Alumina Al2O3

spore: profile
id: alumina
spore_version: 0.2
family: oxide-ceramics
name: Alumina
abbreviation: Al2O3
role: structural/insulating ceramic
category: ceramics
type: oxides
summary: >
  Alumina is aluminium oxide (Al2O3) sintered into a hard, white, electrically insulating technical ceramic. Its numbers depend
  on purity grade: in one manufacturer chart the nominal 99.5% grade (AD-995) has a density of 3.9 g/cm3, a flexural strength of
  379 MPa and a maximum use temperature of 1750 °C with no load on the part. Like most ceramics it is brittle, with a fracture
  toughness of only 4 to 5 MPa·m½. The only space-related sources we could open are NASA ground tests: a reactor irradiation of
  alumina insulators for a space power system and a thermal model of a NASA initiator.
best_for: "Hard, stiff, electrically insulating parts that must stay stable at high temperature (CoorsTek chart: AD-995 volume resistivity above 10^14 ohm-cm at 25 °C)"
weakest_at: "Brittle fracture and sudden temperature change (fracture toughness 4 to 5 MPa·m½ for AD-995; thermal shock temperature difference of 200 °C for Kyocera's 99% grade)"
identity:
  formula: Al2O3
  cas: "1344-28-1"
  source: nist-webbook
  where: NIST Chemistry WebBook entry for aluminium oxide (formula Al2O3, molecular weight 101.9613, CAS Registry Number 1344-28-1)
tags:
  environments: []
  stresses: [total-radiation-dose, extreme-heat]
  applications: [electronics-and-chips, mechanisms]
properties:
  - benchmark: density
    label: Density, 96% grade (AD-96)
    value: 3.72
    unit: g/cm3
    scope: material
    conditions: {grade: "CoorsTek AD-96, nominal 96% Al2O3", test: "ASTM C20", form: "sintered ceramic, water absorption 0%", chart: "Ceramic Properties Standard, 8510-1042 Rev. J (2008)"}
    method: Typical value from a manufacturer property chart
    status: ground
    source: coorstek-chart
    where: Properties table, Density row, AD-96 column
  - benchmark: density
    label: Density, 99.5% grade (AD-995)
    value: 3.9
    unit: g/cm3
    scope: material
    conditions: {grade: "CoorsTek AD-995, nominal 99.5% Al2O3", test: "ASTM C20", form: "sintered ceramic, water absorption 0%", chart: "Ceramic Properties Standard, 8510-1042 Rev. J (2008)"}
    method: Typical value from a manufacturer property chart (printed as 3.90)
    status: ground
    source: coorstek-chart
    where: Properties table, Density row, AD-995 column
  - benchmark: melting_point
    label: Melting point as listed in PubChem
    value: 2030
    value_high: 2072
    bound: range
    unit: °C
    scope: material
    conditions: {material: "aluminium oxide, no grade or purity given", basis: "PubChem lists 2030 °C (Hawley's, 2007), 2054 °C (ILO-WHO ICSC 0351) and 2072 °C (PAC Chemical Database)"}
    method: Range spanning three handbook and database entries quoted in PubChem
    status: ground
    note: Three different sources, not one measurement; PubChem also lists 3632 °F from CAMEO, NIOSH and OSHA.
    source: pubchem-alumina
    where: Experimental Properties, Melting Point (CID 9989226)
  - benchmark: flexural_strength
    label: Flexural strength, 99.5% grade (AD-995)
    value: 379
    unit: MPa
    scope: material
    conditions: {grade: "CoorsTek AD-995, nominal 99.5% Al2O3", temperature: "20 °C", test: "ASTM F417 (modulus of rupture)", chart: "printed as 379 MPa (55 psi x 10^3)"}
    method: Typical value from a manufacturer property chart
    status: ground
    note: In the same chart, sintered Y2O3-stabilised zirconia (YTZP) is listed at 1240 MPa. The chart states that values vary with method of manufacture, size and shape of part.
    source: coorstek-chart
    where: Properties table, Flexural Strength (MOR) row, AD-995 column
  - benchmark: elastic_modulus
    label: Elastic modulus, 99.5% grade (AD-995)
    value: 370
    unit: GPa
    scope: material
    conditions: {grade: "CoorsTek AD-995, nominal 99.5% Al2O3", temperature: "20 °C", test: "ASTM C848"}
    method: Typical value from a manufacturer property chart
    status: ground
    source: coorstek-chart
    where: Properties table, Elastic Modulus row, AD-995 column
  - benchmark: fracture_toughness
    label: Fracture toughness, 99.5% grade (AD-995)
    value: 4
    value_high: 5
    bound: range
    unit: MPa·√m
    scope: material
    conditions: {grade: "CoorsTek AD-995, nominal 99.5% Al2O3", symbol: "K(Ic)", test: "notched beam"}
    method: Range printed in a manufacturer property chart as 4-5
    status: ground
    note: In the same chart, sintered Y2O3-stabilised zirconia (YTZP) is listed at 13 and the 96% grade (AD-96) also at 4-5.
    source: coorstek-chart
    where: Properties table, Fracture Toughness row, AD-995 column
  - benchmark: vickers_hardness
    label: Vickers hardness, grade of at least 99% Al2O3
    value: 15.2
    unit: GPa
    scope: material
    conditions: {grade: "Kyocera AO479O, 99% or more Al2O3", test: "JIS R 1610, HV 9.807 N", datasheet_date: "2023.04.03", form: "dense sintered alumina"}
    method: Typical value from a manufacturer datasheet
    status: ground
    source: kyocera-ao479o
    where: Mechanical and physical characteristics table, Vickers hardness row
  - benchmark: thermal_conductivity
    label: Thermal conductivity, 99.5% grade (AD-995)
    value: 30
    unit: W/(m·K)
    scope: material
    conditions: {grade: "CoorsTek AD-995, nominal 99.5% Al2O3", temperature: "20 °C", test: "ASTM C408", chart: "printed as 30.0"}
    method: Typical value from a manufacturer property chart
    status: ground
    note: In the same chart, sintered Y2O3-stabilised zirconia (YTZP) is listed at 2.2.
    source: coorstek-chart
    where: Properties table, Thermal Conductivity row, AD-995 column
  - benchmark: cte
    label: Thermal expansion, 99.5% grade (AD-995)
    value: 8.2
    unit: ppm/K
    scope: material
    conditions: {grade: "CoorsTek AD-995, nominal 99.5% Al2O3", temperature_range: "25 to 1000 °C", test: "ASTM C372", chart_unit: "1 x 10-6 per °C"}
    method: Mean coefficient from a manufacturer property chart
    status: ground
    source: coorstek-chart
    where: Properties table, Coefficient of Thermal Expansion row, AD-995 column
  - benchmark: max_service_temp
    label: Maximum use temperature, 99.5% grade (AD-995)
    value: 1750
    unit: °C
    scope: material
    conditions: {grade: "CoorsTek AD-995, nominal 99.5% Al2O3", load: "no load on the part (chart condition: NO-LOAD COND.)"}
    method: Rating from a manufacturer property chart
    status: ground
    note: In the same chart, the 96% grade (AD-96) is rated 1700 and sintered Y2O3-stabilised zirconia (YTZP) 1500.
    source: coorstek-chart
    where: Properties table, Maximum Use Temperature row, AD-995 column
  - benchmark: thermal_shock_dt
    label: Thermal shock temperature difference, grade of at least 99% Al2O3
    value: 200
    unit: °C
    scope: material
    conditions: {grade: "Kyocera AO479O, 99% or more Al2O3", test: "JIS R 1648", datasheet_date: "2023.04.03"}
    method: Typical value from a manufacturer datasheet (the largest sudden temperature difference the sample withstood in that test)
    status: ground
    source: kyocera-ao479o
    where: Mechanical and physical characteristics table, Thermal shock temperature difference row
  - benchmark: dielectric_constant
    label: Dielectric constant, 99.5% grade (AD-995)
    value: 9.7
    unit: "-"
    scope: material
    conditions: {grade: "CoorsTek AD-995, nominal 99.5% Al2O3", frequency: "1 MHz", temperature: "25 °C", test: "ASTM D150"}
    method: Typical value from a manufacturer property chart
    status: ground
    note: In the same chart, sintered Y2O3-stabilised zirconia (YTZP) is listed at 29.0.
    source: coorstek-chart
    where: Properties table, Dielectric Constant row, AD-995 column
  - benchmark: dielectric_loss
    label: Dielectric loss (tan delta), 99.5% grade (AD-995)
    value: 0.0001
    unit: tan delta
    scope: material
    conditions: {grade: "CoorsTek AD-995, nominal 99.5% Al2O3", frequency: "1 MHz", temperature: "25 °C", test: "ASTM D150"}
    method: Typical value from a manufacturer property chart
    status: ground
    source: coorstek-chart
    where: Properties table, Dielectric Loss (tan delta) row, AD-995 column
  - benchmark: volume_resistivity
    label: Volume resistivity at 25 °C, 99.5% grade (AD-995)
    value: 1.0e14
    bound: lower
    unit: ohm-cm
    scope: material
    conditions: {grade: "CoorsTek AD-995, nominal 99.5% Al2O3", temperature: "25 °C", test: "ASTM D1829", chart_entry: "> 10¹⁴ ohm-cm"}
    method: Lower bound printed in a manufacturer property chart
    status: ground
    source: coorstek-chart
    where: Properties table, Volume Resistivity row (25 °C), AD-995 column
  - benchmark: volume_resistivity
    label: Volume resistivity at 1000 °C, 99.5% grade (AD-995)
    value: 2.0e6
    unit: ohm-cm
    scope: material
    conditions: {grade: "CoorsTek AD-995, nominal 99.5% Al2O3", temperature: "1000 °C", test: "ASTM D1829", chart_entry: "2 x 10⁶ ohm-cm"}
    method: Typical value from a manufacturer property chart
    status: ground
    note: The same chart lists 2 x 10¹⁰ ohm-cm at 500 °C. Resistivity falls steeply as the temperature rises.
    source: coorstek-chart
    where: Properties table, Volume Resistivity row (1000 °C), AD-995 column
  - benchmark: radiation_resistance_change
    label: Change in electrical resistance of alumina insulator layers after reactor irradiation
    value: 3
    value_high: 5
    bound: range
    unit: times the pre-irradiation resistance
    scope: material
    conditions: {specimen: "two alumina trilayers (alumina layer 0.25 mm thick between two 0.38 mm niobium layers), purity grade not stated", irradiation: "Engineering Test Reactor at an average of about 1200 K", fast_neutron_fluence: "2.3 x 10²¹ to 2.6 x 10²¹ neutrons/cm2 (energy above 1 MeV)", measured: "1 kHz ac resistance in a vacuum furnace, 700 to 1275 K", result: "increase fairly uniform over 700 to 1275 K"}
    method: Resistance of bonded insulator layers measured before and after irradiation
    status: ground
    note: The report also saw signs of grain boundary weakening in the alumina, thin cracks in the alumina body, and a 0.4 to 0.9 percent increase in sample diameters and lengths (both ceramics). A 1971 OCR copy of a scanned report was read; one earlier test cited in it found a five to tenfold increase, and another found decreases.
    source: mayer1971
    where: Summary; Resistance Measurements (Fig. 13(c) and (d)); Summary of Results
corrosion:
  - environment: Hydrochloric acid, 2.34 mol/L, 25 °C
    headline: "In a short electrochemical test, 99.85% alumina corroded very slowly in hydrochloric acid."
    effect: "Potentiodynamic polarization (an electrochemical test that sweeps the voltage and measures the corrosion current) of spark-plasma-sintered alumina in 2.34 mol/L HCl gave a corrosion current of 1.12 nA and a corrosion rate of 5.07 x 10^-3 mpy (mils per year). The authors say corrosion in alumina is generally intergranular, meaning it follows the grain boundaries, and that acids attack more at lower concentrations."
    rating: low
    conditions: {material: "99.85% pure alumina powder, spark plasma sintered at 1500 °C for 10 min, 99.8% dense", temperature: "25 °C", method: "three-electrode cell, 0.2 mV/s, 0.22 cm2 exposed area", note: "short electrochemical test, not a long immersion"}
    source: alashwan2020
    where: Results and Discussion, Table 1; Materials and Methods
  - environment: Sodium hydroxide, 6.5 mol/L, 25 °C
    headline: "In the same short test, alumina also corroded slowly in strong sodium hydroxide, about two and a half times faster than in the acid."
    effect: "The same alumina in 6.5 mol/L NaOH gave a corrosion current of 2.82 nA and a corrosion rate of 12.8 x 10^-3 mpy. The authors state that alkaline bases are more corrosive at higher concentrations."
    rating: low
    conditions: {material: "99.85% pure alumina powder, spark plasma sintered at 1500 °C for 10 min, 99.8% dense", temperature: "25 °C", method: "three-electrode cell, 0.2 mV/s, 0.22 cm2 exposed area", note: "short electrochemical test, not a long immersion; ratio of the two rates calculated by Space Mushroom from Table 1"}
    source: alashwan2020
    where: Results and Discussion, Table 1
  - environment: Nitric acid, 0.50 to 2.00 mol/dm3, 25 to 55 °C, up to 240 h
    headline: "Alumina lost only trace amounts of aluminium to nitric acid, and its density did not change in any measurable way."
    effect: "Hybrid-microwave-sintered 99.8345 wt.% alumina released at most 14.805 µg/cm2 of aluminium ions (at 55 °C, 2.00 mol/dm3, 132 h). Post-test density stayed between 3.767 and 3.809 g/cm3, which the authors call negligible change. They conclude corrosion mostly comes from dissolution of impurities segregated at grain boundaries."
    rating: low
    conditions: {material: "99.8345 wt.% Al2O3 with MgO sintering aid and Fe2O3, CaO, SiO2, Na2O impurities; density 3.784 g/cm3; relative porosity 5.1%; average grain size 2.1 µm", exposure: "10 cm3 of HNO3 in sealed polypropylene tubes, 24 to 240 h", measured: "metal ions in the acid by ICP, density by water displacement"}
    source: curkovic2022
    where: Sections 2.1, 2.3, 3.1 to 3.3; Table 5; Conclusions
risks:
  hazards:
    - text: "PubChem reports that aluminium oxide does not meet GHS hazard criteria for 92.8% (2917 of 3142) of all company reports. Always check the safety data sheet of the supplier for the grade and form you handle."
      ghs: []
      source: pubchem-alumina
      where: Safety and Hazards, GHS Classification (CID 9989226)
    - text: "The minority classifications listed in PubChem are H335 (may cause respiratory irritation, 100% of reports in the ECHA notification for EC 618-619-5) and H372 (causes damage to organs through prolonged or repeated exposure, NITE-CMC classification, signal word Danger). These concern the powder or dust, not a finished sintered part."
      ghs: [H335, H372]
      source: pubchem-alumina
      where: Safety and Hazards, GHS Classification (CID 9989226)
  failure_risks:
    - mode: Brittle fracture under tension or impact
      trigger: "Tensile load, bending or impact on a part with a flaw or sharp corner"
      consequence: "AD-995 has a fracture toughness of only 4 to 5 MPa·√m and a tensile strength of 262 MPa (ACMA test #4), lower than its flexural strength of 379 MPa. Ceramic parts crack suddenly instead of bending."
      severity: moderate
      source: coorstek-chart
      where: Properties table, Fracture Toughness, Tensile Strength and Flexural Strength rows, AD-995 column
    - mode: Thermal shock (cracking from sudden temperature change)
      trigger: "Rapid heating or quenching of a part"
      consequence: "Kyocera lists a thermal shock temperature difference of 200 °C for its alumina of at least 99% purity (JIS R 1648)."
      severity: moderate
      source: kyocera-ao479o
      where: Mechanical and physical characteristics table
    - mode: Neutron radiation damage to grain boundaries
      trigger: "Reactor irradiation at about 1200 K to a fast fluence of 2.3 x 10²¹ to 2.6 x 10²¹ neutrons/cm2"
      consequence: "Signs of grain boundary weakening, thin cracks in the alumina body, and a three to five times higher electrical resistance, in a ground test of insulator layers for a thermionic space power system."
      severity: low
      source: mayer1971
      where: Summary; Visual Examination; Metallography; Resistance Measurements
  side_effects:
    - text: "Heat flows quickly through pure alumina at very low temperatures. In a NASA model of the standard initiator, rapid heat transfer from the heated bridgewire into the alumina charge cup caused failures at 10 to 100 K when the wire did not also touch the explosive charge. The abstract gives no conductivity values."
      affects: "Neighbouring materials in a cold, small device"
      source: varghese1989
      where: NTRS record 19890020199, abstract
    - text: "After reactor irradiation the visible part of one alumina insulator had darkened noticeably, and sample diameters and lengths grew by 0.4 to 0.9 percent (both alumina and beryllia samples)."
      affects: "Appearance and dimensions of the insulator layer"
      source: mayer1971
      where: Visual Examination; Summary of Results
  handling: []
  mitigations:
    - text: "Use grade-specific values and ask the supplier for specified values for critical parts: CoorsTek states that property values vary somewhat with method of manufacture, size and shape of part."
      source: coorstek-chart
      where: Chart footnote (disclaimer)
    - text: "Kyocera states that its values are typical material properties and may vary according to the product configuration and manufacturing process."
      source: kyocera-ao479o
      where: Note under the property table
uses:
  - application: electronics-and-chips
    device: "Semiconductor process chambers, wafer handling, laser devices and power tubes (ground industrial use)"
    example: "Morgan Advanced Materials lists its 99.5% alumina for wafer processing and handling devices, components for semiconductor process chambers, laser devices, and power tubes for klystron and x-ray equipment."
    source: morgan-al995
    where: Data sheet, Description and Typical Applications
  - application: mechanisms
    device: "Heat, corrosion and wear resistant parts (ground industrial use)"
    example: "Kyocera lists its alumina of at least 99% purity (AO479O) for heat, corrosion and wear resistant parts."
    source: kyocera-ao479o
    where: Specifications, Main applications
  - application: electronics-and-chips
    device: "Sheath insulator layers for a thermionic space power system (ground reactor test, not flown)"
    example: "NASA Lewis irradiated alumina and beryllia insulator layers bonded between niobium layers in a test reactor. Thermionic sheath insulators sit in a heat-to-electricity converter for space power."
    source: mayer1971
    where: Summary; Introduction
  - application: mechanisms
    device: "Charge cup of the NASA standard initiator (thermal modelling, ground)"
    example: "A 1989 NASA contractor report modelled heat flow from the bridgewire into the zirconium potassium perchlorate charge and the alumina charge cup of the NASA standard initiator, at temperatures from 10 to 500 K."
    source: varghese1989
    where: NTRS record 19890020199, abstract
supply:
  - subject: Alumina (refined from bauxite)
    producers:
      - {country: China, share_percent: 62.0, 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). In the United States about 70% of the alumina produced went to primary aluminum smelters, and the remainder went to nonmetallurgical products such as abrasives, ceramics, chemicals and refractories. U.S. net import reliance for alumina was 71% in 2025."
    substitutes: ["USGS: silicon carbide and alumina zirconia can substitute for alumina and bauxite in abrasives but cost more."]
    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); Domestic Production and Use; Salient Statistics; Recycling; Substitutes. The chapter does not break out the technical-ceramic grade."
  - subject: Bauxite
    producers:
      - {country: Guinea, share_percent: 34.1, year: 2025}
      - {country: Australia, share_percent: 22.0, year: 2025}
      - {country: China, share_percent: 19.8, year: 2025}
      - {country: Brazil, share_percent: 7.5, year: 2025}
    critical_lists: []
    recycling: "USGS: Recycling: None."
    substitutes: ["USGS: bauxite is the only raw material used for alumina on a commercial scale in the United States; vast clay resources are technically feasible but not economically competitive. Synthetic mullite substitutes for bauxite-based refractories."]
    source: usgs-mcs2026-bauxite
    where: "World Alumina Refinery and Bauxite Mine Production table, bauxite 2025e (world total 440,000 thousand t, which excludes U.S. output; shares calculated by Space Mushroom); Substitutes"
documents:
  - {title: "CoorsTek Ceramic Properties Standard chart, 8510-1042 Rev. J (copy hosted by the University of Chicago)", type: datasheet, url: "https://psec.uchicago.edu/ceramics/CoorsTek%208510-1042_Ceramic_Material_Properties.pdf", year: 2008}
  - {title: "Kyocera Fineceramics Europe datasheet AO479O (99% or more alumina)", type: datasheet, url: "https://www.kyocera-fineceramics.de/fileadmin/user_upload/Download/werkstoffdatenblaetter/aluminiumoxid/Kyocera_Fineceramics_Europe_AO479O.pdf", year: 2023}
  - {title: "Morgan Advanced Materials data sheet: 99.5% alumina (AL995)", type: datasheet, url: "https://morgantechnicalceramics.com/media/2297/al995-version-2.pdf", year: 2013}
  - {title: "PubChem: Aluminum oxide (CID 9989226), GHS classification and experimental properties", type: database, url: "https://pubchem.ncbi.nlm.nih.gov/compound/9989226", year: 2026}
  - {title: "NIST Chemistry WebBook: Aluminum oxide", type: database, url: "https://webbook.nist.gov/cgi/cbook.cgi?ID=C1344281&Units=SI", 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}
  - {title: "NASA: Reactor Irradiation of Thermionic Sheath Insulators (Lewis Research Center, 1971)", type: report, url: "https://ntrs.nasa.gov/citations/19710015159", year: 1971}
  - {title: "NASA contractor report: Investigation of heat transfer in zirconium potassium perchlorate at low temperature (NASA standard initiator)", type: report, url: "https://ntrs.nasa.gov/citations/19890020199", year: 1989}
  - {title: "Corrosion Behavior of Spark Plasma Sintered Alumina and Al2O3-SiC-CNT Hybrid Nanocomposite (open access)", type: paper, url: "https://scielo.br/j/mr/a/dM95vWGQgvnNW4Db767LfSb/?lang=en", year: 2020}
  - {title: "Statistical Optimisation of Chemical Stability of Hybrid Microwave-Sintered Alumina Ceramics in Nitric Acid (open access)", type: paper, url: "https://pmc.ncbi.nlm.nih.gov/articles/PMC9785305", year: 2022}
gaps:
  - "No vacuum outgassing (TML/CVCM), atomic-oxygen, ultraviolet or flight result for bulk alumina was found in a source we could open; the only space-related sources are two NASA ground studies (a reactor irradiation and a thermal model)."
  - "The 1971 NASA report is a scanned copy read through text recognition; the fluence exponents were checked against two places in the text, but the alumina purity of the test layers is not stated."
  - "No 96% grade value other than density is included; no second manufacturer was read for the 99.5% grade, so grade-to-grade scatter is not shown. Morgan AL995 (3.86 g/cm3) and Kyocera values were read but are not entered here."
  - "Dielectric strength is not entered: the sheets that give it differ widely in test method (ac versus dc) and sample thickness is not stated."
  - "No hydrofluoric acid, hot caustic or molten-salt result for alumina could be opened (the MDPI Materials 15(7) 2579 paper returned a 403 error); the alkali and acid rows rest on one short electrochemical test and one nitric acid study."
  - "Crystal system and space group (corundum) were not found in a source we opened."
  - "Crustal abundance of aluminium, the USGS 2025 critical minerals listing and the EU critical raw materials listing for aluminium and bauxite were not checked."
  - "Hazard data rest on the PubChem summary only; a supplier safety data sheet for alumina powder could not be opened (the Sigma-Aldrich page timed out) and the Stanford Advanced Materials sheet found describes a 2-propanol mixture."
sources:
  coorstek-chart:
    title: "CoorsTek Ceramic Properties Standard (chart of porcelain, mullite, alumina, zirconia and other grades)"
    id: "CoorsTek F0801 8510-1042 Rev. J, 2008"
    url: "https://psec.uchicago.edu/ceramics/CoorsTek%208510-1042_Ceramic_Material_Properties.pdf"
    year: 2008
    kind: datasheet
    license: supplier document, linked not reproduced
  kyocera-ao479o:
    title: "Kyocera Fineceramics Europe: AO479O (99% or more alumina) material datasheet"
    id: "Kyocera AO479O, dated 2023.04.03"
    url: "https://www.kyocera-fineceramics.de/fileadmin/user_upload/Download/werkstoffdatenblaetter/aluminiumoxid/Kyocera_Fineceramics_Europe_AO479O.pdf"
    year: 2023
    kind: datasheet
    license: supplier document, linked not reproduced
  morgan-al995:
    title: "Morgan Advanced Materials data sheet: 99.5% alumina (AL995)"
    id: "Morgan Technical Ceramics, 2013"
    url: "https://morgantechnicalceramics.com/media/2297/al995-version-2.pdf"
    year: 2013
    kind: datasheet
    license: supplier document, linked not reproduced
  pubchem-alumina:
    title: "PubChem compound record, Aluminum oxide (CID 9989226)"
    id: "CID 9989226; CAS 1344-28-1"
    url: "https://pubchem.ncbi.nlm.nih.gov/compound/9989226"
    year: 2026
    kind: database
    license: public domain (NCBI)
  nist-webbook:
    title: "NIST Chemistry WebBook, Aluminum oxide"
    id: "CAS Registry Number 1344-28-1"
    url: "https://webbook.nist.gov/cgi/cbook.cgi?ID=C1344281&Units=SI"
    year: 2026
    kind: database
    license: public domain (NIST)
  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)
  mayer1971:
    title: "Reactor Irradiation of Thermionic Sheath Insulators (NASA Lewis Research Center technical memorandum)"
    id: "NTRS 19710015159; report E-5955; May 1971"
    url: "https://ntrs.nasa.gov/citations/19710015159"
    year: 1971
    kind: report
    license: public domain (NASA)
  varghese1989:
    title: "Investigation of heat transfer in zirconium potassium perchlorate at low temperature: A study of the failure mechanism of the NASA standard initiator"
    id: "NASA-CR-184774; NTRS 19890020199"
    url: "https://ntrs.nasa.gov/citations/19890020199"
    year: 1989
    kind: report
    license: public domain (NASA)
  alashwan2020:
    title: "Corrosion Behavior of Spark Plasma Sintered Alumina and Al2O3-SiC-CNT Hybrid Nanocomposite"
    id: "doi:10.1590/1980-5373-MR-2019-0496 (Materials Research 23, no. 5)"
    url: "https://scielo.br/j/mr/a/dM95vWGQgvnNW4Db767LfSb/?lang=en"
    year: 2020
    kind: paper
    license: CC BY 4.0
  curkovic2022:
    title: "Statistical Optimisation of Chemical Stability of Hybrid Microwave-Sintered Alumina Ceramics in Nitric Acid"
    id: "doi:10.3390/ma15248823 (Materials 15, 8823, PMC9785305)"
    url: "https://pmc.ncbi.nlm.nih.gov/articles/PMC9785305"
    year: 2022
    kind: paper
    license: CC BY 4.0
license: CC-BY-4.0

updated: "2026-10-17"
review:
  status: draft
  method: assistant
  checked_values: 16
  unreachable: 4
  caveats: 3
  note: "Re-read by an AI assistant on 2026-10-17 against the saved text of each source: 16 of 16 property values match; 4 sources could not be opened (MDPI Materials 15(7) 2579 blocked, a Sigma-Aldrich safety data sheet timed out, a NIST IR 76-839 scan and a 1965 NASA scan were unreadable). Caveats: the 1971 NASA report was read through text recognition; the CoorsTek chart is from 2008; the melting point is a range from three different PubChem entries."

story:
  recipe:
    line: "Al₂O₃ is a metal oxide. Each formula unit combines two aluminium atoms with three oxygen atoms. Aluminium gives up electrons to oxygen, and the resulting strong bonds between the two elements hold the crystal together."
    parts:
      - {name: Aluminium, symbol: Al, atoms: 2, atomic_weight: 26.982, role: "The metal. Each aluminium atom gives electrons to oxygen and sits in a lattice of oxygen neighbours."}
      - {name: Oxygen, symbol: O, atoms: 3, atomic_weight: 15.999, role: "The non-metal. Three oxygen atoms per formula unit balance the charge of the two aluminium atoms."}
  risk_groups:
    - title: For people
      level: 1
      verdict: "Mostly not classified hazardous"
      lead: "Most company reports to the chemical database PubChem say aluminium oxide does not meet hazard criteria, but a minority classify it for respiratory or organ effects. These concern powder and dust, not finished sintered parts."
      points:
        - label: The powder
          line: "PubChem records that aluminium oxide does not meet GHS (the international chemical labelling system) hazard criteria in 92.8% of reports (2917 of 3142)."
        - label: Minority classifications
          line: "One notification to the European Chemicals Agency lists H335, which means the substance may cause respiratory irritation. Another classification lists H372, which means damage to organs through prolonged or repeated exposure, with the signal word Danger."
    - title: If it fails
      lead: "These results come from manufacturer tests and two NASA ground studies, not from incidents in flight."
      points:
        - label: Cracking
          line: "Alumina fails by cracking. The 99.5% grade has a fracture toughness of only 4 to 5 MPa·m½ and a tensile strength of 262 MPa, lower than its flexural strength of 379 MPa."
        - label: Sudden temperature change
          line: "Kyocera lists a thermal shock temperature difference of 200 °C for its alumina of at least 99% purity, so a part should not be heated or cooled faster than its supplier allows."
        - label: Neutron radiation
          line: "After irradiation at about 1200 K to a fast neutron fluence of 2.3 × 10²¹ to 2.6 × 10²¹ neutrons/cm², the alumina showed signs of grain boundary weakening and thin cracks, and its electrical resistance was three to five times higher."
        - label: Very low temperature
          line: "A NASA model found that pure alumina conducts heat well at very low temperatures, and this helped cause failures of an initiator at 10 to 100 K."
    - title: Handling and storage
      gap: "No safety data sheet for alumina powder, storage condition or dust exposure limit could be opened for this profile."
      points:
        - label: Check the grade
          line: "Suppliers state that their values are typical and vary with the method of manufacture, the size and shape of the part, and the configuration. Ask for specified values for critical parts."
        - label: Read the supplier's sheet
          line: "Because the classifications reported to PubChem differ, read the safety data sheet of the supplier for the powder or ceramic form you handle."
  why: >-
    Alumina (aluminium oxide, Al₂O₃) is a technical ceramic. It is made by sintering, which means pressing fine powder into
    shape and heating it until the grains fuse into a dense solid. Producers name grades by their aluminium oxide content, for
    example 96% or 99.5%, and the remainder is sintering additive and impurity that collects at the boundaries between grains.
    Strong bonds between aluminium and oxygen make the solid hard, stiff and a poor conductor of electricity, even at high
    temperature. The same bonds leave it brittle: it cracks before it bends, and its fracture toughness, a measure of
    resistance to crack growth, is only 4 to 5 MPa·m½ for the 99.5% grade. The records collected here describe alumina as a
    stiff, hard insulator for hot, wearing or electrically demanding parts, and they show its limits under tension and sudden
    temperature change. The space record is thin: two NASA ground studies and no flight or vacuum results.
  uses:
    - where: Semiconductor and laser equipment
      line: >-
        Morgan Advanced Materials lists its 99.5% alumina for wafer processing and handling devices, components for
        semiconductor process chambers, laser devices, and power tubes for klystron and x-ray equipment.
    - where: Heat, corrosion and wear resistant parts
      line: >-
        Kyocera lists its alumina of at least 99% purity for heat, corrosion and wear resistant parts.
    - where: Tested on the ground for space power
      line: >-
        NASA Lewis irradiated alumina and beryllia insulator layers, each bonded between niobium layers, in a test reactor.
        Such sheath insulators belong to a thermionic space power system, a converter that turns heat directly into
        electricity. It was a ground test, not a flight.
    - where: Inside a NASA initiator (modelling)
      line: >-
        A 1989 NASA contractor report modelled the alumina charge cup of the NASA standard initiator, a small device that
        sets off a pyrotechnic charge, at temperatures from 10 to 500 K. It is a calculation, not a flight result.
  can_do:
    - label: Strength and stiffness
      value: 379 MPa
      line: >-
        The CoorsTek chart lists a flexural strength (the stress at which a bar breaks when bent) of 379 MPa for its nominal
        99.5% grade, AD-995, at 20 °C, and an elastic modulus (stiffness) of 370 GPa. The chart states that values vary with
        the method of manufacture, size and shape of the part.
    - label: Hardness
      value: 15.2 GPa
      line: >-
        Kyocera's alumina of at least 99% purity has a Vickers hardness of 15.2 GPa. Hardness is resistance to being
        indented by a diamond point; it is the reason alumina is chosen for wear parts.
    - label: Heat
      value: 1750 °C
      line: >-
        CoorsTek lists a maximum use temperature of 1750 °C for AD-995 with no load on the part, and a thermal conductivity of
        30 W/(m·K) at 20 °C. Sudden temperature change is a weakness: Kyocera lists a thermal shock temperature difference of
        200 °C for its alumina of at least 99% purity.
    - label: Electrical insulation
      value: above 10¹⁴ Ω·cm
      line: >-
        For AD-995 the volume resistivity at 25 °C is above 10¹⁴ Ω·cm and falls to 2 × 10⁶ Ω·cm at 1000 °C. At 1 MHz and 25 °C
        the dielectric constant is 9.7 and the dielectric loss (the fraction of an alternating signal lost as heat, tan delta)
        is 0.0001.
    - label: Neutron radiation
      value: 3 to 5 times the resistance
      line: >-
        In a NASA test reactor, alumina insulator layers were exposed at about 1200 K to a fast neutron fluence of
        2.3 × 10²¹ to 2.6 × 10²¹ neutrons/cm². Afterwards their electrical resistance, measured from 700 to 1275 K, was three to
        five times higher, and the alumina showed signs of weakened grain boundaries. The purity of the layers is not stated.
  compare: >-
    The CoorsTek chart also lists sintered yttria-stabilised zirconia (YTZP), a common structural ceramic alternative.
    Compared with it, 99.5% alumina is weaker and less tough: its flexural strength is 379 MPa against 1240 MPa, and its
    fracture toughness is 4 to 5 against 13 MPa·m½. It conducts heat far better, at 30 against 2.2 W/(m·K), and its
    no-load use temperature is higher, at 1750 against 1500 °C.
  compare_rows:
    - {label: Heat conduction, benchmark: thermal_conductivity}
    - {label: Highest use temperature, benchmark: max_service_temp}
    - {label: Thermal expansion, benchmark: cte}
  handling:
    - Bulk sintered alumina is a solid; the hazard classifications on record concern powder and dust. Read the supplier's safety data sheet.
    - Ask the supplier for specified values for critical parts, because listed values are typical.
    - Avoid sudden heating or cooling, and avoid tension and impact loads on unsupported parts.
  good_for:
    - "Electrical insulation at high temperature. The volume resistivity of AD-995 is above 10¹⁴ Ω·cm at 25 °C and 2 × 10⁶ Ω·cm at 1000 °C."
    - "Hard, stiff parts. Vickers hardness is 15.2 GPa and the elastic modulus of AD-995 is 370 GPa."
    - "Conducting heat for a ceramic insulator. Thermal conductivity is 30 W/(m·K), against 2.2 for yttria-stabilised zirconia in the same chart."
  watch_out:
    - "Brittle fracture. The fracture toughness of AD-995 is 4 to 5 MPa·m½, against 13 for yttria-stabilised zirconia in the same chart."
    - "Thermal shock. Kyocera lists a thermal shock temperature difference of only 200 °C for its alumina of at least 99% purity."
    - "Grade and maker matter. Density is 3.72 g/cm³ for the 96% grade and 3.9 g/cm³ for the 99.5% grade in the same chart, and suppliers say their values vary with manufacture."
    - "No vacuum, outgassing or atomic-oxygen result for alumina was found in a source we opened."
  verdict: "Alumina is a dependable hard, high-temperature insulator as long as the design keeps it out of tension and away from sudden temperature change. The space-specific evidence collected here is limited to two NASA ground studies."