Sapphire (single-crystal alpha-alumina) Al2O3

spore: profile
id: sapphire
spore_version: 0.2
family: optical-crystals
name: Sapphire (single-crystal alpha-alumina)
abbreviation: Al2O3
role: optical window, substrate and insulator crystal
category: glasses-optics
type: optical-crystals
summary: |
  Sapphire is alpha-alumina (Al2O3) grown as one crystal and then cut, ground and polished. Crystran gives a transmission range of 0.17 to 5.5 µm for its optical grade. Kyocera grows it by edge-defined film-fed growth and gives a density of 3.97 g/cm3, a Vickers hardness of 22.5 GPa and a flexural strength of 690 MPa. A 1981 NASA review ranked sapphire first of four optical materials for radiation resistance, and its simulated space exposure gave a solar absorptance rise of only 0.009 after 503 hours. Suppliers' numbers differ by orientation and by source, so each value is kept with its own source.
best_for: Hard, radiation-tolerant optical windows and substrates that must pass light from the ultraviolet to the near infrared (NASA 1981 ranked sapphire first for radiation resistance)
weakest_at: 'Brittle fracture and edge chipping: flexural strength is 480 to 895 MPa in one supplier''s sheet and 690 MPa in another, and Crystran''s safety sheet warns about chipping and sharp edges'
identity:
  formula: Al2O3
  cas: 1344-28-1
  crystal_system: trigonal (rhombohedral lattice); Kyocera describes the hexagonal axes a = 4.763 Å and c = 13.003 Å
  space_group: R-3c
  source: crystran-sapphire
  where: Product Data table, Class/Structure row (Trigonal (hex), R3c) and Molecular Weight 101.96; R-3c from the Valley Design crystal system row; CAS 1344-28-1 from crystran-msds section 3.1
tags:
  environments: []
  stresses:
    - total-radiation-dose
  applications:
    - electronics-and-chips
    - optics-and-cameras
properties:
  - benchmark: density
    label: Density, optical grade
    value: 3.97
    unit: g/cm3
    scope: material
    conditions:
      form: single crystal, optical grade
      temperature: not stated on the page
    method: Value printed on a manufacturer product data page
    status: ground
    source: crystran-sapphire
    where: Product Data table, Density row
  - benchmark: density
    label: Density (20 °C)
    value: 3.98
    unit: g/cm3
    scope: material
    conditions:
      form: single crystal, wafer or substrate
      temperature: 20 °C
    method: Typical value from a supplier property page
    status: ground
    source: valley-sapphire
    where: Sapphire properties table, Density (20 °C) row
  - benchmark: melting_point
    label: Melting point, range
    value: 2040
    value_high: 2054
    bound: range
    unit: °C
    scope: material
    conditions:
      form: single crystal
    method: Range printed on a supplier property page
    status: ground
    note: Kyocera prints 2,053 °C and the Crystran safety sheet prints 2053 °C; the Crystran product data page prints 2040 °C.
    source: valley-sapphire
    where: Sapphire properties table, Melting point row (printed as about 2,040 to 2,054 °C)
  - benchmark: melting_point
    label: Melting point, Kyocera sheet
    value: 2053
    unit: °C
    scope: material
    conditions:
      form: single crystal, Kyocera EFG product
    method: Value printed in a manufacturer characteristics table
    status: ground
    source: kyocera-sapphire
    where: Characteristics table, Thermal Characteristics, Melting Point row
  - benchmark: boiling_point
    label: Boiling point at 760 mmHg
    value: 2977
    unit: °C
    scope: material
    conditions:
      pressure: 760 mmHg
    method: Value printed in a safety data sheet
    status: ground
    source: crystran-msds
    where: Section 9.1, Boiling point row
  - benchmark: vickers_hardness
    label: Vickers hardness, Kyocera sheet
    value: 22.5
    unit: GPa
    scope: material
    conditions:
      test: HV1, load 9.807 N
      form: single crystal (EFG)
    method: Typical value from a manufacturer characteristics table
    status: ground
    note: The sheet says each crystal orientation has different characteristics and that the values are representative.
    source: kyocera-sapphire
    where: Mechanical characteristics table, Vickers Hardness row
  - benchmark: mohs_hardness
    label: Mohs hardness
    value: 9
    unit: '-'
    scope: material
    conditions:
      scale: Mohs
    method: Value quoted in a NASA report
    status: ground
    source: nasa1982
    where: Section 3.1, reason 1
  - benchmark: flexural_strength
    label: Flexural strength, Kyocera sheet
    value: 690
    unit: MPa
    scope: material
    conditions:
      form: single crystal (EFG)
      temperature: not stated
      orientation: not stated
    method: Typical value from a manufacturer characteristics table
    status: ground
    source: kyocera-sapphire
    where: Mechanical characteristics table, Flexural Strength row
  - benchmark: flexural_strength
    label: Flexural strength, range across suppliers
    value: 480
    value_high: 895
    bound: range
    unit: MPa
    scope: material
    conditions:
      form: single crystal substrate or wafer
      temperature: not stated
    method: Range printed on a supplier property page
    status: ground
    note: The same page lists a modulus of rupture of 350 to 690 MPa, which is a different test.
    source: valley-sapphire
    where: Sapphire properties table, Flexural strength row
  - benchmark: ultimate_tensile_strength
    label: Tensile strength of a 0.25 mm filament
    value: 2250
    unit: MPa
    scope: material
    conditions:
      form: 0.25 mm diameter filament, not bulk
      temperature: 25 °C
    method: Value printed in a manufacturer characteristics table
    status: ground
    note: Filament value, not for bulk parts. The bulk value from a supplier page is 275 to 400 MPa.
    source: kyocera-sapphire
    where: Mechanical characteristics table, Tensile Strength row
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, bulk range
    value: 275
    value_high: 400
    bound: range
    unit: MPa
    scope: material
    conditions:
      form: bulk single crystal
      temperature: not stated
    method: Range printed on a supplier property page
    status: ground
    source: valley-sapphire
    where: Sapphire properties table, Tensile strength row
  - benchmark: compressive_strength
    label: Compressive strength
    value: 2940
    unit: MPa
    scope: material
    conditions:
      form: single crystal (EFG)
      temperature: not stated
    method: Value printed in a manufacturer characteristics table
    status: ground
    source: kyocera-sapphire
    where: Mechanical characteristics table, Compressive Strength row
  - benchmark: apparent_elastic_limit
    label: Apparent elastic limit
    value: 300
    unit: MPa
    scope: material
    conditions:
      form: single crystal, optical grade
    method: Value printed on a manufacturer product data page
    status: ground
    source: crystran-sapphire
    where: Product Data table, Apparent Elastic Limit row
  - benchmark: elastic_modulus
    label: Young's modulus, Kyocera sheet
    value: 470
    unit: GPa
    scope: material
    conditions:
      form: single crystal (EFG)
      temperature: not stated
    method: Value printed in a manufacturer characteristics table
    status: ground
    source: kyocera-sapphire
    where: Mechanical characteristics table, Young's Modulus row
  - benchmark: elastic_modulus
    label: Young's modulus, Crystran product data
    value: 335
    unit: GPa
    scope: material
    conditions:
      form: single crystal, optical grade
      temperature: not stated
    method: Value printed on a manufacturer product data page
    status: ground
    source: crystran-sapphire
    where: Product Data table, Young's Modulus (E) row
  - benchmark: elastic_modulus
    label: Young's modulus, range across suppliers
    value: 335
    value_high: 435
    bound: range
    unit: GPa
    scope: material
    conditions:
      form: single crystal substrate or wafer
    method: Range printed on a supplier property page, with a typical value of about 345 GPa
    status: ground
    source: valley-sapphire
    where: Sapphire properties table, Young's modulus row
  - benchmark: shear_modulus
    label: Shear modulus
    value: 148.1
    unit: GPa
    scope: material
    conditions:
      form: single crystal, optical grade
    method: Value printed on a manufacturer product data page
    status: ground
    source: crystran-sapphire
    where: Product Data table, Shear Modulus (G) row
  - benchmark: bulk_modulus
    label: Bulk modulus
    value: 240
    unit: GPa
    scope: material
    conditions:
      form: single crystal, optical grade
    method: Value printed on a manufacturer product data page
    status: ground
    source: crystran-sapphire
    where: Product Data table, Bulk Modulus (K) row
  - benchmark: poissons_ratio
    label: Poisson's ratio, range
    value: 0.18
    value_high: 0.29
    bound: range
    unit: '-'
    scope: material
    conditions:
      form: single crystal (EFG)
    method: Range printed in a manufacturer characteristics table
    status: ground
    source: kyocera-sapphire
    where: Mechanical characteristics table, Poisson's Ratio row
  - benchmark: poissons_ratio
    label: Poisson's ratio, Crystran
    value: 0.25
    unit: '-'
    scope: material
    conditions:
      form: single crystal, optical grade
    method: Value printed on a manufacturer product data page
    status: ground
    source: crystran-sapphire
    where: Product Data table, Poisson Ratio row
  - benchmark: thermal_conductivity
    label: Thermal conductivity at 20 °C, Kyocera sheet
    value: 42
    unit: W/(m·K)
    scope: material
    conditions:
      temperature: 20 °C
      form: single crystal (EFG)
    method: Value printed in a manufacturer characteristics table
    status: ground
    source: kyocera-sapphire
    where: Thermal characteristics table, Thermal Conductivity row
  - benchmark: thermal_conductivity
    label: Thermal conductivity at 300 K, Crystran
    value: 27.21
    unit: W/(m·K)
    scope: material
    conditions:
      temperature: 300 K
      form: single crystal, optical grade
    method: Value printed on a manufacturer product data page
    status: ground
    source: crystran-sapphire
    where: Product Data table, Thermal Conductivity row
  - benchmark: thermal_conductivity
    label: Thermal conductivity, perpendicular to c axis
    value: 23
    unit: W/(m·K)
    scope: material
    conditions:
      temperature: 23 °C
      orientation: perpendicular to the c axis
    method: Value printed on a supplier property page
    status: ground
    note: The same page gives 16.8 W/(m·K) at 77 °C and says conductivity falls steeply as temperature rises.
    source: valley-sapphire
    where: Thermal properties, Thermal conductivity perpendicular to c axis row (23°C / 77°C)
  - benchmark: thermal_conductivity
    label: Thermal conductivity, parallel to c axis
    value: 25.8
    unit: W/(m·K)
    scope: material
    conditions:
      temperature: 24 °C
      orientation: parallel to the c axis
    method: Value printed on a supplier property page
    status: ground
    note: The same page gives 17.35 W/(m·K) at 70 °C.
    source: valley-sapphire
    where: Thermal properties, Thermal conductivity parallel to c axis row (24°C / 70°C)
  - benchmark: cte
    label: Thermal expansion, parallel to c axis, 40 to 400 °C
    value: 7.7
    unit: ppm/K
    scope: material
    conditions:
      temperature_range: 40 to 400 °C
      orientation: parallel to the c axis
    method: Value printed in a manufacturer characteristics table
    status: ground
    source: kyocera-sapphire
    where: Thermal characteristics table, Coefficient of Linear Thermal Expansion row
  - benchmark: cte
    label: Thermal expansion, perpendicular to c axis, 40 to 400 °C
    value: 7
    unit: ppm/K
    scope: material
    conditions:
      temperature_range: 40 to 400 °C
      orientation: perpendicular to the c axis
    method: Value printed in a manufacturer characteristics table
    status: ground
    source: kyocera-sapphire
    where: Thermal characteristics table, Coefficient of Linear Thermal Expansion row
  - benchmark: cte
    label: Thermal expansion, parallel to c axis, Crystran
    value: 5.6
    unit: ppm/K
    scope: material
    conditions:
      temperature: not stated
      orientation: parallel to the c axis
    method: Value printed on a manufacturer product data page
    status: ground
    note: Crystran notes that manufacturers disagree on thermal expansion figures.
    source: crystran-sapphire
    where: Product Data table, Thermal Expansion row
  - benchmark: specific_heat
    label: Specific heat, Kyocera sheet
    value: 0.75
    unit: J/(g·K)
    scope: material
    conditions:
      temperature: not stated
    method: Value printed in a manufacturer characteristics table
    status: ground
    source: kyocera-sapphire
    where: Thermal characteristics table, Specific Heat Capacity row
  - benchmark: specific_heat
    label: Specific heat at 293 K, Crystran
    value: 763
    unit: J/(kg·K)
    scope: material
    conditions:
      temperature: 293 K
    method: Value printed on a manufacturer product data page
    status: ground
    source: crystran-sapphire
    where: Product Data table, Specific Heat Capacity row
  - benchmark: dielectric_constant
    label: Dielectric constant, parallel to c axis, 1 MHz
    value: 11.5
    unit: '-'
    scope: material
    conditions:
      frequency: 1 MHz
      orientation: parallel to the c axis
    method: Value printed in a manufacturer characteristics table
    status: ground
    source: kyocera-sapphire
    where: Electrical characteristics table, Dielectric Constant row (C parallel to C axis)
  - benchmark: dielectric_constant
    label: Dielectric constant, perpendicular to c axis, 1 MHz
    value: 9.3
    unit: '-'
    scope: material
    conditions:
      frequency: 1 MHz
      orientation: perpendicular to the c axis
    method: Value printed in a manufacturer characteristics table
    status: ground
    source: kyocera-sapphire
    where: Electrical characteristics table, Dielectric Constant row (C perpendicular to C axis)
  - benchmark: dissipation_factor
    label: Dielectric loss tangent, maximum
    value: 0.0001
    bound: upper
    unit: '-'
    scope: material
    conditions:
      frequency: 1 MHz
      note: sheet prints the loss angle as less than 1 x 10^-4 at 1 MHz
    method: Maximum printed in a manufacturer characteristics table
    status: ground
    source: kyocera-sapphire
    where: Electrical characteristics table, Dielectric Loss Tangent row and Dielectric Loss Angle row
  - benchmark: refractive_index
    label: Refractive index, ordinary ray at 589 nm
    value: 1.768
    unit: '-'
    scope: material
    conditions:
      wavelength: 589 nm
      ray: ordinary (No)
    method: Value printed in a manufacturer characteristics table
    status: ground
    source: kyocera-sapphire
    where: Optical characteristics table, Index of Reflection row (No = 1.768)
  - benchmark: refractive_index
    label: Refractive index, extraordinary ray at 589 nm
    value: 1.76
    unit: '-'
    scope: material
    conditions:
      wavelength: 589 nm
      ray: extraordinary (Ne)
    method: Value printed in a manufacturer characteristics table
    status: ground
    source: kyocera-sapphire
    where: Optical characteristics table, Index of Reflection row (Ne = 1.760)
  - benchmark: refractive_index
    label: Refractive index, ordinary ray at 1.06 µm
    value: 1.75449
    unit: '-'
    scope: material
    conditions:
      wavelength: 1.06 µm
      ray: ordinary (No)
      source_note: Crystran cites the Palik handbook for this figure
    method: Value printed on a manufacturer product data page
    status: ground
    source: crystran-sapphire
    where: Product Data table, Refractive Index row (No = 1.75449; Ne = 1.74663)
  - benchmark: optical_transmission_range
    label: Transmission range
    value: 0.17
    value_high: 5.5
    bound: range
    unit: µm
    scope: material
    conditions:
      form: single crystal, optical grade
      note: Crystran notes the range depends on thickness and coating
    method: Range printed on a manufacturer product data page
    status: ground
    note: Not a canonical property name. Valley Design prints about 0.15 to 5.5 µm.
    source: crystran-sapphire
    where: Product Data table, Transmission Range row
  - benchmark: water_solubility
    label: Solubility in water at 20 °C
    value: 0.000098
    unit: g/100 g water
    scope: material
    conditions:
      temperature: 20 °C
    method: Value printed on a manufacturer product data page
    status: ground
    note: Not a canonical property name. The safety sheet calls sapphire practically insoluble in water.
    source: crystran-sapphire
    where: Product Data table, Solubility row (printed as 98 x 10-6 g per 100 g water)
  - benchmark: mohs_hardness
    label: Mohs hardness on a supplier page
    value: 9
    unit: '-'
    scope: material
    conditions:
      scale: Mohs
    method: Value printed on a supplier property page
    status: ground
    source: valley-sapphire
    where: Sapphire properties table, Hardness row (Mohs 9)
  - benchmark: solar_absorptance_change
    label: Change in solar absorptance after 503 h of simulated space exposure
    value: 0.009
    unit: '-'
    scope: material
    conditions:
      specimen: Union Carbide Czochralski sapphire, 25.4 mm diameter, 2 mm thick, one half coated with aluminium and then silica to make a mirror
      environment: simulated solar UV (one sun), vacuum UV at Lyman-alpha, 50 keV electrons at 1e9 e/cm2 s, 30 keV protons at 1e9 p/cm2 s, vacuum at least 5e-8 torr, 20 °C
      pre_exposure_value: '0.109'
      value_after_503_h: '0.118'
    method: Change in solar absorptance calculated from absolute reflectance spectra in a Boeing space-simulation test
    status: ground
    note: The report calls the sapphire change very small and close to the accuracy limit of the measurement.
    source: nasa1982
    where: Section 3.4, Table 2 (sapphire row, 503 h column)
  - benchmark: transmission_change_1064nm
    label: Change in 1064 nm transmission after electron exposure
    value: -0.5
    unit: '%'
    scope: material
    conditions:
      wavelength: 1064 nm
      specimen: Meller Optics bare sapphire, no antireflection coating, about 5.25 in diameter, 0.457 in thick
      exposure: 1 MeV electrons at 8 x 10^6 e/cm2 s for 5 hours at NASA Goddard Radiation Effects Facility
    method: Power measured before and after exposure with an integrating sphere and a 1064 nm filter
    status: ground
    note: Sample B. The change is within the stated measurement uncertainty; the sample A test used 10 keV electrons and gave a smaller change.
    source: nasa2010
    where: Table 1, Sample B row (84.0 to 83.6, delta -0.4 (-0.5%))
  - benchmark: wet_etch_rate
    label: Calibrated wet etch rate, direction-dependent, 3:1 sulfuric to phosphoric acid at 503 K
    value: 8
    value_high: 59
    bound: range
    unit: nm/min
    scope: material
    conditions:
      etchant: H2SO4:H3PO4 = 3:1 by volume
      temperature: 503 K
      basis: crystal directions used in the model, weights listed in the table
    method: Etch-rate parameters calibrated in a continuum level-set model against published etch experiments (Shen et al.); not a direct immersion measurement
    status: calculated
    note: The table lists six direction values (24, 59, 36, 57, 39 and 8 nm/min); the page does not name the directions in the lines read.
    source: toifl2021
    where: Table 2, model parameters for etchant mixture M3-1 at 503 K, etch rate R row
corrosion:
  - environment: Hot sulfuric and phosphoric acid mixture (H2SO4:H3PO4 = 3:1) at 503 K
    headline: Hot acid mixtures etch sapphire in a way that depends on crystal direction, which forms facets on the surface.
    effect: A continuum model of wet etching, calibrated on experiments in this mixture at 503 K, gives direction-dependent etch rates from 8 to 59 nm/min. The authors use the anisotropy to pattern sapphire substrates for LEDs.
    rating: moderate
    conditions:
      etchant: sulfuric and phosphoric acid mixtures
      temperature: 503 K
      basis: model-calibrated rates, not an immersion test
    source: toifl2021
    where: Abstract; Table 2 (M3-1 at 503 K)
  - environment: Water at 20 °C
    headline: Sapphire is practically insoluble in water.
    effect: Crystran lists a solubility of 98 x 10-6 g per 100 g of water at 20 °C, and its safety sheet calls the product practically insoluble. No corrosion in water was reported.
    rating: low
    conditions:
      temperature: 20 °C
      note: solubility figure, not a corrosion rate
    source: crystran-sapphire
    where: Product Data table, Solubility row; crystran-msds section 9.1
  - environment: Simulated space radiation in vacuum (solar UV, electrons and protons) for 503 h at 20 °C
    headline: Under simulated space radiation, sapphire showed very little change, and the report ranks it first of four optical materials for radiation resistance.
    effect: Solar absorptance rose from 0.109 before exposure to 0.118 after 503 h, an increase of 0.009. The authors saw no new absorption regions for any specimen, and they describe the sapphire change as very small.
    rating: low
    conditions:
      test: Boeing simulated space exposure, see the solar absorptance row
      note: ground test, not in orbit
    source: nasa1982
    where: Section 3.1 (ranking), Section 3.4 and Table 2
  - environment: 1 MeV electron exposure, 8 x 10^6 e/cm2 s for 5 h, sapphire optic at 1064 nm
    headline: A bare sapphire optic lost about half a percent of its 1064 nm transmission after strong electron exposure.
    effect: Transmission fell from 84.0 to 83.6 (a change of -0.5 percent). The authors saw about four current spikes during exposure and no visible surface or bulk change. They describe the transmission loss as very slight.
    rating: low
    conditions:
      specimen: bare sapphire, no coating
      note: pre-launch test of a flight instrument optic
    source: nasa2010
    where: Table 1, Sample B row; Conclusion
risks:
  hazards:
    - text: Crystran's safety data sheet says the sapphire optical crystal is not classified as dangerous under EC directives and has no label elements.
      ghs: []
      source: crystran-msds
      where: Sections 2.1 and 2.2
    - text: PubChem reports that aluminium oxide does not meet GHS hazard criteria in 92.8% of reports (2917 of 3142). Its minority classifications, H335 and H372, concern powder and dust, not a solid crystal.
      ghs:
        - H335
        - H372
      source: pubchem-alumina
      where: Safety and Hazards, GHS Classification (CID 9989226)
    - text: The safety sheet gives an occupational exposure limit of 10 mg/m3 as an 8 hour time-weighted average for dust. It says to avoid making dust.
      ghs: []
      source: crystran-msds
      where: Section 8.1 and Section 6.1
  failure_risks:
    - mode: Brittle fracture and edge chipping
      trigger: Impact, bending or chipping of a polished piece or a sharp edge
      consequence: Sapphire breaks rather than bends. Flexural strength is 690 MPa on the Kyocera sheet and 480 to 895 MPa on the Valley Design sheet. The Crystran safety sheet names chipping and sharp edges as the hazard in handling.
      severity: moderate
      source: kyocera-sapphire
      where: Mechanical characteristics table; crystran-msds sections 6.3 and 8.2
    - mode: Gradual darkening under combined solar UV, electron and proton exposure
      trigger: Long exposure to simulated solar UV, electrons and protons in vacuum
      consequence: Solar absorptance rose by 0.009 over 503 h in the 1981 test, which the authors call very small. Larger effects were seen in the crown and low-expansion glasses tested alongside.
      severity: low
      source: nasa1982
      where: Section 3.4, Table 2
  side_effects: []
  handling:
    - text: Wear suitable protective clothing and PVA gloves, and use safety goggles where chipping or dust may occur. Provide ventilation at the point of dust creation.
      source: crystran-msds
      where: Section 8.2
    - text: Avoid making dust. Take up pieces with containers for disposal, and avoid sharp edges. Keep away from ethylene oxide and chlorine trifluoride, which the safety sheet lists as incompatible.
      source: crystran-msds
      where: Sections 6.1, 6.3 and 10.5
  mitigations:
    - text: Ask the supplier for orientation and property values for the part, because the values differ by orientation and source (the Kyocera sheet notes each crystal orientation has different characteristics).
      source: kyocera-sapphire
      where: Characteristics table footnotes
    - text: Specify the orientation of the optic axis when birefringence matters. Crystran says general purpose infrared windows are cut at random unless an orientation is selected.
      source: crystran-sapphire
      where: Product text, Crystran sapphire background
uses:
  - application: optics-and-cameras
    device: Lunar Orbiter Laser Altimeter (LOLA) on NASA's Lunar Reconnaissance Orbiter, sapphire optic at 1064 nm
    example: A NASA Goddard paper tested bare and coated sapphire optics for the altimeter, a flight instrument, for transmission loss under electron charging before launch.
    source: nasa2010
    where: Introduction; Configuration; Table 1
  - application: optics-and-cameras
    device: Front elements of spacecraft optical systems
    example: NASA's 1981 study names sapphire and Corning 7940 fused silica as the standard radiation-resistant optical materials for spacecraft, used as the front elements of optical systems whenever possible.
    source: nasa1982
    where: Section 2.1
  - application: electronics-and-chips
    device: LED substrate for blue, green, ultraviolet and white LEDs
    example: Kyocera calls single crystal sapphire a widely used substrate for blue, green, ultraviolet and white LEDs, and a base for GaN deposition.
    source: kyocera-sapphire
    where: Sapphire Products, Substrate application
  - application: electronics-and-chips
    device: Semiconductor process equipment parts, including windows and microwave entrance tubes
    example: Kyocera lists sapphire carrier plates, microwave entrance tubes, handling arms, vacuum chucks and windows for semiconductor process equipment, citing its high anti-plasma and high anti-heat characteristics.
    source: kyocera-sapphire
    where: Sapphire Products, Semiconductor Process Equipment Parts
supply:
  - subject: Alumina feedstock for sapphire growth (world alumina production, 2025 estimate)
    producers:
      - country: China
        share_percent: 62
        year: 2025
      - country: Australia
        share_percent: 11.3
        year: 2025
      - country: Brazil
        share_percent: 7.3
        year: 2025
      - country: India
        share_percent: 5.5
        year: 2025
    critical_lists: []
    recycling: 'USGS: Recycling: None (bauxite and alumina chapter).'
    substitutes:
      - 'USGS: silicon carbide and alumina zirconia can substitute for alumina in abrasives but not in optics. No substitute for single-crystal optical material is named in the USGS chapter.'
    source: usgs-mcs2026-bauxite
    where: World Alumina Refinery and Bauxite Mine Production table, alumina 2025e (world total 150,000 thousand t; shares calculated by Space Mushroom from the country values, China 93,000, Australia 17,000, Brazil 11,000, India 8,200). The chapter does not give sapphire crystal output.
documents:
  - title: 'Kyocera Fineceramics: Single Crystal Sapphire product brochure (EFG method, characteristics table; undated PDF)'
    type: datasheet
    url: https://global.kyocera.com/prdct/fc/product/pdf/s_c_sapphire.pdf
    year: 2026
  - title: 'Crystran: Sapphire (Al2O3) product page, product data table and refractive index table'
    type: datasheet
    url: https://crystran.com/optical-materials/sapphire-al2o3
    year: 2026
  - title: 'Crystran: Safety Data Sheet, Sapphire Optical Crystal (revision 2026, issued 6 July 2026)'
    type: sds
    url: https://www.crystran.com/wp-content/uploads/2025/09/sapphire-al2o3-msds.pdf
    year: 2026
  - title: 'Valley Design: Properties of sapphire substrate and sapphire wafers (supplier page)'
    type: datasheet
    url: https://www.valleydesign.com/sappprop.htm
    year: 2026
  - title: 'NASA Marshall and IITRI: Evaluation of the Effects of Solar Radiation on Glasses (IITRI-M06055-10, August 1981)'
    type: report
    url: https://ntrs.nasa.gov/citations/19820003334
    year: 1981
  - title: 'NASA Goddard: Effect of charging electron exposure on 1064 nm transmission through bare sapphire optics (LOLA, LRO)'
    type: report
    url: https://ntrs.nasa.gov/citations/20100019258
    year: 2010
  - title: 'Toifl et al.: Continuum level-set model for anisotropic wet etching of patterned sapphire substrates (Semiconductor Science and Technology 36, 045016, open access)'
    type: paper
    url: https://doi.org/10.1088/1361-6641/abe49b
    year: 2021
  - title: 'PubChem: Aluminum oxide (CID 9989226), GHS classification summary'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/9989226
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Bauxite and Alumina'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-bauxite-alumina.pdf
    year: 2026
gaps:
  - No vacuum outgassing (TML/CVCM), atomic-oxygen or flight result for sapphire was found in a source we could open. The space-related sources are a 1981 ground simulation (Boeing, NASA Marshall) and a pre-launch electron test of a flight optic.
  - 'Knoop hardness is not entered: the Crystran sheet prints 1800 (parallel) and 2200 (perpendicular), and the Valley Design sheet prints 1,800 to 2,200, without a unit. Vickers and Mohs values are entered instead.'
  - Fracture toughness and thermal shock temperature difference for single-crystal sapphire were not found in the sources opened. Values for a 99% polycrystalline alumina exist elsewhere and are not used here.
  - Vickers hardness, compressive strength, Mohs hardness and apparent elastic limit are not canonical names; they are snake_case or other names and are kept as printed.
  - 'Dielectric strength and volume resistance are left out: the Kyocera PDF prints their exponents as superscripts (48 x 10^6 V/m; more than 10^14 ohm-cm at 20 °C; 10^11 ohm-cm at 500 °C), and the value check could not match them. Re-read the PDF in an image viewer before adding them back.'
  - 'Most strength values carry no temperature, orientation or grade: the Kyocera flexural strength (690 MPa) prints no test condition, and the 480 to 895 MPa range is from a supplier page.'
  - Crystal growth output and country shares for sapphire crystals were not found. The supply section uses USGS world alumina shares, which are feedstock figures, not sapphire boule output. Critical-mineral status for aluminium was not checked against the USGS 2025 list.
  - 'Producers: Kyocera says it grows, machines and supplies sapphire in a vertically integrated way. Crystran (UK) sells and finishes it and gives no growth share; Valley Design says it does not grow sapphire. No country share for sapphire crystals was found.'
  - 'No UNS, EN or other grade designations were applied: optical and substrate sapphire is sold by orientation and surface finish, and none of the sources read prints a standard grade code for it.'
  - The Kyocera sheet carries no publication date in the text read; its year is the access year (2026). The Crystran safety sheet is dated by its revision (2026).
  - The 1981 NASA report is a scanned copy read through text recognition; the solar absorptance values 0.109 and 0.118 were checked against the table layout but the column headers were partly garbled.
  - The wet etch rates are calibrated model parameters from a simulation paper, not measured immersion data, and the table lines read do not name the crystal directions for each value.
  - The Crystran transmission data table and the Kyocera transmission graph were not read as numbers. Transmission values come from the Crystran range and the Valley Design range only.
  - Hazard data rest on the Crystran safety sheet and the PubChem aluminium oxide summary. The PubChem entry covers the powder and the Crystran sheet covers the sapphire crystal; no other supplier sheet for sapphire was read, and no storage data beyond the sheet was found.
sources:
  kyocera-sapphire:
    title: 'Kyocera Fineceramics: Single Crystal Sapphire (EFG method, shapes, characteristics table)'
    id: Kyocera s_c_sapphire.pdf (undated)
    url: https://global.kyocera.com/prdct/fc/product/pdf/s_c_sapphire.pdf
    year: 2026
    kind: datasheet
    license: supplier document, linked not reproduced
  crystran-sapphire:
    title: 'Crystran: Sapphire Al2O3 product page (product data, refractive index table)'
    id: crystran.com/optical-materials/sapphire-al2o3 (page undated)
    url: https://crystran.com/optical-materials/sapphire-al2o3
    year: 2026
    kind: datasheet
    license: supplier document, linked not reproduced
  crystran-msds:
    title: 'Crystran: Safety Data Sheet, Sapphire Optical Crystal (REACH format, revision 2026)'
    id: Revision 2026, issued 6 July 2026; CAS 1344-28-1; EC 215-691-6
    url: https://www.crystran.com/wp-content/uploads/2025/09/sapphire-al2o3-msds.pdf
    year: 2026
    kind: datasheet
    license: supplier document, linked not reproduced
  valley-sapphire:
    title: 'Valley Design: Properties of sapphire substrate and sapphire wafers (supplier page)'
    id: valleydesign.com/sappprop.htm (page undated)
    url: https://www.valleydesign.com/sappprop.htm
    year: 2026
    kind: web
    license: supplier page, linked not reproduced
  nasa1982:
    title: Evaluation of the Effects of Solar Radiation on Glasses (IIT Research Institute for NASA Marshall, final report)
    id: NTRS 19820003334; report IITRI-M06055-10; August 1981
    url: https://ntrs.nasa.gov/citations/19820003334
    year: 1981
    kind: report
    license: public domain (NASA)
  nasa2010:
    title: Effect of charging electron exposure on 1064 nm transmission through bare sapphire optics (LOLA, LRO; NASA Goddard)
    id: NTRS 20100019258
    url: https://ntrs.nasa.gov/citations/20100019258
    year: 2010
    kind: report
    license: public domain (NASA)
  toifl2021:
    title: Continuum level-set model for anisotropic wet etching of patterned sapphire substrates (Toifl et al.)
    id: doi:10.1088/1361-6641/abe49b (Semicond. Sci. Technol. 36, 045016)
    url: https://doi.org/10.1088/1361-6641/abe49b
    year: 2021
    kind: paper
    license: open access (IOP Publishing)
  pubchem-alumina:
    title: PubChem compound record, Aluminum oxide (CID 9989226), GHS classification
    id: CID 9989226; CAS 1344-28-1
    url: https://pubchem.ncbi.nlm.nih.gov/compound/9989226
    year: 2026
    kind: database
    license: public domain (NCBI)
  usgs-mcs2026-bauxite:
    title: Mineral Commodity Summaries 2026, Bauxite and Alumina
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-bauxite-alumina.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 41
  unreachable: 0
  caveats: 4
  note: 'Written by an AI assistant on 2026-10-26 from pages and PDFs read in the same run. Caveats: the 1981 NASA report was read through text recognition; the Kyocera sheet carries no publication date; the etch-rate values are model parameters; the Crystran transmission table was not read as numbers.'
story:
  recipe:
    line: Sapphire is alumina grown as one crystal. Each formula unit combines two aluminium atoms with three oxygen atoms, and the crystal has a trigonal lattice. Crystran names Verneuil and Czochralski growth as the usual methods for standard grade, Kyropoulos growth for higher-purity electronic substrates, and ribbon growth for large thin sheets. Kyocera uses edge-defined film-fed growth (EFG) and says it grows the crystal, machines it and supplies shaped parts.
    parts:
      - name: Aluminium
        symbol: Al
        role: The metal. Two aluminium atoms per formula unit, with Al2O3 molecular weight 101.96 (Crystran).
      - name: Oxygen
        symbol: O
        role: The non-metal. Three oxygen atoms per formula unit.
  risk_groups:
    - title: For people
      level: 1
      verdict: Not classified as dangerous in the supplier's safety sheet
      lead: The Crystran safety sheet for sapphire optical crystal says the product is not classified under EC directives and has no label elements. The PubChem minority classifications for alumina concern powder and dust.
      points:
        - label: Dust
          line: The safety sheet gives an occupational limit of 10 mg/m3 as an 8 hour average for dust, and says to avoid making dust.
        - label: Minority classifications
          line: PubChem lists H335 (may cause respiratory irritation) and H372 (organ damage with prolonged exposure) for some aluminium oxide notifications. These concern powder, not a solid crystal.
    - title: If it fails
      lead: The failure results come from manufacturer data and two NASA tests, not from flight incidents.
      points:
        - label: Breaking
          line: Sapphire breaks rather than bends. Flexural strength is 690 MPa on the Kyocera sheet and 480 to 895 MPa on the Valley Design sheet, and the Crystran sheet warns about chipping and sharp edges.
        - label: Radiation
          line: In a 1981 ground test, solar absorptance rose by 0.009 over 503 hours of simulated solar UV, electron and proton exposure. The authors call it very small.
        - label: Electron exposure
          line: A bare sapphire optic for the LOLA altimeter lost 0.5 percent of its 1064 nm transmission after 1 MeV electron exposure, within the stated measurement uncertainty.
    - title: Handling and storage
      gap: The sources read give no storage temperature or humidity limit for sapphire. The safety sheet says no special storage conditions apply.
      points:
        - label: Protective equipment
          line: The safety sheet asks for PVA gloves, goggles where chipping or dust may occur, and ventilation where dust forms.
        - label: Incompatible materials
          line: The safety sheet lists ethylene oxide and chlorine trifluoride as incompatible materials.
  why: Sapphire is alpha-alumina (Al2O3) grown as a single crystal. Kyocera describes it as high in strength, rigidity, abrasion resistance, heat resistance and corrosion resistance, and gives a Vickers hardness of 22.5 GPa. The 1981 NASA review gives a Mohs hardness of 9. The records collected here describe a hard, radiation-tolerant optical window and substrate. Its strength and thermal values vary by orientation and by supplier, and it is brittle, so it cracks rather than bends.
  uses:
    - where: Spacecraft optics
      line: NASA's 1981 review names sapphire and Corning 7940 fused silica as the standard radiation-resistant optical materials for spacecraft, used as the front elements of optical systems whenever possible.
    - where: Lunar altimeter optic
      line: A NASA Goddard paper tested bare sapphire optics for the LOLA altimeter on the Lunar Reconnaissance Orbiter. The test came before launch and found a transmission change of about half a percent at 1064 nm after strong electron exposure.
    - where: LED substrates
      line: Kyocera calls single crystal sapphire a widely used substrate for blue, green, ultraviolet and white LEDs, and a base for gallium nitride deposition.
    - where: Semiconductor process equipment
      line: Kyocera lists sapphire carrier plates, microwave entrance tubes, vacuum chucks and windows for semiconductor process equipment, citing its anti-plasma and heat resistance.
  can_do:
    - label: Strength
      value: 690 MPa
      line: Kyocera's flexural strength (the stress at which a bar breaks when bent) is 690 MPa. Another supplier prints 480 to 895 MPa, and a stiffness of 470 GPa (Kyocera) or 335 GPa (Crystran).
    - label: Hardness
      value: 22.5 GPa
      line: Kyocera's Vickers hardness at a 9.807 N load is 22.5 GPa. The 1981 NASA review gives a Mohs hardness of 9.
    - label: Heat
      value: 2053 °C
      line: Kyocera and the Crystran safety sheet give a melting point of 2053 °C. Thermal conductivity is 42 W/(m·K) at 20 °C on the Kyocera sheet, and 27.21 W/(m·K) at 300 K on the Crystran page.
    - label: Light
      value: 0.17 to 5.5 µm
      line: Crystran gives a transmission range of 0.17 to 5.5 µm for its optical grade. Kyocera gives a refractive index of 1.768 for the ordinary ray at 589 nm.
    - label: Radiation
      value: 0.009 absorptance rise
      line: Solar absorptance rose only 0.009 after 503 hours of simulated space exposure in the NASA review. Sapphire ranked first of four optical materials tested for radiation resistance.
    - label: Dielectric constant and loss
      value: 9.3 to 11.5
      line: Kyocera gives a dielectric constant of 11.5 parallel to the c axis and 9.3 perpendicular to it at 1 MHz, and a dielectric loss tangent of at most 1 x 10^-4 at 1 MHz.
  compare: In the NASA 1981 review's ranking of radiation resistance, sapphire came first and fused silica second. In the same space simulation, fused silica's solar absorptance also changed very little (Table 2; the OCR copy of the table is partly garbled). The review says crown glass and low-expansion glass darkened appreciably. The sources read give no cost or availability comparison.
  compare_rows:
    - label: Heat conduction
      benchmark: thermal_conductivity
    - label: Thermal expansion
      benchmark: cte
    - label: Stiffness
      benchmark: elastic_modulus
  handling:
    - Bulk sapphire is a solid; the classifications on record concern powder and dust. Read the supplier's safety data sheet for the grade you handle.
    - Avoid making dust when cutting, grinding or cleaning, and dispose of broken pieces in containers to avoid sharp edges.
    - Keep sapphire away from ethylene oxide and chlorine trifluoride, which the safety sheet lists as incompatible.
  good_for:
    - Radiation-tolerant optical windows and front elements. NASA's 1981 review ranks sapphire first of four optical materials tested, with a solar absorptance rise of 0.009 after 503 hours.
    - Hard substrates for LEDs and semiconductor process parts (Kyocera). The Kyocera sheet gives a melting point of 2053 °C and a Vickers hardness of 22.5 GPa.
    - Ultraviolet to near-infrared optics, with a transmission range of 0.17 to 5.5 µm on the Crystran page.
  watch_out:
    - Brittle fracture. Flexural strength is 480 to 895 MPa on one supplier sheet and 690 MPa on another, and the values depend on orientation and source.
    - Orientation. Thermal conductivity is 42 W/(m·K) on the Kyocera sheet and about 23 to 26 W/(m·K) on the Valley Design sheet at room temperature, and the thermal expansion differs by orientation.
    - Source differences. The Crystran page and the Kyocera sheet give different Young's moduli (335 and 470 GPa), so the design value must come from the supplier for the orientation used.
    - No flight outgassing, atomic-oxygen or long-duration orbital result for sapphire was found in a source we could open.
  verdict: Sapphire is a hard, stiff and radiation-tolerant optical crystal and a standard electronics substrate. Its records show good radiation resistance in ground tests and small transmission loss in one pre-launch electron test, while its brittleness and its orientation-dependent values set the limits for design.