n-Hexadecane (paraffin phase change material)

spore: profile
id: n-hexadecane-pcm
spore_version: '0.2'
family: paraffins
name: n-Hexadecane (paraffin phase change material)
role: phase change material for passive thermal control
category: thermal-protection
type: multi-layer-insulation
summary: |
  n-Hexadecane (C16H34) is a straight-chain alkane that melts at 18.18 °C and stores heat as latent heat while it melts. Three mini-packs holding 40.69 g of it flew on the IceCube 3U CubeSat in low Earth orbit, and NASA reports that the instrument stayed near 18 °C most of the time. PubChem's hazard data give an aspiration hazard (H304), and sources disagree on the flash point (135 °C and 136 °C).
best_for: Passive temperature hold near 18 °C in a small spacecraft instrument, as flown on IceCube (NASA)
weakest_at: Combustibility and an aspiration hazard (H304 in PubChem's ECHA notifications); no ageing or thermal-conductivity data found
identity:
  formula: C16H34
  cas: 544-76-3
  source: wikipedia-hexadecane
  where: 'Lead and infobox: chemical formula C16H34 and CAS number 544-76-3 (PubChem CID 11006 gives the same CAS)'
tags:
  environments:
    - low-earth-orbit
  stresses:
    - thermal-cycling
  applications:
    - thermal-control
properties:
  - benchmark: melting_point
    label: Melting point, Tfus (NIST phase change data)
    value: 291
    unit: K
    scope: material
    uncertainty: ± 1 K
    conditions:
      basis: average of 52 out of 54 values, as printed by NIST
    method: Phase change data table, average of measured values
    status: ground
    source: nist-webbook
    where: Phase change data table, row Tfus
  - benchmark: melting_point
    label: Melting point (CRC Handbook value printed on PubChem)
    value: 18.18
    unit: °C
    scope: material
    conditions:
      basis: CRC Handbook value as printed on PubChem
    method: Printed on the PubChem record as the CRC Handbook value
    status: ground
    source: pubchem-hexadecane
    where: 3.2.5 Melting Point, first entry
  - benchmark: melting_point
    label: Melting point of the PCM as flown (NASA)
    value: 18
    unit: °C
    scope: material
    conditions:
      use: paraffin PCM mini-packs on IceCube
      mass: 40.69 g n-Hexadecane
    method: Stated in the NASA paper's description of the paraffin PCM
    status: ground
    source: nasa-ntrs-pcm
    where: Section II (Why Paraffin PCM is Flown on IceCube Instrument), paragraph on the paraffin
  - benchmark: boiling_point
    label: Boiling point, Tboil (NIST)
    value: 554
    unit: K
    scope: material
    uncertainty: ± 10 K
    conditions:
      basis: average of 10 values, as printed by NIST
    method: Phase change data table, average of measured values
    status: ground
    source: nist-webbook
    where: Phase change data table, row Tboil
  - benchmark: critical_temperature
    label: Critical temperature, Tc (NIST)
    value: 722
    unit: K
    scope: material
    uncertainty: ± 4 K
    conditions:
      basis: average of 9 values, as printed by NIST
    method: Phase change data table, average of measured values
    status: ground
    source: nist-webbook
    where: Phase change data table, row Tc
  - benchmark: density
    label: Density (CRC Handbook value printed on PubChem)
    value: 0.7701
    unit: g/cm3
    scope: material
    conditions:
      temperature: 25 °C
      printed_unit: g/cu cm
    method: Printed on the PubChem record as the CRC Handbook value at 25 °C
    status: ground
    source: pubchem-hexadecane
    where: 3.2.8 Density, entry citing Haynes, CRC Handbook 95th ed.
  - benchmark: flash_point
    label: Flash point, closed cup (PubChem, citing a Sigma-Aldrich SDS)
    value: 135
    unit: °C
    scope: material
    conditions:
      test_method: closed cup
      printed_value: 135 °C (275 °F) - closed cup
    method: Printed on the PubChem record, which cites a Sigma-Aldrich safety data sheet (product 52209); that SDS was not read directly
    status: ground
    source: pubchem-hexadecane
    where: 3.2.6 Flash Point, closed cup entry
  - benchmark: flash_point
    label: Flash point (Wikipedia infobox)
    value: 136
    unit: °C
    scope: material
    conditions:
      printed_value: 136 °C (277 °F; 409 K)
      test_method: not stated
    method: Printed in the Wikipedia infobox; the test method is not given
    status: ground
    note: Differs by one degree from the PubChem closed-cup value; both are recorded and the test method is not stated for this one.
    source: wikipedia-hexadecane
    where: Infobox, flash point row
  - benchmark: refractive_index
    label: Refractive index (n_D)
    value: 1.4329
    unit: '-'
    scope: material
    conditions:
      temperature: 25 °C
      wavelength: not stated
    method: Printed on the PubChem record as the CRC Handbook value
    status: ground
    source: pubchem-hexadecane
    where: 3.2.18 Refractive Index
  - benchmark: dynamic_viscosity
    label: Dynamic viscosity
    value: 3.474
    unit: mPa s
    scope: material
    conditions:
      temperature: 20 °C
    method: Printed on the PubChem record, citing Ullmann's Encyclopedia of Industrial Chemistry
    status: ground
    source: pubchem-hexadecane
    where: 3.2.14 Viscosity
  - benchmark: enthalpy_of_vaporization
    label: Enthalpy of vaporization at standard conditions (NIST)
    value: 81.3
    unit: kJ/mol
    scope: material
    uncertainty: ± 0.6 kJ/mol
    conditions:
      basis: average of 9 values; standard conditions per NIST notes
    method: Phase change data table, average of measured values
    status: ground
    source: nist-webbook
    where: Phase change data table, row ΔvapH°
  - benchmark: latent_heat_of_fusion
    label: Enthalpy of fusion (NASA)
    value: 235
    unit: kJ/kg
    scope: material
    conditions:
      basis: as quoted by NASA with its handbook references
    method: Stated in the NASA paper, which cites earlier handbooks and a company report
    status: ground
    source: nasa-ntrs-pcm
    where: Section II, paragraph on the paraffin
  - benchmark: enthalpy_of_fusion
    label: Enthalpy of fusion, DSC (NIST list)
    value: 53
    unit: kJ/mol
    scope: material
    conditions:
      temperature: 290.7 K
      method_as_printed: DSC
    method: Printed in the NIST enthalpy of fusion list, row Mondieig, Rajabalee, et al., 2004
    status: ground
    source: nist-webbook
    where: Enthalpy of fusion list, row Mondieig, Rajabalee, et al., 2004
  - benchmark: molar_heat_capacity_liquid
    label: Constant-pressure heat capacity of the liquid (NIST, Costas, Huu, et al., 1988)
    value: 500.21
    unit: J/mol*K
    scope: material
    conditions:
      temperature: 298.15 K
      pressure: not stated
      phase: liquid
    method: Printed in the NIST liquid heat capacity table; other rows in that table differ slightly
    status: ground
    source: nist-webbook-cp
    where: Constant pressure heat capacity of liquid table, row Costas, Huu, et al., 1988
  - benchmark: autoignition_temperature
    label: Autoignition temperature
    value: 202
    unit: °C
    scope: material
    conditions:
      printed_value: 396 °F (202 °C)
    method: Printed on the PubChem record, citing the NFPA Fire Protection Guide to Hazardous Materials, 14th ed.
    status: ground
    source: pubchem-hexadecane
    where: 3.2.12 Autoignition Temperature, second entry
  - benchmark: latent_heat_storage
    label: Latent heat stored by the flown PCM mass
    value: 9.562
    unit: kJ
    scope: material
    conditions:
      mass: 40.69 g n-Hexadecane
      form: PCM mini-packs flown on IceCube
    method: Stated in the NASA paper as the thermal energy the PCM can store as latent heat
    status: calculated
    source: nasa-ntrs-pcm
    where: Section II, paragraph on the PCM mass
  - benchmark: instrument_temperature_in_flight
    label: Instrument temperature held by the PCM in flight
    value: 18
    unit: °C
    scope: material
    conditions:
      platform: IceCube 3U CubeSat instrument in ISS orbit
      period: day of year 250 to 255 in 2017
      condition: most of the time, as printed
    method: Flight temperature telemetry reported in the NASA paper
    status: flight
    source: nasa-ntrs-pcm
    where: Abstract
corrosion:
  - environment: Repeated melting and freezing (organic PCMs in general)
    headline: Repeated phase changes can degrade organic PCMs; no cycling test on n-hexadecane was found.
    effect: Wikipedia states that repeated phase transitions can lead to material degradation in the case of organic PCMs. No cycling or ageing result for n-hexadecane was found in the sources read.
    rating: unknown
    conditions:
      basis: general statement about organic PCMs, not a test on this grade
    source: wikipedia-phase-change-material
    where: Phase-change material article, organic PCM discussion
  - environment: Flight melting and freezing on IceCube (ISS orbit)
    headline: The flown mini-packs cycled through melting and freezing and were reported functional.
    effect: NASA reports that the flight results validated the functionality of the paraffin PCM mini-packs. The paper reports no chemical change or loss of latent heat for n-hexadecane after flight.
    rating: unknown
    conditions:
      platform: IceCube 3U CubeSat, ISS orbit
      period: day of year 250 to 255 in 2017
    source: nasa-ntrs-pcm
    where: Final paragraphs of the paper, concluding discussion
  - environment: Heating to decomposition
    headline: Heated to decomposition, it gives off acrid smoke and irritating vapors.
    effect: PubChem, quoting Sax's Dangerous Properties of Industrial Materials, states that when heated to decomposition hexadecane emits acrid smoke and irritating vapors. No decomposition temperature was found.
    rating: unknown
    conditions:
      basis: qualitative statement, no temperature given
    source: pubchem-hexadecane
    where: 3.2.13 Decomposition
risks:
  hazards:
    - text: 'PubChem''s ECHA-based summary gives GHS H304 for 96.9% of notifications: May be fatal if swallowed and enters airways. Signal word Danger. PubChem also notes it does not meet GHS hazard criteria for 0.1% (2 of 1815) of reports.'
      ghs:
        - H304
      source: pubchem-hexadecane
      where: 11.1.1 GHS Classification
    - text: PubChem gives the NFPA 704 rating for hexadecane as health 1, fire 1 and instability 0.
      ghs: []
      source: pubchem-hexadecane
      where: 11.1.3 NFPA Hazard Classification
    - text: PubChem records both 'Flammable' and 'Combustible' for hexadecane, both from NTP (1992).
      ghs: []
      source: pubchem-hexadecane
      where: 11.1.4 Health Hazards and 11.1.5 Fire Hazards
    - text: 'Skin irritation is recorded inconsistently: PubChem quotes Sax''s Dangerous Properties calling hexadecane a severe human skin irritant, and Patty''s Toxicology calling it a mild eye and mucous membrane irritant and primary skin irritant.'
      ghs: []
      source: pubchem-hexadecane
      where: 11.1.7 Skin, Eye, and Respiratory Irritations
  failure_risks:
    - mode: PCM mass too small for the operation scheme
      trigger: The Day-On/Night-Off operation scheme in flight, which had large deviations from the pre-launch design power-on time for the 40.69 g PCM
      consequence: NASA states the mass of the paraffin is not adequate for this operation scheme.
      severity: moderate
      source: nasa-ntrs-pcm
      where: Thermal energy balance discussion of the Day-On/Night-Off scheme
  side_effects:
    - text: When heated to decomposition, hexadecane emits acrid smoke and irritating vapors (Sax, quoted by PubChem).
      affects: People near a fire or overheated container
      source: pubchem-hexadecane
      where: 3.2.13 Decomposition
  handling:
    - text: 'PubChem''s first-aid text for hexadecane says: DO NOT INDUCE VOMITING.'
      source: pubchem-hexadecane
      where: 11.3.1 First Aid, ingestion entry (NTP, 1992)
    - text: 'PubChem quotes a Sigma-Aldrich safety data sheet (product 52209) as stating: Stable under recommended storage conditions.'
      source: pubchem-hexadecane
      where: 3.2.11 Stability / Shelf Life
  mitigations: []
uses:
  - application: thermal-control
    device: Paraffin PCM mini-packs on the IceCube 3U CubeSat instrument
    example: Three paraffin phase change material mini-packs were flown on the IceCube instrument in the International Space Station (ISS) orbit. They contained a total of 40.69 g of n-Hexadecane.
    source: nasa-ntrs-pcm
    where: Abstract
  - application: thermal-control
    device: Latent-heat storage in the IceCube instrument (flight design)
    example: The paper states that the PCM is capable of storing 9.562 kJ of thermal energy as latent heat.
    source: nasa-ntrs-pcm
    where: Section II (Why Paraffin PCM is Flown on IceCube Instrument)
supply:
  - subject: Paraffin feedstock (petroleum slack wax), the general source of paraffin
    abundance: Not stated for n-hexadecane; the Wikipedia article describes the feedstock for paraffin wax in general
    producers: []
    critical_lists: []
    recycling: Not described in the source read
    substitutes: []
    source: wikipedia-paraffin-wax
    where: 'Sourcing and refining section: paraffin is derived from petroleum, coal, or oil shale, and the feedstock is slack wax'
gaps:
  - No thermal cycling or long-term ageing test on n-hexadecane was found in the sources read; the only in-flight result is a single period from day of year 250 to 255 in 2017.
  - Thermal conductivity of n-hexadecane, solid or liquid, was not found in any source read.
  - 'Specific heat in J/(kg K) was not found: NIST gives only a molar heat capacity, recorded as molar_heat_capacity_liquid.'
  - Outgassing, total mass loss, radiation and atomic oxygen data for n-hexadecane in vacuum were not found.
  - Producer shares and the production route for n-hexadecane were not found; the supply entry covers paraffin feedstock in general from Wikipedia.
  - The Sigma-Aldrich safety data sheet (product 52209) was not read; its flash point and stability statements are cited through PubChem.
  - The HSDB record (captcha) and ChemIDplus (connection reset) could not be read in this run, so their values are not recorded.
  - 'Benchmark names not in the canonical list: latent_heat_of_fusion, enthalpy_of_fusion, enthalpy_of_vaporization, molar_heat_capacity_liquid, critical_temperature, autoignition_temperature, dynamic_viscosity, latent_heat_storage, instrument_temperature_in_flight.'
  - No taxonomy type fits a phase change material; multi-layer-insulation is the nearest passive thermal-control type.
  - NIST gives standard atomic weights as intervals, so no single atomic weight is recorded for carbon or hydrogen.
sources:
  nist-webbook:
    title: 'NIST Chemistry WebBook: hexadecane, phase change data'
    id: CAS 544-76-3; NIST Standard Reference Database 69
    url: https://webbook.nist.gov/cgi/cbook.cgi?Mask=4&ID=C544763
    kind: database
    license: US government data
  nist-webbook-cp:
    title: 'NIST Chemistry WebBook: hexadecane, condensed phase thermochemistry (constant-pressure heat capacity of liquid)'
    id: CAS 544-76-3; NIST Standard Reference Database 69
    url: https://webbook.nist.gov/cgi/cbook.cgi?ID=C544763&Units=SI&Mask=2
    kind: database
    license: US government data
  nist-atomic-weights:
    title: NIST Atomic Weights and Isotopic Compositions for All Elements (C and H rows)
    id: C and H standard atomic weight intervals; H page https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=H&all=all&ascii=html
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=C&all=all&ascii=html
    kind: database
    license: US government data
  wikipedia-hexadecane:
    title: Hexadecane, Wikipedia
    id: Hexadecane article, lead and infobox
    url: https://en.wikipedia.org/wiki/Hexadecane
    kind: web
    license: CC BY-SA 4.0, linked not reproduced
  wikipedia-paraffin-wax:
    title: Paraffin wax, Wikipedia
    id: Paraffin wax article, sourcing and refining section
    url: https://en.wikipedia.org/wiki/Paraffin_wax
    kind: web
    license: CC BY-SA 4.0, linked not reproduced
  wikipedia-phase-change-material:
    title: Phase-change material, Wikipedia
    id: Phase-change material article, definition and organic PCM discussion
    url: https://en.wikipedia.org/wiki/Phase-change_material
    kind: web
    license: CC BY-SA 4.0, linked not reproduced
  wikipedia-cetane-number:
    title: Cetane number, Wikipedia
    id: 'Article text: hexadecane (also named n-hexadecane) is assigned a cetane number of 100'
    url: https://en.wikipedia.org/wiki/Cetane_number
    kind: web
    license: CC BY-SA 4.0, linked not reproduced
  nasa-ntrs-pcm:
    title: Thermal Assessment of Paraffin Phase Change Material Mini-Packs on IceCube 3U CubeSat in Flight
    id: Choi, AIAA Propulsion and Energy Forum 2018, GSFC-E-DAA-TN54685, NTRS 20180004470
    url: https://ntrs.nasa.gov/citations/20180004470
    year: 2018
    kind: paper
    license: NASA public document
  pubchem-hexadecane:
    title: PubChem compound record, Hexadecane (CID 11006)
    id: CID 11006; CAS 544-76-3
    url: https://pubchem.ncbi.nlm.nih.gov/compound/Hexadecane
    kind: database
    license: public domain (NCBI)
documents:
  - title: 'NIST Chemistry WebBook: hexadecane, phase change data'
    type: database
    url: https://webbook.nist.gov/cgi/cbook.cgi?Mask=4&ID=C544763
  - title: 'PubChem: Hexadecane (CID 11006), GHS classification and physical properties'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/Hexadecane
  - title: Choi, Thermal Assessment of Paraffin Phase Change Material Mini-Packs on IceCube 3U CubeSat in Flight (AIAA 2018)
    type: paper
    url: https://ntrs.nasa.gov/citations/20180004470
    year: 2018
  - title: 'NIST Atomic Weights and Isotopic Compositions: carbon'
    type: database
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=C&all=all&ascii=html
license: CC-BY-4.0
updated: '2026-11-01'
review:
  status: draft
  method: assistant
  checked_values: 17
  unreachable: 6
  caveats: 2
  note: Values were read by an AI assistant on 2026-11-01 from the pages named in each entry. The NASA paper was read from its PDF. The PubChem values come from its rendered page text. The flash point differs between PubChem (closed cup) and Wikipedia; both are recorded.
story:
  recipe:
    line: n-Hexadecane is the unbranched saturated alkane C16H34, with sixteen carbons in a straight chain (Wikipedia). The sources read do not describe how it is made; the paraffin feedstock is slack wax from petroleum refining (see supply).
    parts:
      - name: Carbon
        symbol: C
        role: Sixteen carbons form the straight chain.
        share_note: standard atomic weight interval, see NIST
        source: nist-atomic-weights
        where: C row
      - name: Hydrogen
        symbol: H
        role: Thirty-four hydrogens complete the chain.
        share_note: standard atomic weight interval, see NIST
        source: nist-atomic-weights
        where: H row
  risk_groups:
    - title: For people
      lead: PubChem's hazard data for hexadecane include an aspiration hazard from company notifications.
      level: 2
      verdict: Aspiration hazard (H304) in notifications
      points:
        - label: Classification
          line: 'The ECHA-based summary on PubChem gives H304 for 96.9% of notifications: May be fatal if swallowed and enters airways. The signal word is Danger.'
        - label: Skin
          line: PubChem quotes one source calling it a severe human skin irritant and another calling it a mild eye and skin irritant.
    - title: If it fails
      lead: The failure routes in these sources are a PCM mass too small for the operation scheme, and fire.
      level: 2
      points:
        - label: Mass
          line: NASA states the paraffin mass was not adequate for the Day-On/Night-Off operation scheme flown on IceCube.
        - label: Fire
          line: PubChem lists it as flammable and combustible (NTP, 1992), with an NFPA 704 fire rating of 1.
        - label: Decomposition
          line: Heated to decomposition, it gives off acrid smoke and irritating vapors (Sax, quoted by PubChem).
    - title: Storage
      points:
        - label: Stability
          line: 'A Sigma-Aldrich safety data sheet, as quoted on PubChem, states: Stable under recommended storage conditions.'
  why: 'n-Hexadecane is a phase change material (PCM): a substance that absorbs or releases large amounts of heat when it changes phase, here solid to liquid at about 18 °C. It is also called cetane, and Wikipedia gives it a cetane number of 100. NASA flew three mini-packs holding 40.69 g of it on the IceCube 3U CubeSat in ISS orbit, and the instrument stayed near 18 °C most of the time.'
  uses:
    - where: Thermal control on a CubeSat
      line: NASA flew three paraffin mini-packs holding 40.69 g of n-Hexadecane in total on the IceCube instrument. The paper says the latent heat change maintained the instrument temperature at about 18 °C most of the time.
    - where: Latent-heat storage
      line: Per NASA, the 40.69 g PCM mass stores 9.562 kJ of thermal energy as latent heat.
  can_do:
    - label: Melting point
      benchmark: melting_point
      value: 18.18 °C
      line: The CRC Handbook value printed on PubChem is 18.18 °C. NIST gives 291 K for the same transition.
    - label: Stored heat
      benchmark: latent_heat_storage
      value: 9.562 kJ
      line: Per NASA, 40.69 g stores 9.562 kJ as latent heat. NASA quotes an enthalpy of fusion of 235 kJ/kg.
    - label: Flight hold
      benchmark: instrument_temperature_in_flight
      value: about 18 °C
      line: In flight on IceCube, from day of year 250 to 255 in 2017, the instrument temperatures stayed near 18 °C most of the time.
  compare: n-Hexadecane is one defined alkane, which is not the same as paraffin wax. Paraffin wax is a mixture of hydrocarbons with a range of chain lengths (Wikipedia), so its melting range is wider and its values are not used here. The table lists the melting point, density and latent heat of fusion recorded for this grade.
  compare_rows:
    - label: Melting point
      benchmark: melting_point
    - label: Density
      benchmark: density
    - label: Latent heat of fusion
      benchmark: latent_heat_of_fusion
  handling:
    - 'Do not induce vomiting after swallowing: PubChem''s first-aid text says so, and the aspiration hazard (H304) is the main concern.'
    - Keep it away from ignition sources. It is combustible, with a flash point of 135 °C closed cup on PubChem and 136 °C on Wikipedia.
    - Check the supplier's safety data sheet for your grade, since PubChem's hazard data come from company notifications.
  good_for:
    - 'Passive buffering near 18 °C, as flown on IceCube: the instrument stayed near 18 °C most of the time in orbit (NASA).'
    - A melting point of 18.18 °C on PubChem, from the CRC Handbook.
  watch_out:
    - 'Aspiration hazard: PubChem''s ECHA-based summary gives H304 for 96.9% of notifications.'
    - 'Flammable: PubChem lists both Flammable and Combustible, from NTP (1992).'
    - Sources disagree on the flash point (135 °C on PubChem, 136 °C on Wikipedia) and on skin irritation.
    - The NASA paper says the paraffin mass was not adequate for the in-flight operation scheme, so the mass must match the scheme.
    - No thermal conductivity, cycling or outgassing data for this grade were found in the sources read.
  verdict: n-Hexadecane is a paraffin phase change material with a melting point of 18.18 °C. It held an IceCube instrument near 18 °C in low Earth orbit, according to NASA. Its aspiration hazard (H304), combustibility and missing ageing data are the limits, so the PCM mass must be sized to the operation scheme.