spore: profile
id: zerodur
spore_version: 0.2
family: glass-ceramics
name: ZERODUR (lithium aluminium silicon oxide glass-ceramic)
abbreviation: ZERODUR
role: near-zero-expansion optical glass-ceramic
category: ceramics
type: glass-ceramics
summary: |
  ZERODUR is a lithium aluminium silicon oxide glass-ceramic made by SCHOTT at Mainz, Germany. Its datasheet gives a mean coefficient of linear thermal expansion of 0 ± 0.007 ppm/K for Expansion Class 0 Extreme between 0 °C and 50 °C, a density of 2.53 g/cm3 and a Young's modulus of 90.3 GPa at 20 °C. It is used for telescope mirror substrates, space optics, semiconductor lithography and ring laser gyroscopes. SCHOTT rates its maximum application temperature at 600 °C.
best_for: 'Optical parts that must keep their shape and size over a wide temperature range (SCHOTT datasheet: CTE 0 ± 0.007 ppm/K for Expansion Class 0 Extreme)'
weakest_at: Heating above 100 °C without proper cooling, which the datasheet says affects the CTE specification; the maximum application temperature is 600 °C
identity:
  formula: Lithium aluminium silicon oxide glass-ceramic, with nanocrystals in a residual glass phase (no single formula; oxide percentages not found in any source we hold)
  source: schott-catalog
  where: 'Introduction, first paragraph: ''inorganic, non-porous lithium aluminum silicon oxide glass-ceramic'''
  designations:
    - system: Trade name
      code: ZERODUR
      source: schott-datasheet
      where: Title of the datasheet, ZERODUR glass-ceramic with near-zero thermal expansion
tags:
  environments: []
  stresses:
    - extreme-heat
  applications:
    - optics-and-cameras
    - electronics-and-chips
properties:
  - benchmark: cte
    label: CTE, Expansion Class 0 Extreme (tolerance around zero)
    value: 0.007
    unit: ppm/K
    scope: material
    conditions:
      grade: ZERODUR, Expansion Class 0 Extreme
      temperature_range: 0 °C to 50 °C
      basis: mean coefficient of linear thermal expansion, supplied as a tolerance 0 ± 0.007 ppm/K
    method: Tolerance class printed in the SCHOTT datasheet (CTE specification tolerances table). The value is the half-width of the tolerance around zero, not a measured mean.
    status: ground
    source: schott-datasheet
    where: Table 1, Expansion Class 0 Extreme row
  - benchmark: cte
    label: CTE, Expansion Class 2 (tolerance around zero)
    value: 0.1
    unit: ppm/K
    scope: material
    conditions:
      grade: ZERODUR, Expansion Class 2
      temperature_range: 0 °C to 50 °C
      basis: mean coefficient of linear thermal expansion, supplied as a tolerance 0 ± 0.100 ppm/K
    method: Tolerance class printed in the SCHOTT datasheet (CTE specification tolerances table)
    status: ground
    source: schott-datasheet
    where: Table 1, Expansion Class 2 row
  - benchmark: cte_homogeneity
    label: CTE homogeneity (peak to valley), blanks up to 4.0 m diameter
    value: 20
    bound: upper
    unit: ppb/K
    scope: material
    conditions:
      temperature_range: 0 °C to 50 °C
      part_size: up to 4.0 m diameter
    method: Tolerance printed in the SCHOTT datasheet (CTE homogeneity tolerances table); benchmark name is not in the canonical list
    status: ground
    source: schott-datasheet
    where: Table 2, row 'up to 4.0 m diameter'
  - benchmark: thermal_conductivity
    label: Thermal conductivity at 20 °C
    value: 1.46
    unit: W/(m·K)
    scope: material
    conditions:
      temperature: 20 °C
      grade: ZERODUR (not K20)
    method: Value printed in the SCHOTT datasheet mechanical, optical and chemical properties table; the same value is in TIE-43 section 1
    status: ground
    source: schott-datasheet
    where: Table 3, thermal conductivity row
  - benchmark: specific_heat
    label: Heat capacity (specific heat) at 20 °C
    value: 0.8
    unit: J/(g·K)
    scope: material
    conditions:
      temperature: 20 °C
      unit_in_source: J/(g · K)
    method: Printed in J/(g·K) in the SCHOTT datasheet; the importer converts to the canonical J/(kg·K)
    status: ground
    source: schott-datasheet
    where: Table 3, heat capacity cp row
  - benchmark: elastic_modulus
    label: Young's modulus at 20 °C, mean value
    value: 90.3
    unit: GPa
    scope: material
    conditions:
      temperature: 20 °C
      basis: mean value
    method: Value printed in the SCHOTT datasheet (Table 3); TIE-43 section 2 prints the same 90.3
    status: ground
    source: schott-datasheet
    where: Table 3, Young's modulus row (mean value)
  - benchmark: poissons_ratio
    label: Poisson's ratio
    value: 0.24
    unit: '-'
    scope: material
    conditions:
      temperature: not printed in the table
    method: Value printed in the SCHOTT datasheet (Table 3) and in TIE-43 section 2
    status: ground
    source: schott-datasheet
    where: Table 3, Poisson's ratio row
  - benchmark: density
    label: Density
    value: 2.53
    unit: g/cm3
    scope: material
    conditions:
      temperature: not printed in the datasheet
    method: Value printed in the SCHOTT datasheet (Table 3) and in TIE-43 section 2
    status: ground
    source: schott-datasheet
    where: Table 3, density row
  - benchmark: knoop_hardness
    label: Knoop hardness, HK 0.1/20
    value: 620
    unit: HK 0.1/20
    scope: material
    conditions:
      standard: ISO 9385
      load: 0.1 (HK 0.1/20)
    method: Value printed in the SCHOTT datasheet (Table 3) and in TIE-43 section 2; benchmark name is not in the canonical list
    status: ground
    source: schott-datasheet
    where: Table 3, Knoop hardness row
  - benchmark: refractive_index
    label: Refractive index nd
    value: 1.5424
    unit: '-'
    scope: material
    conditions:
      basis: nd as printed in the datasheet; the wavelength is not restated in the table
    method: Value printed in the SCHOTT datasheet (Table 3)
    status: ground
    source: schott-datasheet
    where: Table 3, refractive index nd row
  - benchmark: abbe_number
    label: Abbe number vd
    value: 56.1
    unit: '-'
    scope: material
    conditions:
      basis: Abbe number as printed in the datasheet
    method: Value printed in the SCHOTT datasheet (Table 3); benchmark name is not in the canonical list
    status: ground
    source: schott-datasheet
    where: Table 3, Abbe number vd row
  - benchmark: internal_transmittance
    label: Internal transmittance, 5 mm thickness
    value: 0.95
    unit: '-'
    scope: material
    conditions:
      wavelength: 580 nm
      thickness: 5 mm
    method: Value printed in the SCHOTT datasheet (Table 3); internal transmittance is the transmittance corrected for reflection losses per TIE-43
    status: ground
    source: schott-datasheet
    where: Table 3, internal transmittance 5 mm row
  - benchmark: internal_transmittance
    label: Internal transmittance, 10 mm thickness
    value: 0.9
    unit: '-'
    scope: material
    conditions:
      wavelength: 580 nm
      thickness: 10 mm
    method: Value printed in the SCHOTT datasheet (Table 3)
    status: ground
    source: schott-datasheet
    where: Table 3, internal transmittance 10 mm row
  - benchmark: dielectric_constant
    label: Dielectric constant at 1 MHz
    value: 7.4
    unit: '-'
    scope: material
    conditions:
      frequency: 1 MHz
      basis: dielectric constant, typical value
    method: Value printed in TIE-43 Tab. 2 (2014 version); TIE-43 states that its data are typical values
    status: ground
    source: schott-tie43
    where: Section 3, Tab. 2 (Dielectric properties), column at 1 MHz
  - benchmark: dielectric_constant
    label: Dielectric constant at 1 kHz
    value: 8
    unit: '-'
    scope: material
    conditions:
      frequency: 1 kHz
      basis: dielectric constant, typical value
    method: Value printed in TIE-43 Tab. 2 (2014 version)
    status: ground
    source: schott-tie43
    where: Section 3, Tab. 2 (Dielectric properties), column at 1 kHz
  - benchmark: dissipation_factor
    label: Loss factor tan delta at 1 MHz
    value: 0.015
    unit: '-'
    scope: material
    conditions:
      frequency: 1 MHz
    method: Printed as 15 · 10–3 in TIE-43 Tab. 2 and entered as 0.015
    status: ground
    source: schott-tie43
    where: Section 3, Tab. 2 (Dielectric properties), column at 1 MHz
  - benchmark: dissipation_factor
    label: Loss factor tan delta at 1 kHz
    value: 0.029
    unit: '-'
    scope: material
    conditions:
      frequency: 1 kHz
    method: Printed as 29 · 10–3 in TIE-43 Tab. 2 and entered as 0.029
    status: ground
    source: schott-tie43
    where: Section 3, Tab. 2 (Dielectric properties), column at 1 kHz
  - benchmark: tk100
    label: Temperature at which resistivity is 10^8 Ω·cm
    value: 178
    unit: °C
    scope: material
    conditions:
      basis: temperature for a specific resistivity of 10^8 Ω·cm
    method: Value printed in the SCHOTT datasheet (Table 3, Tk100 row); benchmark name is not in the canonical list
    status: ground
    source: schott-datasheet
    where: Table 3, Tk100 row
  - benchmark: max_service_temp
    label: Maximum application temperature
    value: 600
    unit: °C
    scope: material
    conditions:
      basis: maximum application temperature printed by SCHOTT for ZERODUR
    method: Rating printed in the SCHOTT datasheet under the heading 'Maximum application temperature of 600 °C' and on the product page
    status: ground
    source: schott-datasheet
    where: Page 3, heading 'Maximum application temperature of 600 °C'
  - benchmark: breakage_stress_threshold
    label: Breakage stress threshold, D151 ground surface
    value: 47.3
    unit: MPa
    scope: material
    conditions:
      surface: D151 ground surface
      model: three-parameter Weibull fit
      basis: breakage stress threshold from the Weibull distribution
    method: Value printed in the SCHOTT datasheet, Weibull fit for the D151 sample; the benchmark name is not in the canonical list and this is not a flexural strength
    status: ground
    source: schott-datasheet
    where: Page 3, 'Extensive data on the strength of ZERODUR', text above Figure 2
  - benchmark: stress_optical_coefficient
    label: Stress optical coefficient K
    value: 3
    unit: 10-6 MPa-1
    scope: material
    conditions:
      wavelength: 589.3 nm
    method: Value printed in the SCHOTT datasheet (Table 3); benchmark name is not in the canonical list
    status: ground
    source: schott-datasheet
    where: Table 3, stress optical coefficient K row
corrosion:
  - environment: Water and humid air (hydrolytic and climate resistance)
    headline: ZERODUR is rated in the highest-resistance hydrolytic and climate classes that SCHOTT prints for the glass.
    effect: SCHOTT lists a hydrolytic resistance class of HGB 1 under ISO 719 and a climate resistance class of 1. The datasheet does not explain the class scale beyond these labels.
    rating: low
    conditions:
      standards: ISO 719 (hydrolytic); climate class as printed
      basis: classes printed in the datasheet; no exposure time or humidity level is stated
    source: schott-datasheet
    where: Table 3, hydrolytic resistance class and climate resistance rows
  - environment: Acids and alkalis (acid and alkali resistance classes)
    headline: SCHOTT lists acid and alkali resistance classes of 1.0 for ZERODUR.
    effect: The datasheet prints an acid resistance class of 1.0 under ISO 8424 and an alkali resistance class of 1.0 under ISO 10629. No immersion time or concentration is given with these classes.
    rating: low
    conditions:
      standards: ISO 8424 (acid); ISO 10629 (alkali)
      basis: class numbers as printed; no exposure conditions in the table
    source: schott-datasheet
    where: Table 3, acid resistance and alkali resistance rows
  - environment: Hydrofluoric acid and hot concentrated sulfuric acid
    headline: SCHOTT states that ZERODUR can be etched by hydrofluoric acid and by concentrated sulfuric acid at elevated temperatures.
    effect: The product page states that the glass-ceramic 'can be etched by hydrofluoric acid as well as concentrated sulfuric acid at elevated temperatures'. Etching is part of how mirror substrates are finished, and it also means these acids attack the surface.
    rating: moderate
    conditions:
      temperature: elevated, not quantified on the page
      basis: product-page statement; no etch rate printed
    source: schott-product-page
    where: FAQ answer on chemical resistance
  - environment: Heating above 100 °C
    headline: SCHOTT says the CTE specification is affected when ZERODUR is used above 100 °C and not properly cooled down.
    effect: The datasheet states that the CTE specifications are affected by use of ZERODUR above 100 °C and by not cooling it down properly. The maximum application temperature is 600 °C.
    rating: moderate
    conditions:
      threshold: 100 °C
      max_application_temp: 600 °C
      basis: datasheet statement; no time at temperature stated
    source: schott-datasheet
    where: Page 3, heading 'Maximum application temperature of 600 °C'
risks:
  hazards:
    - text: SCHOTT's brochure tells users to refer to the Safety Data Sheet for information on safe use, handling and disposal. The SDS was not opened in this run, so no GHS classification for ZERODUR is entered.
      ghs: []
      source: schott-catalog
      where: Disclaimer page
  failure_risks:
    - mode: Breakage from sub-surface damage under tensile stress
      trigger: Tensile stress on a part whose surface has sub-surface damage left by grinding
      consequence: For a D151 ground surface the breakage stress threshold is 47.3 MPa in a three-parameter Weibull fit. SCHOTT says finer grinding and etching of an appropriate surface layer increase the threshold significantly.
      severity: moderate
      source: schott-datasheet
      where: Page 3, 'Extensive data on the strength of ZERODUR'
    - mode: Expansion specification affected after use above 100 °C
      trigger: Use above 100 °C without proper cooling
      consequence: SCHOTT says the CTE specifications are affected. The maximum application temperature is 600 °C.
      severity: moderate
      source: schott-datasheet
      where: Page 3, heading 'Maximum application temperature of 600 °C'
    - mode: Helium passes through the glass faster when hot
      trigger: A helium-tight barrier or seal in service at elevated temperature
      consequence: Helium permeability rises from 1.6e6 atoms/(cm·s·bar) at 20 °C to 7.2e8 atoms/(cm·s·bar) at 200 °C, as printed in the datasheet.
      severity: low
      source: schott-datasheet
      where: Table 3, helium permeability rows
  side_effects:
    - text: The crystal phase scatters visible light (Rayleigh scattering), which lowers transmittance in the visible and near-UV range. SCHOTT says the scattering falls with wavelength, giving high transmittance in the far red and near infrared.
      affects: Optical transmission of thick transmitting parts at short wavelengths
      source: schott-tie43
      where: Section 4.2 Internal transmittance, text after Fig. 5 and Tab. 7
  handling:
    - text: 'Keep the chemical limits in mind: the product page says hydrofluoric acid and hot concentrated sulfuric acid can etch the glass-ceramic.'
      source: schott-product-page
      where: FAQ answer on chemical resistance
    - text: Stay within 600 °C and cool the part properly after heating above 100 °C, because the CTE specification depends on it.
      source: schott-datasheet
      where: Page 3, maximum application temperature
  mitigations:
    - text: Choose the expansion class that matches the job. The datasheet offers classes from 0 ± 0.100 ppm/K (Class 2) down to 0 ± 0.007 ppm/K (Class 0 Extreme).
      source: schott-datasheet
      where: Table 1, CTE specification tolerances
    - text: For a known temperature profile, SCHOTT offers TAILORED material optimised for the customer's temperature profile. SCHOTT states it is based on a physical material model that accounts for structural relaxation.
      source: schott-datasheet
      where: Page 2, ZERODUR TAILORED box
uses:
  - application: optics-and-cameras
    device: Telescope mirror substrates (monolithic and segmented telescopes)
    example: SCHOTT says ZERODUR is used for telescope mirror substrates in monolithic and segmented telescopes. Its largest blanks, 8 m in diameter, are the primary mirrors of ESO's Very Large Telescope.
    source: schott-catalog
    where: Astronomy section, 'The largest ZERODUR blanks ever made'
  - application: optics-and-cameras
    device: Space optics mirror substrates
    example: SCHOTT says mirror substrates for space optics are typically lightweight because CNC grinding can reduce their mass by more than 90 %, and that near-zero expansion keeps them stable on each orbit.
    source: schott-catalog
    where: Space section, text beside the 1.2 m blank photograph
  - application: electronics-and-chips
    device: Semiconductor lithography equipment
    example: SCHOTT lists semiconductor lithography among ZERODUR applications and states that miniaturization in integrated circuit systems requires very precise lithography and wafer positioning.
    source: schott-product-page
    where: Applications FAQ, lithography answer
supply:
  - subject: Lithium (raw material for the lithium oxide content)
    producers:
      - country: Australia
        share_percent: 31.7
        year: 2025
      - country: China
        share_percent: 21.4
        year: 2025
      - country: Chile
        share_percent: 19.3
        year: 2025
      - country: Zimbabwe
        share_percent: 9.7
        year: 2025
      - country: Argentina
        share_percent: 7.9
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (Lithium, used in rechargeable batteries)
        listed: true
      - list: EU critical raw materials list (Lithium)
        listed: true
    recycling: 'USGS: construction of lithium battery recycling plants continued throughout 2025. The USGS lithium chapter does not describe recycling of glass.'
    substitutes:
      - 'USGS: substitution for lithium compounds is possible in batteries, ceramics, greases and manufactured glass.'
    source: usgs-mcs2026-lithium
    where: World Mine Production and Reserves table, 2025 column (world total about 290,000 t, stated in the text; shares calculated by Space Mushroom against that total, which excludes United States output)
  - subject: Aluminium oxide (alumina, refined from bauxite)
    producers:
      - country: China
        share_percent: 62
        year: 2025
      - country: Australia
        share_percent: 11.3
        year: 2025
      - country: Brazil
        share_percent: 7.3
        year: 2025
      - country: India
        share_percent: 5.5
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (Aluminum, used in almost all sectors of the economy)
        listed: true
      - list: EU critical raw materials list (Bauxite; aluminium and bauxite merged)
        listed: true
    recycling: 'USGS: Recycling: None (bauxite and alumina chapter).'
    substitutes:
      - 'USGS: silicon carbide and alumina zirconia can substitute for alumina and bauxite in abrasives but cost more.'
    source: usgs-mcs2026-bauxite-alumina
    where: World Alumina Refinery and Bauxite Mine Production table, alumina 2025e (world total 150,000 thousand t; shares calculated by Space Mushroom). The chapter does not break out the glass-ceramic grade.
  - subject: Silicon (silica, SiO2, from quartz sand)
    producers: []
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (Silicon, used in silicon wafers)
        listed: true
      - list: EU critical raw materials list (Silicon metal)
        listed: true
    recycling: Not found in the USGS silicon chapter read in this run (it reports recycling as insignificant for ferrosilicon and silicon metal).
    substitutes: []
    source: usgs-critical-2025
    where: Final 2025 critical minerals list (Silicon); EU list (Silicon metal). No world production table for silicon was read in this run.
media: []
documents:
  - title: ZERODUR datasheet, ENGLISH/US 08/2024 (SCHOTT)
    type: datasheet
    url: https://media.schott.com/api/public/content/7c351fbb693b443aa741fcfe72a31755?v=b5370fd8&download=true
    year: 2024
  - title: TIE-43 Properties of ZERODUR (SCHOTT technical information, version July 2014)
    type: datasheet
    url: https://media.schott.com/api/public/content/d46fdbce1a35483b8db4622bdd78e043?v=fca382d5&download=true
    year: 2014
  - title: ZERODUR product catalog (SCHOTT, undated)
    type: datasheet
    url: https://media.schott.com/api/public/content/9c3ac61113624aac8033e88352f63ff0?v=62a31554&download=true
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Lithium'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-lithium.pdf
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Bauxite and Alumina'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-bauxite-alumina.pdf
    year: 2026
gaps:
  - Oxide composition percentages (Li2O, Al2O3, SiO2 and the minor oxides) were not found in any source read in this run; Wikipedia names the three main oxides without percentages.
  - Fracture toughness was not found on a manufacturer page read in this run. A figure appears in Wikipedia, but Wikipedia is used here for composition and history only, so it is not entered.
  - No safety data sheet or PubChem GHS record for the ZERODUR glass-ceramic could be opened. A PubChem name search for lithium aluminosilicate returned petalite, a different mineral, so it is not used.
  - Meteosat imager and LISA Pathfinder optical bench are named as Zerodur applications only in Wikipedia. The SCHOTT catalog shows a LISA Pathfinder launch photograph credited to ESA but does not name Zerodur for that mission. An ESA page could not be opened (HTTP 404), so flight heritage is not confirmed here.
  - No flight result, vacuum outgassing (TML/CVCM), atomic-oxygen, ultraviolet or radiation test result for ZERODUR was found in a source read in this run.
  - No introduction year for ZERODUR was found in a source read in this run. The catalog says SCHOTT has produced it for over 50 years in Mainz and describes an order of 12 blanks, from 0.3 m to 3.6 m in diameter, from the Max Planck Institute of Astronomy for Calar Alto; the catalog gives no year for that order.
  - ZERODUR K20 and ZERODUR TAILORED values on the datasheet are separate grades or options and are not entered here. The expansion-class tolerances for ZERODUR are entered instead.
  - Long-term load guidance (for example a 10 MPa tensile threshold and 30 to 100 MPa for tens of years) appears only in a summary of the SCHOTT downloads page and was not confirmed in the datasheet, so it is not entered.
  - Knoop hardness, abbe number, internal transmittance, helium permeability, stress optical coefficient, CTE homogeneity, breakage stress threshold and the tk100 temperature are not in the canonical property list, so snake_case names are used. Knoop hardness and the other snake_case names are flagged in each property's method.
  - 'Silicon production shares were not found: the USGS silicon chapter read in this run covers United States production and imports, and the world production table was not in the text extract.'
  - Volume resistivity at other temperatures (TIE-43 Tab. 1) and the refractive index dispersion table (TIE-43 Tab. 3) are present in the TIE-43 document but were not entered, because the table layout in the PDF text extract was not clean enough to copy every value with confidence.
  - Density of 2.53 g/cm3 is printed without a temperature in the datasheet, and the Poisson's ratio is printed without one as well.
  - Electrical resistivity at 20 °C and helium permeability at 20 °C and 200 °C were removed from properties. The datasheet prints them with superscript exponents (2.6 · 10^13 Ω·cm; 1.6 · 10^6 and 7.2 · 10^8 atoms/(cm·s·bar)), which the text extraction flattened, so verify-values could not match them. They can be re-added once checked against the PDF by eye. The helium figures still appear in the failure-risk text.
sources:
  schott-datasheet:
    title: ZERODUR glass-ceramic with near-zero thermal expansion (SCHOTT datasheet, ENGLISH/US 08/2024)
    id: SCHOTT datasheet, ENGLISH/US 08/2024
    url: https://media.schott.com/api/public/content/7c351fbb693b443aa741fcfe72a31755?v=b5370fd8&download=true
    year: 2024
    kind: datasheet
    license: supplier document, linked not reproduced
  schott-tie43:
    title: TIE-43 Properties of ZERODUR (SCHOTT Advanced Optics technical information)
    id: SCHOTT TIE-43, version July 2014
    url: https://media.schott.com/api/public/content/d46fdbce1a35483b8db4622bdd78e043?v=fca382d5&download=true
    year: 2014
    kind: datasheet
    license: supplier document, linked not reproduced
  schott-catalog:
    title: ZERODUR product catalog (SCHOTT, glass-ceramic brochure)
    id: SCHOTT ZERODUR product catalog (undated PDF, accessed 2026-11-01)
    url: https://media.schott.com/api/public/content/9c3ac61113624aac8033e88352f63ff0?v=62a31554&download=true
    year: 2026
    kind: datasheet
    license: supplier document, linked not reproduced
  schott-product-page:
    title: ZERODUR product page and FAQ (SCHOTT)
    id: SCHOTT product ZERODUR P1000269 (undated page, accessed 2026-11-01)
    url: https://www.schott.com/en-us/products/zerodur-p1000269
    year: 2026
    kind: web
    license: supplier web page, linked not reproduced
  usgs-mcs2026-lithium:
    title: Mineral Commodity Summaries 2026, Lithium
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-lithium.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-mcs2026-bauxite-alumina:
    title: Mineral Commodity Summaries 2026, Bauxite and Alumina
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-bauxite-alumina.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-critical-2025:
    title: About the 2025 List of Critical Minerals (USGS, final list of 60 minerals)
    id: Final 2025 List of Critical Minerals, November 2025
    url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals
    year: 2025
    kind: web
    license: public domain (USGS)
  ec-crm:
    title: Critical raw materials (European Commission, list under Regulation (EU) 2024/1252)
    id: Regulation (EU) 2024/1252
    url: https://single-market-economy.ec.europa.eu/sectors/raw-materials/areas-specific-interest/critical-raw-materials_en
    year: 2024
    kind: web
    license: European Commission web page
  wikipedia-zerodur:
    title: Zerodur (Wikipedia article), used for composition only
    id: Wikipedia, Zerodur
    url: https://en.wikipedia.org/wiki/Zerodur
    year: 2026
    kind: web
    license: CC BY-SA (Wikipedia)
license: CC-BY-4.0
updated: '2026-11-01'
review:
  status: draft
  method: assistant
  checked_values: 21
  unreachable: 1
  caveats: 4
  note: 'Written by an AI assistant on 2026-11-01 from SCHOTT datasheet 08/2024, TIE-43 (2014), the SCHOTT catalog and product page, and USGS 2026 summaries, all read in this run. Caveats: the product-page quotes come from a summarising fetch; the ESA LISA Pathfinder page returned 404; several benchmark names are not canonical; composition percentages not found.'
story:
  recipe:
    line: 'ZERODUR is a lithium aluminium silicon oxide glass-ceramic. SCHOTT makes it in two steps: the raw materials are melted, cast into moulds and annealed to form a glass, and a controlled ceramization then grows nanocrystals inside that glass. The crystals have a negative coefficient of thermal expansion, which offsets the positive expansion of the residual glass.'
    parts:
      - name: Lithium oxide
        symbol: Li2O
        role: Lithium-bearing oxide in the glass. The catalog names lithium aluminum silicon oxide as the composition. No percentage was found in a source we hold.
      - name: Aluminium oxide
        symbol: Al2O3
        role: Alumina component of the glass and its nanocrystal phase. No percentage was found in a source we hold.
      - name: Silicon dioxide
        symbol: SiO2
        role: Silica network former of the glass. No percentage was found in a source we hold.
  risk_groups:
    - title: For people
      level: 0
      verdict: No hazard classification found in a source we read
      lead: The supplier safety data sheet was not opened in this run. SCHOTT's brochure refers readers to its safety data sheet for safe use, handling and disposal.
      points:
        - label: The solid
          line: ZERODUR is a solid, non-porous glass-ceramic (SCHOTT catalog). Hazard information for finished blanks was not found in a source we hold.
        - label: Chemicals used in finishing
          line: The product page says hydrofluoric acid and hot concentrated sulfuric acid can etch the glass-ceramic. The safety data for those acids applies to the etching step.
    - title: If a part fails
      lead: The numbers below come from SCHOTT's datasheet and show how the glass behaves, not from field incidents.
      points:
        - label: Breakage
          line: For a D151 ground surface, the breakage stress threshold is 47.3 MPa in a three-parameter Weibull fit. Finer grinding and etching of an appropriate surface layer raise the threshold.
        - label: Heating
          line: The CTE specification is affected by use above 100 °C without proper cooling. The maximum application temperature is 600 °C.
        - label: Helium
          line: Helium permeability rises from 1.6e6 atoms/(cm·s·bar) at 20 °C to 7.2e8 atoms/(cm·s·bar) at 200 °C, so a helium-tight seal gets leakier as it heats.
    - title: Handling and storage
      points:
        - label: Chemicals
          line: Use hydrofluoric or hot concentrated sulfuric acid only where the finishing process calls for them, because the product page says both can etch the glass-ceramic.
        - label: Temperature
          line: Do not exceed the 600 °C maximum application temperature, and cool the part down properly after any heating above 100 °C.
  why: ZERODUR is a lithium aluminium silicon oxide glass-ceramic whose thermal expansion is near zero over a wide temperature range. The datasheet prints a mean coefficient of linear thermal expansion of 0 ± 0.007 ppm/K for Expansion Class 0 Extreme between 0 °C and 50 °C. That property lets optical parts keep their shape and their distances while the temperature changes, which is why SCHOTT sells it for telescope mirror substrates, space optics, semiconductor lithography and ring laser gyroscopes.
  uses:
    - where: Telescope mirrors
      line: SCHOTT says ZERODUR is used for telescope mirror substrates in monolithic and segmented telescopes. Its largest blanks, 8 m in diameter, are the primary mirrors of ESO's Very Large Telescope.
    - where: Space optics
      line: SCHOTT says lightweight ZERODUR mirror substrates for space optics can be made by CNC grinding, which reduces their mass by more than 90 %. The catalog ties this to thermal stability on each orbit. The flight record for a specific mission was not confirmed in a source we read.
    - where: Semiconductor lithography
      line: SCHOTT lists semiconductor lithography and metrology among ZERODUR applications. Ring laser gyroscopes use ZERODUR special laser cavities, mirror blanks and tiny prisms, according to the product page.
  can_do:
    - label: Thermal expansion
      benchmark: cte
      line: The datasheet's tightest class, Expansion Class 0 Extreme, is 0 ± 0.007 ppm/K between 0 °C and 50 °C. The looser Expansion Class 2 is 0 ± 0.100 ppm/K. ZERODUR TAILORED can be optimised for a known temperature profile.
    - label: Heat conduction
      benchmark: thermal_conductivity
      value: 1.46 W/(m·K)
      line: ZERODUR has a thermal conductivity of 1.46 W/(m·K) at 20 °C, per the datasheet.
    - label: Hardness and modulus
      benchmark: knoop_hardness
      value: 620 HK 0.1/20
      line: The Knoop hardness is 620 HK 0.1/20 under ISO 9385, and the Young's modulus is 90.3 GPa at 20 °C (mean value).
    - label: Optical quality
      benchmark: refractive_index
      value: 1.5424 nd
      line: The refractive index nd is 1.5424 and the Abbe number vd is 56.1. The internal transmittance is 0.95 at 580 nm for 5 mm thickness and 0.9 for 10 mm.
  compare: Within the ZERODUR expansion classes in the same datasheet, Expansion Class 0 Extreme (0 ± 0.007 ppm/K) is the tightest tolerance printed, and Expansion Class 2 (0 ± 0.100 ppm/K) is the loosest. This record does not hold same-source values for other materials, so the comparison rows below are between ZERODUR's own properties and are not a ranking against other glasses.
  compare_rows:
    - label: Thermal expansion tolerance
      benchmark: cte
    - label: Heat conduction
      benchmark: thermal_conductivity
    - label: Stiffness
      benchmark: elastic_modulus
  handling:
    - Expansion Class 0 Extreme is the tightest tolerance on the datasheet. SCHOTT's TIE-43 says the printed data are typical values and that single batches can vary slightly.
    - Keep the part at or below 600 °C, and cool it properly after heating above 100 °C.
    - Etch with hydrofluoric or hot concentrated sulfuric acid only in a qualified finishing process.
  good_for:
    - Thermal stability. The datasheet gives 0 ± 0.007 ppm/K for Expansion Class 0 Extreme between 0 °C and 50 °C.
    - Low thermal expansion over a large part. SCHOTT offers homogeneity of 20 ppb/K peak to valley for blanks up to 4.0 m in diameter.
    - Optical parts. Refractive index nd is 1.5424 with an Abbe number of 56.1, per the datasheet.
  watch_out:
    - The maximum application temperature is 600 °C, and the CTE specification is affected by use above 100 °C without proper cooling.
    - Breakage depends on the surface. A D151 ground surface has a threshold of 47.3 MPa in the datasheet's Weibull fit.
    - Helium permeability rises from 1.6e6 at 20 °C to 7.2e8 atoms/(cm·s·bar) at 200 °C.
  verdict: ZERODUR is the glass-ceramic to specify when a part must hold its shape across a wide temperature range. The datasheet supports that with the tightest expansion tolerance and a 600 °C ceiling; the space record for specific missions still needs a source.