{
  "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.\n",
  "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",
    "designations": [],
    "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,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "density",
      "label": "Density (20 °C)",
      "value": 3.98,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "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)",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "melting_point",
      "label": "Melting point, Kyocera sheet",
      "value": 2053,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "boiling_point",
      "label": "Boiling point at 760 mmHg",
      "value": 2977,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "vickers_hardness",
      "label": "Vickers hardness, Kyocera sheet",
      "value": 22.5,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "mohs_hardness",
      "label": "Mohs hardness",
      "value": 9,
      "bound": "exact",
      "unit": "-",
      "scope": "material",
      "conditions": {
        "scale": "Mohs"
      },
      "method": "Value quoted in a NASA report",
      "status": "ground",
      "source": "nasa1982",
      "where": "Section 3.1, reason 1",
      "source_detail": {
        "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)"
      }
    },
    {
      "benchmark": "flexural_strength",
      "label": "Flexural strength, Kyocera sheet",
      "value": 690,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "ultimate_tensile_strength",
      "label": "Tensile strength of a 0.25 mm filament",
      "value": 2250,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "compressive_strength",
      "label": "Compressive strength",
      "value": 2940,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "apparent_elastic_limit",
      "label": "Apparent elastic limit",
      "value": 300,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "elastic_modulus",
      "label": "Young's modulus, Kyocera sheet",
      "value": 470,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "elastic_modulus",
      "label": "Young's modulus, Crystran product data",
      "value": 335,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "shear_modulus",
      "label": "Shear modulus",
      "value": 148.1,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "bulk_modulus",
      "label": "Bulk modulus",
      "value": 240,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "poissons_ratio",
      "label": "Poisson's ratio, Crystran",
      "value": 0.25,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "thermal_conductivity",
      "label": "Thermal conductivity at 20 °C, Kyocera sheet",
      "value": 42,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "thermal_conductivity",
      "label": "Thermal conductivity at 300 K, Crystran",
      "value": 27.21,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "thermal_conductivity",
      "label": "Thermal conductivity, perpendicular to c axis",
      "value": 23,
      "bound": "exact",
      "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)",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "thermal_conductivity",
      "label": "Thermal conductivity, parallel to c axis",
      "value": 25.8,
      "bound": "exact",
      "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)",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "cte",
      "label": "Thermal expansion, parallel to c axis, 40 to 400 °C",
      "value": 7.7,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "cte",
      "label": "Thermal expansion, perpendicular to c axis, 40 to 400 °C",
      "value": 7,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "cte",
      "label": "Thermal expansion, parallel to c axis, Crystran",
      "value": 5.6,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "specific_heat",
      "label": "Specific heat, Kyocera sheet",
      "value": 0.75,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "specific_heat",
      "label": "Specific heat at 293 K, Crystran",
      "value": 763,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "dielectric_constant",
      "label": "Dielectric constant, parallel to c axis, 1 MHz",
      "value": 11.5,
      "bound": "exact",
      "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)",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "dielectric_constant",
      "label": "Dielectric constant, perpendicular to c axis, 1 MHz",
      "value": 9.3,
      "bound": "exact",
      "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)",
      "source_detail": {
        "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"
      }
    },
    {
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "refractive_index",
      "label": "Refractive index, ordinary ray at 589 nm",
      "value": 1.768,
      "bound": "exact",
      "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)",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "refractive_index",
      "label": "Refractive index, extraordinary ray at 589 nm",
      "value": 1.76,
      "bound": "exact",
      "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)",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "refractive_index",
      "label": "Refractive index, ordinary ray at 1.06 µm",
      "value": 1.75449,
      "bound": "exact",
      "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)",
      "source_detail": {
        "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"
      }
    },
    {
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "water_solubility",
      "label": "Solubility in water at 20 °C",
      "value": 0.000098,
      "bound": "exact",
      "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)",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "mohs_hardness",
      "label": "Mohs hardness on a supplier page",
      "value": 9,
      "bound": "exact",
      "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)",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "solar_absorptance_change",
      "label": "Change in solar absorptance after 503 h of simulated space exposure",
      "value": 0.009,
      "bound": "exact",
      "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)",
      "source_detail": {
        "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)"
      }
    },
    {
      "benchmark": "transmission_change_1064nm",
      "label": "Change in 1064 nm transmission after electron exposure",
      "value": -0.5,
      "bound": "exact",
      "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%))",
      "source_detail": {
        "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)"
      }
    },
    {
      "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",
      "source_detail": {
        "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)"
      }
    }
  ],
  "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."
    }
  ],
  "media": [],
  "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."
  ],
  "story": {
    "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",
        "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).",
        "scope": "material",
        "value": "690 MPa"
      },
      {
        "label": "Hardness",
        "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.",
        "scope": "material",
        "value": "22.5 GPa"
      },
      {
        "label": "Heat",
        "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.",
        "scope": "material",
        "value": "2053 °C"
      },
      {
        "label": "Light",
        "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.",
        "scope": "material",
        "value": "0.17 to 5.5 µm"
      },
      {
        "label": "Radiation",
        "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.",
        "scope": "material",
        "value": "0.009 absorptance rise"
      },
      {
        "label": "Dielectric constant and loss",
        "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.",
        "scope": "material",
        "value": "9.3 to 11.5"
      }
    ],
    "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",
        "scope": "material"
      },
      {
        "label": "Thermal expansion",
        "benchmark": "cte",
        "scope": "material"
      },
      {
        "label": "Stiffness",
        "benchmark": "elastic_modulus",
        "scope": "material"
      }
    ],
    "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.",
    "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",
        "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."
          }
        ],
        "level": 1,
        "verdict": "Not classified as dangerous in the supplier's safety sheet"
      },
      {
        "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",
        "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."
          }
        ],
        "gap": "The sources read give no storage temperature or humidity limit for sapphire. The safety sheet says no special storage conditions apply."
      }
    ]
  },
  "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."
  },
  "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",
  "url": "https://spacemushroom.com/profiles/sapphire/"
}