Fused silica SiO2 glass
SiO2, amorphous silicon dioxide (fused silica, fused quartz)
Fused silica, also called fused quartz, is amorphous silicon dioxide made by melting pure silica, with no crystal structure.
Evidence level
2 of 5
Lab-measured
- 0Predicted only. No one has made it, or no measurement exists.
- 1Calculated. Only calculated or predicted values from sources.
- 2Lab-measured. Measured properties with their conditions stated.
- 3Space-relevant tests. Measured in conditions relevant to space, such as vacuum or atomic oxygen.
- 4Ground-qualified. Qualified for an application on the ground.
- 5Flown or field-proven. Flight or field results exist.
Stay dimensionally stable
5.5e-7 m/(m·°C)
Bend light cleanly
1.45704 at 632.8 nm
Recipe, share of the weight
- Si 46.7%Silicon
- O 53.3%Oxygen
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
Risk at a glance
- People Low. Dust caution only
- If it fails Moderate. Brittle fracture
- Corrosion Severe. Hydrofluoric acid is the fastest etchant in the table: 0.230 mg/cm2 lost in 20 minutes.
Quick facts: SiO2 glass
| Property | Value | Basis |
|---|---|---|
| Density | 2.2 g/cm³ | 1 sourced value |
| Young's modulus | 72.7 GPa | 1 sourced value |
| Thermal conductivity | 1.3 to 1.4 W/(m·K) | 2 sourced values across conditions |
| Thermal expansion (CTE) | 0.55 ppm/K | 1 sourced value |
| Specific heat | 720 J/(kg·K) | 1 sourced value |
| Maximum service temperature | 1,080 °C | 1 sourced value |
What is the density of Fused silica (SiO2 glass)?
Fused silica (SiO2 glass) has a density of 2.2 g/cm³. The source and test conditions are listed in the properties table on this page.
What is the thermal conductivity of Fused silica (SiO2 glass)?
Fused silica (SiO2 glass) has a thermal conductivity of 1.3 to 1.4 W/(m·K). The range covers 2 sourced values across the tempers, forms and test conditions the sources report; room-temperature values are used where a source states a temperature.
What is the coefficient of thermal expansion of Fused silica (SiO2 glass)?
Fused silica (SiO2 glass) has a coefficient of thermal expansion of 0.55 ppm/K. The source and test conditions are listed in the properties table on this page.
What is the Young's modulus of Fused silica (SiO2 glass)?
Fused silica (SiO2 glass) has a Young's modulus of 72.7 GPa. The source and test conditions are listed in the properties table on this page.
What is the maximum service temperature of Fused silica (SiO2 glass)?
Fused silica (SiO2 glass) has a maximum service temperature of 1,080 °C. The source and test conditions are listed in the properties table on this page.
What is Fused silica (SiO2 glass) used for?
Uses recorded in the sources include Optical window, lens and mirror substrate; Solar-cell cover glass; Crewed spacecraft windows (Space Shuttle forward windows).
Why it exists
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.
Where it's used
Solar-cell cover glass
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.
Crewed spacecraft windows
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.
Recipe
SiO2, amorphous silicon dioxide (fused silica, fused quartz)
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.
| Ingredient | Atoms per unit | Share of the weight | What it does |
|---|---|---|---|
| Silicon Si | 1 | 46.7% | The network former. Silicon and oxygen make up the whole amorphous network, with no crystal lattice. |
| Oxygen O | 2 | 53.3% | Completes the composition. Pure fused silica contains only silicon and oxygen, although commercial grades carry trace impurities. |
Weight shares are calculated from standard atomic weights.
What it can do
Stay dimensionally stable
5.5e-7 m/(m·°C)
measured
The thermal expansion is 5.5e-7 m/(m·°C) between 20 and 320 °C, which is why it suits precision optics.
Bend light cleanly
1.45704 at 632.8 nm
measured
The refractive index at 632.8 nm is 1.45704 for a typical sample, with an extinction coefficient of 0.
How it compares
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.
The same measurements for each material, so you can compare them. Each row names the key condition under the value; the full conditions and methods are in the numbered notes under Technical details. Compare every grade in the family.
| Measurement | SiO2 glass |
|---|---|
| Thermal behavior and safety | |
| Thermal conductivity, fused silicaValue printed on a property page | 1.4 W/(m·°C) |
| Thermal conductivity, HPFS 7980 standard grade fused silica | 1.3 W/m K2 |
| Specific heat capacity, fused silicaValue printed on a property page | 720 J/(kg·K) |
| Physical and electrical | |
| Density, fused silica | 2.2 g/cm³1 |
| Other measurements | |
| Coefficient of thermal expansion, fused silicaValue printed on a property page | 5.5×10^-7 m/(m·°C) |
| Maximum temperature, mechanical, fused silica | 1080 °C3 |
| Softening point, fused silicaValue printed on a property page | 1683 °C |
| Annealing point, fused silicaValue printed on a property page | 1215 °C |
| Strain point, fused silicaValue printed on a property page | 1120 °C |
| Young's modulus, fused silicaValue printed on a property page | 72.7 GPa |
| Poisson's ratio, fused silicaValue printed on a property page | 0.17 dimensionless |
| Abbe constant, fused silica | 67.6 dimensionless4 |
| Refractive index, typical synthetic fused silica at 633 nm | 1.457 dimensionless5 |
| Refractive index, typical synthetic fused silica at 1064 nm | 1.45 dimensionless6 |
| Refractive index, typical fused silica at 632.8 nmValue stated on a refractive index database page | 1.457 dimensionless7 |
Why choose it, and why not
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 for
- 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.
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.
Technical details
For scientists and researchers. Everything above comes from the record below: every number with its method, its conditions and its source.
Notes
The method, full conditions and any caveat for the numbered rows above.
| # | Measurement | Method | Conditions | Caveat |
|---|---|---|---|---|
| 1 | Density, fused silica | Value printed on a manufacturer-style property page | temperature not stated | — |
| 2 | Thermal conductivity, HPFS 7980 standard grade fused silica | Value printed on the Corning HPFS 7980 data sheet, Mechanical and Thermal Properties | temperature 25 °Cbasis unless otherwise stated, values on the sheet are at 25 °C | — |
| 3 | Maximum temperature, mechanical, fused silica | Value printed on a property page, labelled Maximum Temperature Mechanical | basis mechanical limit as labelled on the page | — |
| 4 | Abbe constant, fused silica | Value printed on a property page labelled Abbe constant | wavelengths not stated | — |
| 5 | Refractive index, typical synthetic fused silica at 633 nm | Value listed in a wavelength-indexed table on a property page | wavelength 0.633 µmsample typical synthetic fused silicatemperature not stated | — |
| 6 | Refractive index, typical synthetic fused silica at 1064 nm | Value listed in a wavelength-indexed table on a property page | wavelength 1.064 µmsample typical synthetic fused silicatemperature not stated | — |
| 7 | Refractive index, typical fused silica at 632.8 nm | — | wavelength 632.8 nmextinction coefficient 0sample typical sample of SiO2temperature not stated | — |
Corrosion and compatibility
What happens when it meets other materials and environments.
| Environment | Concern | What happens |
|---|---|---|
| 10% hydrofluoric acid by weight, 25 °C, 20 minutes | severe | Hydrofluoric acid is the fastest etchant in the table: 0.230 mg/cm2 lost in 20 minutes.1 |
| 5% sodium hydroxide, 95 °C, 6 hours | moderate | Hot alkali removes the most glass of any solution in the table: 0.453 mg/cm2 in 6 hours.2 |
| 5% hydrochloric acid, 0.02 N sulfuric acid and deionized water, 95 °C, 24 hours | low | Acids and water barely attack the glass: losses below 0.010 mg/cm2 for the acids, 0.015 mg/cm2 for water.3 |
| 1 MeV electron irradiation to 1e15 electrons/cm2, a space radiation test of solar-cell cover glass | low | Synthetic fused silica showed no radiation-induced darkening; undoped cover glass lost 3.85 and 3.60 percent.4 |
| # | Environment | Details | Test conditions |
|---|---|---|---|
| 1 | 10% hydrofluoric acid by weight, 25 °C, 20 minutes | 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. | test Chemical durability table, 25 °C, weight loss in mg/cm2caveat row order read from the printed table; check against the printed sheet |
| 2 | 5% sodium hydroxide, 95 °C, 6 hours | 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. | test 95 °C immersion, weight loss in mg/cm2caveat row order read from the printed table; check against the printed sheet |
| 3 | 5% hydrochloric acid, 0.02 N sulfuric acid and deionized water, 95 °C, 24 hours | 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. | test 95 °C immersion, weight loss in mg/cm2caveat row order read from the printed table; check against the printed sheet |
| 4 | 1 MeV electron irradiation to 1e15 electrons/cm2, a space radiation test of solar-cell cover glass | 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. | dose 1 MeV electrons, 1e15 e/cm2samples coated and uncoated synthetic fused silica, and undoped Micro-Sheetmeasure wideband and spectral transmission before and after irradiation |
Risks and side effects
Hazards to people, what happens when a cell overheats, and how the material is handled and stored.
For people
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.
- Substance
- 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.
If it fails
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.
- Brittleness
- 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.
Handling and storage
- Thermal limit
- The page lists a mechanical maximum of 1080 °C and a softening point of 1683 °C.
Test details
The original wording and numbers from the sources, for readers who want them.
Failure risks
| Failure | Trigger and consequence |
|---|---|
| Brittle fracturemoderate severity | Mechanical shock or point load on a thin glassThe fetched pages give no fracture-toughness value, so the severity could not be quantified from them. |
| Fracture of a damaged window pane under tensile stressmoderate severity | Hypervelocity or low-velocity impacts on a pane, then tensile stress from the mount or pressureDamage 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. |
Handling and storage
- 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.
Mitigations
- Mount the panes so they carry minimal mechanical stress, enough only to seal the glass to the vehicle.
Supply and geography
How common the raw materials are and where they come from.
Silicon (feedstock for fused silica: quartz sand or quartzite)
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.
- Top producers (2025)
- China 80%
- Critical mineral lists
- US: listed
- Recycling
- USGS silicon chapter: recycling 'Insignificant'.
Documents
Datasheets, safety data sheets, papers and standards you can open.
Full record
The complete spore, as stored. Free to reuse under CC-BY-4.0. Images keep the licence shown with each one.
Show the full YAML
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)
References
Every number above carries a reference number. Click one to see the source and where in it the value comes from.