{ "spore": "profile", "id": "boron", "spore_version": "0.2", "family": "semiconductor-materials", "name": "Boron", "abbreviation": "B", "role": "neutron absorber, hard amorphous powder and reinforcing fibre", "category": "semiconductors", "type": "silicon", "summary": "Boron is element 5. Free boron is not found in nature; USGS says it occurs only in combined form, as borates. Elemental boron is made as an amorphous powder or as a fibre. The element melts at 2,075 degC (CRC value, reproduced on PubChem), and the fibre is boron deposited on a tungsten core. The boron-10 isotope captures thermal neutrons strongly: NIST gives 3835 barns for 10B and 767 barns for natural boron at 2200 m/s, so the enriched isotope is the useful absorber. NASA's 1995 shielding study called boron the best light-weight material for thermal-neutron absorption in spacecraft.\n", "best_for": "Thermal-neutron absorption where boron-10 content matters (NIST cross sections; NASA 1995 shielding report) and boron fibre for stiff composite plies (Specialty Materials datasheet)", "weakest_at": "Oxidation and reactivity: amorphous boron powder can ignite spontaneously as dust and reacts violently with steam at red heat (Materion; PubChem, citing Bretherick)", "identity": { "formula": "B, elemental boron (crystalline and amorphous forms; PubChem lists amorphous, alpha-rhombohedral, alpha-tetragonal and beta-rhombohedral densities)", "cas": "7440-42-8", "designations": [], "source": "pubchem-boron", "where": "Chemical and Physical Properties, Density section (polymorph list); Materion MSDS Section I (reference number 7440-42-8, formula B)" }, "tags": { "environments": [], "stresses": [], "applications": [ "structures", "radiation-shielding", "electronics-and-chips" ] }, "properties": [ { "benchmark": "density", "label": "Density, amorphous boron", "value": 2.35, "bound": "exact", "unit": "g/cm3", "scope": "material", "conditions": { "form": "amorphous", "basis": "value as printed in the Merck Index entry that PubChem reproduces" }, "method": "Density listed in a handbook entry reproduced on the PubChem record", "status": "ground", "source": "pubchem-density", "where": "Chemical and Physical Properties, Density section, first value (Merck Index 13th ed., p. 225, as cited)", "source_detail": { "title": "PubChem compound record, Boron (CID 5462311): Density section", "id": "CID 5462311, pug_view heading Density", "url": "https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/5462311/JSON?heading=Density", "year": 2026, "kind": "database", "license": "public domain (NCBI)" } }, { "benchmark": "density", "label": "Density, alpha-rhombohedral boron", "value": 2.46, "bound": "exact", "unit": "g/cm3", "scope": "material", "conditions": { "form": "alpha-rhombohedral crystal", "basis": "value as printed in the Merck Index entry that PubChem reproduces" }, "method": "Density listed in a handbook entry reproduced on the PubChem record", "status": "ground", "source": "pubchem-density", "where": "Chemical and Physical Properties, Density section, first value (Merck Index 13th ed., p. 225, as cited)", "source_detail": { "title": "PubChem compound record, Boron (CID 5462311): Density section", "id": "CID 5462311, pug_view heading Density", "url": "https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/5462311/JSON?heading=Density", "year": 2026, "kind": "database", "license": "public domain (NCBI)" } }, { "benchmark": "density", "label": "Density of solid boron (WebElements)", "value": 2460, "bound": "exact", "unit": "kg/m3", "scope": "material", "conditions": { "form": "solid, polymorph not stated on the page" }, "method": "Value printed on a periodic-table reference site", "status": "ground", "source": "webelements-boron", "where": "Physical properties page, Density properties, Density of solid", "source_detail": { "title": "WebElements: Boron, physical properties", "id": "WebElements, Mark Winter", "url": "https://www.webelements.com/boron/physics.html", "year": 2026, "kind": "database", "license": "site terms (cited, not reproduced)" } }, { "benchmark": "melting_point", "value": 2075, "bound": "exact", "unit": "degC", "scope": "material", "conditions": { "pressure": "atmospheric", "basis": "value as printed in the CRC Handbook 81st ed. entry that PubChem reproduces" }, "method": "Melting point listed in a handbook entry reproduced on the PubChem record", "status": "ground", "source": "pubchem-melting", "where": "Melting Point section, first value (CRC Handbook of Chemistry and Physics, 81st ed., p. 4-47, as cited)", "source_detail": { "title": "PubChem compound record, Boron (CID 5462311): Melting Point section", "id": "CID 5462311, pug_view heading Melting Point", "url": "https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/5462311/JSON?heading=Melting+Point", "year": 2026, "kind": "database", "license": "public domain (NCBI)" } }, { "benchmark": "boiling_point", "value": 4000, "bound": "exact", "unit": "degC", "scope": "material", "conditions": { "pressure": "760 mmHg", "basis": "value as printed in the CRC Handbook 81st ed. entry that PubChem reproduces" }, "method": "Boiling point listed in a handbook entry reproduced on the PubChem record", "status": "ground", "source": "pubchem-boiling", "where": "Boiling Point section, first value (CRC Handbook, 81st ed., p. 4-47, as cited)", "source_detail": { "title": "PubChem compound record, Boron (CID 5462311): Boiling Point section", "id": "CID 5462311, pug_view heading Boiling Point", "url": "https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/5462311/JSON?heading=Boiling+Point", "year": 2026, "kind": "database", "license": "public domain (NCBI)" } }, { "benchmark": "thermal_conductivity", "value": 27, "bound": "exact", "unit": "W/(m·K)", "scope": "material", "conditions": { "temperature": "not stated on the page" }, "method": "Value printed on a periodic-table reference site", "status": "ground", "source": "webelements-boron", "where": "Physical properties page, Heat and conduction, Thermal conductivity", "source_detail": { "title": "WebElements: Boron, physical properties", "id": "WebElements, Mark Winter", "url": "https://www.webelements.com/boron/physics.html", "year": 2026, "kind": "database", "license": "site terms (cited, not reproduced)" } }, { "benchmark": "cte", "label": "Coefficient of linear thermal expansion", "value": 6, "bound": "exact", "unit": "ppm/K", "scope": "material", "conditions": { "printed_as": "6 x 10^-6 K^-1", "temperature": "not stated on the page" }, "method": "Value printed on a periodic-table reference site", "status": "ground", "source": "webelements-boron", "where": "Physical properties page, Heat and conduction, Coefficient of linear thermal expansion", "source_detail": { "title": "WebElements: Boron, physical properties", "id": "WebElements, Mark Winter", "url": "https://www.webelements.com/boron/physics.html", "year": 2026, "kind": "database", "license": "site terms (cited, not reproduced)" } }, { "benchmark": "bulk_modulus", "value": 320, "bound": "exact", "unit": "GPa", "scope": "material", "conditions": { "note": "The same page gives no data for Young's modulus, so this is the only elastic value sourced here" }, "method": "Value printed on a periodic-table reference site", "status": "ground", "source": "webelements-boron", "where": "Physical properties page, Elastic properties, Bulk modulus", "source_detail": { "title": "WebElements: Boron, physical properties", "id": "WebElements, Mark Winter", "url": "https://www.webelements.com/boron/physics.html", "year": 2026, "kind": "database", "license": "site terms (cited, not reproduced)" } }, { "benchmark": "vickers_hardness", "label": "Vickers hardness", "value": 49000, "bound": "exact", "unit": "MN/m2", "scope": "material", "conditions": { "printed_as": "49000 MN m-2 (about 49 GPa)", "form": "elemental boron, form not stated" }, "method": "Value printed on a periodic-table reference site", "status": "ground", "note": "Not a canonical property name; kept as a snake_case name and listed in gaps.", "source": "webelements-boron", "where": "Physical properties page, Hardnesses, Vickers hardness", "source_detail": { "title": "WebElements: Boron, physical properties", "id": "WebElements, Mark Winter", "url": "https://www.webelements.com/boron/physics.html", "year": 2026, "kind": "database", "license": "site terms (cited, not reproduced)" } }, { "benchmark": "mineral_hardness", "label": "Mineral hardness (Mohs scale)", "value": 9.3, "bound": "exact", "unit": "-", "scope": "material", "conditions": { "scale": "mineral hardness as printed" }, "method": "Value printed on a periodic-table reference site", "status": "ground", "note": "Not a canonical property name; kept as a snake_case name and listed in gaps.", "source": "webelements-boron", "where": "Physical properties page, Hardnesses, Mineral hardness", "source_detail": { "title": "WebElements: Boron, physical properties", "id": "WebElements, Mark Winter", "url": "https://www.webelements.com/boron/physics.html", "year": 2026, "kind": "database", "license": "site terms (cited, not reproduced)" } }, { "benchmark": "neutron_absorption_cross_section", "label": "Thermal-neutron absorption cross section, 10B", "value": 3835, "bound": "exact", "unit": "barn", "scope": "material", "conditions": { "isotope": "10B", "neutron_energy": "2200 m/s", "uncertainty": "9 barn, printed as 3835.(9.)" }, "method": "Absorption cross section tabulated by NIST (from the 1992 Neutron News compilation, as the table states)", "status": "ground", "note": "Not a canonical property name; kept as a snake_case name and listed in gaps.", "source": "nist-neutron", "where": "Neutron scattering lengths and cross sections table, row 10B, column 8 (absorption cross section for 2200 m/s neutrons)", "source_detail": { "title": "NIST Center for Neutron Research: Neutron scattering lengths and cross sections (table of elements and isotopes)", "id": "NIST NCNR, from Neutron News 3(3), 1992", "url": "https://www.ncnr.nist.gov/resources/n-lengths/list.html", "year": 1992, "kind": "database", "license": "public domain (NIST)" } }, { "benchmark": "neutron_absorption_cross_section", "label": "Thermal-neutron absorption cross section, natural boron", "value": 767, "bound": "exact", "unit": "barn", "scope": "material", "conditions": { "isotope": "natural boron (10B and 11B)", "neutron_energy": "2200 m/s", "uncertainty": "8 barn, printed as 767.(8.)" }, "method": "Absorption cross section tabulated by NIST (from the 1992 Neutron News compilation, as the table states)", "status": "ground", "note": "Not a canonical property name; kept as a snake_case name and listed in gaps.", "source": "nist-neutron", "where": "Neutron scattering lengths and cross sections table, row B (natural), column 8", "source_detail": { "title": "NIST Center for Neutron Research: Neutron scattering lengths and cross sections (table of elements and isotopes)", "id": "NIST NCNR, from Neutron News 3(3), 1992", "url": "https://www.ncnr.nist.gov/resources/n-lengths/list.html", "year": 1992, "kind": "database", "license": "public domain (NIST)" } }, { "benchmark": "isotope_abundance", "label": "Natural abundance of 10B", "value": 20, "bound": "exact", "unit": "%", "scope": "material", "conditions": { "isotope": "10B", "note": "NIST prints the abundance as a whole number; 11B is printed as 80" }, "method": "Natural abundance printed in a neutron data table", "status": "ground", "note": "Not a canonical property name; kept as a snake_case name and listed in gaps.", "source": "nist-neutron", "where": "Neutron scattering lengths and cross sections table, row 10B, column 2 (Natural abundance)", "source_detail": { "title": "NIST Center for Neutron Research: Neutron scattering lengths and cross sections (table of elements and isotopes)", "id": "NIST NCNR, from Neutron News 3(3), 1992", "url": "https://www.ncnr.nist.gov/resources/n-lengths/list.html", "year": 1992, "kind": "database", "license": "public domain (NIST)" } }, { "benchmark": "fibre_diameter", "label": "Boron fibre diameter, 4.0-mil product", "value": 102, "bound": "exact", "unit": "um", "scope": "material", "conditions": { "product": "4.0-mil boron fibre on a tungsten substrate", "basis": "typical value on the datasheet" }, "method": "Typical value on a manufacturer datasheet", "status": "ground", "note": "Not a canonical property name; kept as a snake_case name and listed in gaps.", "source": "specmat-boron-fiber", "where": "Boron fiber properties table, Diameter row, 4-mil column (the page also lists 142 and 76 um)", "source_detail": { "title": "Specialty Materials: Boron fiber, properties table and product description", "id": "Specialty Materials boron fiber product page", "url": "https://www.specmaterials.com/boron-fiber-test-page", "year": 2026, "kind": "datasheet", "license": "supplier document, linked not reproduced" } }, { "benchmark": "density", "label": "Boron fibre density, 4.0-mil product", "value": 2.61, "bound": "exact", "unit": "g/cc", "scope": "material", "conditions": { "product": "4.0-mil boron fibre", "basis": "typical value on the datasheet" }, "method": "Typical value on a manufacturer datasheet", "status": "ground", "source": "specmat-boron-fiber", "where": "Boron fiber properties table, Density row, 4-mil column", "source_detail": { "title": "Specialty Materials: Boron fiber, properties table and product description", "id": "Specialty Materials boron fiber product page", "url": "https://www.specmaterials.com/boron-fiber-test-page", "year": 2026, "kind": "datasheet", "license": "supplier document, linked not reproduced" } }, { "benchmark": "ultimate_tensile_strength", "label": "Boron fibre tensile strength, 4.0-mil product", "value": 4000, "bound": "exact", "unit": "MPa", "scope": "material", "conditions": { "product": "4.0-mil boron fibre", "basis": "typical value on the datasheet" }, "method": "Typical value on a manufacturer datasheet", "status": "ground", "source": "specmat-boron-fiber", "where": "Boron fiber properties table, Tensile Strength row, 4-mil column (the 5.6-mil column also gives 4,000 MPa)", "source_detail": { "title": "Specialty Materials: Boron fiber, properties table and product description", "id": "Specialty Materials boron fiber product page", "url": "https://www.specmaterials.com/boron-fiber-test-page", "year": 2026, "kind": "datasheet", "license": "supplier document, linked not reproduced" } }, { "benchmark": "elastic_modulus", "label": "Boron fibre tensile modulus, 4.0-mil product", "value": 428, "bound": "exact", "unit": "GPa", "scope": "material", "conditions": { "product": "4.0-mil boron fibre", "basis": "typical value on the datasheet" }, "method": "Typical value on a manufacturer datasheet", "status": "ground", "source": "specmat-boron-fiber", "where": "Boron fiber properties table, Tensile Modulus row, 4-mil column", "source_detail": { "title": "Specialty Materials: Boron fiber, properties table and product description", "id": "Specialty Materials boron fiber product page", "url": "https://www.specmaterials.com/boron-fiber-test-page", "year": 2026, "kind": "datasheet", "license": "supplier document, linked not reproduced" } }, { "benchmark": "cte", "label": "Boron fibre thermal expansion, 4.0-mil product", "value": 4.5, "bound": "exact", "unit": "ppm/degC", "scope": "material", "conditions": { "product": "4.0-mil boron fibre", "printed_as": "PPM/degC 4.5" }, "method": "Typical value on a manufacturer datasheet", "status": "ground", "source": "specmat-boron-fiber", "where": "Boron fiber properties table, Thermal Expansion row, 4-mil column", "source_detail": { "title": "Specialty Materials: Boron fiber, properties table and product description", "id": "Specialty Materials boron fiber product page", "url": "https://www.specmaterials.com/boron-fiber-test-page", "year": 2026, "kind": "datasheet", "license": "supplier document, linked not reproduced" } }, { "benchmark": "oxidation_activation_energy", "label": "Activation energy, early-stage oxidation of amorphous boron", "value": 148, "bound": "exact", "unit": "kJ/mol", "scope": "material", "conditions": { "uncertainty": "6 kJ/mol", "material": "95% pure amorphous boron powder, pre-treated to thin the hydrated oxide layer", "atmosphere": "oxygen-argon mixture, non-isothermal thermogravimetry", "model": "core-shell particle model" }, "method": "Kinetic parameter from a thermogravimetric study, reported in the abstract", "status": "ground", "note": "Not a canonical property name; kept as a snake_case name and listed in gaps.", "source": "njit-boron-oxidation", "where": "Abstract, final paragraph of the abstract text", "source_detail": { "title": "Heterogeneous reaction kinetics for oxidation and combustion of boron", "id": "NJIT Digital Commons, faculty publications 7148 (publication date 2019-12-01)", "url": "https://digitalcommons.njit.edu/fac_pubs/7148", "year": 2019, "kind": "paper", "license": "repository record (abstract read)" } } ], "corrosion": [ { "environment": "Room-temperature air, amorphous boron powder", "headline": "The powder oxidizes slowly at room temperature, and dust can ignite spontaneously in air.", "effect": "Materion's safety data sheet says boron metal powder is highly reactive, oxidizes slowly at room temperature and that dust may ignite spontaneously in air. The sheet does not give a rate or an oxide thickness, so the risk is the fine powder rather than bulk surface attack.", "rating": "low", "conditions": { "form": "amorphous powder", "exposure": "room temperature air; exposure time not stated" }, "source": "materion-msds-boron", "where": "Section IV, Unusual fire and explosion hazards" }, { "environment": "Oxygen at high temperature (thermogravimetric test, amorphous boron powder)", "headline": "Early oxidation of amorphous boron has an activation energy of 148 kJ/mol.", "effect": "Non-isothermal thermogravimetric tests of 95% pure amorphous boron in oxygen-argon, at several heating rates, were fitted with a core-shell particle model. The early stage of oxidation has an activation energy of 148 plus or minus 6 kJ/mol. The abstract gives no onset temperature, so the temperature at which oxidation becomes significant is not stated here.", "rating": "moderate", "conditions": { "material": "95% pure amorphous boron, pre-treated with acetonitrile and water", "atmosphere": "oxygen-argon mixture", "method": "non-isothermal thermogravimetry" }, "source": "njit-boron-oxidation", "where": "Abstract" }, { "environment": "Steam or water at red heat (powdered boron)", "headline": "Powdered boron and steam may react violently at red heat.", "effect": "PubChem, citing Bretherick's Handbook of Reactive Chemical Hazards, says the interaction of powdered boron and steam may become violent at red heat, and that highly exothermic reactions with water might become combustive or explosive at sufficiently high temperatures and pressures.", "rating": "severe", "conditions": { "temperature": "red heat (not given as a number on the page)", "medium": "steam or water" }, "source": "pubchem-boron", "where": "Firefighting Hazards section" }, { "environment": "Gaseous chlorine or fluorine at room temperature", "headline": "Boron powder may ignite on contact with gaseous chlorine or fluorine at room temperature.", "effect": "Materion's sheet lists chlorine and fluorine gas as ignition risks at room temperature, and says boron may react exothermically with metals above 900 degC.", "rating": "severe", "conditions": { "form": "powder", "reagent": "gaseous Cl2 or F2" }, "source": "materion-msds-boron", "where": "Section IV, Unusual fire and explosion hazards" } ], "risks": { "hazards": [ { "text": "PubChem: 52.2% (253 of 485) of company reports say the substance does not meet GHS hazard criteria. The statements it lists for the other reports are H302, H332, H335 and H412, with the Warning signal word. The percentages are as PubChem prints them.", "ghs": [ "H302", "H332", "H335", "H412" ], "source": "pubchem-boron", "where": "Safety and Hazards, GHS Classification" }, { "text": "Höganäs grade sheet PD-4031: Grade I is not classified under EU Regulation 1272/2008. Grades II and III are classified Repr. 1B, with H360FD (may damage fertility; may damage the unborn child) and the signal word Danger.", "ghs": [ "H360FD" ], "source": "hoganas-pd4031", "where": "Hazards identification in Advertising, one entry per grade" } ], "failure_risks": [ { "mode": "Spontaneous ignition of boron dust", "trigger": "Fine boron powder dispersed or dusting in air", "consequence": "Materion says dust may ignite spontaneously in air, and that the powder is highly reactive.", "severity": "high", "source": "materion-msds-boron", "where": "Section IV, Unusual fire and explosion hazards" }, { "mode": "Violent reaction with steam or water", "trigger": "Powdered boron at red heat with steam, or water at high temperature and pressure", "consequence": "Reaction may become violent at red heat; exothermic reactions with water may become combustive or explosive at high temperature and pressure.", "severity": "high", "source": "pubchem-boron", "where": "Firefighting Hazards section" }, { "mode": "Ignition with halogen gas", "trigger": "Contact with gaseous chlorine or fluorine at room temperature", "consequence": "Boron powder may ignite; Materion also lists bromine, chlorine, nitric acid and copper oxide among materials to avoid.", "severity": "high", "source": "materion-msds-boron", "where": "Section IV and Section V, incompatible materials" } ], "side_effects": [ { "text": "Boron metal may emit toxic fumes if involved in a fire; the hazardous combustion product named is boron oxide.", "affects": "Firefighters and anyone downwind of a fire", "source": "materion-msds-boron", "where": "Section IV, Hazardous combustion products; Section V, decomposition products" } ], "handling": [ { "text": "Store in a closed container, as the Höganäs grade sheet directs.", "source": "hoganas-pd4031", "where": "Storage and Handling section" }, { "text": "Use a Class D or other suitable metal extinguishing agent for boron powder fires.", "source": "materion-msds-boron", "where": "Section IV, Extinguishing media" }, { "text": "Keep away from the materials Materion lists as incompatible, including chlorine, bromine, fluorine compounds, nitric acid, potassium chlorate and potassium nitrate.", "source": "materion-msds-boron", "where": "Section V, Incompatibility" } ], "mitigations": [] }, "uses": [ { "application": "structures", "device": "Boron fibre epoxy composites (stiffening plies)", "example": "The Specialty Materials datasheet says adding boron fibre to composites with standard and intermediate-modulus fibres increases tensile and compression modulus, which allows fewer plies or less thickness for the same stiffness.", "source": "specmat-boron-fiber", "where": "Boron fiber product page, bullet list under the properties table" }, { "application": "radiation-shielding", "device": "Spacecraft thermal-neutron shielding (ground study with boron powder in polymer films)", "example": "NASA-funded work at the College of William and Mary (1995) concluded that boron is the best light-weight material for thermal-neutron absorption in spacecraft, because 10B captures neutrons and gives stable products. In a 600 MeV/amu iron-ion test, adding boron powder to a polyetherimide film did not significantly change its cosmic-ray shielding.", "source": "nasa-cr-199720", "where": "Introduction, paragraph on thermal-neutron absorption; Computer design and results on boron-containing polyetherimide" }, { "application": "electronics-and-chips", "device": "Semiconductor manufacturing", "example": "The USGS says that boron was used in abrasives, cleaning products, insecticides, insulation and the production of semiconductors, and that glass and ceramics were the leading domestic users in 2025.", "source": "usgs-mcs2026-boron", "where": "Domestic Production and Use paragraph" } ], "supply": [ { "subject": "Boron (produced as borates; USGS says elemental boron has limited commercial applications and does not occur in nature in elemental form)", "abundance": "Not found in a fetched source", "producers": [ { "country": "Turkey", "share_percent": 51.4, "year": 2025 }, { "country": "Bolivia", "share_percent": 13, "year": 2025 }, { "country": "Chile", "share_percent": 10.3, "year": 2025 }, { "country": "China", "share_percent": 7.9, "year": 2025 }, { "country": "Peru", "share_percent": 7.5, "year": 2025 }, { "country": "Argentina", "share_percent": 5.8, "year": 2025 }, { "country": "Russia", "share_percent": 2.7, "year": 2025 }, { "country": "Germany", "share_percent": 1.4, "year": 2025 } ], "critical_lists": [ { "list": "USGS 2025 List of Critical Minerals (boron added in the final 2025 list)", "listed": true } ], "recycling": "USGS: insignificant.", "substitutes": [ "USGS: substitution is possible in detergents, enamels, insulation and soaps. The chapter does not discuss neutron-absorbing or electronic uses." ], "source": "usgs-mcs2026-boron", "where": "World Production and Reserves table, 2025 column (thousand metric tons, as printed; the table lists boric oxide equivalent for China and crude or refined forms for other countries, so the shares are not on one basis). Shares calculated by Space Mushroom against the 2,920 thousand t total of the listed countries, because the USGS world total is not given (XX). US production is withheld (W). US imports 2021-24: Turkey 90%, Bolivia 6%, other 4%. Reserves (thousand t): Turkey 950,000; Russia 40,000; United States 48,000; Chile 35,000; China 9,100; Peru 4,000." } ], "media": [], "documents": [ { "title": "PubChem: Boron (CID 5462311), chemical and physical properties and GHS classification", "type": "database", "url": "https://pubchem.ncbi.nlm.nih.gov/compound/5462311", "year": 2026 }, { "title": "NIST: Neutron scattering lengths and cross sections", "type": "database", "url": "https://www.ncnr.nist.gov/resources/n-lengths/list.html", "year": 1992 }, { "title": "WebElements: Boron physical properties", "type": "database", "url": "https://www.webelements.com/boron/physics.html", "year": 2026 }, { "title": "USGS Mineral Commodity Summaries 2026: Boron", "type": "report", "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-boron.pdf", "year": 2026 }, { "title": "Specialty Materials: Boron fiber datasheet", "type": "datasheet", "url": "https://www.specmaterials.com/boron-fiber-test-page", "year": 2026 }, { "title": "Heterogeneous reaction kinetics for oxidation and combustion of boron (NJIT)", "type": "paper", "url": "https://digitalcommons.njit.edu/fac_pubs/7148", "year": 2019 }, { "title": "NASA-CR-199720: Shielding Materials for Highly Penetrating Space Radiations", "type": "report", "url": "https://ntrs.nasa.gov/api/citations/19960007435/downloads/19960007435.pdf", "year": 1995 }, { "title": "Materion boron powder MSDS", "type": "sds", "url": "https://www.physics.purdue.edu/primelab/safety/MSDS/Retired%20SDS%20and%20MSDS/2017%20removed%20safety%20sheets/MSDS%20updated%20to%20SDS/boron%20powder%20%20-%20Materion.pdf", "year": 2001 }, { "title": "Höganäs PD-4031: Amorphous boron grades", "type": "datasheet", "url": "https://chinafytarget.hoganas.com/globalassets/downloads/stc/pd-4031.pdf", "year": 2025 } ], "gaps": [ "Specific heat of boron not found in a fetched source (WebElements gives no value on the physical-properties page).", "Young's modulus of crystalline boron not found (WebElements prints no data). The only elastic value here is the bulk modulus.", "No neutron-absorber use in reactor control rods was sourced. The only spacecraft shielding source is the NASA-funded 1995 report.", "Crustal abundance of boron not found in a fetched source (the WebElements abundance page did not return a value).", "The European Commission critical raw materials list was not checked for boron.", "ChemicalBook and Strem safety sheets returned HTML, not PDF, so their hazard entries (H228, H302, H332, H335) are not used here.", "Materion's sheet prints a melting point of 2300 degC and a boiling point of 2550 degC. These conflict with the CRC values from PubChem, so the CRC values are used and the Materion figures are left out.", "The Knoop hardness of the boron fibre (3,200) is printed without a unit on the datasheet, so it is left out.", "WebElements prints the electrical resistivity as a garbled expression (> 10 12 x 10-8 ohm m). It is left out.", "The boron fibre core diameter and the tungsten-core structure are not taken from a fetched datasheet value; the Specialty Materials page describes the core but gives no number.", "Hazard data differ by grade and by supplier. The PubChem GHS percentages are as printed and rest on company notifications, not a single test.", "Oxidation onset temperature for amorphous boron not found in the fetched abstract.", "The NIST table prints the 10B abundance as a whole number (20). A more precise natural abundance was not taken from a fetched source." ], "story": { "why": "Elemental boron is a metalloid, and the USGS states that it has limited commercial use in its elemental form. It is used in two forms in the sources read here: an amorphous powder whose boron content depends on grade (Höganäs' grade sheet), and a fibre that Specialty Materials makes by depositing boron on a tungsten wire. Its main value in space work is its neutron capture, which comes almost entirely from the 10B isotope.", "uses": [ { "where": "Neutron shielding in spacecraft", "line": "NASA-funded work at the College of William and Mary (1995) called boron the best light-weight material for absorbing thermal neutrons in a spacecraft. This was a shielding study and ground test, not a flight result." }, { "where": "Stiffening composite plies", "line": "Specialty Materials' boron fibre is 102 micrometres in its 4-mil form, with a tensile modulus of 428 GPa and a tensile strength of 4000 MPa. The datasheet says it is used to stiffen composites that already use standard or intermediate-modulus fibres." }, { "where": "Semiconductor manufacturing", "line": "The USGS lists boron among the uses in semiconductor production. The chapter does not give the size of that use." } ], "can_do": [ { "label": "Neutron absorption", "line": "NIST gives an absorption cross section of 3835 barns for 10B at 2200 m/s neutrons, against 767 barns for natural boron. Enriched boron is therefore worth far more as an absorber than the natural mix.", "benchmark": "neutron_absorption_cross_section", "scope": "material", "value": "3835 barn" }, { "label": "Stiffness of the fibre", "line": "The 4-mil boron fibre has a tensile modulus of 428 GPa on Specialty Materials' datasheet, with a density of 2.61 g/cc.", "benchmark": "elastic_modulus", "scope": "material", "value": "428 GPa" }, { "label": "Melting point", "line": "The CRC Handbook value, reproduced on PubChem, is 2,075 degC for the element.", "benchmark": "melting_point", "scope": "material", "value": "2075 degC" }, { "label": "Oxidation", "line": "Early oxidation of 95% pure amorphous boron in oxygen has an activation energy of 148 plus or minus 6 kJ/mol. The abstract gives no onset temperature.", "benchmark": "oxidation_activation_energy", "scope": "material", "value": "148 kJ/mol" } ], "compare": "Boron is a light solid, with a density of 2.35 to 2.46 g/cm3, and it melts at 2,075 degC. Its strongest engineering property is its neutron capture, which depends on the isotope: the 10B isotope has a cross section about five times that of natural boron. Its weak point is its reactivity. Amorphous powder can ignite as dust, and the powder reacts with steam and halogen gases, so it needs more care in handling than a stable structural solid. The table compares boron with the other entries in this collection on its main properties.", "compare_rows": [ { "label": "Density", "benchmark": "density", "scope": "material" }, { "label": "Melting point", "benchmark": "melting_point", "scope": "material" }, { "label": "Thermal conductivity", "benchmark": "thermal_conductivity", "scope": "material" } ], "handling": [ "Store in a closed container. The powder can ignite as dust, so keep dust out of the air.", "Keep it away from chlorine, bromine, fluorine compounds, nitric acid and potassium nitrate or chlorate.", "Use a Class D or other suitable metal extinguishing agent on a fire.", "Check the grade's hazard classification before use, because Grades II and III carry a reproductive-toxicity classification." ], "good_for": [ "Neutron absorption where the 10B isotope is enriched. NIST gives 3835 barns for 10B against 767 barns for natural boron.", "Stiff fibre for composites. Specialty Materials gives a tensile modulus of 428 GPa for the 4-mil fibre." ], "watch_out": [ "Dust and reactive powder. Materion says dust can ignite spontaneously in air.", "Steam and halogen gases. PubChem and Materion both name reactions that can turn violent at high temperature.", "Hazard data differ by grade. Grade I shows no classification, while Grades II and III are classified as Repr. 1B." ], "verdict": "Elemental boron is a strong neutron absorber when enriched in 10B, and it is a stiff fibre. Its powder is reactive and needs careful handling, and the hazard classification depends on the grade.", "recipe": { "line": "Elemental boron, symbol B. Natural boron is a mix of two isotopes: 10B, which absorbs thermal neutrons strongly, and 11B. Specialty Materials says its boron fibre is deposited on a fine tungsten wire by chemical vapor deposition.", "parts": [ { "name": "Boron-10", "symbol": "10B", "role": "The neutron absorber. Its capture cross section is about 3835 barns at 2200 m/s, against 767 barns for natural boron.", "share_percent": 20 }, { "name": "Boron-11", "symbol": "11B", "role": "The main isotope of natural boron. It has a much smaller thermal-neutron capture cross section, so it contributes little to shielding.", "share_percent": 80 }, { "name": "Boron", "symbol": "B", "role": "Element as a whole. The Materion sheet gives its molecular weight.", "atoms": 1, "atomic_weight": 10.81 } ] }, "risk_groups": [ { "title": "For people", "lead": "The grades differ. Some suppliers list no hazard for the powder, and others classify it as a reproductive toxicant.", "points": [ { "label": "Grade I powder", "line": "Höganäs lists no hazard classification under EU Regulation 1272/2008 for amorphous boron Grade I. Its specification is at least 95% boron." }, { "label": "Grades II and III", "line": "The same sheet classifies Grades II and III as Repr. 1B with H360FD and the signal word Danger. PubChem's summary records H302 and H332 for the reports that do classify the substance." }, { "label": "Dust", "line": "Materion says dust can ignite spontaneously in air, so the fine powder is the main hazard in handling." } ], "level": 0, "verdict": "Hazard depends on the grade" }, { "title": "In a fire", "lead": "Boron powder is the fire hazard. Water, steam and halogen gases are the reactions to avoid.", "points": [ { "label": "Extinguishing", "line": "Materion says to use a Class D or other suitable metal extinguishing agent." }, { "label": "Reaction with steam", "line": "PubChem, citing Bretherick, says powdered boron and steam may react violently at red heat." }, { "label": "Halogens", "line": "Materion says boron powder may ignite on contact with gaseous chlorine or fluorine at room temperature." } ] }, { "title": "Handling and storage", "points": [ { "label": "Container", "line": "Store the powder in a closed container, as the Höganäs grade sheet directs." }, { "label": "Incompatible materials", "line": "Materion lists chlorine, bromine, fluorine compounds, nitric acid, potassium chlorate and potassium nitrate among the materials to avoid." } ] } ] }, "updated": "2026-10-26", "review": { "status": "draft", "method": "assistant", "checked_values": 19, "unreachable": 0, "caveats": 3, "note": "Written by an AI assistant on 2026-10-26 from pages fetched in this run. verify-values finds all 19 values in their cited sources. Caveats: non-canonical property names (7 values), grade-dependent hazard data, and a melting point on one supplier sheet that conflicts with the CRC value." }, "sources": { "pubchem-boron": { "title": "PubChem compound record, Boron (CID 5462311): chemical and physical properties, safety and hazards", "id": "CID 5462311", "url": "https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/5462311/JSON", "year": 2026, "kind": "database", "license": "public domain (NCBI)" }, "nist-neutron": { "title": "NIST Center for Neutron Research: Neutron scattering lengths and cross sections (table of elements and isotopes)", "id": "NIST NCNR, from Neutron News 3(3), 1992", "url": "https://www.ncnr.nist.gov/resources/n-lengths/list.html", "year": 1992, "kind": "database", "license": "public domain (NIST)" }, "webelements-boron": { "title": "WebElements: Boron, physical properties", "id": "WebElements, Mark Winter", "url": "https://www.webelements.com/boron/physics.html", "year": 2026, "kind": "database", "license": "site terms (cited, not reproduced)" }, "usgs-mcs2026-boron": { "title": "Mineral Commodity Summaries 2026, Boron", "id": "USGS MCS 2026, February 2026", "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-boron.pdf", "year": 2026, "kind": "report", "license": "public domain (USGS)" }, "specmat-boron-fiber": { "title": "Specialty Materials: Boron fiber, properties table and product description", "id": "Specialty Materials boron fiber product page", "url": "https://www.specmaterials.com/boron-fiber-test-page", "year": 2026, "kind": "datasheet", "license": "supplier document, linked not reproduced" }, "njit-boron-oxidation": { "title": "Heterogeneous reaction kinetics for oxidation and combustion of boron", "id": "NJIT Digital Commons, faculty publications 7148 (publication date 2019-12-01)", "url": "https://digitalcommons.njit.edu/fac_pubs/7148", "year": 2019, "kind": "paper", "license": "repository record (abstract read)" }, "nasa-cr-199720": { "title": "Shielding Materials for Highly Penetrating Space Radiations (NASA-CR-199720, final technical report, NCC-1-151)", "id": "NTRS 19960007435; NASA-CR-199720; November 1995", "url": "https://ntrs.nasa.gov/api/citations/19960007435/downloads/19960007435.pdf", "year": 1995, "kind": "report", "license": "public domain (NASA)" }, "materion-msds-boron": { "title": "Materion Advanced Chemicals: Material Safety Data Sheet, Boron, powder (product B-MSDS0070)", "id": "Materion MSDS, reference 7440-42-8 (revision 05/03/2001, generated 2011)", "url": "https://www.physics.purdue.edu/primelab/safety/MSDS/Retired%20SDS%20and%20MSDS/2017%20removed%20safety%20sheets/MSDS%20updated%20to%20SDS/boron%20powder%20%20-%20Materion.pdf", "year": 2001, "kind": "datasheet", "license": "supplier document, linked not reproduced" }, "hoganas-pd4031": { "title": "Höganäs: Powders for special applications, Amorphous boron grades I, II and III (PD-4031, issue 3, 2025)", "id": "Hoganas PD-4031, issue 3-08.08.2025", "url": "https://chinafytarget.hoganas.com/globalassets/downloads/stc/pd-4031.pdf", "year": 2025, "kind": "datasheet", "license": "supplier document, linked not reproduced" }, "pubchem-density": { "title": "PubChem compound record, Boron (CID 5462311): Density section", "id": "CID 5462311, pug_view heading Density", "url": "https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/5462311/JSON?heading=Density", "year": 2026, "kind": "database", "license": "public domain (NCBI)" }, "pubchem-melting": { "title": "PubChem compound record, Boron (CID 5462311): Melting Point section", "id": "CID 5462311, pug_view heading Melting Point", "url": "https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/5462311/JSON?heading=Melting+Point", "year": 2026, "kind": "database", "license": "public domain (NCBI)" }, "pubchem-boiling": { "title": "PubChem compound record, Boron (CID 5462311): Boiling Point section", "id": "CID 5462311, pug_view heading Boiling Point", "url": "https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/5462311/JSON?heading=Boiling+Point", "year": 2026, "kind": "database", "license": "public domain (NCBI)" } }, "license": "CC-BY-4.0", "url": "https://spacemushroom.com/profiles/boron/" }