spore: profile
id: molybdenum-rhenium
spore_version: 0.2
family: refractory-metals
name: Molybdenum-rhenium alloy
abbreviation: Mo-Re
role: ductile refractory alloy for space reactor cladding and structures, and for high-temperature thermoelements
category: metals
type: refractory-metals
summary: |
  Molybdenum-rhenium alloys add rhenium to molybdenum as a solid solution. The two grades in this profile are Mo-41Re (41 wt% Re) and Mo-47.5Re (47.5 wt% Re). Rhenium raises strength and ductility and makes the metal easier to weld. Mo-41Re has a density of 14.6 g/cm3 at 20 °C and a melting point above 2610 °C (Plansee safety data sheet). In air it oxidises strongly from about 600 °C and its oxide MoO3 sublimes from about 700 °C (Plansee). In one ORNL test, annealed Mo-41Re sheet had a room-temperature yield strength of 557 MPa and a tensile strength of 719 MPa, but only after it had been oxidised. Mo-47.5Re can form a brittle sigma phase when aged at about 1398 K.
best_for: Structural and cladding use at high temperature in vacuum or inert gas, for example fuel cladding and core structures in space reactors, where ductility must survive welding
weakest_at: Oxidation in air above about 600 °C, and embrittlement by the sigma phase in Mo-47.5Re and by irradiation above about 1100 K
identity:
  formula: 'Solid solution of rhenium in molybdenum (body-centred cubic): Mo-41Re is 59 wt% Mo and 41 wt% Re; Mo-47.5Re is about 52.5 wt% Mo and 47.5 wt% Re'
  source: plansee-mo-re-sds
  where: Section 3 (Composition), mass fractions molybdenum 59 % and rhenium 41 % for Mo5Re and Mo41Re; the 47.5 wt% grade is the one ORNL and NASA describe
  designations:
    - system: UNS
      code: R03700
      note: Mo-47.5Re sheet and wire, as printed on the listing pages
      source: sam-mo47-5re-sheet
      where: Product table, row Grade (UNS R03700) for Mo-47.5Re sheet
    - system: ASTM
      code: B386
      note: Mo-47.5Re sheet and plate listing (reseller)
      source: sam-mo47-5re-sheet
      where: Product table, row Standard (ASTM B386, ASTM F3273) for Mo-47.5Re sheet
    - system: ASTM
      code: B387
      note: Mo-47.5Re wire listing (reseller)
      source: sam-mo47-5re-wire
      where: Product table, row Standard (ASTM B387) for Mo-47.5Re wire
tags:
  environments: []
  applications:
    - structures
    - thermal-control
properties:
  - benchmark: density
    label: Density of Mo-41Re at 20 °C
    value: 14.6
    unit: g/cm3
    scope: material
    conditions:
      form: Mo41Re alloy, Plansee product
      temperature: 20 °C
    method: Value printed in the manufacturer safety data sheet
    status: ground
    source: plansee-mo-re-sds
    where: Section 9 (Physical and chemical properties), Density, Mo41Re row, printed as 14,6 g/cm³ at 20°C
  - benchmark: melting_point
    label: Melting point of Mo-41Re
    value: 2610
    bound: lower
    unit: °C
    scope: material
    conditions:
      form: Mo5Re and Mo41Re, as listed in the same SDS
      meaning: printed as more than 2610 °C
    method: Value printed in the manufacturer safety data sheet
    status: ground
    source: plansee-mo-re-sds
    where: Section 9 (Physical and chemical properties), Melting point
  - benchmark: ductile_brittle_transition_temperature
    label: Ductile-to-brittle transition, 41 % Re alloy
    value: -150
    unit: °C
    scope: material
    conditions:
      composition: 41 % Re
      unit_in_source: about -150° C (about 125 K)
    method: Statement in the background of a US patent on Mo-Re alloys (Rhenium Alloys Inc., 1995)
    status: ground
    note: A patent statement, not a test report from this run. The patent calls it too high for most space applications.
    source: us-patent-5437744
    where: Definitions section, first sentence
  - benchmark: sigma_phase_precipitation_temperature
    label: Temperature range where sigma phase precipitates in Mo-47.5Re
    value: 1075
    value_high: 1275
    bound: range
    unit: °C
    scope: material
    conditions:
      composition: 47.5 % Re
      unit_in_source: about 1075°-1275° C (about 1350-1550 K)
    method: Statement in the same US patent, which says the sigma phase lowers low-temperature ductility to the same order as Mo-41Re
    status: ground
    source: us-patent-5437744
    where: Definitions section, sentence on the 47.5 % Re alloy
  - benchmark: yield_strength
    label: Yield strength, arc-cast Mo-41Re sheet at room temperature after oxidation
    value: 557
    unit: MPa
    scope: material
    conditions:
      material: Mo-41Re arc-cast sheet, SS-3 subsize tensile specimens (ORNL laboratory material, not a standard product)
      temper: annealed 2 h at 1400 °C in vacuum before oxidation
      temperature: room temperature
      state: after oxidation, sample M25 (weight-change column printed as +3,883 wppm)
    method: Value printed in an ORNL tensile table, read from the text layer of the PDF
    status: ground
    source: ornl-tm-2000-291
    where: Table 2, row M25, RT, YS column
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, arc-cast Mo-41Re sheet at room temperature after oxidation
    value: 719
    unit: MPa
    scope: material
    conditions:
      material: Mo-41Re arc-cast sheet, SS-3 subsize tensile specimens (ORNL laboratory material, not a standard product)
      temper: annealed 2 h at 1400 °C in vacuum before oxidation
      temperature: room temperature
      state: after oxidation, sample M25
    method: Value printed in an ORNL tensile table
    status: ground
    source: ornl-tm-2000-291
    where: Table 2, row M25, RT, UTS column
  - benchmark: elongation
    label: Total elongation, arc-cast Mo-41Re sheet at room temperature after oxidation
    value: 18
    unit: '%'
    scope: material
    conditions:
      material: Mo-41Re arc-cast sheet, SS-3 subsize tensile specimens
      temperature: room temperature
      state: after oxidation, sample M25
    method: Value printed in an ORNL tensile table
    status: ground
    source: ornl-tm-2000-291
    where: Table 2, row M25, RT, total elongation column
  - benchmark: yield_strength
    label: Yield strength, arc-cast Mo-41Re sheet at 650 °C after oxidation
    value: 266
    unit: MPa
    scope: material
    conditions:
      material: Mo-41Re arc-cast sheet, SS-3 subsize tensile specimens
      temper: annealed 2 h at 1400 °C in vacuum before oxidation
      temperature: 650 °C
      state: after oxidation, sample M13
    method: Value printed in an ORNL tensile table
    status: ground
    source: ornl-tm-2000-291
    where: Table 2, row M13, 650 °C, YS column
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, arc-cast Mo-41Re sheet at 650 °C after oxidation
    value: 480
    unit: MPa
    scope: material
    conditions:
      material: Mo-41Re arc-cast sheet, SS-3 subsize tensile specimens
      temper: annealed 2 h at 1400 °C in vacuum before oxidation
      temperature: 650 °C
      state: after oxidation, sample M13
    method: Value printed in an ORNL tensile table
    status: ground
    source: ornl-tm-2000-291
    where: Table 2, row M13, 650 °C, UTS column
  - benchmark: yield_strength
    label: Yield strength, arc-cast Mo-41Re sheet at 900 °C after oxidation
    value: 348
    unit: MPa
    scope: material
    conditions:
      material: Mo-41Re arc-cast sheet, SS-3 subsize tensile specimens
      temper: annealed 2 h at 1400 °C in vacuum before oxidation
      temperature: 900 °C
      state: after oxidation, sample M5
    method: Value printed in an ORNL tensile table
    status: ground
    source: ornl-tm-2000-291
    where: Table 2, row M5, 900 °C, YS column
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, arc-cast Mo-41Re sheet at 900 °C after oxidation
    value: 446
    unit: MPa
    scope: material
    conditions:
      material: Mo-41Re arc-cast sheet, SS-3 subsize tensile specimens
      temper: annealed 2 h at 1400 °C in vacuum before oxidation
      temperature: 900 °C
      state: after oxidation, sample M5
    method: Value printed in an ORNL tensile table
    status: ground
    source: ornl-tm-2000-291
    where: Table 2, row M5, 900 °C, UTS column
  - benchmark: oxidation_onset_temperature
    label: Strong oxidation in air, onset
    value: 600
    bound: lower
    unit: °C
    scope: material
    conditions:
      atmosphere: air
      meaning: strong oxidation begins around 600 °C as printed
    method: Statement in the manufacturer safety data sheet, stability section
    status: ground
    note: A name that the canon file does not hold, so the SDS statement is kept under oxidation_onset_temperature. It is a qualitative onset, not a rate.
    source: plansee-mo-re-sds
    where: 'Section 10 (Stability and reactivity), conditions to be avoided: high temperatures in air'
  - benchmark: oxide_scale_onset_temperature
    label: Oxide scale formation in oxidising environments, onset
    value: 350
    bound: lower
    unit: °C
    scope: material
    conditions:
      atmosphere: oxidising environments
      meaning: above about 350 °C as printed in the abstract
    method: Statement in the abstract of an ORNL report on Mo-41Re
    status: ground
    source: ornl-tm-2000-291
    where: Abstract
  - benchmark: sublimation_onset_temperature
    label: Sublimation of MoO3 from Mo-Re in air, onset
    value: 700
    bound: lower
    unit: °C
    scope: material
    conditions:
      atmosphere: air
      meaning: sublimation of MoO3 beginning around 700 °C as printed
    method: Statement in the manufacturer safety data sheet, stability section
    status: ground
    note: The SDS does not say whether the figure is for a particular Re content.
    source: plansee-mo-re-sds
    where: Section 10 (Stability and reactivity)
  - benchmark: embrittlement_onset_temperature
    label: Irradiation embrittlement, Mo-41Re and Mo-47.5Re, onset
    value: 1100
    bound: lower
    unit: K
    scope: material
    conditions:
      condition: tensile tests after irradiation to about 0.7 dpa at 1073, 1223 and 1373 K in the HFIR reactor
      meaning: severe embrittlement and intergranular failure with increasing temperature above 1100 K, even at the lowest fluence
    method: Statement in the abstract of an ORNL irradiation study
    status: ground
    source: busby-2007-irradiation
    where: Abstract
corrosion:
  - environment: Air above about 350 °C
    headline: Oxide scales form readily in oxidising gas above about 350 °C.
    effect: The ORNL report says both Mo and Re have low oxygen solubility but readily form oxide scales when exposed to oxidising environments above about 350 °C. It also says refractory metals generally lack satisfactory oxidation resistance above 300 to 400 °C.
    rating: moderate
    conditions:
      atmosphere: oxidising environments; air is not named in the abstract
    source: ornl-tm-2000-291
    where: Abstract and Section 1 (Introduction)
  - environment: Air above about 600 °C
    headline: Strong oxidation from about 600 °C, with volatile MoO3 above about 700 °C.
    effect: The Plansee SDS says high temperatures in air cause strong oxidation beginning around 600 °C, and that MoO3 sublimes beginning around 700 °C. A protective coating or a vacuum or inert atmosphere is needed for hot service.
    rating: severe
    conditions:
      temperature: above about 600 °C in air
    source: plansee-mo-re-sds
    where: Section 10 (Stability and reactivity)
  - environment: Vacuum or argon with low oxygen partial pressure, 600 to 1100 °C
    headline: Oxygen-poor gas gives weight gain from MoO2, and weight loss from MoO3 evaporation above about 1e-3 Pa.
    effect: At 1e-3 to 1e-6 Pa in vacuum, Mo-41Re gained weight as a thin MoO2 layer. Above 1e-3 Pa the weight change turned negative from MoO3 evaporation. In argon with about 5 ppm O2 at 900 °C for 100 h, the sample picked up about 200 wppm oxygen. Tensile strength and ductility showed no systematic change with the growth of the oxidised zone, although a hard internal oxidation zone formed.
    rating: moderate
    conditions:
      pressure: 10-3 to 10-6 Pa in vacuum (printed in torr in the source)
      atmosphere: argon with about 5 wppm O2 at 900 °C for 100 h, or 10 wppm at 1100 °C for 500 h
    source: ornl-tm-2000-291
    where: Sections 3.1, 3.2 and 4 (Discussion); Summary
  - environment: Thermal ageing at 1098 to 1398 K for 1100 h
    headline: Mo-41Re stays single phase; Mo-47.5Re forms sigma and chi phases that lower its ductility.
    effect: Mo-41Re kept a single-phase solid solution after 1100 h at all three ageing temperatures, with changes in resistivity and hardness at 1098 K. Mo-47.5Re annealed 1 h at 1773 K formed a two-phase alpha-Mo plus sigma structure, and ageing at 1398 K added sigma along the grain boundaries, which raised resistivity, hardness and tensile strength and reduced ductility. Ageing Mo-47.5Re at 1098 and 1248 K formed chi phase at grain boundaries without loss of ductility.
    rating: moderate
    conditions:
      time: 1100 h
      temperatures: 1098, 1248 and 1398 K
    source: busby-2007-aging
    where: Abstract
  - environment: Water, acids and bases
    headline: Insoluble in water, acids and bases; soluble only in complexing acids or with a strong oxidiser.
    effect: The Plansee SDS says the alloy is insoluble in water, acids and bases. It is soluble only in complex-forming acids (sulphuric or phosphoric) or in bases combined with a strong oxidising agent.
    rating: low
    conditions:
      basis: solubility statement as printed, no rate given
    source: plansee-mo-re-sds
    where: Section 9 (Physical and chemical properties), Solubility
  - environment: Liquid alkali metals (Li, Na, K) at high temperature
    headline: Good corrosion resistance to liquid alkali metals, as the ORNL introduction states.
    effect: The ORNL report says Mo-Re alloys have excellent high-temperature strength and corrosion resistance to liquid alkali metals, and that rhenium does not change the corrosion resistance of unalloyed molybdenum. A 2023 review also lists Li, Na and K as compatible heat-pipe coolants for Mo-Re cores.
    rating: low
    conditions:
      basis: qualitative statement in a report introduction; no corrosion rate given
    source: ornl-tm-2000-291
    where: Section 1 (Introduction)
risks:
  hazards:
    - text: The Plansee SDS for Mo5Re and Mo41Re classifies the alloy as not hazardous under Regulation (EC) 1272/2008. No labelling is required, and it is described as a compact metal with no risk to human health or the environment.
      ghs: []
      source: plansee-mo-re-sds
      where: Sections 2 and 15 (Hazards identification; Regulatory information)
    - text: PubChem aggregates ECHA notifications for rhenium. Of 393 company reports, 137 say it does not meet GHS criteria. H228 (flammable solid) is printed for 63.9 %, with the signal word Danger. The aggregated record does not separate the notifications by form, and the alloy is not covered by these notifications.
      ghs:
        - H228
      source: pubchem-re
      where: Safety and Hazards, GHS Classification, ECHA C and L Notifications Summary
  failure_risks:
    - mode: Oxidation in hot air
      trigger: Metal held above about 600 °C in air
      consequence: Strong oxidation forms MoO3, which sublimes from about 700 °C, so metal is lost from the part. A coating, vacuum or inert gas is needed for hot service.
      severity: critical
      source: plansee-mo-re-sds
      where: Section 10 (Stability and reactivity)
    - mode: Sigma-phase embrittlement of Mo-47.5Re
      trigger: Annealing 1 h at 1773 K, followed by ageing 1100 h at 1398 K
      consequence: Sigma phase forms along the grain boundaries, raising resistivity, hardness and tensile strength while reducing ductility. Mo-41Re did not show this precipitation under the same ageing.
      severity: high
      source: busby-2007-aging
      where: Abstract
    - mode: Radiation-induced embrittlement at high temperature
      trigger: Irradiation to about 0.7 dpa at 1073 to 1373 K, then tensile test at the irradiation temperature
      consequence: The tensile tests and fractography show severe embrittlement and intergranular failure above 1100 K, even at the lowest fluence. The authors link this to transmutation and radiation-induced segregation.
      severity: high
      source: busby-2007-irradiation
      where: Abstract
    - mode: Brittleness at cold temperature
      trigger: Service near -150 °C for the 41 % Re alloy
      consequence: The ductile-to-brittle transition is about -150 °C, which the patent says is too high for most space applications.
      severity: moderate
      source: us-patent-5437744
      where: Definitions section, first sentence
  side_effects: []
  handling:
    - text: 'Dust: avoid dust formation. Use suction cleaning, and suction cleaning when processing at high temperatures because sublimate forms. Wear at least one FFP2 respirator where dust is handled.'
      source: plansee-mo-re-sds
      where: Sections 7 and 8 (Handling; Exposure controls)
    - text: 'The SDS gives workplace limits for the molybdenum content: 10 mg/m3 inhalable fraction (mean daily value) and general dust 5 mg/m3. It cites Austrian legal regulations.'
      source: plansee-mo-re-sds
      where: Section 8 (Exposure controls)
  mitigations:
    - text: Use Mo-41Re rather than Mo-47.5Re where sigma phase matters. Mo-41Re kept a single-phase solid solution after 1100 h at 1098, 1248 and 1398 K.
      source: busby-2007-aging
      where: Abstract
    - text: NASA TP-3402 says brittleness from the sigma phase is avoided by keeping the rhenium content below 50 wt%. The patent reports sigma precipitation in the 47.5 % Re alloy, so the limit is not settled across these sources.
      source: nasa-tp-3402
      where: Introduction
uses:
  - application: structures
    device: Fuel cladding and core structural material for spacecraft reactors
    example: A 2005 review states that Mo-Re alloys have been suggested for fuel cladding and core structural materials in spacecraft reactors, and that the 41 to 47.5 wt% Re alloys have good ductility in base metal and welds.
    source: busby-2005-ans
    where: Abstract
  - application: thermal-control
    device: Core of a space heat-pipe reactor
    example: A 2023 Chinese review names Mo-Re alloys as candidates for heat-pipe reactor cores, especially for space reactors at extreme temperatures, citing their strength and their compatibility with UO2, UN, UC fuels and with Li, Na and K coolants.
    source: mater-rep-2023
    where: Abstract
  - application: thermal-control
    device: High-temperature thermoelements (temperature measurement)
    example: The Plansee SDS names high-temperature thermoelements as an example use of the Mo5Re and Mo41Re products.
    source: plansee-mo-re-sds
    where: Section 1 (Identification of the substance and use)
supply:
  - subject: Molybdenum (mine production, molybdenum content; 59 to about 52.5 % of the alloy by weight)
    producers:
      - country: China
        share_percent: 37.3
        year: 2025
      - country: Chile
        share_percent: 16.2
        year: 2025
      - country: United States
        share_percent: 15.4
        year: 2025
      - country: Peru
        share_percent: 15
        year: 2025
      - country: Mexico
        share_percent: 6.5
        year: 2025
    critical_lists: []
    recycling: The USGS says molybdenum is recycled from catalysts, ferrous scrap and superalloy scrap, and that recycled material may be as much as 30 % of apparent supply.
    substitutes:
      - 'USGS: little substitution in steels and cast irons. Graphite, tantalum and tungsten are named for refractory materials in high-temperature electric furnaces.'
    source: usgs-mcs2026-molybdenum
    where: World Mine Production and Reserves table, 2025e (world total 260,000 t; shares calculated by Space Mushroom from the country values). Recycling and Substitutes paragraphs.
  - subject: Rhenium (about 41 to 47.5 % of the alloy by weight)
    producers:
      - country: Chile
        share_percent: 37
        year: 2025
      - country: China
        share_percent: 24.7
        year: 2025
      - country: Poland
        share_percent: 12.3
        year: 2025
      - country: United States
        share_percent: 12.1
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (rhenium added in the 2025 revision)
        listed: true
    recycling: The USGS says nickel-base superalloy scrap and scrapped turbine parts are recycled hydrometallurgically to make rhenium metal, and that rhenium is recovered from spent catalysts in a closed loop. The United States relies on imports for 75 % of its apparent consumption (2025e).
    substitutes:
      - 'USGS: substitutes for rhenium are being evaluated in platinum-rhenium catalysts, where an iridium and tin catalyst has reached commercial success. The substitutes paragraph covers catalysts.'
    source: usgs-mcs2026-rhenium
    where: Domestic Production and Use; World Mine Production and Reserves table, 2025e (world total 81,000 kg; shares calculated by Space Mushroom from the country values, Chile 30,000, China 20,000, Poland 10,000, United States 9,800); Recycling; Substitutes
documents:
  - title: 'Plansee safety data sheet: Molybdenum-Rhenium, Mo5Re and Mo41Re, SDS no. SD-MR-02 (copy hosted by Purdue University)'
    type: sds
    url: https://www.physics.purdue.edu/primelab/safety/MSDS/Retired%20SDS%20and%20MSDS/2017%20removed%20safety%20sheets/MSDS%20updated%20to%20SDS/Molybdenum-Rhenium%20Alloys.pdf
    year: 2012
  - title: 'Oxidation of Mo-41Re at Low Oxygen Pressures: 2000 Status Report, ORNL/TM-2000/291'
    type: report
    url: https://info.ornl.gov/sites/publications/Files/Pub57542.pdf
    year: 2000
  - title: Molybdenum-rhenium alloys for spacecraft reactor applications (ANS Space Nuclear Conference 2005)
    type: paper
    url: https://impact.ornl.gov/en/publications/molybdenum-rhenium-alloys-for-spacecraft-reactor-applications/
    year: 2005
  - title: Microstructural and mechanical property changes with aging of Mo-41Re and Mo-47.5Re alloys, J. Nucl. Mater. 366 (2007) 369-387
    type: paper
    url: https://impact.ornl.gov/en/publications/microstructural-and-mechanical-property-changes-with-aging-of-mo-/
    year: 2007
  - title: Radiation-damage in molybdenum-rhenium alloys for space reactor applications, J. Nucl. Mater. 366 (2007) 388-406
    type: paper
    url: https://impact.ornl.gov/en/publications/radiation-damage-in-molybdenum-rhenium-alloys-for-space-reactor-a/
    year: 2007
  - title: US Patent 5,437,744, Molybdenum-rhenium alloy (Rhenium Alloys Inc.)
    type: report
    url: https://patents.google.com/patent/US5437744
    year: 1995
  - title: 'NASA TP-3402: Surface compositional variations of Mo-47Re alloy as a function of temperature'
    type: report
    url: https://ntrs.nasa.gov/api/citations/19940020635/downloads/19940020635.pdf
    year: 1993
  - title: Research progress of molybdenum-rhenium alloys used in heat pipe reactor, Materials Reports 37(2), 21020011
    type: paper
    url: https://www.mater-rep.com/EN/10.11896/cldb.21020011
    year: 2023
  - title: 'USGS Mineral Commodity Summaries 2026: Rhenium'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-rhenium.pdf
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Molybdenum'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-molybdenum.pdf
    year: 2026
  - title: 'PubChem compound record: rhenium (CID 23947), GHS classification summary'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/23947
    year: 2026
  - title: Stanford Advanced Materials listing RD7706, Molybdenum-rhenium alloy sheet Mo-47.5Re (reseller)
    type: datasheet
    url: https://www.samaterials.com/item/re7706-molybdenum-rhenium-alloy-sheet-mo-475re-02-inch-thickness.html
    year: 2026
  - title: Stanford Advanced Materials listing RD7725, Molybdenum-rhenium alloy wire Mo-47.5Re (reseller)
    type: datasheet
    url: https://www.samaterials.com/item/re7725-molybdenum-rhenium-alloy-wire-mo-475re-dia-01-mm.html
    year: 2026
gaps:
  - No thermal conductivity, coefficient of thermal expansion, Young's modulus or Poisson's ratio for Mo-41Re or Mo-47.5Re was found in a readable source in this run. The Plansee pure-molybdenum values are not transferred to the alloy.
  - Room-temperature and high-temperature tensile values come from one ORNL laboratory sheet, after oxidation, not from an unoxidised baseline or a standard product minimum. The unoxidised values are referred to in the report but were not readable in the text layer. ASTM B386 and B387 minima for Mo-Re were not read.
  - The tensile numbers were read from the text layer of a PDF table. They should be checked against the page image.
  - Reseller pages (Stanford Advanced Materials) print theoretical tensile strength, yield strength, elongation and melting point for Mo-41Re and Mo-47.5Re. These are labelled theoretical data, so they are not used. The same page lists a density of about 12.7 g/cm3 for Mo-41Re, which conflicts with the Plansee value of 14.6 g/cm3 and is not used.
  - The 1995 patent is the only source for the -150 °C transition and for the sigma-phase temperature range. No test report for either was read in this run.
  - The patent says Mo alloys above about 45 % Re may embrittle during welding. This was not verified. ORNL 2005 says the 41 to 47.5 % Re alloys have good weld ductility. The sources disagree and this profile does not state a welding limit.
  - Hardness of Mo-41Re and Mo-47.5Re was not read as a value. The aging study reports hardness changes only in words.
  - No EN, DIN, JIS or W.Nr. designation was found for either grade. UNS R03700 and ASTM B386 and B387 come from reseller listings for Mo-47.5Re and were not confirmed in the standards. Mo-41Re has no designation in the sources read.
  - Critical-mineral status of molybdenum (USGS list and EU list) was not checked for this profile. Rhenium is listed on the 2025 USGS list (read in the USGS 2026 rhenium summary). The EU list was not checked for either metal.
  - The PubChem H228 notification is for the rhenium element, not for the alloy. It has not been confirmed for Mo-Re.
  - Irradiation evidence rests on the abstracts of the 2007 ORNL papers. No irradiated tensile numbers were read. Space radiation dose, atomic oxygen and outgassing were not searched.
  - Exposure limits come only from the SDS, which gives molybdenum thresholds. No OSHA, ACGIH or rhenium limit was read.
  - Heat-pipe compatibility is stated in words only. No corrosion rate or test time for Li, Na or K was read.
  - Supply shares for rhenium are calculated from the 81,000 kg world total in the USGS 2026 summary. Shares for molybdenum are the same as in the molybdenum profile.
sources:
  plansee-mo-re-sds:
    title: Plansee safety data sheet, Molybdenum-Rhenium (Mo5Re, Mo41Re), SDS no. SD-MR-02, revised 24 Oct 2012 (copy hosted by Purdue University)
    id: SDS no. SD-MR-02; REACH registration 01-2119472304-43-0000
    url: https://www.physics.purdue.edu/primelab/safety/MSDS/Retired%20SDS%20and%20MSDS/2017%20removed%20safety%20sheets/MSDS%20updated%20to%20SDS/Molybdenum-Rhenium%20Alloys.pdf
    year: 2012
    kind: datasheet
    license: supplier document, linked not reproduced
  ornl-tm-2000-291:
    title: 'Oxidation of Mo-41Re at Low Oxygen Pressures: 2000 Status Report (DiStefano and Chitwood, Oak Ridge National Laboratory)'
    id: ORNL/TM-2000/291
    url: https://info.ornl.gov/sites/publications/Files/Pub57542.pdf
    year: 2000
    kind: report
    license: US government report (DOE), public
  busby-2005-ans:
    title: Molybdenum-rhenium alloys for spacecraft reactor applications (Busby et al., ANS Embedded Topical Meeting, 2005 Space Nuclear Conference, pp. 276-285)
    id: ANS 2005, ISBN 0894486969
    url: https://impact.ornl.gov/en/publications/molybdenum-rhenium-alloys-for-spacecraft-reactor-applications/
    year: 2005
    kind: paper
    license: abstract page cited, not reproduced
  busby-2007-aging:
    title: Microstructural and mechanical property changes with aging of Mo-41Re and Mo-47.5Re alloys, J. Nucl. Mater. 366 (2007) 369-387
    id: doi:10.1016/j.jnucmat.2007.03.027
    url: https://impact.ornl.gov/en/publications/microstructural-and-mechanical-property-changes-with-aging-of-mo-/
    year: 2007
    kind: paper
    license: abstract page cited, not reproduced
  busby-2007-irradiation:
    title: Radiation-damage in molybdenum-rhenium alloys for space reactor applications, J. Nucl. Mater. 366 (2007) 388-406 (Busby, Leonard and Zinkle)
    id: doi:10.1016/j.jnucmat.2007.03.028
    url: https://impact.ornl.gov/en/publications/radiation-damage-in-molybdenum-rhenium-alloys-for-space-reactor-a/
    year: 2007
    kind: paper
    license: abstract page cited, not reproduced
  us-patent-5437744:
    title: US Patent 5,437,744, Molybdenum-rhenium alloy (inventor Jan C. Carlen, Rhenium Alloys Inc.), published 1995-08-01
    id: US 5,437,744
    url: https://patents.google.com/patent/US5437744
    year: 1995
    kind: web
    license: patent document, public
  nasa-tp-3402:
    title: 'NASA Technical Paper 3402: Surface Compositional Variations of Mo-47Re Alloy as a Function of Temperature (Hoekje, Outlaw and Sankaran)'
    id: NTRS 19940020635
    url: https://ntrs.nasa.gov/api/citations/19940020635/downloads/19940020635.pdf
    year: 1993
    kind: report
    license: public domain (NASA)
  mater-rep-2023:
    title: Research progress of molybdenum-rhenium alloys used in heat pipe reactor (Qiu et al., Materials Reports 37(2), 21020011)
    id: doi:10.11896/cldb.21020011
    url: https://www.mater-rep.com/EN/10.11896/cldb.21020011
    year: 2023
    kind: paper
    license: journal abstract cited, not reproduced
  usgs-mcs2026-rhenium:
    title: Mineral Commodity Summaries 2026, Rhenium (U.S. Geological Survey, February 2026)
    id: USGS MCS 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-rhenium.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-mcs2026-molybdenum:
    title: Mineral Commodity Summaries 2026, Molybdenum (U.S. Geological Survey, February 2026)
    id: USGS MCS 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-molybdenum.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  pubchem-re:
    title: PubChem compound record, rhenium (CID 23947), GHS classification and ECHA C and L notifications summary
    id: CID 23947; CAS 7440-15-5
    url: https://pubchem.ncbi.nlm.nih.gov/compound/23947
    year: 2026
    kind: database
    license: public domain (NCBI); notifications attributed to ECHA
  sam-mo47-5re-sheet:
    title: Stanford Advanced Materials, product RD7706, Molybdenum-rhenium alloy sheet Mo-47.5Re, 0.2 inch (reseller listing)
    id: catalogue RD7706
    url: https://www.samaterials.com/item/re7706-molybdenum-rhenium-alloy-sheet-mo-475re-02-inch-thickness.html
    year: 2026
    kind: web
    license: reseller page cited, not reproduced
  sam-mo47-5re-wire:
    title: Stanford Advanced Materials, product RD7725, Molybdenum-rhenium alloy wire Mo-47.5Re, 0.1 mm (reseller listing)
    id: catalogue RD7725
    url: https://www.samaterials.com/item/re7725-molybdenum-rhenium-alloy-wire-mo-475re-dia-01-mm.html
    year: 2026
    kind: web
    license: reseller page cited, not reproduced
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 15
  unreachable: 0
  caveats: 6
  note: 'Values read by an AI assistant on 2026-10-26 from the pages and PDFs named in each entry. Caveats: no modulus, thermal conductivity or expansion value for the alloy; tensile values come from one ORNL sheet after oxidation; the -150 °C and sigma-phase values come from a patent; reseller pages used only for designations; the density value uses a decimal comma in the SDS.'
story:
  recipe:
    line: Mo-Re is a solid solution of rhenium in body-centred cubic molybdenum. The two grades named in the sources are Mo-41Re (41 wt% Re) and Mo-47.5Re (47.5 wt% Re). The ORNL laboratory material was arc cast into sheet, then annealed 2 h at 1400 °C in vacuum before testing.
    parts:
      - name: Molybdenum
        symbol: Mo
        share_percent: 59
        basis: mass fraction, Mo-41Re
        role: The host metal. Molybdenum forms the body-centred cubic matrix, which gives the alloy its high melting point and heat conduction.
      - name: Rhenium
        symbol: Re
        share_percent: 41
        basis: mass fraction, Mo-41Re
        role: The alloying addition. ORNL says rhenium raises strength and ductility and improves fabricability, especially welding. The 47.5 % Re grade can form sigma phase on ageing.
  risk_groups:
    - title: For people
      level: 1
      verdict: Not classified hazardous
      lead: The Plansee SDS classifies the alloy as not hazardous. Dust is the main concern, and the rhenium element has notifications that are not specific to the alloy.
      points:
        - label: The alloy
          line: The Plansee safety data sheet classifies Mo5Re and Mo41Re as not hazardous and requires no label. It describes the metal as having no known toxic effects.
        - label: Dust
          line: Dust should be avoided. The SDS calls for suction cleaning and at least one FFP2 respirator where dust forms.
        - label: Rhenium notifications
          line: PubChem gives 137 of 393 company reports as not meeting GHS criteria, and prints H228 (flammable solid) for 63.9 %. The record does not separate these notifications by form, and they concern rhenium, not the alloy.
    - title: If it fails
      lead: These failure routes come from the sources. The oxidation route is a qualitative onset, not a rate.
      points:
        - label: Hot air
          line: Above about 600 °C in air the alloy oxidises strongly, and MoO3 sublimes from about 700 °C. Hot service needs a vacuum, an inert gas or a coating.
        - label: Sigma phase
          line: A Mo-47.5Re sample annealed at 1773 K and aged 1100 h at 1398 K formed sigma phase along its grain boundaries, lowering ductility. Mo-41Re kept one phase under the same ageing.
        - label: Irradiation
          line: Irradiated to about 0.7 dpa, both grades showed severe embrittlement and intergranular failure above 1100 K, even at the lowest dose tested.
        - label: Cold
          line: The 41 % Re alloy has a ductile-to-brittle transition near -150 °C, which the patent says is too high for most space applications.
    - title: Handling and storage
      points:
        - label: Dust control
          line: Use suction cleaning, and at high temperature too, because sublimate forms. Wear an FFP2 respirator where dust is handled.
        - label: Hot service
          line: Keep the metal out of air above about 600 °C. Use a vacuum, an inert gas or a protective coating.
  why: Mo-Re alloys are molybdenum with enough rhenium added to keep the metal ductile and easy to weld at high temperature. The sources name two grades, Mo-41Re and Mo-47.5Re. Mo-41Re melts above 2610 °C and has a density of 14.6 g/cm3 at 20 °C (Plansee). Space reactor studies propose it for fuel cladding and core structures, and heat-pipe reactor cores (ORNL; Materials Reports). The USGS says rhenium is recovered as a byproduct of roasting molybdenum concentrates, so supply follows molybdenum mining.
  uses:
    - where: Space reactor cladding and structures
      line: A 2005 ORNL-led review says Mo-Re alloys have been suggested for fuel cladding and core structural materials in spacecraft reactors, and that the 41 to 47.5 % Re grades have good ductility in base metal and welds.
    - where: Heat-pipe reactor cores
      line: A 2023 review from the Nuclear Power Institute of China names Mo-Re as a candidate for space heat-pipe reactor cores, citing strength at high temperature and compatibility with UO2, UN and UC fuels and with Li, Na and K coolants.
    - where: High-temperature thermoelements
      line: The Plansee SDS names high-temperature thermoelements as a use of its Mo5Re and Mo41Re products.
  can_do:
    - label: Stay solid when hot
      benchmark: melting_point
      value: above 2610 °C
      line: Plansee gives a melting point above 2610 °C for the Mo5Re and Mo41Re products.
    - label: Strength after oxidation at 650 °C
      benchmark: yield_strength
      value: 266 MPa yield
      line: In ORNL tensile tests on oxidised arc-cast Mo-41Re sheet, samples tested at 650 °C gave a yield strength of 266 MPa and a tensile strength of 480 MPa. The report says oxidation changed the tensile strength only slightly.
    - label: Ductility at room temperature
      benchmark: elongation
      value: 18 % total
      line: One oxidised, annealed sheet sample tested at room temperature stretched 18 % before failure, with a tensile strength of 719 MPa.
    - label: Density
      benchmark: density
      value: 14.6 g/cm3
      line: Plansee gives 14.6 g/cm3 at 20 °C for Mo41Re. Reseller pages list about 12.7 g/cm3, which is not used here.
  compare: Mo-41Re trades weight for ductility and weldability. The ORNL review says rhenium adds strength, ductility and weldability to molybdenum. In air the alloy oxidises strongly from about 600 °C (Plansee), and the ORNL report says refractory metals generally lack satisfactory oxidation resistance above 300 to 400 °C. The alloy therefore needs a vacuum, inert gas or coating for hot service, the same as its base metal.
  compare_rows:
    - label: Density at 20 °C
      benchmark: density
    - label: Melting point
      benchmark: melting_point
    - label: Yield strength after oxidation at room temperature
      benchmark: yield_strength
  handling:
    - Use suction cleaning and an FFP2 respirator where dust forms.
    - Keep hot Mo-Re out of air. Use a vacuum, argon or a protective coating above about 600 °C.
    - For Mo-47.5Re, avoid long ageing near 1100 to 1400 °C, where sigma phase forms (the patent gives 1075 to 1275 °C).
    - Choose Mo-41Re where ageing stability matters. It stayed single phase after 1100 h.
  good_for:
    - Melting point above 2610 °C (Plansee) for vacuum or inert service.
    - Ductility after welding and a strength gain over pure molybdenum, as the ORNL review states.
    - Heat-pipe reactor cores and fuel cladding studied for space reactors.
  watch_out:
    - Oxidation in air above about 600 °C, with MoO3 sublimation from about 700 °C.
    - Sigma phase in Mo-47.5Re after ageing near 1100 to 1400 °C, which lowers ductility.
    - Embrittlement after irradiation above about 1100 K.
    - Cold brittleness below about -150 °C for the 41 % Re alloy (patent).
    - No modulus, thermal conductivity or expansion value for the alloy was found in readable sources.
  verdict: Mo-41Re is the more stable of the two grades named in the sources. It stays single phase after long ageing, keeps ductility after oxidation, and melts above 2610 °C. It oxidises strongly in air above about 600 °C, and it needs vacuum or inert gas for hot service. Mo-47.5Re has sigma-phase and irradiation risks. The profile lacks a modulus and conductivity from an accepted source.