Magnesium oxide (magnesia) MgO

spore: profile
id: magnesia-mgo
spore_version: 0.2
family: oxide-ceramics
name: Magnesium oxide (magnesia)
abbreviation: MgO
role: refractory and electrical-insulating ceramic (magnesia)
category: ceramics
type: oxides
summary: |
  Magnesium oxide (MgO, magnesia) is a white ionic oxide that crystallises in the rock-salt structure. Two forms are read for this profile: an optical single crystal from Crystran (density 3.58 g/cc, thermal conductivity 42 W/(m·K) at 273 K, refractive index 1.7085 at 2 µm), and crushable sintered grades from Morgan Advanced Materials (Luminex 998, 99.68 % MgO, bulk density 2.20 to 2.49 g/cm3, flexural strength 7 to 71 MPa). The CoorsTek magnesia page lists an open porous material with a flexural strength of 82 to 103 MPa at 20 °C. No space test result for bulk MgO was found in a source we could open.
best_for: Electrically insulating, heat-conducting filler and sheath for heaters and mineral-insulated cable, from the Morgan Luminex 998 grade (crushable, bulk density 2.20 to 2.49 g/cm3)
weakest_at: 'Strength and moisture: the crushable grades have a flexural strength of 7 to 71 MPa (Luminex 998, 3-point), and the powder is hygroscopic and reacts with strong acids (ICSC 0504)'
identity:
  formula: MgO
  cas: 1309-48-4
  source: icsc-0504
  where: 'ICSC 0504 header, CAS #: 1309-48-4, Formula: MgO; PubChem CID 14792 also lists CAS 1309-48-4 under Other Identifiers'
  designations:
    - system: Trade name
      code: Luminex 998
      note: Morgan trademarked grade; values for this grade are the Luminex 998 column
      source: morgan-luminex
      where: Magnesium Oxide Luminex section, Physical Properties table, column Luminex 998
    - system: ASTM
      code: E1652
      note: magnesium oxide for mineral-insulated cable; the page says the Luminex purity conforms to it
      source: morgan-luminex
      where: Magnesium Oxide Luminex section, first paragraph (conforms to current ASTM E1652 standards)
tags:
  environments: []
  stresses:
    - extreme-heat
  applications:
    - thermal-control
    - electronics-and-chips
properties:
  - benchmark: density
    label: Density, MgO crystal (optical grade)
    value: 3.58
    unit: g/cm3
    scope: material
    conditions:
      form: MgO crystal, Crystran product listing
      temperature: not printed on the page
      unit_in_source: g/cc
    method: Typical value printed on the manufacturer product page
    status: ground
    source: crystran-mgo
    where: Product Data table, Density row
  - benchmark: density
    label: Density, MgO (PubChem experimental entry)
    value: 3.6
    unit: g/cm3
    scope: material
    conditions:
      form: magnesium oxide, no grade given
      temperature: 25 °C
      unit_in_source: g/cu cm
    method: Experimental property entry in the PubChem compound record
    status: ground
    source: pubchem-mgo
    where: Chemical and Physical Properties, Experimental Properties, Density (entry 3.6 @25 °C)
  - benchmark: melting_point
    label: Melting point, magnesium oxide
    value: 2800
    unit: °C
    scope: material
    conditions:
      form: magnesium oxide, no grade given
    method: Value printed in the ICSC physical and chemical information block
    status: ground
    source: icsc-0504
    where: 'PHYSICAL and CHEMICAL INFORMATION block, line with Boiling point and Melting point (Melting point: 2800°C)'
  - benchmark: boiling_point
    label: Boiling point, magnesium oxide
    value: 3600
    unit: °C
    scope: material
    conditions:
      form: magnesium oxide, no grade given
    method: Value printed in the ICSC physical and chemical information block
    status: ground
    source: icsc-0504
    where: 'PHYSICAL and CHEMICAL INFORMATION block, line with Boiling point and Melting point (Boiling point: 3600°C)'
  - benchmark: thermal_conductivity
    label: Thermal conductivity, MgO crystal (optical grade)
    value: 42
    unit: W/(m·K)
    scope: material
    conditions:
      form: MgO crystal, Crystran product listing
      temperature: 273 K
      unit_in_source: W m-1 K-1 @ 273 K
    method: Typical value printed on the manufacturer product page
    status: ground
    source: crystran-mgo
    where: Product Data table, Thermal Conductivity row
  - benchmark: thermal_conductivity
    label: Thermal conductivity, sintered magnesium oxide
    value: 36
    unit: W/(m·K)
    scope: material
    conditions:
      form: sintered magnesium oxide
      temperature: 100 °C
      unit_in_source: W/(mK) at T = 100 °C
    method: Value quoted in the Introduction of Hornak et al. 2018 for sintered MgO; not measured by the authors
    status: ground
    source: hornak2018
    where: Section 1 Introduction, paragraph on physical properties of magnesium oxide
  - benchmark: cte
    label: Coefficient of thermal expansion, MgO crystal (optical grade)
    value: 10.8
    unit: ppm/K
    scope: material
    conditions:
      form: MgO crystal, Crystran product listing
      temperature: 273 K
      unit_in_source: 10.8 x 10-6/°C @ 273 K
    method: Typical value printed on the manufacturer product page
    status: ground
    source: crystran-mgo
    where: Product Data table, Thermal Expansion row
  - benchmark: cte
    label: Coefficient of thermal expansion, open porous magnesia (CoorsTek)
    value: 12
    value_high: 14
    unit: ppm/K
    scope: material
    conditions:
      grade: CoorsTek magnesia, open porous material
      unit_in_source: 1x10-6/°C
    method: Range printed in the manufacturer properties table; test standard not printed
    status: ground
    source: coorstek-magnesia
    where: Properties table, Coefficient of Thermal Expansion row, Value column (12 - 14)
  - benchmark: cte
    label: Coefficient of thermal expansion, Luminex 998 (20 to 500 °C)
    value: 11.7
    unit: ppm/K
    scope: material
    conditions:
      grade: Morgan Luminex 998, crushable magnesium oxide
      temperature: 20 to 500 °C
      unit_in_source: 10-6 K-1
    method: Typical value printed in the Morgan property table
    status: ground
    source: morgan-luminex
    where: Physical Properties table, Thermal expansion row, Luminex 998 column, @ 20-500°C
  - benchmark: cte
    label: Coefficient of thermal expansion, Luminex 998 (200 to 1000 °C)
    value: 13
    unit: ppm/K
    scope: material
    conditions:
      grade: Morgan Luminex 998, crushable magnesium oxide
      temperature: 200 to 1000 °C
      unit_in_source: 10-6 K-1
    method: Typical value printed in the Morgan property table
    status: ground
    source: morgan-luminex
    where: Physical Properties table, Thermal expansion row, Luminex 998 column, @ 200-1000°C
  - benchmark: specific_heat
    label: Specific heat capacity, MgO crystal (optical grade)
    value: 877
    unit: J/(kg·K)
    scope: material
    conditions:
      form: MgO crystal, Crystran product listing
      unit_in_source: J Kg-1 K-1
    method: Typical value printed on the manufacturer product page; temperature not printed
    status: ground
    source: crystran-mgo
    where: Product Data table, Specific Heat Capacity row
  - benchmark: elastic_modulus
    label: Young's modulus, MgO crystal (optical grade)
    value: 249
    unit: GPa
    scope: material
    conditions:
      form: MgO crystal, Crystran product listing
    method: Typical value printed on the manufacturer product page; test not printed
    status: ground
    source: crystran-mgo
    where: Product Data table, Young's Modulus (E) row
  - benchmark: shear_modulus
    label: Shear modulus, MgO crystal (optical grade)
    value: 155
    unit: GPa
    scope: material
    conditions:
      form: MgO crystal, Crystran product listing
    method: Typical value printed on the manufacturer product page; test not printed
    status: ground
    source: crystran-mgo
    where: Product Data table, Shear Modulus (G) row
  - benchmark: bulk_modulus
    label: Bulk modulus, MgO crystal (optical grade)
    value: 155
    unit: GPa
    scope: material
    conditions:
      form: MgO crystal, Crystran product listing
    method: Typical value printed on the manufacturer product page; test not printed
    status: ground
    source: crystran-mgo
    where: Product Data table, Bulk Modulus (K) row
  - benchmark: dielectric_constant
    label: Dielectric constant, MgO crystal (optical grade)
    value: 9.65
    unit: '-'
    scope: material
    conditions:
      form: MgO crystal, Crystran product listing
      frequency: 1 MHz
    method: Typical value printed on the manufacturer product page
    status: ground
    source: crystran-mgo
    where: Product Data table, Dielectric Constant row (9.65 at 1 MHz)
  - benchmark: refractive_index
    label: Refractive index, MgO crystal (optical grade)
    value: 1.7085
    unit: '-'
    scope: material
    conditions:
      form: MgO crystal, Crystran product listing
      wavelength: 2 µm
    method: Value printed on the manufacturer product page (reference 1 on that page)
    status: ground
    source: crystran-mgo
    where: Product Data table, Refractive Index row (1.7085 at 2 µm)
  - benchmark: knoop_hardness
    label: Knoop hardness, MgO crystal (optical grade)
    value: 692
    unit: Knoop
    scope: material
    conditions:
      form: MgO crystal, Crystran product listing
      load: 600 g indenter
    method: Typical value printed on the manufacturer product page
    status: ground
    source: crystran-mgo
    where: Product Data table, Hardness row (Knoop 692 with 600g indenter)
  - benchmark: mohs_hardness
    label: Mohs hardness, magnesium oxide
    value: 5
    unit: Mohs
    scope: material
    conditions:
      form: magnesium oxide, sintered or crystal not stated
    method: Value quoted in the Introduction of Hornak et al. 2018
    status: ground
    source: hornak2018
    where: Section 1 Introduction, paragraph on physical properties (around 5 on Mohs scale)
  - benchmark: flexural_strength
    label: Flexural strength, Luminex 998 (crushable grade)
    value: 7
    value_high: 71
    unit: MPa
    scope: material
    conditions:
      grade: Morgan Luminex 998, crushable magnesium oxide
      test: 3-point bending
      unit_in_source: MPa
    method: Range printed in the Morgan property table; test standard not printed
    status: ground
    source: morgan-luminex
    where: Physical Properties table, Flexural strength (3-point) row, Luminex 998 column
  - benchmark: flexural_strength
    label: Flexural strength, open porous magnesia (CoorsTek)
    value: 82
    value_high: 103
    unit: MPa
    scope: material
    conditions:
      grade: CoorsTek magnesia, open porous material
      temperature: 20 °C
      test: not printed on the page
    method: Range printed in the manufacturer properties table; the page says the strength of the open porous material can be adapted to application requirements
    status: ground
    source: coorstek-magnesia
    where: Properties table, Flexural Strength, MOR (20 °C) row
  - benchmark: compressive_strength
    label: Compressive strength, Luminex 998 (crushable grade)
    value: 12
    value_high: 170
    unit: MPa
    scope: material
    conditions:
      grade: Morgan Luminex 998, crushable magnesium oxide
    method: Range printed in the Morgan property table; test standard not printed
    status: ground
    source: morgan-luminex
    where: Physical Properties table, Compressive strength row, Luminex 998 column
  - benchmark: open_porosity
    label: Open porosity, Luminex 998 (crushable grade)
    value: 28
    value_high: 38
    unit: '%'
    scope: material
    conditions:
      grade: Morgan Luminex 998, crushable magnesium oxide
      basis: vol %
    method: Range printed in the Morgan property table
    status: ground
    source: morgan-luminex
    where: Physical Properties table, Porosity (open) row, Luminex 998 column
  - benchmark: bulk_density
    label: Bulk density, Luminex 998 (crushable grade)
    value: 2.2
    value_high: 2.49
    unit: g/cm3
    scope: material
    conditions:
      grade: Morgan Luminex 998, crushable magnesium oxide
      note: bulk density of a crushable grade, not the solid density
    method: Range printed in the Morgan property table
    status: ground
    source: morgan-luminex
    where: Physical Properties table, Bulk density row, Luminex 998 column
  - benchmark: lattice_parameter
    label: Lattice parameter a, magnesium oxide (X-ray)
    value: 4.2119
    unit: Å
    scope: material
    conditions:
      form: high-purity MgO recrystallised as a pressed disk at 1500 °C
      structure: cubic cell (fcc), z = 4
      method_as_printed: X-ray diffraction
    method: Value from the Brown 1965 X-ray study evaluated in the NIST database
    status: ground
    source: nist-scd-mgo
    where: Material Specification and Properties for MgO, Crystal Cell Axes table, axis a (4.2119(5) Å)
  - benchmark: water_solubility
    label: Solubility in water, magnesium oxide
    value: 86
    unit: mg/L
    scope: material
    conditions:
      temperature: 30 °C
      unit_in_source: 86 mg/L at 30 °C
    method: Experimental entry in the PubChem record
    status: ground
    source: pubchem-mgo
    where: Chemical and Physical Properties, Experimental Properties, Solubility (In water, 86 mg/L at 30 °C)
corrosion:
  - environment: Moist air and water
    headline: Magnesium oxide is hygroscopic and reacts with water to form magnesium hydroxide.
    effect: Wikipedia states that magnesium hydroxide forms in the presence of water (MgO + H2O → Mg(OH)2), and that heating reverses it to remove moisture. ICSC 0504 describes the powder as hygroscopic. Hornak et al. 2018 found that an as-delivered MgO pellet held significant water, and that dehydration on heating changed its dielectric loss.
    rating: unknown
    conditions:
      basis: qualitative statements in the sources; no mass gain or time was printed
      note: the rating is not given in any source
    source: wikipedia-mgo
    where: Magnesium oxide article, Lead paragraph (hygroscopic solid; Mg(OH)2 formation); ICSC 0504 Physical and Chemical Information; Hornak 2018, discussion of dehydration in the frequency and temperature results
  - environment: Strong acids
    headline: Magnesium oxide reacts with strong acids, and ICSC 0504 says it reacts violently.
    effect: ICSC 0504 lists 'Reacts violently with strong acids' under chemical dangers and says to keep the powder separated from strong acids. Wikipedia states that MgO is soluble in acid, where it reacts to form soluble salts such as magnesium chloride in hydrochloric acid.
    rating: unknown
    conditions:
      basis: qualitative statements; no concentration or temperature was printed
    source: icsc-0504
    where: Chemical dangers; Storage; Wikipedia Chembox infobox, Solubility row
  - environment: Water at 30 °C
    headline: Magnesium oxide is poorly soluble in water.
    effect: PubChem gives an experimental solubility of 86 mg/L in water at 30 °C, and ICSC 0504 describes solubility in water as poor.
    rating: none
    conditions:
      basis: experimental value at 30 °C; a short-term solubility, not a corrosion test
    source: pubchem-mgo
    where: Chemical and Physical Properties, Experimental Properties, Solubility
risks:
  hazards:
    - text: 'Fisher Scientific SDS for magnesium oxide powder: classification under the 2012 OSHA Hazard Communication Standard, criteria not met; label elements none required; hazards not otherwise classified none identified.'
      ghs: []
      source: fisher-mgo-sds
      where: Section 2, Classification and Label Elements
    - text: ICSC 0504 states no hazard classification according to UN GHS criteria. The card says the powder may cause mechanical irritation and gives a TLV of 10 mg/m3 for the inhalable fraction (TWA).
      ghs: []
      source: icsc-0504
      where: Classification and Labelling; Exposure and Health Effects
    - text: PubChem reports Not Classified as the aggregate result (1586 of 1807 company reports). The minority notifications list H319 (causes serious eye irritation) and H335 (may cause respiratory irritation), signal word Warning.
      ghs:
        - H319
        - H335
      source: pubchem-mgo
      where: Safety and Hazards, GHS Classification
  failure_risks:
    - mode: Crushing of crushable or open porous parts
      trigger: Mechanical load on a crushable MgO part, such as a Luminex 998 tube or an open porous magnesia insulator
      consequence: Luminex 998 has a 3-point flexural strength of 7 to 71 MPa and a compressive strength of 12 to 170 MPa. The open porous CoorsTek magnesia has a flexural strength of 82 to 103 MPa at 20 °C.
      severity: moderate
      source: morgan-luminex
      where: Physical Properties table, Flexural strength and Compressive strength rows, Luminex 998 column
    - mode: Hydration in damp service
      trigger: Exposure of the powder or a porous part to water or moist air
      consequence: MgO converts to magnesium hydroxide in the presence of water (Wikipedia). The sources read do not quantify any change in properties.
      severity: low
      source: wikipedia-mgo
      where: Magnesium oxide article, Lead paragraph
    - mode: Violent reaction with strong acids
      trigger: Contact of the powder with strong acids
      consequence: ICSC 0504 says the substance reacts violently with strong acids and must be stored separately from them.
      severity: high
      source: icsc-0504
      where: Chemical dangers; Storage
  side_effects: []
  handling:
    - text: Store dry and well closed, and separate from strong acids (ICSC 0504, Storage).
      source: icsc-0504
    - text: For spills, sweep into covered containers and moisten the powder first if appropriate to prevent dusting (ICSC 0504, Spillage disposal).
      source: icsc-0504
    - text: Use a particulate filter respirator adapted to the airborne concentration (ICSC 0504, Personal protection).
      source: icsc-0504
  mitigations: []
uses:
  - application: thermal-control
    device: Crushable insulation in cartridge heaters, tubular heaters, MI thermocouples and heat-trace cables
    example: Morgan lists its Luminex magnesium oxide for cartridge heaters, tubular and coiled heaters, MI thermocouples, heat trace cables and medium voltage heaters. Its crushable tubes are used for mineral-insulated cable.
    source: morgan-luminex
    where: Magnesium Oxide Luminex section, introduction paragraph and Applications list
  - application: electronics-and-chips
    device: Oxide barrier in spin-tunnelling devices (magnetron-sputtered films)
    example: Wikipedia states that MgO is used as an oxide barrier in spin-tunnelling devices, where crystalline sputtered films reach about 85 % spin polarisation against 40 to 60 % for aluminium oxide, and a tunnel magnetoresistance of 600 % at room temperature.
    source: wikipedia-mgo
    where: Niche uses section, Oxide barrier paragraph
  - application: electronics-and-chips
    device: Nanoparticle filler in epoxy electrical insulation (laboratory study, not flown)
    example: Hornak et al. 2018 added 20 nm MgO nanoparticles to an epoxy resin for electrical insulation, and set the optimal filler loading at 1 wt %, the level they used for their dielectric and X-ray measurements.
    source: hornak2018
    where: Section 1 Introduction; text after the filler-amount measurements (optimal weight ratio set to 1 wt %)
supply:
  - subject: Magnesium oxide from magnesite, brines and seawater (magnesium compounds)
    demand: In 2025 about 400 thousand tons of magnesium compounds, as MgO content, were produced in the United States (2025e), against apparent consumption of 980 thousand tons. U.S. net import reliance was 59 % in 2025e.
    routes: 'USGS: magnesium compounds were produced from seawater and natural brines, and magnesite was mined in Nevada. Magnesite is calcined to magnesia; Wikipedia states that magnesium hydroxide is precipitated from seawater or magnesium chloride solutions and then calcined. Calcining at 1500 to 2000 °C gives dead-burned magnesia used as a refractory.'
    producers:
      - country: China
        share_percent: 60.5
        year: 2025
      - country: Brazil
        share_percent: 8.6
        year: 2025
      - country: Russia
        share_percent: 8.1
        year: 2025
      - country: Turkey
        share_percent: 7.6
        year: 2025
    critical_lists: []
    recycling: 'USGS: some magnesia-based refractories are recycled as construction aggregate, reused in refractory, and as foundry sand.'
    substitutes:
      - 'USGS: alumina, chromite and silica substitute for magnesia in some refractory applications.'
    abundance: 'USGS: identified world magnesite and brucite resources total 13 billion tons, and magnesium compounds can be recovered from seawater and natural brines.'
    source: usgs-mcs2026-magnesium
    where: World Magnesite Mine Production table, 2025 column, country rows. Shares are calculated by Space Mushroom from the printed 2025 values (China 12,700 of a world total of 21,000 thousand t). The table is magnesite gross weight, not MgO content, and excludes U.S. output; the U.S. figures are in MgO content (Salient Statistics, Production row, 2025e). Also Import Sources (2021-24), Domestic Production and Use, Recycling, Substitutes.
  - subject: Dead-burned and fused magnesia (refractory grades), imports to the United States
    demand: Caustic-calcined magnesia imports were 74 % from China in 2021 to 2024, and dead-burned and fused magnesia 69 % from China and 17 % from Brazil.
    routes: ''
    producers:
      - country: China
        share_percent: 69
        year: 2024
      - country: Brazil
        share_percent: 17
        year: 2024
    critical_lists: []
    recycling: ''
    substitutes: []
    source: usgs-mcs2026-magnesium
    where: Import Sources (2021-24) paragraph; the share is printed for 2021 to 2024 and is entered against the last year of that range
  - subject: MgO optical single crystal
    demand: Crystran says MgO crystal is quite difficult to source.
    routes: 'Crystran: magnesium oxide is grown in relatively small sizes, mainly in Japan and China. A UK grower ceased trading, so supply is limited.'
    producers: []
    critical_lists: []
    recycling: ''
    substitutes: []
    source: crystran-mgo
    where: Crystran product page, body text on supply (paragraph beginning Magnesium Oxide is grown in relatively small sizes)
documents:
  - title: 'USGS Mineral Commodity Summaries 2026: Magnesium Compounds'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-magnesium-compounds.pdf
    year: 2026
  - title: PubChem compound record, Magnesium oxide (CID 14792), experimental properties and GHS
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/14792/JSON
    year: 2026
  - title: NIST Structural Ceramics Database, MgO (SCD citation Z00628)
    type: database
    url: https://srdata.nist.gov/CeramicDataPortal/Scd/Z00628
    year: 2015
  - title: NIST Atomic Weights and Isotopic Compositions for All Elements (Mg and O rows)
    type: database
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Mg&all=all&ascii=html
  - title: CoorsTek magnesia product page, Properties table
    type: datasheet
    url: https://coorstek.com/en/materials/magnesia/
  - title: Morgan Advanced Materials, Magnesium Oxide (Luminex) product page
    type: datasheet
    url: https://www.morgantechnicalceramics.com/en-gb/materials/magnesium-oxide/
  - title: Crystran, Magnesium Oxide MgO product page and data sheet
    type: datasheet
    url: https://www.crystran.com/optical-materials/magnesium-oxide-mgo
  - title: 'Hornak et al. 2018, Magnesium Oxide Nanoparticles: Dielectric Properties, Surface Functionalization and Improvement of Epoxy-Based Composites Insulating Properties, Nanomaterials 8(6), 381'
    type: paper
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC6027305/
    year: 2018
  - title: Wikipedia, Magnesium oxide
    type: report
    url: https://en.wikipedia.org/wiki/Magnesium_oxide
  - title: ICSC 0504, Magnesium oxide (ILO and WHO International Chemical Safety Card)
    type: sds
    url: http://www.inchem.org/documents/icsc/icsc/eics0504.htm
    year: 2010
  - title: Fisher Scientific safety data sheet, Magnesium oxide powder (revision 13-May-2014)
    type: sds
    url: https://www.physics.purdue.edu/primelab/safety/MSDS/SDS/magnesium%20oxide%20powder%20%20-Fisher.pdf
    year: 2014
gaps:
  - 'No space-environment result for bulk magnesium oxide was found in a source we could open: no outgassing, atomic oxygen, ultraviolet, radiation or thermal-cycling data.'
  - Volume resistivity was read on the Morgan Luminex and CoorsTek pages but is printed as powers of ten (for example 1.0 x 10 10 ohm.cm at 600 °C), and the checker could not match that printed form, so these values are left out. Dielectric strength and dielectric loss are also left out.
  - 'Non-canonical property names used because no canonical name fits: knoop_hardness, mohs_hardness, compressive_strength, open_porosity, bulk_density (crushable grade, not solid density), lattice_parameter and water_solubility.'
  - The Crystran values are for an optical MgO crystal and the Hornak thermal conductivity and Mohs values are literature quotes for sintered MgO; no grade-specific sintered thermal conductivity was read from a manufacturer page.
  - The Morgan Luminex and CoorsTek pages print no test standard for the strength or thermal expansion values, so the conditions are as far as the pages state.
  - ASTM E1652 is named on the Morgan page as the standard the Luminex purity conforms to. The standard itself was not opened, so no requirement from it is recorded.
  - Shares in the supply entry are calculated from magnesite mine production (gross carbonate weight), not from MgO output. No producer tonnage for magnesium oxide itself was found.
  - No critical-mineral list entry for magnesium compounds was read in the USGS chapter (critical_lists left empty). The EU critical raw materials list was not checked.
  - The H315 and H335 codes shown on Wikipedia's infobox were not recorded; the PubChem and Fisher pages were used for hazard statements.
  - Corrosion and ageing ratings are not stated in any source read, so they are entered as unknown; no flight or long-term exposure data were found.
sources:
  usgs-mcs2026-magnesium:
    title: Mineral Commodity Summaries 2026, Magnesium Compounds
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-magnesium-compounds.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  pubchem-mgo:
    title: PubChem compound record, Magnesium oxide (CID 14792)
    id: CID 14792; CAS 1309-48-4
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/14792/JSON
    year: 2026
    kind: database
    license: public domain (NCBI)
  nist-scd-mgo:
    title: NIST Structural Ceramics Database, MgO
    id: SCD citation Z00628, NIST Standard Reference Database 30
    url: https://srdata.nist.gov/CeramicDataPortal/Scd/Z00628
    year: 2015
    kind: database
    license: public domain (NIST)
  nist-atomic-weights:
    title: NIST Atomic Weights and Isotopic Compositions for All Elements
    id: Standard atomic weights, Mg and O rows
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Mg&all=all&ascii=html
    kind: database
    license: public domain (NIST)
  coorstek-magnesia:
    title: CoorsTek magnesia (MgO) product page, properties table
    id: CoorsTek magnesia family page
    url: https://coorstek.com/en/materials/magnesia/
    kind: datasheet
    license: manufacturer web page, linked not reproduced
  morgan-luminex:
    title: Morgan Advanced Materials, Magnesium Oxide Luminex product page
    id: Luminex 970, 993 and 998 physical properties
    url: https://www.morgantechnicalceramics.com/en-gb/materials/magnesium-oxide/
    kind: datasheet
    license: manufacturer web page, linked not reproduced
  crystran-mgo:
    title: Crystran, Magnesium Oxide MgO product page and data sheet
    id: Crystran optical materials, MgO crystal
    url: https://www.crystran.com/optical-materials/magnesium-oxide-mgo
    kind: datasheet
    license: supplier web page, linked not reproduced
  hornak2018:
    title: 'Magnesium Oxide Nanoparticles: Dielectric Properties, Surface Functionalization and Improvement of Epoxy-Based Composites Insulating Properties'
    id: Hornak et al., Nanomaterials 8(6), 381, 2018, PMC6027305
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC6027305/
    year: 2018
    kind: paper
    license: open access article, linked not reproduced
  wikipedia-mgo:
    title: Magnesium oxide, Wikipedia
    id: Magnesium oxide article (lead, structure, production, uses)
    url: https://en.wikipedia.org/wiki/Magnesium_oxide
    kind: web
    license: CC BY-SA 4.0, linked not reproduced
  icsc-0504:
    title: ICSC 0504, Magnesium oxide, ILO and WHO International Chemical Safety Card
    id: ICSC 0504 (May 2010), CAS 1309-48-4
    url: http://www.inchem.org/documents/icsc/icsc/eics0504.htm
    year: 2010
    kind: datasheet
    license: international chemical safety card, linked not reproduced
  fisher-mgo-sds:
    title: Fisher Scientific safety data sheet, Magnesium oxide powder
    id: Revision date 13-May-2014
    url: https://www.physics.purdue.edu/primelab/safety/MSDS/SDS/magnesium%20oxide%20powder%20%20-Fisher.pdf
    year: 2014
    kind: datasheet
    license: supplier SDS, linked not reproduced
license: CC-BY-4.0
updated: '2026-10-25'
review:
  status: draft
  method: assistant
  checked_values: 25
  unreachable: 1
  caveats: 4
  note: 'Values were read by an AI assistant on 2026-10-25 from the pages named in each entry. Unreachable: the Crystran PDF data sheet link returned HTML, so only the product page was read; the ASTM E1652 standard was not opened. Caveats: the Crystran values are for an optical crystal; the Luminex and CoorsTek strength and expansion values print no test standard; the sintered thermal conductivity and Mohs values are literature quotes; the supply shares are calculated from magnesite mine production.'
story:
  recipe:
    line: 'Magnesium oxide is an ionic compound: each formula unit pairs one magnesium ion (Mg2+) with one oxide ion (O2-) in a cubic rock-salt (halite) lattice (Wikipedia; NIST gives a cubic cell of a = 4.2119 Å). It is made by calcining magnesium carbonate or magnesium hydroxide. Magnesium hydroxide is precipitated from seawater or magnesium chloride solution with limewater (Wikipedia). Calcining at 1500 to 2000 °C gives dead-burned magnesia for refractories. Morgan''s Luminex 998 is a seawater-derived grade printed as 99.68 % MgO.'
    parts:
      - name: Magnesium
        symbol: Mg
        atoms: 1
        atomic_weight: 24.304
        share_note: NIST standard atomic weight, Mg row; the lower bound of the printed interval is entered
        role: Divalent metal cation (Mg2+). One magnesium per formula unit, in the octahedral site of the rock-salt lattice.
      - name: Oxygen
        symbol: O
        atoms: 1
        atomic_weight: 15.99903
        share_note: NIST standard atomic weight, O row; the lower bound of the printed interval is entered
        role: Divalent oxide anion (O2-). One oxygen per formula unit, balancing the charge of the magnesium ion.
  risk_groups:
    - title: For people
      lead: The SDS and safety card read for this profile do not classify magnesium oxide powder as hazardous, but PubChem lists a minority of notifications for eye and respiratory irritation.
      level: 1
      verdict: Mostly not classified
      points:
        - label: Classification
          line: The Fisher Scientific SDS states that the OSHA 2012 criteria are not met, and ICSC 0504 states no hazard classification under UN GHS criteria.
        - label: Minority notifications
          line: PubChem reports 1586 of 1807 company reports as not meeting GHS criteria. The notified minority classes are H319 (serious eye irritation) and H335 (respiratory irritation), signal word Warning.
        - label: Dust and exposure
          line: ICSC 0504 gives a TLV of 10 mg/m3 for the inhalable fraction (TWA), and notes that mechanical irritation may occur.
    - title: If it fails
      lead: The failure routes in these sources are crushing of the porous grades, hydration by moisture, and reaction with strong acid.
      points:
        - label: Crushing
          line: Luminex 998 has a 3-point flexural strength of 7 to 71 MPa and a compressive strength of 12 to 170 MPa. The open porous CoorsTek magnesia has a flexural strength of 82 to 103 MPa at 20 °C.
        - label: Moisture
          line: Magnesium oxide is hygroscopic and reacts with water to give magnesium hydroxide, which heating reverses (Wikipedia; ICSC 0504).
        - label: Strong acid
          line: ICSC 0504 says the powder reacts violently with strong acids, and must be stored away from them.
    - title: Handling and storage
      lead: Store the powder dry and sealed, and read the supplier safety data sheet for the grade you use.
      points:
        - label: Storage
          line: Store dry and well closed, separated from strong acids (ICSC 0504).
        - label: Spills
          line: Sweep spilled powder into covered containers and moisten it first where appropriate to prevent dusting (ICSC 0504).
  why: 'Magnesium oxide (MgO, magnesia) is a high-melting ionic ceramic. The sources read describe it as a refractory and a good electrical insulator that still conducts heat well. Its melting point is 2800 °C and its boiling point is 3600 °C (ICSC 0504). Crushable grades such as Morgan''s Luminex 998 are made as tubes and insulating fill for heaters and mineral-insulated cable, while optical crystals serve as windows and substrates. The space record is thin: no flight, outgassing or atomic-oxygen result for bulk MgO was found.'
  uses:
    - where: Heaters and mineral-insulated cable
      line: Morgan lists its Luminex magnesium oxide for cartridge heaters, tubular and coiled heaters, MI thermocouples, heat trace cables and medium voltage heaters.
    - where: Spin-tunnelling devices
      line: Wikipedia states that MgO is used as an oxide barrier in spin-tunnelling devices, where sputtered crystalline films give about 85 % spin polarisation against 40 to 60 % for aluminium oxide.
    - where: Epoxy insulation filler (laboratory study)
      line: Hornak et al. 2018 added 20 nm MgO nanoparticles to an epoxy resin and set the optimal filler loading at 1 wt %. This is a laboratory study, not a flight result.
  can_do:
    - label: Heat conduction
      value: 42 W/(m·K)
      line: Crystran lists a thermal conductivity of 42 W/(m·K) at 273 K for its MgO crystal. Hornak et al. quote 36 W/(m·K) at 100 °C for sintered MgO.
    - label: Electrical insulation
      value: 9.65 at 1 MHz
      line: The Crystran crystal has a dielectric constant of 9.65 at 1 MHz. The Morgan Luminex grades are described as excellent electrical insulators, though their volume resistivity values are left out of this profile.
    - label: Stiffness
      value: 249 GPa
      line: Crystran lists a Young's modulus of 249 GPa and a shear modulus of 155 GPa for its MgO crystal.
    - label: Lattice
      value: 4.2119 Å
      line: The NIST SCD entry gives a cubic cell with lattice parameter a of 4.2119 Å from X-ray diffraction on high-purity MgO.
  compare: The sources read show MgO in two very different forms, so the values are not directly comparable. The optical crystal from Crystran has a thermal conductivity of 42 W/(m·K) at 273 K and a Young's modulus of 249 GPa, while the crushable Luminex 998 has a flexural strength of only 7 to 71 MPa and a bulk density of 2.20 to 2.49 g/cm3. The CoorsTek open porous magnesia is stronger, at 82 to 103 MPa, than the crushable Morgan grade. Density, thermal expansion and strength should be read against the grade and form named in each row.
  compare_rows:
    - label: Density
      benchmark: density
    - label: Thermal conductivity
      benchmark: thermal_conductivity
    - label: Flexural strength
      benchmark: flexural_strength
  handling:
    - Store dry and sealed, and separate from strong acids (ICSC 0504).
    - Read the supplier safety data sheet for the grade and form, because the classifications in the sources read differ.
    - Ask the supplier for specified values for critical parts, since the listed values are typical.
  good_for:
    - Heater and cable insulation. Luminex 998 is a crushable grade of 99.68 % MgO for cartridge heaters and mineral-insulated cable (Morgan).
    - Heat-conducting optical or substrate material. The MgO crystal has a thermal conductivity of 42 W/(m·K) at 273 K and a refractive index of 1.7085 at 2 µm (Crystran).
  watch_out:
    - Moisture. MgO is hygroscopic and reacts with water to form magnesium hydroxide (Wikipedia; ICSC 0504).
    - Low strength in crushable grades. Luminex 998 has a flexural strength of only 7 to 71 MPa (3-point).
    - Acids. ICSC 0504 says the powder reacts violently with strong acids.
    - No space data. No outgassing, atomic oxygen or radiation result for bulk MgO was found in a source we could open.
  verdict: Magnesium oxide is a high-melting insulator that conducts heat well, with a melting point of 2800 °C and a crystal thermal conductivity of 42 W/(m·K). It is weak in crushable form and reacts with moisture and strong acids, and the space record for bulk MgO is empty in this profile.