org/a_mirrors_perfect_reflection/ |access-date=10 May 2024 |website=W.M. Keck Observatory|date=28 May 2010 }}</ref>  the [[Gran Telescopio Canarias]],<ref>{{cite web |title=Description of the GTC |url=https://www.gtc.iac.es/observing/GTCoptics.php |access-date=10 May 2024 |website=Gran Telescopio CANARIAS}}</ref> the [[3.6m Devasthal Optical Telescope|Devasthal Optical Telescope]],<ref>{{Cite web |title=3.6 m DOT Telescope |url=https://aries.res.in/facilities/astronomical-telescopes/360cm-telescope/telescope |access-date=July 7, 2024 |website=ARIES}}</ref> the [[European Southern Observatory]]'s 8.2 m [[Very Large Telescope]],<ref>{{cite web |title=Very Large Telescope |url=https://www.eso.org/public/teles-instr/paranal-observatory/vlt/?lang |access-date=10 May 2024 |website=ESO}}</ref> and the 39 m [[Extremely Large Telescope]].<ref>{{cite web |title=Mirrors and Optical Design |url=https://elt.eso.org/mirror/M1/ |access-date=10 May 2024 |website=ESO}}</ref>
It also has been used for the primary mirror of [[SOFIA]]'s airborne telescope.<ref>{{cite journal |last1=Krabbe |first1=Alfred |editor-first1=Ramsey K. |editor-first2=Hans-Peter |editor-last1=Melugin |editor-last2=Roeser |date=June 2000 |title=SOFIA telescope |url=https://www.spiedigitallibrary.org/conference-proceedings-of-spie/4014/0000/SOFIA-telescope/10.1117/12.389103.short |journal=Proceedings, Airborne Telescope Systems |series=Airborne Telescope Systems |volume=4014 |page=276 |doi=10.1117/12.389103 |access-date=10 May 2024|arxiv=astro-ph/0004253 |bibcode=2000SPIE.4014..276K }}</ref>

ASA also produces some telescopes with zerodur.<ref>{{Cite web |title=ASA 2.5-Meter Telescope AZ2500 |url=https://observatorysolutions.com/telescopes/asa-az2500/ |access-date=2025-01-08 |website=Observatory Solutions |language=en-US}}</ref>

In space, it has been used for the imager in [[Meteosat]] [[Earth observation satellite|Earth observation satellites]],<ref>{{Cite web |title=MTG (Meteosat Third Generation) - eoPortal |url=https://www.eoportal.org/satellite-missions/meteosat-third-generation#fci-flexible-combined-imager |access-date=2024-07-12 |website=www.eoportal.org |language=en}}</ref> and for the optical bench in the [[LISA Pathfinder]] mission.<ref>{{cite web |title=LISA Technology Package Optical Bench Interferometer During Calibration |url=https://sci.esa.int/web/lisa-pathfinder/-/47279-optical-bench-interferometer |access-date=10 May 2024 |website=ESA}}</ref> 

In microlithography, Zerodur is used in [[Stepper|wafer steppers]] and scanner machines for precise and reproducible wafer positioning.<ref>{{cite web |last1=Hartmann |first1=Peter |title=SCHOTT – Ultra low expansion glass ceramic ZERODUR |url=https://svn.mpia.de/trac/gulli/att/raw-attachment/wiki/AlteVortraege2015S1/2015-01-30_Zerodur.pdf |access-date=10 May 2024 |website=Max-Planck-Institut für Astronomie |page=49}}</ref><ref>{{cite book |last1=Jedamzik |first1=Ralf |title=Optical Microlithography XXVII |chapter=Glass ceramic ZERODUR enabling nanometer precision |editor-first1=Kafai |editor-first2=Andreas |editor-last1=Lai |editor-last2=Erdmann |date=2014 |series=Proceedings of the SPIE |volume=9052 |pages=90522I |doi=10.1117/12.2046352 |bibcode=2014SPIE.9052E..2IJ }}</ref>  It is also used as a component in refractive optics for [[photolithography]].<ref>{{cite journal |last1=Mitra |first1=Ina |date=September 2022 |title=ZERODUR: a glass-ceramic material enabling optical technologies |url=https://opg.optica.org/ome/fulltext.cfm?uri=ome-12-9-3563&id=491435 |journal=Optical Materials Express |volume=12 |issue=9 |page=3563 |doi=10.1364/OME.460265 |access-date=10 May 2024|doi-access=free }}</ref>     

In inertial measurement units, Zerodur is used in [[Ring laser gyroscope|ring laser gyroscopes]].<ref>{{cite journal |last1=Pinckney |first1=Linda R. |date=2003 |title=Glass-Ceramics |url=https://www.sciencedirect.com/science/article/abs/pii/B0122274105002933 |journal=Encyclopedia of Physical Science and Technology (Third Edition) |pages=807–816 |doi=10.1016/B0-12-227410-5/00293-3 |isbn=978-0-12-227410-7 |access-date=10 May 2024|url-access=subscription }}</ref>

==Properties==
Zerodur has both an [[amorphous]] (vitreous) component and a [[crystalline]] component. Its most important properties<ref>{{cite web|url=https://www.schott.com/en-us/products/zerodur-p1000269/technical-details|title=Technical Details ZERODUR®|website=schott.com|access-date=6 September 2024}}</ref> are:
* The material exhibits a particularly low thermal expansion, with a mean value of 0 ± 0.007×10<sup>−6</sup> K<sup>−1</sup> within the temperature range of 0 to 50 °C.<ref name="Hartmann">{{cite journal |last1=Hartmann|first1=Peter|last2=Jedamzik |first2=Ralf |last3=Carré |first3=Antoine |last4=Krieg |first4=Janina |last5=Westerhoff |first5=Thomas |title=Glass ceramic ZERODUR®: Even closer to zero thermal expansion: a review, part 2|journal=Journal of Astronomical Telescopes, Instruments, and Systems  |date=24 March 2006 |volume=7 |issue=2 |doi=10.1117/1.JATIS.7.2.020902|doi-access=free }}</ref>
* High 3D [[Homogeneity (physics)|homogeneity]]<ref name="Hartmann"/> with few inclusions, bubbles and internal stria.
* Hardness similar to that of [[borosilicate glass]].
* High affinity for [[Optical coating|coatings]].
* Low [[helium]] permeability.
* Non-porous.
* Good chemical stability.
* [[Fracture toughness]] approximately 0.9 MPa·m<sup>1/2</sup>.<ref name="Viens1">{{Cite web |last=Viens |first=Michael J |date=April 1990 |title=Fracture Toughness and Crack Growth of Zerodur |url=https://ntrs.nasa.gov/citations/19900011871 |access-date=6 September 2024 |work=NASA Technical Memorandum 4185 |publisher=NASA}}</ref><ref name= "Hartmann1">{{Cite journal| last = Hartmann| first = P.| title = ZERODUR - Deterministic Approach for Strength Design| journal = Optical Engineering| publisher = NASA| date = 18 December 2012| volume = 51| issue = 12| page = 124002| doi = 10.1117/1.OE.51.12.124002| bibcode = 2012OptEn..51l4002H| s2cid = 120843972| url = http://opticalengineering.spiedigitallibrary.org/article.aspx?articleid=1486944| format = PDF| access-date = 11 September 2013| url-access = subscription}}</ref>

===Physical properties===
* [[Dispersion (optics)|Dispersion]]: (''n''<sub>F</sub> − ''n''<sub>C</sub>) = 0.00967
* [[Density]]: 2.53&nbsp;g/cm<sup>3</sup> at 25&nbsp;°C
* [[Young's modulus]]: 9.1{{e|10}}&nbsp;[[Pascal (unit)|Pa]]
* [[Poisson's ratio|Poisson ratio]]: 0.24
* [[Specific heat capacity]] at 25&nbsp;°C: 0.196&nbsp;cal/(g·K) = 0.82&nbsp;J/(g·K)
* [[Coefficient of thermal expansion]] (20&nbsp;°C to 300&nbsp;°C) : 0.05 ± 0.10{{e|-6}}/K
* [[Thermal conductivity]]: at 20&nbsp;°C: 1.46&nbsp;W/(m·K)
* Maximum application temperature: 600&nbsp;°C
* [[Impact resistance]] behavior is substantially similar to other [[glass]]<ref name ="Senf1">{{Cite journal| last = Senf| first = H|author2=E Strassburger |author3=H Rothenhausler | title = A study of Damage during Impact in Zerodur| journal = J Phys IV France| volume = 7| issue = Colloque C3, Suppltment au Journal de Physique I11 d'aotit 1997| date = 1997| pages = C3-1015-C3-1020| doi = 10.1051/jp4:19973171| url = http://hal.archives-ouvertes.fr/docs/00/25/54/63/PDF/ajp-jp4199707C3171.pdf| access-date = 31 August 2011}}</ref>

==History==
Schott began developing glass-ceramics in the 1960s lead by Jürgen Petzoldt, in response to demand for low expansion glass ceramics for telescopes.<ref name = "Pannhorst" />

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 {{convert| 3.6 |m|ft|sigfig=2|abbr=on}} mirror blank, along with ten smaller mirror substrates. The mirrors were delivered by late 1975,<ref name = "Pannhorst">{{cite book |last=Pannhorst |first=Wolfgang |date= 1995 |editor-last=Bach |editor-first=Hans |title=Low Thermal Expansion Glass Ceramics |publisher=Springer |pages=107–121 |chapter=Chapter 4: Zerodur® - A Low Thermal Expansion Glass Ceramic for Optical Precision Applications |isbn=3-540-58598-2}}</ref> and went into operation in 1984 in a telescope at the [[Calar Alto Observatory]] in Spain. Further orders for mirror blanks followed.<ref>{{Cite book |last=Lemke |first=Dietrich |title=Im Himmel über Heidelberg - 50 Jahre Max-Planck-Institut für Astronomie in Heidelberg (1969 – 2019) |url=https://www.archiv-berlin.mpg.de/49042/hausreihe_21.pdf |orig-date=2019 |location=Berlin, Heidelberg |language=DE}}</ref>

==See also==
* [[CorningWare]]
* [[Macor]]
* [[Ring laser gyroscope]]
* [[Sitall]]

==References==
<references/>

==External links==
{{Glass science}}
{{Glass makers and brands}}

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