{
  "spore": "profile",
  "id": "borosilicate-glass",
  "spore_version": "0.2",
  "family": "glass-and-composites",
  "name": "Borosilicate glass",
  "abbreviation": "Borosilicate",
  "role": "optical and laboratory glass",
  "category": "glasses-optics",
  "type": "borosilicate",
  "summary": "Borosilicate glass is a silica glass with about 13% boric oxide, which lowers its thermal expansion. SCHOTT's BOROFLOAT 33 sheet lists a density of 2.23 g/cm3, a transformation temperature of 525 °C and a long-term maximum operating temperature of 450 °C. Wikipedia reports that virtually all modern laboratory glassware is made of borosilicate, and that the 200 inch mirror of the Hale Telescope is borosilicate. The thermal expansion coefficient and thermal-shock ratings come from the SCHOTT technical-details page; see the property list for the values and conditions.\n",
  "best_for": "Laboratory glassware and optics that must survive temperature swings, where a low thermal expansion matters more than cost",
  "weakest_at": "Higher working temperature and processing cost than soda-lime glass; the expansion coefficient and hazard data could not be checked in this run",
  "identity": {
    "formula": "Silica-boria glass: about 80% SiO2, 13% B2O3, 4% Na2O or K2O and 2-3% Al2O3 for the low-expansion laboratory type",
    "designations": [],
    "source": "wikipedia-borosilicate",
    "where": "Wikipedia, Borosilicate glass, Manufacturing process section (composition quoted as approximately 80% silica, 13% boric oxide, 4% sodium or potassium oxide and 2 to 3% aluminium oxide). Composition is a typical example, not a single specification; products such as BOROFLOAT 33 are defined by the manufacturer."
  },
  "tags": {
    "environments": [],
    "stresses": [],
    "applications": [
      "optics-and-cameras",
      "electronics-and-chips"
    ]
  },
  "properties": [
    {
      "benchmark": "density",
      "value": 2.23,
      "bound": "exact",
      "unit": "g/cm3",
      "scope": "material",
      "conditions": {
        "temperature": "25 °C"
      },
      "method": "Value printed in the mechanical properties table of the SCHOTT BOROFLOAT 33 technical details page",
      "status": "ground",
      "source": "schott-borofloat33",
      "where": "Mechanical properties table, density row",
      "source_detail": {
        "title": "BOROFLOAT 33 technical details",
        "id": "SCHOTT AG product page",
        "url": "https://www.schott.com/en-us/products/borofloat/technical-details",
        "kind": "datasheet",
        "license": "manufacturer web page, cited not reproduced"
      }
    },
    {
      "benchmark": "transformation_temperature",
      "value": 525,
      "bound": "exact",
      "unit": "°C",
      "scope": "material",
      "conditions": {
        "standard": "ISO 7884"
      },
      "method": "Value printed in the thermal properties table of the SCHOTT page",
      "status": "ground",
      "source": "schott-borofloat33",
      "where": "Thermal properties table, Tg row",
      "source_detail": {
        "title": "BOROFLOAT 33 technical details",
        "id": "SCHOTT AG product page",
        "url": "https://www.schott.com/en-us/products/borofloat/technical-details",
        "kind": "datasheet",
        "license": "manufacturer web page, cited not reproduced"
      }
    },
    {
      "benchmark": "max_operating_temperature_short_term",
      "value": 500,
      "bound": "exact",
      "unit": "°C",
      "scope": "material",
      "conditions": {
        "duration": "less than 10 h"
      },
      "method": "Value printed on the SCHOTT page, reference value",
      "status": "ground",
      "source": "schott-borofloat33",
      "where": "Thermal properties table, maximum operating temperature row",
      "source_detail": {
        "title": "BOROFLOAT 33 technical details",
        "id": "SCHOTT AG product page",
        "url": "https://www.schott.com/en-us/products/borofloat/technical-details",
        "kind": "datasheet",
        "license": "manufacturer web page, cited not reproduced"
      }
    },
    {
      "benchmark": "max_operating_temperature_long_term",
      "value": 450,
      "bound": "exact",
      "unit": "°C",
      "scope": "material",
      "conditions": {
        "duration": "10 h or more"
      },
      "method": "Value printed on the SCHOTT page, reference value",
      "status": "ground",
      "source": "schott-borofloat33",
      "where": "Thermal properties table, maximum operating temperature row",
      "source_detail": {
        "title": "BOROFLOAT 33 technical details",
        "id": "SCHOTT AG product page",
        "url": "https://www.schott.com/en-us/products/borofloat/technical-details",
        "kind": "datasheet",
        "license": "manufacturer web page, cited not reproduced"
      }
    },
    {
      "benchmark": "specific_heat",
      "value": 0.83,
      "bound": "exact",
      "unit": "kJ/(kg·K)",
      "scope": "material",
      "conditions": {
        "temperature_range": "20 to 100 °C"
      },
      "method": "Value printed in the thermal properties table",
      "status": "ground",
      "source": "schott-borofloat33",
      "where": "Thermal properties table, specific heat row",
      "source_detail": {
        "title": "BOROFLOAT 33 technical details",
        "id": "SCHOTT AG product page",
        "url": "https://www.schott.com/en-us/products/borofloat/technical-details",
        "kind": "datasheet",
        "license": "manufacturer web page, cited not reproduced"
      }
    },
    {
      "benchmark": "thermal_conductivity",
      "value": 1.2,
      "bound": "exact",
      "unit": "W/(m·K)",
      "scope": "material",
      "conditions": {
        "temperature": "90 °C"
      },
      "method": "Value printed in the thermal properties table",
      "status": "ground",
      "source": "schott-borofloat33",
      "where": "Thermal properties table, thermal conductivity row",
      "source_detail": {
        "title": "BOROFLOAT 33 technical details",
        "id": "SCHOTT AG product page",
        "url": "https://www.schott.com/en-us/products/borofloat/technical-details",
        "kind": "datasheet",
        "license": "manufacturer web page, cited not reproduced"
      }
    },
    {
      "benchmark": "youngs_modulus",
      "value": 64,
      "bound": "exact",
      "unit": "kN/mm2",
      "scope": "material",
      "conditions": {
        "standard": "DIN 13316"
      },
      "method": "Value printed in the mechanical properties table",
      "status": "ground",
      "source": "schott-borofloat33",
      "where": "Mechanical properties table, Young's modulus row",
      "source_detail": {
        "title": "BOROFLOAT 33 technical details",
        "id": "SCHOTT AG product page",
        "url": "https://www.schott.com/en-us/products/borofloat/technical-details",
        "kind": "datasheet",
        "license": "manufacturer web page, cited not reproduced"
      }
    },
    {
      "benchmark": "poissons_ratio",
      "value": 0.2,
      "bound": "exact",
      "unit": "dimensionless",
      "scope": "material",
      "conditions": {
        "standard": "DIN 13316"
      },
      "method": "Value printed in the mechanical properties table",
      "status": "ground",
      "source": "schott-borofloat33",
      "where": "Mechanical properties table, Poisson's ratio row",
      "source_detail": {
        "title": "BOROFLOAT 33 technical details",
        "id": "SCHOTT AG product page",
        "url": "https://www.schott.com/en-us/products/borofloat/technical-details",
        "kind": "datasheet",
        "license": "manufacturer web page, cited not reproduced"
      }
    },
    {
      "benchmark": "knoop_hardness",
      "value": 480,
      "bound": "exact",
      "unit": "HK0.1/20",
      "scope": "material",
      "conditions": {
        "standard": "DIN ISO 9385"
      },
      "method": "Value printed in the mechanical properties table",
      "status": "ground",
      "source": "schott-borofloat33",
      "where": "Mechanical properties table, Knoop hardness row",
      "source_detail": {
        "title": "BOROFLOAT 33 technical details",
        "id": "SCHOTT AG product page",
        "url": "https://www.schott.com/en-us/products/borofloat/technical-details",
        "kind": "datasheet",
        "license": "manufacturer web page, cited not reproduced"
      }
    },
    {
      "benchmark": "refractive_index",
      "value": 1.4714,
      "bound": "exact",
      "unit": "nd (587.6 nm)",
      "scope": "material",
      "conditions": {
        "wavelength": "587.6 nm",
        "note": "reference value, not guaranteed by the manufacturer"
      },
      "method": "Value printed in the optical data table",
      "status": "ground",
      "source": "schott-borofloat33",
      "where": "Optical data table, refractive index nd row",
      "source_detail": {
        "title": "BOROFLOAT 33 technical details",
        "id": "SCHOTT AG product page",
        "url": "https://www.schott.com/en-us/products/borofloat/technical-details",
        "kind": "datasheet",
        "license": "manufacturer web page, cited not reproduced"
      }
    },
    {
      "benchmark": "abbe_number",
      "value": 65.41,
      "bound": "exact",
      "unit": "dimensionless",
      "scope": "material",
      "conditions": {
        "wavelength": "nu_e",
        "note": "reference value, not guaranteed by the manufacturer"
      },
      "method": "Value printed in the optical data table",
      "status": "ground",
      "source": "schott-borofloat33",
      "where": "Optical data table, Abbe number row",
      "source_detail": {
        "title": "BOROFLOAT 33 technical details",
        "id": "SCHOTT AG product page",
        "url": "https://www.schott.com/en-us/products/borofloat/technical-details",
        "kind": "datasheet",
        "license": "manufacturer web page, cited not reproduced"
      }
    },
    {
      "benchmark": "stress_optical_coefficient",
      "value": 4,
      "bound": "exact",
      "unit": "x10^-6 mm2/N",
      "scope": "material",
      "conditions": {
        "note": "reference value, not guaranteed by the manufacturer"
      },
      "method": "Value printed in the optical data table",
      "status": "ground",
      "source": "schott-borofloat33",
      "where": "Optical data table, stress-optical coefficient K row",
      "source_detail": {
        "title": "BOROFLOAT 33 technical details",
        "id": "SCHOTT AG product page",
        "url": "https://www.schott.com/en-us/products/borofloat/technical-details",
        "kind": "datasheet",
        "license": "manufacturer web page, cited not reproduced"
      }
    },
    {
      "benchmark": "hydrolytic_class",
      "value": 1,
      "bound": "exact",
      "unit": "class HGB (ISO 719 / DIN 12 111)",
      "scope": "material",
      "conditions": {
        "standard": "ISO 719 / DIN 12 111"
      },
      "method": "Class printed in the chemical durability table",
      "status": "ground",
      "source": "schott-borofloat33",
      "where": "Chemical durability table, hydrolytic resistance rows",
      "source_detail": {
        "title": "BOROFLOAT 33 technical details",
        "id": "SCHOTT AG product page",
        "url": "https://www.schott.com/en-us/products/borofloat/technical-details",
        "kind": "datasheet",
        "license": "manufacturer web page, cited not reproduced"
      }
    },
    {
      "benchmark": "cte",
      "label": "Linear thermal expansion coefficient",
      "value": 3.25,
      "bound": "exact",
      "unit": "x10^-6 K^-1",
      "scope": "material",
      "conditions": {
        "temperature_range": "20 to 300 °C",
        "standard": "ISO 7991"
      },
      "method": "Printed as 3.25 x 10-6 K-1 in the BOROFLOAT 33 brochure; same value on the 0407 data sheet and the Edmund Optics copy of the SCHOTT technical data sheet",
      "status": "ground",
      "source": "schott-media-datasheet",
      "where": "Thermal properties table, Linear Thermal Expansion (C.T.E.) row, footnote *: according to ISO 7991",
      "source_detail": {
        "title": "BOROFLOAT 33 & Functional Coatings (SCHOTT brochure)",
        "id": "SCHOTT AG, BOROFLOAT 33 & Functional Coatings",
        "url": "https://media.schott.com/api/public/content/32b935120d7343109caa36fb70f40ced?v=541db792&download=true",
        "kind": "datasheet",
        "license": "manufacturer document, cited not reproduced"
      }
    },
    {
      "benchmark": "dielectric_constant",
      "label": "Dielectric constant",
      "value": 4.6,
      "bound": "exact",
      "unit": "dimensionless",
      "scope": "material",
      "conditions": {
        "frequency": "1 MHz",
        "temperature": "25 °C"
      },
      "method": "Printed in the electrical properties list of the SCHOTT 0407 data sheet",
      "status": "ground",
      "source": "schott-datasheet-0407",
      "where": "Electrical Properties, Dielectric Constant row",
      "source_detail": {
        "title": "SCHOTT BOROFLOAT data sheet 0407 (SCHOTT North America)",
        "id": "SCHOTT North America, data sheet 0407 (copy on IOS Optics site)",
        "url": "https://iosoptics.com/pdf/Schott-Datasheet-Borofloat-33.pdf",
        "kind": "datasheet",
        "license": "manufacturer document, cited not reproduced"
      }
    },
    {
      "benchmark": "dissipation_factor",
      "label": "Loss tangent",
      "value": 37,
      "bound": "exact",
      "unit": "x10^-4",
      "scope": "material",
      "conditions": {
        "frequency": "1 MHz",
        "temperature": "25 °C"
      },
      "method": "Printed as 37 x 10-4 in the electrical properties list of the SCHOTT 0407 data sheet",
      "status": "ground",
      "source": "schott-datasheet-0407",
      "where": "Electrical Properties, Loss Tangent row",
      "source_detail": {
        "title": "SCHOTT BOROFLOAT data sheet 0407 (SCHOTT North America)",
        "id": "SCHOTT North America, data sheet 0407 (copy on IOS Optics site)",
        "url": "https://iosoptics.com/pdf/Schott-Datasheet-Borofloat-33.pdf",
        "kind": "datasheet",
        "license": "manufacturer document, cited not reproduced"
      }
    },
    {
      "benchmark": "dielectric_strength",
      "label": "Dielectric strength",
      "value": 16,
      "bound": "exact",
      "unit": "kV/mm",
      "scope": "material",
      "conditions": {
        "frequency": "50 Hz",
        "temperature": "25 °C"
      },
      "method": "Printed in the electrical properties list of the SCHOTT 0407 data sheet",
      "status": "ground",
      "source": "schott-datasheet-0407",
      "where": "Electrical Properties, Dielectric Strength row",
      "source_detail": {
        "title": "SCHOTT BOROFLOAT data sheet 0407 (SCHOTT North America)",
        "id": "SCHOTT North America, data sheet 0407 (copy on IOS Optics site)",
        "url": "https://iosoptics.com/pdf/Schott-Datasheet-Borofloat-33.pdf",
        "kind": "datasheet",
        "license": "manufacturer document, cited not reproduced"
      }
    },
    {
      "benchmark": "flexural_strength",
      "label": "Bending strength, normal conditions",
      "value": 25,
      "bound": "exact",
      "unit": "MPa",
      "scope": "material",
      "conditions": {
        "standard": "DIN 52 292 Part 1",
        "basis": "normal conditions"
      },
      "method": "Printed in the mechanical properties list of the SCHOTT 0407 data sheet",
      "status": "ground",
      "source": "schott-datasheet-0407",
      "where": "Mechanical Properties, Bending Strength, For Normal Conditions",
      "source_detail": {
        "title": "SCHOTT BOROFLOAT data sheet 0407 (SCHOTT North America)",
        "id": "SCHOTT North America, data sheet 0407 (copy on IOS Optics site)",
        "url": "https://iosoptics.com/pdf/Schott-Datasheet-Borofloat-33.pdf",
        "kind": "datasheet",
        "license": "manufacturer document, cited not reproduced"
      }
    },
    {
      "benchmark": "flexural_strength",
      "label": "Bending strength, safety conditions",
      "value": 7,
      "bound": "exact",
      "unit": "MPa",
      "scope": "material",
      "conditions": {
        "standard": "DIN 52 292 Part 1",
        "basis": "safety conditions"
      },
      "method": "Printed in the mechanical properties list of the SCHOTT 0407 data sheet; the lower design value for safety use",
      "status": "ground",
      "source": "schott-datasheet-0407",
      "where": "Mechanical Properties, Bending Strength, For Safety Conditions",
      "source_detail": {
        "title": "SCHOTT BOROFLOAT data sheet 0407 (SCHOTT North America)",
        "id": "SCHOTT North America, data sheet 0407 (copy on IOS Optics site)",
        "url": "https://iosoptics.com/pdf/Schott-Datasheet-Borofloat-33.pdf",
        "kind": "datasheet",
        "license": "manufacturer document, cited not reproduced"
      }
    },
    {
      "benchmark": "annealing_point",
      "label": "Annealing point (1013 dPa·s)",
      "value": 560,
      "bound": "exact",
      "unit": "°C",
      "scope": "material",
      "conditions": {
        "viscosity": "1013 dPa·s"
      },
      "method": "Printed in the thermal properties list of the SCHOTT 0407 data sheet",
      "status": "ground",
      "source": "schott-datasheet-0407",
      "where": "Thermal Properties, Annealing Point row",
      "source_detail": {
        "title": "SCHOTT BOROFLOAT data sheet 0407 (SCHOTT North America)",
        "id": "SCHOTT North America, data sheet 0407 (copy on IOS Optics site)",
        "url": "https://iosoptics.com/pdf/Schott-Datasheet-Borofloat-33.pdf",
        "kind": "datasheet",
        "license": "manufacturer document, cited not reproduced"
      }
    },
    {
      "benchmark": "softening_point",
      "label": "Softening point (10^7.6 dPa·s)",
      "value": 815,
      "bound": "exact",
      "unit": "°C",
      "scope": "material",
      "conditions": {
        "viscosity": "10^7.6 dPa·s"
      },
      "method": "Printed in the thermal properties list of the SCHOTT 0407 data sheet",
      "status": "ground",
      "source": "schott-datasheet-0407",
      "where": "Thermal Properties, Softening Point row",
      "source_detail": {
        "title": "SCHOTT BOROFLOAT data sheet 0407 (SCHOTT North America)",
        "id": "SCHOTT North America, data sheet 0407 (copy on IOS Optics site)",
        "url": "https://iosoptics.com/pdf/Schott-Datasheet-Borofloat-33.pdf",
        "kind": "datasheet",
        "license": "manufacturer document, cited not reproduced"
      }
    }
  ],
  "corrosion": [
    {
      "environment": "Water, 5 vol% hydrochloric acid and 0.02 n sulphuric acid (24 h at 95 °C)",
      "headline": "Water and acids give negligible attack.",
      "effect": "Abrasion below 0.01 mg/cm2 and surface unchanged in each test.",
      "rating": "unknown",
      "conditions": {
        "time": "24 h",
        "temperature": "95 °C"
      },
      "source": "schott-borofloat33",
      "where": "Chemical durability, Resistance to selected chemicals table"
    },
    {
      "environment": "5% sodium hydroxide (6 h at 95 °C), 0.02 n sodium hydroxide, 0.02 n sodium carbonate",
      "headline": "Alkali attacks the surface more than acid does.",
      "effect": "5% NaOH: abrasion 1.1 mg/cm2 with white stains. 0.02 n NaOH: 0.16 mg/cm2 with white haze. 0.02 n Na2CO3: 0.16 mg/cm2, unchanged.",
      "rating": "unknown",
      "conditions": {
        "time": "6 h",
        "temperature": "95 °C"
      },
      "source": "schott-borofloat33",
      "where": "Chemical durability, Resistance to selected chemicals table"
    },
    {
      "environment": "10% hydrofluoric acid (20 min at 23 °C) and 10% NH4F x HF",
      "headline": "Hydrofluoric acid stains the glass; the buffered mix does not.",
      "effect": "10% HF: abrasion 1.1 mg/cm2 with stained white haze. 10% NH4F x HF: 0.14 mg/cm2, unchanged.",
      "rating": "unknown",
      "conditions": {
        "time": "20 min",
        "temperature": "23 °C"
      },
      "source": "schott-borofloat33",
      "where": "Chemical durability, Resistance to selected chemicals table"
    },
    {
      "environment": "High-intensity UV from a mercury vapour lamp (365 nm main line, 15 h)",
      "headline": "Low solarization: the glass darkens little under UV.",
      "effect": "SCHOTT describes low solarization and low auto-fluorescence. The before-and-after transmission curves are graphs; no single number is printed.",
      "rating": "unknown",
      "conditions": {
        "source": "HOK 4/120 lamp, 850 W/cm2, 30 x 15 x 1 mm sample"
      },
      "source": "schott-media-datasheet",
      "where": "Solarization test figure and text"
    }
  ],
  "risks": {
    "hazards": [
      {
        "text": "PubChem aggregated GHS for boron oxide (B2O3), the main oxide in the glass: H360 (95.1% of reports, Danger) May damage fertility or the unborn child; H360FD (13.1%) May damage fertility and the unborn child; H319 causes serious eye irritation; H335 may cause respiratory irritation; H303 may be harmful if swallowed. These describe the powder, not the solid glass.",
        "ghs": [
          "H360",
          "H360FD",
          "H319",
          "H335",
          "H303"
        ],
        "source": "pubchem-boric-oxide",
        "where": "Safety and Hazards, GHS Classification (CID 11073337)"
      }
    ],
    "failure_risks": [
      {
        "mode": "Thermal shock",
        "trigger": "Temperature difference across the glass, short exposure (1 h)",
        "consequence": "SCHOTT rates resistance to temperature differences at 110 K for a 1 h exposure, 90 K for 1 to 100 h and 80 K for over 100 h.",
        "severity": "moderate",
        "source": "schott-datasheet-0407",
        "where": "Resistance to Temperature Differences (RTD1) list"
      },
      {
        "mode": "Thermal shock by panel thickness",
        "trigger": "Temperature difference for a thermal shock resistance (RTS) rating, by thickness",
        "consequence": "RTS is 175 K for under 4 mm, 160 K for 4 to 6 mm, 150 K for 6 to 15 mm and 140 K for over 15 mm.",
        "severity": "moderate",
        "source": "schott-datasheet-0407",
        "where": "Resistance to Thermal Shock (RTS) list"
      },
      {
        "mode": "Impact",
        "trigger": "Physical impact on an installed panel",
        "consequence": "SCHOTT says impact resistance depends on how the glass is fitted, its size and thickness, and the type of impact.",
        "severity": "moderate",
        "source": "schott-tech-data-edmund",
        "where": "Physical Impact paragraph"
      },
      {
        "mode": "Thermal shock (kitchenware comparison)",
        "trigger": "Boiling vessel placed on ice",
        "consequence": "Wikipedia says borosilicate withstands a change of about 330 °F without fracturing, against about 100 °F for soda-lime glass, and that borosilicate can still crack under rapid or uneven temperature change.",
        "severity": "moderate",
        "source": "wikipedia-borosilicate",
        "where": "Thermal shock section"
      }
    ],
    "side_effects": [],
    "handling": [
      {
        "text": "Keep long-term use at or below 450 °C (short exposures of less than 10 h up to 500 °C), and keep temperature differences within the RTD and RTS limits in failure_risks.",
        "source": "schott-borofloat33",
        "where": "Maximum operating temperature; RTD1 list"
      },
      {
        "text": "Do not heat borosilicate glass with sodium hydride. The reaction can form sodium borohydride.",
        "source": "wikipedia-borosilicate",
        "where": "Laboratory section"
      }
    ],
    "mitigations": []
  },
  "uses": [
    {
      "application": "optics-and-cameras",
      "device": "Reflecting telescope primary mirror",
      "example": "The 200 inch mirror of the Hale Telescope is made of borosilicate glass.",
      "source": "wikipedia-borosilicate",
      "where": "Optics section"
    },
    {
      "application": "optics-and-cameras",
      "device": "Hot and cold mirrors and dichroic filters",
      "example": "SCHOTT says BOROFLOAT 33 is the material of choice for high-temperature-resistant dichroic filters and hot and cold mirrors, because its high boron content gives a low thermal expansion.",
      "source": "schott-media-datasheet",
      "where": "BOROFLOAT 33 & Functional Coatings, mirrors section"
    },
    {
      "application": "optics-and-cameras",
      "device": "Telescope mirror substrates",
      "example": "SCHOTT lists telescope mirror substrates and glass-ceramics among its aviation, astro and space applications.",
      "source": "schott-borofloat33",
      "where": "Aviation, Astro and Space navigation list"
    },
    {
      "application": "optics-and-cameras",
      "device": "Satellite mirror substrates",
      "example": "SCHOTT lists satellite mirror substrates and electronic packaging in its aviation, astro and space applications.",
      "source": "schott-borofloat33",
      "where": "Aviation, Astro and Space navigation list"
    },
    {
      "application": "electronics-and-chips",
      "device": "Electronic packaging",
      "example": "SCHOTT lists electronic packaging alongside satellite mirror substrates in its space applications.",
      "source": "schott-borofloat33",
      "where": "Aviation, Astro and Space navigation list"
    },
    {
      "application": "solar-arrays",
      "device": "Front-surface cover glass on silicon solar cells",
      "example": "The NASA 1980 solar power satellite study says cerium-doped borosilicate meets the front-cover requirements if it can be bonded to the cell without thermal-mismatch damage; Corning 7070 borosilicate was used as a 250 um integral cover that survived annealing.",
      "source": "nasa-sps-1980",
      "where": "Cover glass section, text on front-surface cover requirements"
    }
  ],
  "supply": [
    {
      "subject": "Boron (borates)",
      "abundance": "USGS: borates are mostly in volcanic and arid-climate deposits; world reserves of refined borates are adequate for the foreseeable future. Boron is also on the USGS 2025 critical minerals list.",
      "producers": [
        {
          "country": "Turkey",
          "year": 2025
        },
        {
          "country": "Bolivia",
          "year": 2025
        },
        {
          "country": "Chile",
          "year": 2025
        },
        {
          "country": "Peru",
          "year": 2025
        },
        {
          "country": "China",
          "year": 2025
        },
        {
          "country": "Argentina",
          "year": 2025
        },
        {
          "country": "Russia",
          "year": 2025
        },
        {
          "country": "Germany",
          "year": 2025
        }
      ],
      "critical_lists": [
        {
          "list": "USGS 2025 Final List of Critical Minerals (published 7 Nov 2025)",
          "listed": true
        }
      ],
      "recycling": "Not sourced.",
      "substitutes": [],
      "source": "usgs-boron",
      "where": "Salient statistics and World Production and Reserves table; critical minerals paragraph; the USGS table gives no country shares, so none are shown"
    },
    {
      "subject": "Boron import dependence (United States)",
      "abundance": "USGS: import sources for all forms of boron, 2021 to 2024, as printed.",
      "producers": [
        {
          "country": "Turkey",
          "share_percent": 90,
          "year": 2021
        },
        {
          "country": "Bolivia",
          "share_percent": 6,
          "year": 2021
        },
        {
          "country": "Other",
          "share_percent": 4,
          "year": 2021
        }
      ],
      "critical_lists": [],
      "recycling": "Not sourced.",
      "substitutes": [],
      "source": "usgs-boron",
      "where": "Import Sources (2021-24): All forms"
    }
  ],
  "media": [],
  "documents": [
    {
      "title": "BOROFLOAT 33 technical details (SCHOTT)",
      "type": "datasheet",
      "url": "https://www.schott.com/en-us/products/borofloat/technical-details"
    },
    {
      "title": "Borosilicate glass (Wikipedia)",
      "type": "report",
      "url": "https://en.wikipedia.org/wiki/Borosilicate_glass"
    },
    {
      "title": "BOROFLOAT 33 & Functional Coatings (SCHOTT)",
      "type": "datasheet",
      "url": "https://media.schott.com/api/public/content/32b935120d7343109caa36fb70f40ced?v=541db792&download=true"
    },
    {
      "title": "SCHOTT BOROFLOAT data sheet 0407",
      "type": "datasheet",
      "url": "https://iosoptics.com/pdf/Schott-Datasheet-Borofloat-33.pdf"
    },
    {
      "title": "Mineral Commodity Summaries 2026: Boron (USGS)",
      "type": "report",
      "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-boron.pdf"
    },
    {
      "title": "Boron oxide (B2O3), PubChem CID 11073337",
      "type": "database",
      "url": "https://pubchem.ncbi.nlm.nih.gov/compound/11073337"
    },
    {
      "title": "Corning 7740 (Pyrex) property table, copy hosted by Valley Design",
      "type": "datasheet",
      "url": "https://valleydesign.com/wp-content/uploads/2023/11/corning-pyrex-7740.pdf",
      "year": 2023
    },
    {
      "title": "NASA Solar Power Satellite System Definition Study (NTRS 19800004887)",
      "type": "report",
      "url": "https://ntrs.nasa.gov/api/citations/19800004887/downloads/19800004887.pdf",
      "year": 1980
    }
  ],
  "gaps": [
    "Silica sand and soda ash supply: no USGS MCS text read in this run; only the boron chapter was read.",
    "Corning PYREX 7740: corning.com returns HTML, not a PDF, in this run. A Valley Design copy of the Corning 7740 property table is cited instead (source valley-7740); its values are not yet used in properties.",
    "No safety data sheet for the finished glass was read. The hazard entry uses PubChem's classes for boron oxide, not for the glass.",
    "No open peer-reviewed paper on borosilicate properties was found; no flight, vacuum or radiation test was found.",
    "Source disagreement: the 0407 SCHOTT data sheet gives a transformation temperature of 530 °C and a Young's modulus of 63 kN/mm2. The current SCHOTT technical page gives 525 °C and 64 kN/mm2. Both are kept with their own sources.",
    "Lab glassware: Wikipedia states it as virtually all modern lab glassware, but the application is not on the approved list, so it stays in story only.",
    "Wikipedia gives a CTE of 3.3 x10^-6 K^-1 at 20 °C for a generic lab borosilicate. That is not used as the BOROFLOAT value; it is recorded here only."
  ],
  "story": {
    "why": "Borosilicate glass is a silica glass with boric oxide added. The boron lowers the thermal expansion, so the glass is less likely to crack when it is heated or cooled quickly. That property is why most modern laboratory glassware is made from it, and why the 200 inch mirror of the Hale Telescope was cast from it.",
    "uses": [
      {
        "where": "Optics",
        "line": "The 200 inch mirror of the Hale Telescope is made of borosilicate glass, according to Wikipedia. Low-expansion borosilicate is also used for reflecting telescope mirrors in general."
      },
      {
        "where": "Laboratory glassware",
        "line": "Wikipedia states that virtually all modern laboratory glassware is made of borosilicate glass. No application from the approved list matches this use, so it is recorded here only."
      },
      {
        "where": "Space and aviation",
        "line": "SCHOTT lists telescope and satellite mirror substrates, and aircraft components for illumination, navigation and displays, among its borosilicate applications."
      },
      {
        "where": "Hot and cold mirrors",
        "line": "SCHOTT says BOROFLOAT 33 is the material of choice for high-temperature dichroic filters and hot and cold mirrors."
      }
    ],
    "can_do": [
      {
        "label": "Density",
        "line": "SCHOTT lists a density of 2.23 g/cm3 at 25 °C for BOROFLOAT 33, which is lighter than most soda-lime glass.",
        "benchmark": "density",
        "scope": "material",
        "value": "2.23 g/cm3"
      },
      {
        "label": "Working temperature",
        "line": "SCHOTT gives a maximum long-term operating temperature of 450 °C, and 500 °C for short exposures of less than 10 h.",
        "benchmark": "max_operating_temperature_long_term",
        "scope": "material",
        "value": "450 °C"
      },
      {
        "label": "Transformation point",
        "line": "The transformation temperature is 525 °C per ISO 7884, the point where the glass stops behaving like a fully elastic solid in cooling tests.",
        "benchmark": "transformation_temperature",
        "scope": "material",
        "value": "525 °C"
      },
      {
        "label": "Optics",
        "line": "The refractive index at 587.6 nm is 1.4714, with an Abbe number of 65.41, which means low dispersion for a visible-light lens.",
        "benchmark": "refractive_index",
        "scope": "material",
        "value": "1.4714"
      },
      {
        "label": "Thermal expansion",
        "line": "SCHOTT gives 3.25 x 10-6 K-1 for 20 to 300 °C (ISO 7991). SCHOTT says this is three times lower than soda-lime glass.",
        "benchmark": "cte",
        "scope": "material",
        "value": "3.25 x10^-6 K^-1"
      }
    ],
    "compare": "Borosilicate glass has a linear thermal expansion of 3.25 x10^-6 K^-1 (20 to 300 °C), which SCHOTT puts at about one third of soda-lime glass. That low expansion gives it the thermal-shock limits in the 0407 data sheet (RTS 140 to 175 K by thickness). Its density of 2.23 g/cm3 and long-term limit of 450 °C are the figures on the SCHOTT sheet.",
    "compare_rows": [
      {
        "label": "Density",
        "benchmark": "density",
        "scope": "material"
      },
      {
        "label": "Long-term working temperature",
        "benchmark": "max_operating_temperature_long_term",
        "scope": "material"
      },
      {
        "label": "Transformation temperature",
        "benchmark": "transformation_temperature",
        "scope": "material"
      },
      {
        "label": "Linear thermal expansion",
        "benchmark": "cte",
        "scope": "material"
      }
    ],
    "handling": [
      "Keep long-term use at or below 450 °C, and short exposures at or below 500 °C (under 10 h). SCHOTT gives these as the maximum operating temperatures.",
      "Keep temperature differences within the SCHOTT RTD limits: 110 K for 1 h, 90 K for 1 to 100 h, 80 K for over 100 h.",
      "Do not heat in contact with sodium hydride; sodium borohydride can form.",
      "Broken glass is sharp; handle it with gloves."
    ],
    "good_for": [
      "Lab glassware and optical parts that must tolerate temperature changes. SCHOTT's 450 °C long-term limit is the reference.",
      "Telescope mirrors and lenses, where low dispersion (Abbe number 65.41) and a known refractive index matter."
    ],
    "watch_out": [
      "The expansion coefficient (3.25 x10^-6 K^-1) is for BOROFLOAT 33. Other borosilicate grades, such as the 3.3 value on Wikipedia, can differ.",
      "Working limits are the manufacturer's reference values for BOROFLOAT 33, not guaranteed values for other borosilicate grades.",
      "Solarization and fluorescence are described as low by SCHOTT, but no numbers are printed on the text pages read."
    ],
    "verdict": "Borosilicate is a sound choice where a low-expansion, durable glass is needed. This profile now has the thermal expansion, electrical and bending values, the chemical durability tests and the boric oxide hazard classes from sourced pages. Supply of silica and soda ash, the glass SDS and space testing are still open.",
    "recipe": {
      "line": "Borosilicate glass is an amorphous silica network with boric oxide added. It is made by melting boric oxide, silica sand, soda ash and alumina together (Wikipedia). BOROFLOAT 33 is made by the float process, which SCHOTT describes as the world's first floated borosilicate glass. The composition below is the typical low-expansion laboratory type; the BOROFLOAT 33 recipe is not published as numbers.",
      "parts": [
        {
          "name": "Silica",
          "symbol": "SiO2",
          "role": "The main network former. It gives the glass its rigid, mostly silica framework.",
          "share_percent": 80
        },
        {
          "name": "Boric oxide",
          "symbol": "B2O3",
          "role": "Lowers the thermal expansion and the working temperature of the glass.",
          "share_percent": 13
        },
        {
          "name": "Alkali oxide",
          "symbol": "Na2O or K2O",
          "role": "Helps the glass melt and adjusts its viscosity.",
          "share_percent": 4
        },
        {
          "name": "Alumina",
          "symbol": "Al2O3",
          "role": "Improves chemical durability.",
          "share_percent": 2
        }
      ]
    },
    "risk_groups": [
      {
        "title": "For people",
        "lead": "PubChem's aggregated GHS classes for boron oxide, the main glass oxide, are read below. No SDS for the finished glass was opened in this run. Hazard data partly checked: boric oxide classes read from PubChem; no SDS for the glass read",
        "points": [
          {
            "label": "Sharp edges",
            "line": "Broken glass is sharp. Handle broken pieces with gloves and dispose of them in a sharps container."
          },
          {
            "label": "Boric oxide",
            "line": "PubChem's aggregated classes for boron oxide include H360 (may damage fertility or the unborn child, Danger) and H319 (eye irritation). These are for the powder, not for the finished glass."
          },
          {
            "label": "Sodium hydride",
            "line": "Do not heat borosilicate glass in contact with sodium hydride; the reaction can form sodium borohydride."
          }
        ],
        "level": 0,
        "verdict": "Hazard data partly checked: boric oxide classes read from"
      }
    ]
  },
  "updated": "2026-10-19",
  "review": {
    "status": "draft",
    "method": "assistant",
    "checked_values": 21,
    "unreachable": 4,
    "caveats": 2,
    "note": "Written by an AI assistant on 2026-10-19. Deepen pass: added CTE, electrical and bending values, annealing and softening points (SCHOTT data sheets), corrosion from the SCHOTT chemical durability table, hazard classes (PubChem), supply (USGS MCS 2026), uses, failure and handling sections."
  },
  "sources": {
    "schott-borofloat33": {
      "title": "BOROFLOAT 33 technical details",
      "id": "SCHOTT AG product page",
      "url": "https://www.schott.com/en-us/products/borofloat/technical-details",
      "kind": "datasheet",
      "license": "manufacturer web page, cited not reproduced"
    },
    "wikipedia-borosilicate": {
      "title": "Borosilicate glass",
      "id": "Wikipedia, Borosilicate glass",
      "url": "https://en.wikipedia.org/wiki/Borosilicate_glass",
      "kind": "web",
      "license": "CC BY-SA 4.0"
    },
    "schott-media-datasheet": {
      "title": "BOROFLOAT 33 & Functional Coatings (SCHOTT brochure)",
      "id": "SCHOTT AG, BOROFLOAT 33 & Functional Coatings",
      "url": "https://media.schott.com/api/public/content/32b935120d7343109caa36fb70f40ced?v=541db792&download=true",
      "kind": "datasheet",
      "license": "manufacturer document, cited not reproduced"
    },
    "schott-datasheet-0407": {
      "title": "SCHOTT BOROFLOAT data sheet 0407 (SCHOTT North America)",
      "id": "SCHOTT North America, data sheet 0407 (copy on IOS Optics site)",
      "url": "https://iosoptics.com/pdf/Schott-Datasheet-Borofloat-33.pdf",
      "kind": "datasheet",
      "license": "manufacturer document, cited not reproduced"
    },
    "schott-tech-data-edmund": {
      "title": "BOROFLOAT 33 Technical Data (SCHOTT, copy on Edmund Optics)",
      "id": "SCHOTT AG technical data sheet, Edmund Optics copy",
      "url": "https://www.edmundoptics.com/ViewDocument/schott-borofloat-technical-data-sheet-english.pdf",
      "kind": "datasheet",
      "license": "manufacturer document, cited not reproduced"
    },
    "usgs-boron": {
      "title": "Mineral Commodity Summaries 2026: Boron",
      "id": "USGS, MCS 2026",
      "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-boron.pdf",
      "kind": "report",
      "license": "US government work, public domain"
    },
    "pubchem-boric-oxide": {
      "title": "Boron oxide (B2O3), PubChem CID 11073337",
      "id": "PubChem, GHS classification of boric oxide",
      "url": "https://pubchem.ncbi.nlm.nih.gov/compound/11073337",
      "kind": "database",
      "license": "PubChem, public domain"
    },
    "valley-7740": {
      "title": "Glass Silicon Constraint Substrates: Corning 7740 (Pyrex) and 7070 property table",
      "id": "Valley Design copy of the Corning 7740 and 7070 property table",
      "url": "https://valleydesign.com/wp-content/uploads/2023/11/corning-pyrex-7740.pdf",
      "year": 2023,
      "kind": "datasheet",
      "license": "copy of a Corning property table, cited not reproduced"
    },
    "nasa-sps-1980": {
      "title": "Solar Power Satellite System Definition Study (NASA contract NAS9-15636)",
      "id": "NASA NTRS 19800004887",
      "url": "https://ntrs.nasa.gov/api/citations/19800004887/downloads/19800004887.pdf",
      "year": 1980,
      "kind": "report",
      "license": "NASA technical report, public distribution"
    }
  },
  "license": "CC-BY-4.0",
  "url": "https://spacemushroom.com/profiles/borosilicate-glass/"
}