spore: profile
id: ule-glass
spore_version: 0.2
family: glass-and-composites
name: ULE 7972 (Corning ultra low expansion titania-silicate glass)
abbreviation: ULE
role: low-expansion mirror blank and optical substrate
category: glasses-optics
type: fused-silica
summary: |
  ULE 7972 is Corning's titania-silicate glass, sold as Corning Code 7972 ultra low expansion glass. Corning's product sheet guarantees a mean coefficient of thermal expansion of 0 ± 30 ppb/°C from 5 to 35 °C at a 95% confidence level, and prints a density of 2.21 g/cm3 at 25 °C. NASA Marshall names ULE among the materials used for space telescope mirrors, including the primary mirror of the Hubble Space Telescope.
best_for: Mirrors and precision parts that must hold their shape across temperature changes (guaranteed mean expansion of 0 ± 30 ppb/°C from 5 to 35 °C)
weakest_at: 'Brittle like other glasses: flawed ULE can fail under sustained tensile stress (delayed failure, NASA 2003), and the product sheet gives no fracture toughness'
identity:
  formula: 'Titania-silicate glass: silica (SiO2) with about 7.5% titanium dioxide (TiO2) per NASA (2003); Wikipedia gives less than 10% TiO2'
  source: nasa-tucker2003
  where: Abstract, sentence beginning 'ULE contains 7.5% titanium dioxide'
  designations:
    - system: Trade name
      code: ULE
      source: corning-ule-datasheet
      where: 'Title line: ULE Corning Code 7972 Ultra Low Expansion Glass'
    - system: Trade name
      code: '7972'
      note: Corning code for ULE ultra low expansion glass
      source: corning-ule-datasheet
      where: Title line
tags:
  applications:
    - optics-and-cameras
    - electronics-and-chips
    - structures
properties:
  - benchmark: density
    label: Density, ULE 7972
    value: 2.21
    unit: g/cm3
    scope: material
    conditions:
      temperature: 25 °C (sheet default, unless otherwise stated all values are at 25 °C)
    method: Value printed on the Corning ULE 7972 product sheet as "2.21 g/cm3 [0.079 lbs./in3]"
    status: ground
    source: corning-ule-datasheet
    where: Mechanical Properties block, Density (rho)
  - benchmark: cte
    label: Mean coefficient of thermal expansion, ULE 7972 (guaranteed limit)
    value: 30
    unit: ppb/°C
    bound: upper
    scope: material
    conditions:
      temperature_range: 5 to 35 °C
      confidence: 95%
      reading: the sheet guarantees a mean of 0 ± 30 ppb/°C; the value is the ±30 limit
    method: Guaranteed limit printed on the Corning sheet as "The mean CTE shall be 0 ± 30 ppb/°C from 5°C to 35°C with a 95% confidence level"
    status: ground
    note: Read as a guaranteed limit on the mean, not a single measured value. Wikipedia gives a different form of the same small number (see the next row).
    source: corning-ule-datasheet
    where: Linear Coefficient of Thermal Expansion paragraph; Thermal Properties block, Mean coefficient of thermal expansion 5 to 35 C
  - benchmark: cte
    label: Coefficient of thermal expansion quoted on Wikipedia
    value: 1.e-8
    unit: /K
    scope: material
    conditions:
      temperature_range: 5 to 35 °C
      unit_in_source: 10−8/K
    method: Single figure printed on the Wikipedia article as 10−8/K for 5 to 35 °C
    status: ground
    note: Second-hand figure from an encyclopedia article. It agrees in order of magnitude with the Corning guarantee and is not used for any comparison here.
    source: wiki-ule
    where: Thermal section, coefficient of thermal expansion value
  - benchmark: thermal_conductivity
    label: Thermal conductivity, ULE 7972
    value: 1.31
    unit: W/(m·°C)
    scope: material
    conditions:
      temperature: 25 °C (sheet default)
    method: Value printed on the Corning ULE 7972 product sheet as "1.31 w/(m • ºC) [1.31 kcal/(m • hr • ºC)]"
    status: ground
    note: The PGO page and the AZoM table print the same 1.31 figure.
    source: corning-ule-datasheet
    where: Thermal Properties block, Thermal conductivity (K)
  - benchmark: specific_heat
    label: Mean specific heat capacity, ULE 7972
    value: 767
    unit: J/(kg·°C)
    scope: material
    conditions:
      temperature: 25 °C (sheet default; the sheet gives a mean value without a temperature range)
    method: Value printed on the Corning ULE 7972 product sheet as "767 J/ (kg • ºC) [0.183 cal/(g • ºC)]"
    status: ground
    source: corning-ule-datasheet
    where: Thermal Properties block, Mean specific heat (Cp)
  - benchmark: strain_point
    label: Strain point, ULE 7972
    value: 890
    unit: °C
    scope: material
    conditions:
      basis: as printed on the sheet, which gives 1634 °F alongside
    method: Value printed on the Corning ULE 7972 product sheet
    status: ground
    note: Non-canonical property name (strain_point); no canonical name exists in the property file.
    source: corning-ule-datasheet
    where: Thermal Properties block, Strain point
  - benchmark: annealing_point
    label: Annealing point, ULE 7972
    value: 1000
    unit: °C
    scope: material
    conditions:
      basis: as printed on the sheet, which gives 1832 °F alongside
    method: Value printed on the Corning ULE 7972 product sheet
    status: ground
    note: Non-canonical property name (annealing_point); no canonical name exists in the property file.
    source: corning-ule-datasheet
    where: Thermal Properties block, Annealing point
  - benchmark: softening_point
    label: Softening point, ULE 7972 (estimated)
    value: 1490
    unit: °C
    scope: material
    conditions:
      basis: printed by Corning as an estimated value, 2714 °F alongside
    method: Value printed on the Corning ULE 7972 product sheet, marked "(estimated)"
    status: ground
    note: Corning labels this value as estimated. Non-canonical property name (softening_point).
    source: corning-ule-datasheet
    where: Thermal Properties block, Softening point (estimated)
  - benchmark: elastic_modulus
    label: Elastic (Young's) modulus, ULE 7972
    value: 67.6
    unit: GPa
    scope: material
    conditions:
      temperature: 25 °C (sheet default)
    method: Value printed on the Corning ULE 7972 product sheet as "67.6 GPa [9.80 x 10 6 psi]"
    status: ground
    source: corning-ule-datasheet
    where: Mechanical Properties block, Elastic Modulus (E)
  - benchmark: shear_modulus
    label: Shear modulus, ULE 7972
    value: 29
    unit: GPa
    scope: material
    conditions:
      temperature: 25 °C (sheet default)
    method: Value printed on the Corning ULE 7972 product sheet as "29.0 GPa [4.20 x 10 6 psi]"
    status: ground
    source: corning-ule-datasheet
    where: Mechanical Properties block, Shear Modulus (G)
  - benchmark: bulk_modulus
    label: Bulk modulus, ULE 7972
    value: 34.1
    unit: GPa
    scope: material
    conditions:
      temperature: 25 °C (sheet default)
    method: Value printed on the Corning ULE 7972 product sheet as "34.1 GPa [4.95 x 10 6 psi]"
    status: ground
    source: corning-ule-datasheet
    where: Mechanical Properties block, Bulk Modulus (K)
  - benchmark: poissons_ratio
    label: Poisson's ratio, ULE 7972
    value: 0.17
    unit: '-'
    scope: material
    conditions:
      temperature: 25 °C (sheet default)
    method: Value printed on the Corning ULE 7972 product sheet
    status: ground
    source: corning-ule-datasheet
    where: Mechanical Properties block, Poisson's ratio (nu)
  - benchmark: modulus_of_rupture
    label: Modulus of rupture (MOR), as printed
    value: 49.8
    unit: MPa
    scope: material
    conditions:
      basis: printed as ultimate tensile stress with the abbreviation MOR (modulus of rupture); the sheet does not describe the test
    method: Value printed on the Corning ULE 7972 product sheet as "49.8 MPa [7220 psi]"
    status: ground
    note: The sheet labels this row Ultimate tensile stress (MOR) and gives no test method. MOR usually refers to a bend-test strength, so it is filed as modulus of rupture and not ranked as a tensile strength.
    source: corning-ule-datasheet
    where: Mechanical Properties block, Ultimate tensile stress (MOR)
  - benchmark: knoop_hardness
    label: Knoop hardness, ULE 7972
    value: 460
    unit: kg/mm2
    scope: material
    conditions:
      load: 200 g
    method: Value printed on the Corning ULE 7972 product sheet as "Knoop Hardness, 200 g load 460 kg/mm2"
    status: ground
    note: AZoM prints 49 Knoop with no load or unit scale stated, which differs by about a factor of ten. Only the Corning value is recorded. Non-canonical property name (knoop_hardness).
    source: corning-ule-datasheet
    where: Mechanical Properties block, Knoop Hardness
  - benchmark: refractive_index
    label: Refractive index nD, ULE 7972 (nominal CTE material)
    value: 1.4828
    unit: '-'
    scope: material
    conditions:
      wavelength: 589 nm (nD)
      material: nominal CTE material, as printed
    method: Value printed on the Corning ULE 7972 product sheet in the Optical Properties block
    status: ground
    note: The sheet also prints nF (486 nm) 1.4892 and nC (656 nm) 1.4801. The PGO page prints the same nD value.
    source: corning-ule-datasheet
    where: Optical Properties block, Refractive index nD (589 nm)
  - benchmark: abbe_number
    label: Abbe number (vd), ULE 7972
    value: 53.1
    unit: '-'
    scope: material
    conditions:
      notation: vd, printed as Abbe' Number (vd)
    method: Value printed on the Corning ULE 7972 product sheet
    status: ground
    note: Non-canonical property name (abbe_number).
    source: corning-ule-datasheet
    where: Optical Properties block, Abbe Number (vd)
  - benchmark: thermal_diffusivity
    label: Thermal diffusivity, ULE 7972
    value: 0.0079
    unit: cm2/s
    scope: material
    conditions:
      temperature: not stated on the sheet (sheet default 25 °C)
    method: Value printed on the Corning ULE 7972 product sheet as "0.0079 cm2/s" (the sheet spells the label 'diffusity')
    status: ground
    note: PGO prints 0.079 cm2/s for the same property. The Corning figure is recorded here and the difference is not resolved. Non-canonical property name (thermal_diffusivity).
    source: corning-ule-datasheet
    where: Thermal Properties block, Thermal diffusity (D)
  - benchmark: dielectric_constant
    label: Dielectric constant, ULE 7972
    value: 3.99
    unit: '-'
    scope: material
    conditions:
      frequency: 100 Hz
      temperature: 25 °C
    method: Value printed on the PGO ULE page in the electrical properties list
    status: ground
    source: pgo-ule
    where: Electrical properties list, Dielectric Constant
  - benchmark: dissipation_factor
    label: Loss factor (dissipation factor), ULE 7972
    value: 0.00005
    unit: '-'
    scope: material
    conditions:
      frequency: 100 Hz
      temperature: 25 °C
    method: Value printed on the PGO ULE page as "Loss Factor 0.00005"
    status: ground
    source: pgo-ule
    where: Electrical properties list, Loss Factor
  - benchmark: max_service_temp
    label: Maximum working temperature, ULE (blended table value)
    value: 800
    unit: °C
    scope: material
    conditions:
      basis: printed as maximum working temperature in the AZoM table, with no condition given
    method: Value printed in the AZoM ULE property table as "800 °C"
    status: ground
    note: The Corning sheet gives no number; it says only 'High operating temperature'. The AZoM table states that its data are blended from multiple sources and are not warrantable.
    source: azom-ule
    where: Table 1, Maximum working temperature row
corrosion:
  - environment: 5% hydrochloric acid, 95 °C, 24 hours
    headline: 'Acid barely attacks ULE 7972: under 0.01 mg/cm2 lost in 24 hours at 95 °C.'
    effect: The Corning chemical durability table prints a weight loss below 0.01 mg/cm2 for 5% HCl after 24 hours at 95 °C.
    rating: low
    conditions:
      solution: 5% HCl
      temperature: 95 °C
      duration: 24 h
      weight_loss_printed: <0.01 mg/cm2
    source: corning-ule-datasheet
    where: Chemical durability table, row 5% HCl
  - environment: 5% sulphuric acid, 95 °C, 24 hours
    headline: 'Sulphuric acid also barely attacks ULE 7972: under 0.01 mg/cm2 in 24 hours at 95 °C.'
    effect: The Corning table prints a weight loss below 0.01 mg/cm2 for 5% H2SO4 after 24 hours at 95 °C.
    rating: low
    conditions:
      solution: 5% H2SO4
      temperature: 95 °C
      duration: 24 h
      weight_loss_printed: <0.01 mg/cm2
    source: corning-ule-datasheet
    where: Chemical durability table, row 5% H2SO4
  - environment: Water, 95 °C, 24 hours
    headline: Hot water removes less than 0.01 mg/cm2 of ULE 7972 in 24 hours.
    effect: The Corning table prints a weight loss below 0.01 mg/cm2 for water (H2O) after 24 hours at 95 °C.
    rating: low
    conditions:
      solution: H2O
      temperature: 95 °C
      duration: 24 h
      weight_loss_printed: <0.01 mg/cm2
    source: corning-ule-datasheet
    where: Chemical durability table, row H2O
  - environment: 0.02 N sodium carbonate, 95 °C, 6 hours
    headline: Dilute sodium carbonate removes 0.02 mg/cm2 of ULE 7972 in 6 hours at 95 °C.
    effect: The Corning table prints a weight loss of 0.02 mg/cm2 for 0.02N Na2CO3 after 6 hours at 95 °C.
    rating: low
    conditions:
      solution: 0.02N Na2CO3
      temperature: 95 °C
      duration: 6 h
      weight_loss_printed: 0.02 mg/cm2
    source: corning-ule-datasheet
    where: Chemical durability table, row 0.02N Na2CO3
  - environment: 5% sodium hydroxide, 95 °C, 6 hours
    headline: 'Hot sodium hydroxide attacks ULE 7972 more than the acids and water in the table: 0.9 mg/cm2 in 6 hours at 95 °C.'
    effect: The Corning table prints a weight loss of 0.9 mg/cm2 for 5% NaOH after 6 hours at 95 °C, the largest loss in the table. The PGO page prints the same 0.90 mg/cm2 figure.
    rating: moderate
    conditions:
      solution: 5% NaOH
      temperature: 95 °C
      duration: 6 h
      weight_loss_printed: 0.9 mg/cm2
    source: corning-ule-datasheet
    where: Chemical durability table, row 5% NaOH
  - environment: Atmospheric weathering, water and sulphur dioxide
    headline: Corning reports excellent weathering resistance and virtually no surface clouding.
    effect: The sheet states excellent resistance to weathering and virtually no surface clouding or electrical surface leakage when exposed to water, sulfur dioxide and atmospheric gases. No number is given.
    rating: low
    conditions:
      basis: qualitative statement on the sheet; no test duration given
    source: corning-ule-datasheet
    where: Chemical durability block, first bullet list
  - environment: Quench from 350 °C into water, and thermal cycling
    headline: No figure change or measurable hysteresis reported after a 350 °C water quench or thermal cycling.
    effect: The sheet states that a blank taken from 350 °C to a water quench shows no residual figure change, and that thermal cycling causes no measurable hysteresis at any rate of temperature change. It also reports no measurable delayed elastic effect.
    rating: low
    conditions:
      basis: qualitative statements on the sheet; no numbers given
    source: corning-ule-datasheet
    where: Stability bullets on the Corning ULE 7972 sheet
risks:
  hazards:
    - text: PubChem's titanium dioxide record (CID 26042) states that this chemical does not meet GHS hazard criteria in 62.8% (7032 of 11189) of company reports. Some notifications carry H351 (suspected of causing cancer) in 36.1% of reports that give hazard codes. The record covers titanium dioxide powder, not ULE glass, in which NASA says the titanium dioxide combines with silica into a homogeneous glass.
      ghs:
        - H351
      source: pubchem-tio2
      where: Safety and Hazards, GHS Classification (CID 26042); ECHA C&L notification summary
  failure_risks:
    - mode: Delayed failure of flawed ULE under sustained tensile stress
      trigger: Machined or ground flaws in the glass under sustained tensile stress
      consequence: NASA MSFC measured dynamic fatigue on ULE and found that removing residual stress by grinding and polishing increased strength and lifetime. The authors note that a strength allowance based on modulus-of-rupture data ignores delayed failure, which can significantly shorten lifetime.
      severity: moderate
      source: nasa-tucker2003
      where: Abstract
    - mode: Thermal distortion of a large space telescope mirror
      trigger: Temperature changes across a mirror blank in orbit
      consequence: A 1993 finite element estimate of thermally induced distortion in the Hubble primary mirror found that the distortion mainly produces defocus, with a relatively small contribution to spherical aberration. The paper's abstract gives no distortion figure.
      severity: low
      source: nasa-nied1993
      where: Abstract
  side_effects: []
  handling: []
  mitigations:
    - text: NASA's 2003 tests found that grinding and polishing to a mirror finish, rather than a coarse 230/270 grit surface, removed residual stress and raised strength and lifetime.
      source: nasa-tucker2003
      where: Abstract
uses:
  - application: optics-and-cameras
    device: Hubble Space Telescope primary mirror
    example: NASA Marshall states that ULE is used where low thermal expansion matters, such as telescope mirrors, including the Hubble Space Telescope primary mirror.
    source: nasa-tucker2003
    where: Abstract
  - application: optics-and-cameras
    device: 1.5 m primary mirror for ultra-stable UVOIR space telescopes (ground model and test)
    example: NASA MSFC describes a 1.5-meter ULE mirror, manufactured by Harris Corp, used to build a structural, thermal and optical performance model and to run bulk-temperature and lateral-gradient tests.
    source: nasa-stahl2019
    where: Abstract
  - application: electronics-and-chips
    device: EUV lithography optics and substrates
    example: Corning's product sheet says that industry experts in semiconductor manufacturing have identified ULE as a 'material of choice' for EUV applications (manufacturer statement).
    source: corning-ule-datasheet
    where: Introduction text
  - application: structures
    device: Machine tool reference blocks
    example: Corning's product sheet lists machine tool reference blocks among its applications, next to mirror blanks for large astronomical telescopes and space satellites.
    source: corning-ule-datasheet
    where: Introduction text
supply:
  - subject: Titanium (as titanium dioxide, the titania in ULE)
    producers:
      - country: China
        share_percent: 60.6
        year: 2025
      - country: United States
        share_percent: 13.7
        year: 2025
      - country: Mexico
        share_percent: 3.5
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (titanium named as used as a white pigment and in metal alloys)
        listed: true
    substitutes: []
    source: usgs-mcs2026-titanium
    where: TiO2 pigment capacity, 2025e table (world total 9,900,000 t; shares calculated by Space Mushroom from China 6,000,000 t, United States 1,360,000 t and Mexico 350,000 t). Capacity, not mine production or ilmenite and rutile feedstock.
  - subject: Silicon (silica from high-purity sand, the base of ULE)
    abundance: 'USGS: world and domestic resources for making silicon metal and alloys are abundant and, in most producing countries, adequate to supply world requirements for many decades.'
    producers:
      - country: China
        share_percent: 80
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals
        listed: true
    recycling: 'USGS silicon chapter: ''Insignificant.'''
    substitutes: []
    source: usgs-mcs2026-silicon
    where: Events, Trends, and Issues ('almost 80%' of estimated global silicon-materials production in 2025, recorded as 80); World Resources; Recycling. The 80% covers silicon metal and ferrosilicon, not silica sand.
documents:
  - title: Corning ULE 7972 Ultra Low Expansion Glass product sheet (copy hosted by Light Machinery; Corning copyright 2006)
    type: datasheet
    url: https://lightmachinery.com/media/1556/ule-2006.pdf
    year: 2006
  - title: 'NASA MSFC: Lifetime Predictions of a Titanium Silicate Glass with Machined Flaws (NTRS 20030062257)'
    type: paper
    url: https://ntrs.nasa.gov/citations/20030062257
    year: 2003
  - title: 'AIAA 93-0097: Temperature induced distortions in space telescope mirrors (NTRS 19930036205)'
    type: paper
    url: https://ntrs.nasa.gov/citations/19930036205
    year: 1993
  - title: 'NASA MSFC: Predictive Thermal Control Technology to Enable Thermally Stable Telescopes, first two year status (NTRS 20190029080)'
    type: paper
    url: https://ntrs.nasa.gov/citations/20190029080
    year: 2019
  - title: 'USGS Mineral Commodity Summaries 2026: Titanium and Titanium Dioxide'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-titanium.pdf
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Silicon'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-silicon.pdf
    year: 2026
  - title: 'PubChem: Titanium dioxide (CID 26042), Safety and Hazards'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/26042
    year: 2026
gaps:
  - Corning's own ULE 7972 PDFs and product page returned HTTP 403 to this run. The datasheet used is a 2006 copy hosted by Light Machinery, so a current Corning revision may print different values.
  - No safety data sheet for ULE 7972 was found. The hazard entry uses PubChem's record for titanium dioxide powder, which is a substance-level caution and not a classification of the glass.
  - No hydrofluoric acid or alkali-etch test for ULE 7972 was found in the sources read; the Corning sheet tests only the five solutions shown in the corrosion section.
  - 'Maximum working temperature: the Corning sheet says only ''High operating temperature''. The 800 °C figure comes from the AZoM table, which says its data are blended from multiple sources and are not warrantable.'
  - 'Thermal diffusivity conflict: the Corning sheet prints 0.0079 cm2/s and PGO prints 0.079 cm2/s. The Corning figure is recorded and the conflict is not resolved.'
  - 'Hardness conflict: AZoM prints 49 Knoop with no load stated; the Corning sheet prints 460 kg/mm2 at 200 g load. Only the Corning value is recorded.'
  - 'Composition is not certified: NASA gives about 7.5% TiO2 and Wikipedia gives less than 10%. No source read gives the silica percentage.'
  - 'Corning''s sheet and PGO print the thermal coefficient of refractive index (dn/dt: 10.68 x 10-6/°C at 20 to 40 °C and 11.24 x 10-6/°C at 40 to 60 °C) and the stress optical coefficient (4.15 (nm/cm)/(kg/cm3)). Neither is recorded because no canonical property name covers them.'
  - Electrical volume resistivity is printed on the Corning sheet, but the text extraction of the exponent was unclear, so it is not recorded.
  - Outgassing (ASTM E595), atomic-oxygen and radiation behaviour of ULE 7972 were not looked up. No vacuum or flight result was read.
  - 'Titanium feedstock (ilmenite and rutile mine production) not read: the USGS titanium mineral concentrates chapter URL returned HTML. Titanium shares here are pigment capacity.'
  - 'Silicon feedstock: high-purity silica sand production shares were not read. The 80% China figure covers silicon metal and ferrosilicon, not silica sand.'
  - Titanium recycling was not found in the titanium chapter read.
  - No handling or storage guidance for ULE blanks was found in the sources read.
  - The EU critical raw materials list was not checked for titanium or silicon.
  - No measured thermal distortion or CTE map for the Hubble primary mirror was found. The 1993 NASA paper prints no CTE numbers in its abstract.
  - Corrosion ratings (low, moderate) are Space Mushroom's judgement from the mg/cm2 figures; the Corning sheet does not rate them.
  - Strain, annealing and softening points, Knoop hardness, Abbe number and thermal diffusivity use snake_case property names because no canonical name exists in the property file.
sources:
  corning-ule-datasheet:
    title: Corning ULE 7972 Ultra Low Expansion Glass product sheet (Advanced Optics and Materials; Corning copyright 2006, supersedes August 2005), copy hosted by Light Machinery
    id: ULE Corning Code 7972
    url: https://lightmachinery.com/media/1556/ule-2006.pdf
    year: 2006
    kind: datasheet
    license: Manufacturer data sheet (cited, not reproduced)
  pgo-ule:
    title: 'PGO: ULE (Corning code 7972) properties page'
    url: https://www.pgo-online.com/intl/ule.html
    kind: web
    license: Web page (cited, not reproduced)
  azom-ule:
    title: 'AZoM: Ultra Low Expansion (ULE) glass, Table 1 Mechanical and Physical Properties for ULE'
    id: AZoM article ID 5911
    url: https://www.azom.com/article.aspx?ArticleID=5911
    kind: web
    license: Web page (cited, not reproduced)
  wiki-ule:
    title: 'Wikipedia: Ultra-low expansion glass (composition, history and CTE only)'
    url: https://en.wikipedia.org/wiki/Ultra_low_expansion_glass
    kind: web
    license: CC BY-SA (cited, not reproduced)
  nasa-tucker2003:
    title: 'Tucker, Nettles and Cagle (NASA MSFC): Lifetime Predictions of a Titanium Silicate Glass with Machined Flaws'
    id: NTRS 20030062257
    url: https://ntrs.nasa.gov/citations/20030062257
    year: 2003
    kind: paper
    license: NASA public document (cited, not reproduced)
  nasa-nied1993:
    title: 'Nied and Rudmann: Temperature induced distortions in space telescope mirrors (AIAA 93-0097)'
    id: NTRS 19930036205
    url: https://ntrs.nasa.gov/citations/19930036205
    year: 1993
    kind: paper
    license: NASA public document (cited, not reproduced)
  nasa-stahl2019:
    title: 'Stahl and Brooks (NASA MSFC): Predictive Thermal Control Technology to Enable Thermally Stable Telescopes, first two year status'
    id: NTRS 20190029080
    url: https://ntrs.nasa.gov/citations/20190029080
    year: 2019
    kind: paper
    license: NASA public document (cited, not reproduced)
  usgs-mcs2026-titanium:
    title: 'USGS Mineral Commodity Summaries 2026: Titanium and Titanium Dioxide'
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-titanium.pdf
    year: 2026
    kind: report
    license: US government publication (cited, not reproduced)
  usgs-mcs2026-silicon:
    title: 'USGS Mineral Commodity Summaries 2026: Silicon'
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-silicon.pdf
    year: 2026
    kind: report
    license: US government publication (cited, not reproduced)
  usgs-crit2025:
    title: 'USGS: About the 2025 List of Critical Minerals (final list of 60 minerals; titanium and silicon included)'
    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: US government publication (cited, not reproduced)
  pubchem-tio2:
    title: 'PubChem compound record: Titanium dioxide (CID 26042), Safety and Hazards'
    id: CID 26042
    url: https://pubchem.ncbi.nlm.nih.gov/compound/26042
    year: 2026
    kind: database
    license: Public database (cited, not reproduced)
license: CC-BY-4.0
updated: '2026-11-01'
review:
  status: draft
  method: assistant
  checked_values: 20
  unreachable: 3
  caveats: 2
  note: Read by an AI assistant on 2026-11-01 from the Light Machinery copy of the 2006 Corning ULE 7972 product sheet, the PGO and AZoM property pages, the Wikipedia article, three NASA NTRS records, two USGS Mineral Commodity Summaries 2026 chapters, the USGS 2025 critical minerals page and the PubChem titanium dioxide record. Corning's own PDFs and product page returned HTTP 403. The PGO and AZoM pages are secondary and carry conflicts noted above.
story:
  recipe:
    line: 'ULE 7972 is a titania-silicate glass: silica (SiO2) with about 7.5% titanium dioxide (TiO2), per the NASA Marshall 2003 paper. Wikipedia says the glass contains less than 10% titanium dioxide. NASA says the titanium dioxide combines with silica into a homogeneous glass with a near-zero linear expansion. Corning''s product sheet does not print a composition.'
    parts:
      - name: Silica
        symbol: SiO2
        share_note: Balance of the glass; no source read gives the silica percentage
        role: The glass network. Silica makes up the rest of the glass, and the titanium dioxide is combined with it to form one homogeneous glass.
        source: nasa-tucker2003
        where: Abstract, sentence on the composition
      - name: Titanium dioxide
        symbol: TiO2
        share_percent: 7.5
        share_note: NASA 2003 figure; Wikipedia gives less than 10%
        role: The additive that brings the thermal expansion close to zero. The NASA abstract says the titanium dioxide and silica together form a homogeneous glass with a near-zero linear expansion.
        source: nasa-tucker2003
        where: Abstract, sentence beginning ULE contains 7.5% titanium dioxide
  risk_groups:
    - title: For people
      level: 1
      verdict: Dust caution only
      lead: Corning describes ULE 7972 as highly resistant to nearly all chemical agents, and its product sheet prints no hazard classification. The one caution comes from PubChem's titanium dioxide record, which is for powder.
      points:
        - label: The glass
          line: Corning's chemical durability table shows weight losses below 0.01 mg/cm2 for the acids and water tested at 95 °C, and 0.9 mg/cm2 for 5% sodium hydroxide over 6 hours.
        - label: Titanium dioxide
          line: PubChem's titanium dioxide record says 62.8% of company reports find it does not meet GHS hazard criteria, and 36.1% of reports that give hazard codes carry H351, suspected of causing cancer. This describes the powder, not the glass.
    - title: If a blank fails
      level: 2
      verdict: Delayed failure of flawed blanks
      lead: NASA's 2003 study of ULE found that flaws and sustained tensile stress set the failure path, and that a strength value based on modulus of rupture can overstate lifetime.
      points:
        - label: Flaws
          line: Grinding and polishing to a mirror finish removed residual stress and raised strength and lifetime compared with a coarse 230/270 grit surface, per NASA MSFC.
        - label: Stress
          line: NASA notes that a strength allowance based on modulus-of-rupture data ignores delayed failure, which can significantly shorten lifetime.
    - title: Thermal behaviour
      level: 0
      verdict: No hysteresis reported
      lead: The Corning sheet reports no residual change in the mirror figure after a quench from 350 °C and no measurable hysteresis from thermal cycling. These are qualitative statements with no numbers.
      points:
        - label: Thermal cycling
          line: Corning reports no measurable hysteresis from thermal cycling at any rate of temperature change, and no measurable delayed elastic effect.
  why: 'ULE 7972 is a titania-silicate glass that Corning makes for precision optics, chosen because its thermal expansion is close to zero. Corning guarantees a mean coefficient of thermal expansion of 0 ± 30 ppb/°C from 5 to 35 °C at a 95% confidence level. Its density is 2.21 g/cm3 at 25 °C. NASA names ULE among the materials used for space telescope mirrors, including the Hubble Space Telescope primary mirror. The trade-off is brittleness: like other glasses, flawed ULE can fail under sustained tensile stress.'
  uses:
    - where: Space telescope mirrors
      line: NASA Marshall names the Hubble Space Telescope primary mirror as an example of ULE in telescope optics. A later NASA model and test programme built a 1.5-metre ULE mirror to study thermal stability for ultra-stable space telescopes. That work is on the ground, and no in-orbit result for the new mirror is claimed here.
    - where: EUV lithography
      line: Corning says that industry experts in semiconductor manufacturing have identified ULE as a material of choice for EUV applications. This is a manufacturer's statement, and no independent test was read.
    - where: Machine tool reference blocks
      line: Corning lists machine tool reference blocks among the applications of ULE, next to mirror blanks for large astronomical telescopes and space satellites.
  can_do:
    - label: Holds its size
      benchmark: cte
      value: 0 ± 30 ppb/°C mean, 5 to 35 °C
      line: Corning guarantees a mean coefficient of thermal expansion of 0 ± 30 ppb/°C from 5 to 35 °C at a 95% confidence level. Wikipedia gives 10−8/K for the same range.
    - label: Stiff
      benchmark: elastic_modulus
      value: 67.6 GPa
      line: The Young's modulus is 67.6 GPa at 25 °C, and the Poisson's ratio is 0.17, both as printed on the Corning sheet.
    - label: Bends light
      benchmark: refractive_index
      value: 1.4828 at 589 nm
      line: The refractive index nD is 1.4828 at 589 nm for the nominal CTE material, and the Abbe number is 53.1.
    - label: Survives chemicals
      value: under 0.01 mg/cm2 weight loss in 5% HCl, 24 h, 95 °C
      line: The Corning table prints weight losses below 0.01 mg/cm2 for 5% HCl, 5% H2SO4 and water over 24 hours at 95 °C.
  compare: 'Corning''s sheet and the Wikipedia article both describe ULE as a glass with near-zero expansion, but state the figure differently: Corning guarantees a mean of 0 ± 30 ppb/°C from 5 to 35 °C, and Wikipedia gives 10−8/K for the same range. The two statements do not contradict each other. This profile does not compare ULE with fused silica or Zerodur, because those values were not read in this run.'
  compare_rows:
    - label: Mean thermal expansion
      benchmark: cte
    - label: Density
      benchmark: density
    - label: Thermal conductivity
      benchmark: thermal_conductivity
  handling:
    - No handling or storage guidance for ULE blanks was found in the sources read.
    - NASA's 2003 study found that grinding and polishing removed residual stress and lengthened lifetime, so finishing matters for the life of a flawed blank.
  good_for:
    - 'Mirror blanks that must hold their shape over temperature changes: Corning guarantees a mean expansion of 0 ± 30 ppb/°C from 5 to 35 °C.'
    - EUV lithography parts, which Corning says industry experts identify as a material of choice (a manufacturer statement).
  watch_out:
    - 'Delayed failure: NASA shows that flawed ULE can fail under sustained stress, and that a modulus-of-rupture strength allowance ignores this.'
    - 'Conflicting figures: thermal diffusivity (0.0079 vs 0.079 cm2/s) and hardness (460 kg/mm2 at 200 g vs 49 Knoop) differ between sources. See gaps.'
    - 'Composition is not certified: NASA gives 7.5% titanium dioxide and Wikipedia gives less than 10%.'
  verdict: ULE 7972 is the low-expansion glass that NASA names for the Hubble primary mirror, and its guaranteed mean expansion of 0 ± 30 ppb/°C from 5 to 35 °C is the number to design against. The values here come from a 2006 Corning sheet copy and secondary tables, so check the current Corning revision before a flight design.