spore: profile
id: fused-silica
spore_version: 0.2
family: glass-and-composites
name: Fused silica
abbreviation: SiO2 glass
role: optical window and cover glass
category: glasses-optics
type: fused-silica
summary: |
  Fused silica, also called fused quartz, is amorphous silicon dioxide made by melting pure silica, with no crystal structure. Typical synthetic fused silica has a density of 2.20 g/cm3, a thermal expansion of 5.5e-7 m/(m·°C) between 20 and 320 °C, and a refractive index of 1.45702 at 633 nm. It is used for optical windows, lenses and mirror substrates, and as solar-cell cover glass.
best_for: 'Optics that must stay stable across temperature swings: very low thermal expansion and transparency from the ultraviolet to the near infrared'
weakest_at: Brittleness, and a damaged pane can fail suddenly under tensile stress; the fetched sources give no outgassing numbers
identity:
  formula: SiO2, amorphous silicon dioxide (fused silica, fused quartz)
  source: pmoptics-fused-silica
  where: Fused Silica Properties table (the page describes it as fused silica of the same chemistry as quartz, without crystal structure)
tags:
  applications:
    - optics-and-cameras
    - structures
    - solar-arrays
properties:
  - benchmark: density
    label: Density, fused silica
    value: 2.2
    unit: g/cm3
    scope: material
    conditions:
      temperature: not stated
    method: Value printed on a manufacturer-style property page
    status: ground
    source: pmoptics-fused-silica
    where: Fused Silica Properties table, row Density
  - benchmark: cte
    label: Coefficient of thermal expansion, fused silica
    value: 5.5e-7
    unit: m/(m·°C)
    scope: material
    conditions:
      temperature: 20 °C to 320 °C
      unit_in_source: 5.5×10⁻⁷ m/(m·°C)
    method: Value printed on a property page
    status: ground
    source: pmoptics-fused-silica
    where: Fused Silica Properties table, row Coefficient of thermal expansion
  - benchmark: thermal_conductivity
    label: Thermal conductivity, fused silica
    value: 1.4
    unit: W/(m·°C)
    scope: material
    conditions:
      temperature: not stated
    method: Value printed on a property page
    status: ground
    source: pmoptics-fused-silica
    where: Fused Silica Properties table, row Thermal conductivity
  - benchmark: thermal_conductivity
    label: Thermal conductivity, HPFS 7980 standard grade fused silica
    value: 1.3
    unit: W/m K
    scope: material
    conditions:
      temperature: 25 °C
      basis: unless otherwise stated, values on the sheet are at 25 °C
    method: Value printed on the Corning HPFS 7980 data sheet, Mechanical and Thermal Properties
    status: ground
    source: corning-7980-valleydesign
    where: Mechanical and Thermal Properties table, row Thermal Conductivity
  - benchmark: specific_heat
    label: Specific heat capacity, fused silica
    value: 720
    unit: J/(kg·K)
    scope: material
    conditions:
      temperature: not stated
    method: Value printed on a property page
    status: ground
    source: makeitfrom-fused-silica
    where: Thermal Properties table, row Specific Heat Capacity (value shown as 720 J/kg-K)
  - benchmark: max_service_temp
    label: Maximum temperature, mechanical, fused silica
    value: 1080
    unit: °C
    scope: material
    conditions:
      basis: mechanical limit as labelled on the page
    method: Value printed on a property page, labelled Maximum Temperature Mechanical
    status: ground
    source: makeitfrom-fused-silica
    where: Thermal Properties table, row Maximum Temperature Mechanical
  - benchmark: softening_point
    label: Softening point, fused silica
    value: 1683
    unit: °C
    scope: material
    conditions:
      temperature: not stated
    method: Value printed on a property page
    status: ground
    source: pmoptics-fused-silica
    where: Fused Silica Properties table, row Softening point
  - benchmark: annealing_point
    label: Annealing point, fused silica
    value: 1215
    unit: °C
    scope: material
    conditions:
      temperature: not stated
    method: Value printed on a property page
    status: ground
    source: pmoptics-fused-silica
    where: Fused Silica Properties table, row Annealing point
  - benchmark: strain_point
    label: Strain point, fused silica
    value: 1120
    unit: °C
    scope: material
    conditions:
      temperature: not stated
    method: Value printed on a property page
    status: ground
    source: pmoptics-fused-silica
    where: Fused Silica Properties table, row Strain point
  - benchmark: elastic_modulus
    label: Young's modulus, fused silica
    value: 72.7
    unit: GPa
    scope: material
    conditions:
      temperature: not stated
    method: Value printed on a property page
    status: ground
    source: pmoptics-fused-silica
    where: Fused Silica Properties table, row Young's modulus
  - benchmark: poisson_ratio
    label: Poisson's ratio, fused silica
    value: 0.17
    unit: dimensionless
    scope: material
    conditions:
      temperature: not stated
    method: Value printed on a property page
    status: ground
    source: pmoptics-fused-silica
    where: Fused Silica Properties table, row Poisson's ratio
  - benchmark: abbe_number
    label: Abbe constant, fused silica
    value: 67.6
    unit: dimensionless
    scope: material
    conditions:
      wavelengths: not stated
    method: Value printed on a property page labelled Abbe constant
    status: ground
    source: pmoptics-fused-silica
    where: Fused Silica Properties table, row Abbe constant
  - benchmark: refractive_index
    label: Refractive index, typical synthetic fused silica at 633 nm
    value: 1.45702
    unit: dimensionless
    scope: material
    conditions:
      wavelength: 0.633 µm
      sample: typical synthetic fused silica
      temperature: not stated
    method: Value listed in a wavelength-indexed table on a property page
    status: ground
    source: pmoptics-fused-silica
    where: Refractive index table, row 0.633
  - benchmark: refractive_index
    label: Refractive index, typical synthetic fused silica at 1064 nm
    value: 1.44962
    unit: dimensionless
    scope: material
    conditions:
      wavelength: 1.064 µm
      sample: typical synthetic fused silica
      temperature: not stated
    method: Value listed in a wavelength-indexed table on a property page
    status: ground
    source: pmoptics-fused-silica
    where: Refractive index table, row 1.064
  - benchmark: refractive_index
    label: Refractive index, typical fused silica at 632.8 nm
    value: 1.45704
    unit: dimensionless
    scope: material
    conditions:
      wavelength: 632.8 nm
      extinction_coefficient: '0'
      sample: typical sample of SiO2
      temperature: not stated
    method: Value stated on a refractive index database page
    status: ground
    source: spts-sio2
    where: Text of the page for SiO2, first statement
corrosion:
  - environment: 10% hydrofluoric acid by weight, 25 °C, 20 minutes
    headline: 'Hydrofluoric acid is the fastest etchant in the table: 0.230 mg/cm2 lost in 20 minutes.'
    effect: Weight loss of 0.230 mg/cm2 in 20 minutes. The fluoride mixture 10% NH4F*HF gave 0.220 mg/cm2 in the same time, so both fluoride etchants attack the glass at similar rates.
    rating: severe
    conditions:
      test: Chemical durability table, 25 °C, weight loss in mg/cm2
      caveat: row order read from the printed table; check against the printed sheet
    source: corning-7980-valleydesign
    where: Chemical Durability and Impurities table, rows 10% HF and 10% NH4F*HF by weight
  - environment: 5% sodium hydroxide, 95 °C, 6 hours
    headline: 'Hot alkali removes the most glass of any solution in the table: 0.453 mg/cm2 in 6 hours.'
    effect: Weight loss of 0.453 mg/cm2 after 6 hours at 95 °C. The 0.02 N sodium carbonate solution at 95 °C for 6 hours lost 0.065 mg/cm2.
    rating: moderate
    conditions:
      test: 95 °C immersion, weight loss in mg/cm2
      caveat: row order read from the printed table; check against the printed sheet
    source: corning-7980-valleydesign
    where: Chemical Durability and Impurities table, rows 5% NaOH and 0.02N Na2CO3
  - environment: 5% hydrochloric acid, 0.02 N sulfuric acid and deionized water, 95 °C, 24 hours
    headline: 'Acids and water barely attack the glass: losses below 0.010 mg/cm2 for the acids, 0.015 mg/cm2 for water.'
    effect: Hydrochloric and sulfuric acid each gave weight losses below 0.010 mg/cm2 after 24 hours at 95 °C. Deionized water gave 0.015 mg/cm2 in the same time.
    rating: low
    conditions:
      test: 95 °C immersion, weight loss in mg/cm2
      caveat: row order read from the printed table; check against the printed sheet
    source: corning-7980-valleydesign
    where: Chemical Durability and Impurities table, rows 5% HCl, 0.02N H2SO4 and deionized H2O
  - environment: 1 MeV electron irradiation to 1e15 electrons/cm2, a space radiation test of solar-cell cover glass
    headline: Synthetic fused silica showed no radiation-induced darkening; undoped cover glass lost 3.85 and 3.60 percent.
    effect: After the 1 MeV electron dose, synthetic fused silica showed no radiation-induced change in spectral transmission. Undoped cover glass (Micro-Sheet) lost 3.85 and 3.60 percent of wideband transmission and turned brownish. Glass doped with 1.5 percent ceria was far less affected and was judged comparable to fused silica.
    rating: low
    conditions:
      dose: 1 MeV electrons, 1e15 e/cm2
      samples: coated and uncoated synthetic fused silica, and undoped Micro-Sheet
      measure: wideband and spectral transmission before and after irradiation
    source: ntrs-d7245
    where: Results, spectral transmission (Fig. 3) and wideband transmission (Table II); Concluding Remarks
risks:
  hazards:
    - text: PubChem's silicon dioxide record (CID 24261) reports that most company notifications do not meet GHS hazard criteria (7,724 of 9,127). Other entries carry skin, eye and respiratory irritation codes (H315, H319, H335). The record covers silicon dioxide in general, not fused silica alone, so it is a dust caution rather than a fused-silica classification.
      ghs: []
      source: pubchem-sio2
      where: Safety and Hazards, GHS Classification (CID 24261)
  failure_risks:
    - mode: Brittle fracture
      trigger: Mechanical shock or point load on a thin glass
      consequence: The fetched pages give no fracture-toughness value, so the severity could not be quantified from them.
      severity: moderate
      source: pmoptics-fused-silica
      where: Mechanical properties not quantified on this page; see gaps
    - mode: Fracture of a damaged window pane under tensile stress
      trigger: Hypervelocity or low-velocity impacts on a pane, then tensile stress from the mount or pressure
      consequence: Damage sites lower the residual strength, and NASA reports that a damaged pane can fail suddenly under tensile stress. A vehicle was never lost to window failure during the Shuttle program.
      severity: moderate
      source: ntrs-cramer
      where: Introduction, paragraphs on impact damage and failure
  side_effects: []
  handling:
    - text: Inspect the glass surfaces carefully before every active cycle, because damage sites shorten the service life of a pane. The Shuttle window crew examined panes after each flight.
      source: ntrs-cramer
      where: Introduction, paragraphs on damage inspection and maintenance
  mitigations:
    - text: Mount the panes so they carry minimal mechanical stress, enough only to seal the glass to the vehicle.
      source: ntrs-cramer
      where: Introduction, paragraph on window mounts
uses:
  - application: optics-and-cameras
    device: Optical window, lens and mirror substrate
    example: Transparency and refractive index are tabulated across the spectrum, from 0.2 µm to 3.7 µm on the page.
    source: pmoptics-fused-silica
    where: Refractive index table
  - application: solar-arrays
    device: Solar-cell cover glass
    example: Synthetic fused silica is the cover used where the radiation environment would discolour cheaper glass. In a 1 MeV electron test it showed no radiation-induced degradation.
    source: ntrs-d7245
    where: Introduction; Results, spectral transmission (Fig. 3)
  - application: structures
    device: Crewed spacecraft windows (Space Shuttle forward windows)
    example: NASA calls fused silica the primary material of choice for crewed spacecraft windows. The Shuttle outer panes were made from Corning 7940 or 7989 fused silica glass.
    source: ntrs-cramer
    where: Introduction; footnote on pane manufacture
supply:
  - subject: 'Silicon (feedstock for fused silica: quartz sand or quartzite)'
    abundance: 'USGS: world resources of silicon are abundant and, in most producing countries, adequate for many decades. The source is silica in natural forms such as quartzite.'
    producers:
      - country: China
        share_percent: 80
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (silicon added in the 2025 update)
        listed: true
    recycling: 'USGS silicon chapter: recycling ''Insignificant''.'
    substitutes: []
    source: usgs-mcs2026-silicon
    where: 'World Resources and Events, Trends, and Issues (China ''almost 80%'' of estimated global silicon-materials production in 2025, recorded here as 80). The production figure is for ferrosilicon and silicon metal, not for silica glass. Critical list: Final 2025 List, Critical Minerals paragraph.'
documents:
  - title: 'PMOptics: Fused Silica property page'
    type: database
    url: https://www.pmoptics.com/Fused_Silica.html
  - title: 'MakeItFrom: Fused Silica (Fused Quartz) material properties'
    type: database
    url: https://www.makeitfrom.com/material-properties/Fused-Silica-Fused-Quartz
  - title: 'SPTS refractive index database: SiO2'
    type: database
    url: https://www.spts.com/products/instruments/refractive-index-database/sio2
  - title: Corning HPFS 7980 data sheet (third-party copy hosted by Valley Design)
    type: datasheet
    url: https://valleydesign.com/Datasheets/Corning-Fused-Silica-7980.pdf
  - title: 'USGS Mineral Commodity Summaries, February 2026: Silicon'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-silicon.pdf
  - title: 'NASA TN D-7245: Effect of 1 MeV electrons on ceria-doped solar cell cover glass'
    type: report
    url: https://ntrs.nasa.gov/api/citations/19730015355/downloads/19730015355.pdf
  - title: 'Cramer, Hayward and Yost: Quantification of residual stress from photonic signatures of fused silica (NASA NTRS 20160005098)'
    type: paper
    url: https://ntrs.nasa.gov/api/citations/20160005098/downloads/20160005098.pdf
  - title: 'PubChem: Silicon dioxide (CID 24261), Safety and Hazards'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/24261
  - title: 'Wikipedia: Fused quartz (manufacturing types and composition)'
    type: database
    url: https://en.wikipedia.org/wiki/Fused_quartz
gaps:
  - The official Corning HPFS 7980 PDF returned HTTP 403. The Corning values come from a third-party copy of the Corning sheet (Valley Design), which is cited as such.
  - 'Heraeus Suprasil data were not recorded: the Heraeus Data and Properties PDF returned HTML, and the Suprasil sheet found by search was not opened in this run.'
  - Edmund Optics fused silica page returned HTTP 403 and was not read. Thorlabs pages were not found by search.
  - NASA's Space Shuttle window page (spaceflight.nasa.gov) returned HTTP 403. The Shuttle window statements come from NASA's Cramer et al. paper (NTRS 20160005098) instead.
  - Full transmission curve not read. The Corning sheet certifies internal transmittance at 185 nm only; no transmission range from a fetched table is recorded beyond that.
  - Bubble and striae grades, OH content and stress birefringence are not recorded, although the Corning sheet prints them for its grades.
  - 'Fracture toughness: no value read. The Knoop hardness on the Corning sheet is not recorded here.'
  - Devitrification (crystallisation at high temperature) was not looked up.
  - Outgassing (ASTM E595) and atomic oxygen behaviour of fused silica were not looked up.
  - 'Hazard data specific to fused silica: no fused-silica safety data sheet was read. The PubChem record covers silicon dioxide in general.'
  - Quartz (silica sand) production shares were not read; the supply entry uses the USGS silicon chapter only.
review:
  status: draft
  method: assistant
  checked_values: 15
  unreachable: 4
  caveats: 3
  note: Values were read by an AI assistant on 2026-10-19 from two property pages, one refractive index database page, and in the deepen pass a third-party copy of the Corning HPFS 7980 sheet, USGS Silicon (2026), NASA TN D-7245, NASA NTRS 20160005098 and the PubChem silicon dioxide record. Official Corning, Heraeus, Edmund and NASA Shuttle pages could not be read. Values from the property pages carry no stated test conditions for most entries.
updated: '2026-10-19'
license: CC-BY-4.0
story:
  risk_groups:
    - title: For people
      lead: The sources describe fused silica as a stable, inert oxide. Its PubChem record is mostly unclassified, but it carries irritation codes on some entries, so dust is the one caution.
      level: 1
      verdict: Dust caution only
      points:
        - label: Substance
          line: PubChem's silicon dioxide record is mostly unclassified, and some entries carry skin, eye and respiratory irritation codes. No fused-silica safety data sheet was read.
    - title: If it fails
      lead: Fused silica is brittle. A damaged pane can fail suddenly under tensile stress, but in a 1 MeV electron test it showed no radiation darkening.
      points:
        - label: Brittleness
          line: The glass is stiff, with a Young's modulus of 72.7 GPa and a Poisson's ratio of 0.17, but no fracture value was read.
    - title: Handling and storage
      points:
        - label: Thermal limit
          line: The page lists a mechanical maximum of 1080 °C and a softening point of 1683 °C.
  recipe:
    line: 'Fused silica is silicon dioxide, SiO2, with no other ingredients in the pure grades. Each formula unit has one silicon atom and two oxygen atoms. Synthetic fused silica is made by flame hydrolysis: silicon tetrachloride is burned in a hydrogen-oxygen flame, or in a water-vapour-free plasma flame. Natural fused quartz is made by melting quartz sand or crystal at a very high temperature, either electrically or in a gas-oxygen flame. Wikipedia names aluminium and titanium as the dominant impurities, and says UV-grade synthetic fused silica has very low metallic impurity content.'
    parts:
      - name: Silicon
        symbol: Si
        atoms: 1
        atomic_weight: 28.085
        role: The network former. Silicon and oxygen make up the whole amorphous network, with no crystal lattice.
      - name: Oxygen
        symbol: O
        atoms: 2
        atomic_weight: 15.999
        role: Completes the composition. Pure fused silica contains only silicon and oxygen, although commercial grades carry trace impurities.
  why: Fused silica is a glass of pure silicon dioxide. It has a very small thermal expansion, 5.5e-7 m/(m·°C) between 20 and 320 °C, and it transmits light from the ultraviolet into the near infrared. Those two traits make it a common choice for windows, lenses, mirror substrates and solar-cell cover glass.
  uses:
    - where: Solar-cell cover glass
      line: In a 1 MeV electron test, synthetic fused silica showed no radiation-induced change in transmission. Undoped cover glass lost 3.85 and 3.60 percent, so fused silica is the cover of choice where discolouring would cost power.
    - where: Crewed spacecraft windows
      line: NASA calls fused silica the primary material of choice for crewed spacecraft windows. The Space Shuttle outer panes were made from Corning 7940 or 7989 fused silica glass.
  can_do:
    - label: Stay dimensionally stable
      value: 5.5e-7 m/(m·°C)
      benchmark: cte
      line: The thermal expansion is 5.5e-7 m/(m·°C) between 20 and 320 °C, which is why it suits precision optics.
    - label: Bend light cleanly
      value: 1.45704 at 632.8 nm
      benchmark: refractive_index
      line: The refractive index at 632.8 nm is 1.45704 for a typical sample, with an extinction coefficient of 0.
  compare: Fused silica has a density of 2.2 g/cm3 and a thermal conductivity of 1.4 W/(m·°C) in the PMOptics table. The Corning HPFS 7980 sheet gives 1.3 W/m K at 25 °C, so the conductivity figure differs between sources. Neither was compared with other glasses in this run.
  compare_rows:
    - scope: material
      label: Thermal expansion
      benchmark: cte
    - scope: material
      label: Density
      benchmark: density
    - scope: material
      label: Thermal conductivity
      benchmark: thermal_conductivity
  handling:
    - 'Treat it as brittle: the fetched pages give stiffness but no fracture value.'
  good_for:
    - 'Optics that must hold shape over temperature: thermal expansion of 5.5e-7 m/(m·°C) between 20 and 320 °C.'
  watch_out:
    - 'Brittle: no fracture toughness was read in this run.'
    - No radiation-darkening number from NASA was read, so a cover glass's darkening over a mission is not quantified here.
  verdict: Fused silica is a stable, transparent glass for optics, with a thermal expansion of 5.5e-7 m/(m·°C) and a refractive index of 1.45704 at 632.8 nm. This profile rests on two property pages and a refractive index database; the Corning, Heraeus and NASA sources were not read.
sources:
  pmoptics-fused-silica:
    title: Fused Silica, PMOptics property page (Fused Silica Properties table and typical refractive index table)
    url: https://www.pmoptics.com/Fused_Silica.html
    kind: web
    license: Web page (cited, not reproduced)
  makeitfrom-fused-silica:
    title: Fused Silica (Fused Quartz), MakeItFrom material properties
    url: https://www.makeitfrom.com/material-properties/Fused-Silica-Fused-Quartz
    kind: web
    license: Web page (cited, not reproduced)
  spts-sio2:
    title: Refractive Index of SiO2, Fused Silica, SPTS refractive index database
    url: https://www.spts.com/products/instruments/refractive-index-database/sio2
    kind: database
    license: Web page (cited, not reproduced)
  corning-7980-valleydesign:
    title: Corning HPFS 7980 Standard Grade fused silica data sheet (third-party copy hosted by Valley Design)
    url: https://valleydesign.com/Datasheets/Corning-Fused-Silica-7980.pdf
    kind: datasheet
    license: Manufacturer data sheet (cited, not reproduced)
  usgs-mcs2026-silicon:
    title: 'USGS Mineral Commodity Summaries, February 2026: Silicon'
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-silicon.pdf
    kind: report
    license: US government publication (cited, not reproduced)
  ntrs-d7245:
    title: 'NASA TN D-7245: Effect of 1 MeV electrons on ceria-doped solar cell cover glass (Haynes, 1973)'
    url: https://ntrs.nasa.gov/api/citations/19730015355/downloads/19730015355.pdf
    kind: report
    license: NASA public document (cited, not reproduced)
  ntrs-cramer:
    title: 'Cramer, Hayward and Yost: Quantification of residual stress from photonic signatures of fused silica (NASA NTRS 20160005098)'
    url: https://ntrs.nasa.gov/api/citations/20160005098/downloads/20160005098.pdf
    kind: paper
    license: NASA public document (cited, not reproduced)
  pubchem-sio2:
    title: 'PubChem: Silicon dioxide (CID 24261), Safety and Hazards'
    url: https://pubchem.ncbi.nlm.nih.gov/compound/24261
    kind: database
    license: Public database (cited, not reproduced)
  wiki-fused-quartz:
    title: 'Wikipedia: Fused quartz (manufacturing types and composition)'
    url: https://en.wikipedia.org/wiki/Fused_quartz
    kind: web
    license: CC BY-SA (cited, not reproduced)