Low-outgassing silicone RTV (DOWSIL 93-500 space-grade encapsulant) RTV

spore: profile
id: silicone-rtv
spore_version: 0.2
family: silicone
name: Low-outgassing silicone RTV (DOWSIL 93-500 space-grade encapsulant)
abbreviation: RTV
role: encapsulant and adhesive
category: seals-adhesives
type: adhesives
summary: |
  DOWSIL 93-500 (formerly Dow Corning 93-500) is a two-part, transparent, solventless room-temperature-vulcanising silicone elastomer sold as a space-grade potting compound and encapsulant. Mixed 10 parts base to 1 part curing agent by weight, it cures at room temperature and stays usable from about -65 to +200 degC. Its manufacturer reports a total mass loss of 0.16 percent and collected volatile condensable material of 0.02 percent in the vacuum outgassing test, which is why it is offered for space hardware. This profile rests on one manufacturer sheet; the other Dow and NuSil documents could not be opened from this environment.
best_for: Potting and encapsulating electronics, power supplies and connectors where low vacuum outgassing and a wide temperature range matter
weakest_at: Low tensile strength (7.0 MPa) and soft cure (Shore A 40), and it is sensitive to cure inhibitors such as tin-catalysed RTVs, polysulfides and amines
identity:
  formula: Two-part RTV silicone elastomer (base and curing agent); the sheet does not disclose the polymer or filler chemistry
  source: dc93500-sheet
  where: Features and Typical Properties (first page); Mixing section (10:1 base to curing agent by weight)
tags:
  environments: []
  stresses:
    - extreme-cold
  applications:
    - electronics-and-chips
    - solar-arrays
properties:
  - benchmark: density
    label: Relative density of the base at 25 degC
    value: 1.08
    unit: g/cm3
    scope: material
    conditions:
      state: as supplied, base component
      temperature: 25 degC
    method: Printed as relative density at 25 C (ASTM D792, CTM 0022); numerically equal to g/cm3
    status: ground
    source: dc93500-sheet
    where: Typical Properties, as-supplied table
  - benchmark: refractive_index
    value: 1.4124
    unit: '-'
    scope: material
    conditions:
      state: cured, 7 days at 77 degC and 50% RH
    method: Printed in the cured physical properties block
    status: ground
    source: dc93500-sheet
    where: Typical Properties, physical properties cured
  - benchmark: viscosity
    value: 8400
    unit: mPa.s
    scope: material
    conditions:
      state: base component
      temperature: 25 degC
      method: ASTM D1084 (CTM 0050)
    method: Printed in the as-supplied table
    status: ground
    source: dc93500-sheet
    where: Typical Properties, as-supplied table (Viscosity at 25 C, base)
  - benchmark: pot_life
    value: 2
    unit: hours
    scope: material
    conditions:
      temperature: 25 degC
      state: after curing agent is added
    method: Printed in the as-supplied table; the text gives a working time of about 1 hour
    status: ground
    source: dc93500-sheet
    where: Typical Properties (Pot life); Working time and curing time
  - benchmark: tack_free_time
    value: 16
    unit: hours
    scope: material
    conditions:
      temperature: 25 degC
      state: with curing agent added
    method: Printed in the as-supplied table
    status: ground
    source: dc93500-sheet
    where: Typical Properties (Tack-free time)
  - benchmark: hardness_shore_a
    label: Durometer hardness, Shore A (cured)
    value: 40
    unit: Shore A
    scope: material
    conditions:
      cure: 7 days at 77 degC and 50% RH
      method: ASTM D2240 (CTM 0099)
    method: Printed in the cured physical properties block
    status: ground
    source: dc93500-sheet
    where: Typical Properties, physical properties cured
  - benchmark: ultimate_tensile_strength
    value: 7
    unit: MPa
    scope: material
    conditions:
      cure: 7 days at 77 degC and 50% RH
      method: ASTM D412 (CTM 0137A)
    method: Printed in the cured physical properties block
    status: ground
    source: dc93500-sheet
    where: Typical Properties, physical properties cured (Tensile strength)
  - benchmark: elongation
    value: 140
    unit: '%'
    scope: material
    conditions:
      cure: 7 days at 77 degC and 50% RH
      method: ASTM D412 (CTM 0137A)
    method: Printed in the cured physical properties block (elongation at break)
    status: ground
    source: dc93500-sheet
    where: Typical Properties, physical properties cured (Elongation at break)
  - benchmark: tml
    label: Total mass loss, 24 h at 125 degC and 1e-6 torr
    value: 0.16
    unit: '%'
    scope: material
    conditions:
      temperature: 125 degC
      pressure: 10^-6 torr (printed as 10ª¦ torr)
      duration: 24 hours
    method: Vacuum weight-loss test as printed by the manufacturer; not the NASA ASTM E595 database entry
    status: ground
    source: dc93500-sheet
    where: Typical Properties, physical properties cured (Total mass loss)
  - benchmark: cvcm
    label: Collected volatile condensable material at 25 degC
    value: 0.02
    unit: '%'
    scope: material
    conditions:
      temperature: 25 degC
      method: CTM 0496A, vacuum weight-loss test
    method: Printed as collected volatile condensable materials during the vacuum weight-loss test
    status: ground
    note: The sheet does not name ASTM E595; the CTM is the manufacturer's corporate method. Check the NASA outgassing database before quoting this as an E595 result.
    source: dc93500-sheet
    where: Typical Properties, physical properties cured (CVCM)
  - benchmark: water_absorption
    value: 0.1
    bound: upper
    unit: '%'
    scope: material
    conditions:
      immersion: 7 days at 25 degC
    method: Printed as less than 0.10 percent
    status: ground
    source: dc93500-sheet
    where: Typical Properties, physical properties (Water absorption)
  - benchmark: thermal_conductivity
    value: 0.146
    unit: W/(m.K)
    scope: material
    conditions:
      state: cured
      temperature: not stated
    method: Printed in the typical properties block
    status: ground
    source: dc93500-sheet
    where: Typical Properties, physical properties (Thermal conductivity)
  - benchmark: max_service_temp
    value: 200
    unit: degC
    scope: material
    conditions:
      basis: stated operating range of the cured encapsulant
      note: short exposure to 300 degC does not degrade it, but volatile generation rises with temperature
    method: Printed in the features list as a wide operating range of -65 to +200 degC
    status: ground
    source: dc93500-sheet
    where: Features (wide range of operating temperatures); Engineering data (short term exposure)
  - benchmark: min_service_temp
    value: -65
    unit: degC
    scope: material
    conditions:
      basis: stated operating range of the cured encapsulant
    method: Printed in the features list as the low end of the operating range
    status: ground
    source: dc93500-sheet
    where: Features (wide range of operating temperatures)
  - benchmark: brittle_point
    value: -65
    unit: degC
    scope: material
    conditions:
      state: cured
    method: Printed as brittle point in the typical properties
    status: ground
    source: dc93500-sheet
    where: Typical Properties, continued (Brittle point)
  - benchmark: dielectric_constant
    value: 2.75
    unit: '-'
    scope: material
    conditions:
      frequency: 100 Hz
      method: ASTM D150 (CTM 0112)
    method: Printed as permittivity at 100 Hz
    status: ground
    source: dc93500-sheet
    where: Typical Properties, electrical properties (Permittivity at 100 Hz)
  - benchmark: dissipation_factor
    value: 0.0011
    unit: '-'
    scope: material
    conditions:
      frequency: 100 Hz
      method: ASTM D150 (CTM 0112)
    method: Printed as dissipation factor at 100 Hz
    status: ground
    source: dc93500-sheet
    where: Typical Properties, electrical properties (Dissipation factor at 100 Hz)
  - benchmark: electrical_resistivity
    value: 690000000000000
    unit: ohm.cm
    scope: material
    conditions:
      method: ASTM D257 (CTM 0249)
    method: Printed as 6.9x10 with a garbled superscript in the PDF text; read as 10^14 ohm.cm. Confirm against the sheet image before quoting
    status: ground
    note: The exponent came from a garbled superscript in the text layer.
    source: dc93500-sheet
    where: Typical Properties, electrical properties (Volume resistivity)
corrosion:
  - environment: Common metals, notably copper, in contact with the cured encapsulant
    headline: No corrosion has been observed on common metals with DOWSIL 93-500.
    effect: The sheet states that no corrosion has been observed on common metals, notably copper, when the encapsulant is used with them. The sheet gives no test method or duration.
    rating: low
    conditions:
      basis: manufacturer statement; no test duration or method given
    source: dc93500-sheet
    where: Compatibility section (Corrosion)
  - environment: Cure-inhibiting contaminants (tin-catalysed RTVs, polysulfides, amine-cured epoxy, plasticised PVC, sulphur and nitrogen compounds)
    headline: These materials inhibit the cure, so the encapsulant may stay soft or tacky.
    effect: The sheet lists materials that inhibit cure, including tin-catalysed silicone RTVs, polysulfides, amine-cured epoxies, plasticised PVC, thiols, sulphides, amides, imides and azides. Cure inhibition can be prevented by washing, by volatilising the contaminants before casting, or by pre-testing each material. Those contaminants also make the material less stable.
    rating: severe
    conditions:
      basis: manufacturer compatibility list
    source: dc93500-sheet
    where: Compatibility; Preparing containers and components
  - environment: 'Vacuum outgassing screening (JAXA outgassing table: data use at TML of 1.0 percent or less and CVCM of 0.1 percent or less)'
    headline: The printed TML of 0.16 percent and CVCM of 0.02 percent are below both screening limits.
    effect: The JAXA table states the TML and CVCM criteria for data use. The DOWSIL 93-500 values read from the Dow sheet (0.16 percent TML, 0.02 percent CVCM) are below both. This is a comparison, not a NASA database result for this product.
    rating: low
    conditions:
      basis: Screening criteria as printed by JAXA; test at 125 degC for 24 h per the Dow sheet
    source: jaxa-outgas-table
    where: Data Application section; compared with the Dow sheet Typical Properties (Total mass loss, CVCM)
risks:
  hazards:
    - text: The sheet refers all safe-handling and hazard information to the supplier's safety data sheet and does not state any GHS classification. No SDS was read in this run.
      ghs: []
      source: dc93500-sheet
      where: Health and Environmental Information; Product Safety Information
  failure_risks:
    - mode: Cure inhibition on contact with incompatible materials
      trigger: Contact with tin-catalysed RTVs, polysulfides, amine-cured epoxies, plasticised PVC or sulphur or nitrogen compounds
      consequence: The encapsulant may not cure, or may cure soft and weak, and its vacuum outgassing performance may degrade
      severity: high
      source: dc93500-sheet
      where: Compatibility; Limitations of cure
    - mode: Thin-section cure failure
      trigger: Coating thinner than 0.25 mm that is not confined or covered
      consequence: Complete cure does not occur, so the material is not recommended for thin coatings
      severity: moderate
      source: dc93500-sheet
      where: Working time and curing time
  side_effects: []
  handling:
    - text: Mix 10 parts base to 1 part curing agent by weight. Entrapped air should be removed before pouring, and a vacuum of 3 to 5 minutes after bubbles collapse is advised for thick sections.
      source: dc93500-sheet
      where: Mixing; How to apply
    - text: Original unopened containers stored at or below 32 degC have a usable life of 24 months from production.
      source: dc93500-sheet
      where: Usable life and storage
    - text: Neither tested nor represented as suitable for medical or pharmaceutical uses.
      source: dc93500-sheet
      where: Limitations
  mitigations:
    - text: 'Quick cure schedules: 65 degC for 4 hours, 100 degC for 1 hour, or 150 degC for 15 minutes. Large parts need extra time in the oven.'
      source: dc93500-sheet
      where: Working time and curing time
    - text: Use DOW CORNING 1200 Primer for adhesion to non-porous surfaces, and pre-test each component because cure can be inhibited.
      source: dc93500-sheet
      where: Surface preparation; Preparing containers and components
uses:
  - application: electronics-and-chips
    device: Potting compound for modules, power supplies, cable connectors and complete electronic assemblies
    example: The sheet says it is used as an embedding and potting compound to protect modules, power supplies, cable connectors and assemblies.
    source: dc93500-sheet
    where: Applications
  - application: solar-arrays
    device: Encapsulant and adhesive for solar cells
    example: The sheet says it is used as an encapsulant for electronic components, circuit boards and solar cell adhesive.
    source: dc93500-sheet
    where: Applications
supply:
  - subject: Silicone elastomer (DOWSIL 93-500)
    abundance: Not sourced in this run.
    producers: []
    critical_lists: []
    recycling: Not sourced.
    substitutes: []
    source: dc93500-sheet
    where: Not found. The sheet names no supply chain or raw material origin.
  - subject: Silicon metal (feedstock for silicone polymers)
    abundance: World and domestic resources for making silicon metal are abundant (USGS, silica as quartzite); see where.
    producers:
      - country: China
        share_percent: 87
        year: 2025
      - country: Brazil
        share_percent: 3.9
        year: 2025
      - country: Norway
        share_percent: 2.8
        year: 2025
    critical_lists: []
    recycling: Insignificant (USGS, silicon).
    substitutes:
      - 'USGS: gallium arsenide and germanium are the principal substitutes for silicon in semiconductor and infrared applications; the substitute list does not cover silicone elastomers.'
    source: usgs-mcs2026-silicon
    where: World Production table, silicon metal 2025 column (China 4,000 of printed world total 4,600 thousand t; Brazil 180; Norway 130). Shares calculated by Space Mushroom against the printed rounded world total. Recycling, Substitutes and World Resources sections. The silicone chain itself is not in this table; silicon metal is the feedstock the USGS describes for silicones.
media: []
documents:
  - title: DOW CORNING 93-500 Space-Grade Encapsulant, product information (ref. 10-1062A-01, Dow Corning)
    type: datasheet
    url: https://www.spacematdb.com/spacemat/manudatasheets/DC93-500.pdf
    year: 1998
  - title: 'Mineral Commodity Summaries 2026: Silicon (USGS)'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-silicon.pdf
    year: 2026
  - title: Spacecraft outgassing data, JAXA outgas measurement table (JAXA MatDB)
    type: database
    url: https://matdb.jaxa.jp/Outgas/Outgasdoc1_e.html
    year: 2026
gaps:
  - Only one source was read. The Dow 93-500 PDF (dowsil-93-500-thixotropic) and the Dow space-grade sealants PDF both return a Dow access-blocked page to curl and to WebFetch, so they could not be opened from this environment.
  - The NASA outgassing database (outgassing.nasa.gov, now etd.gsfc.nasa.gov) loads its material table with JavaScript, and the readable page showed 'Loading filtered data...' with no records. No NASA TML or CVCM values for 93-500 were read, so the ASTM E595 check is not done.
  - NuSil CV-series and Momentive RTV 566 were not read. The NuSil page returned a bot-check challenge, and no Momentive datasheet was fetched.
  - Polymer chemistry (polydimethylsiloxane), filler (silica), cure chemistry (addition or condensation) and composition are not stated in the sheet, so the recipe holds only the mix ratio, not a verified composition.
  - Tensile strength and elongation are given at one cure only (7 days at 77 degC and 50% RH); no lap-shear value was printed in the copy read.
  - Lap-shear strength was not found in the sheet.
  - The CTE value (printed as 9x10 with a garbled exponent) and the dielectric strength (printed as 14.8 with no unit) were left out because the units or exponent could not be read reliably.
  - Hazard and SDS data were not read. The sheet refers readers to the supplier's SDS.
  - Supply chain, producer shares and critical-mineral status were not sourced.
  - Space-environment results (low-earth-orbit or ASTM E595 comparison) were not found beyond the manufacturer's vacuum weight-loss figures.
  - Viscosity, pot life and tack-free time use names that are not in the canonical property file; they are short snake_case names.
  - Only one source was reached; the brief asks for 8 or more. This file is a draft from one datasheet.
  - 'Deepen pass (2026-10-20): RTV ageing numbers could not be read. The MDPI papers (Materials 2018, Polymers 2023, Energies 2017) returned Access Denied, and the Fraunhofer RTV paper returned a bot-check page, so no ageing values are in the file.'
  - 'Deepen pass: no NASA ASTM E595 row for DOWSIL 93-500 was reachable. The NASA outgassing site is JavaScript-driven, and the Wolfram Data Repository mirror returned only a landing page with no 93-500 row. The JAXA table lists other silicones (SH1840, CV-1142, CV2500 NuSil), not 93-500.'
  - 'Deepen pass: hazards are still not sourced. PubChem has no matching CID for DOWSIL 93-500 (the name search returned nothing), and no SDS was reachable. The GHS data for octamethylcyclotetrasiloxane was not used because it is a different substance.'
  - 'Deepen pass: the supply entry is for silicon metal, the feedstock the USGS names for silicones. It does not identify DOWSIL 93-500 producers or their country shares.'
sources:
  dc93500-sheet:
    title: DOW CORNING 93-500 Space-Grade Encapsulant, product information (ref. 10-1062A-01)
    id: Ref. no. 10-1062A-01, DC 3367, dated 05/01/1998 (footer)
    url: https://www.spacematdb.com/spacemat/manudatasheets/DC93-500.pdf
    year: 1998
    kind: datasheet
    license: manufacturer datasheet (cited, not reproduced)
  usgs-mcs2026-silicon:
    title: 'Mineral Commodity Summaries 2026: Silicon'
    id: USGS MCS 2026, silicon chapter
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-silicon.pdf
    year: 2026
    kind: report
    license: public domain (US government work)
  jaxa-outgas-table:
    title: Outgas measurement data, JAXA MatDB
    id: JAXA MatDB outgas table and data application section
    url: https://matdb.jaxa.jp/Outgas/Outgasdoc1_e.html
    year: 2026
    kind: database
    license: cited, not reproduced
license: CC-BY-4.0
updated: '2026-10-19'
review:
  status: draft
  method: assistant
  checked_values: 18
  unreachable: 3
  caveats: 4
  note: Written by an AI assistant on 2026-10-19 from one datasheet (spacematdb copy of the Dow Corning 93-500 sheet). Dow PDFs, NuSil and the NASA outgassing table were not readable from this environment. 17 values read from that sheet; 0 checked against a second source.
story:
  recipe:
    line: DOWSIL 93-500 is a two-part silicone elastomer. The base and a curing agent are mixed 10 to 1 by weight, and the mix cures at room temperature. The sheet does not give its chemistry, so no formula beyond the mix ratio is stated here.
    parts:
      - name: Base encapsulant
        share_note: 10 parts by weight
        role: The silicone elastomer that forms the cured network. The sheet does not name the polymer.
      - name: Curing agent
        share_note: 1 part by weight
        role: Triggers the room-temperature cure. The sheet names no chemical species for it.
  risk_groups:
    - title: For people
      level: 0
      verdict: Alloy not checked against an SDS
      lead: The sheet gives no GHS classification and refers readers to the supplier's safety data sheet. That SDS was not read in this run.
      points:
        - label: Handling
          line: The sheet says the two components present no handling problems in normal industrial practice. Pre-test each combination before use.
        - label: Medical use
          line: Not tested or represented as suitable for medical or pharmaceutical use.
    - title: In service
      level: 1
      verdict: Cure chemistry is the watch point
      lead: The main failure route is incomplete cure from incompatible materials.
      points:
        - label: Cure inhibitors
          line: Tin-catalysed RTVs, polysulfides, amine-cured epoxies and plasticised PVC inhibit the cure.
        - label: Thin sections
          line: Coatings thinner than 0.25 mm do not cure fully unless confined or covered.
  why: DOWSIL 93-500 is a transparent silicone encapsulant that cures at room temperature. The manufacturer offers it for potting electronics and bonding solar cells, and reports low mass loss under vacuum. It stays flexible across -65 to +200 degC, which suits electronics that see wide temperature swings.
  uses:
    - where: Electronics potting
      line: The manufacturer describes it as a potting compound for modules, power supplies, cable connectors and complete electronic assemblies, protecting them from temperature extremes, humidity, radiation, thermal shock and vibration.
    - where: Solar cells
      line: It is also described as an encapsulant for circuit boards and an adhesive for solar cells. The sheet calls it ideally suited to the harsh environment of space, but gives no flight result.
  can_do:
    - label: Vacuum outgassing
      benchmark: tml
      line: In the manufacturer's vacuum test at 125 degC and 10^-6 torr for 24 hours, total mass loss was 0.16 percent, and collected volatile condensable material at 25 degC was 0.02 percent.
    - label: Temperature range
      benchmark: max_service_temp
      line: The sheet gives an operating range of -65 to +200 degC and says short exposure to 300 degC does not degrade it.
    - label: Electrical insulation
      benchmark: dielectric_constant
      line: Permittivity is 2.75 at 100 Hz, with a dissipation factor of 0.0011 at the same frequency.
  compare: The sheet gives no comparison with other space adhesives. Its strength is modest, with a tensile strength of 7.0 MPa and a Shore A hardness of 40, so it suits potting and encapsulation more than structural bonding.
  compare_rows:
    - scope: material
      label: Tensile strength
      benchmark: ultimate_tensile_strength
    - scope: material
      label: Vacuum mass loss
      benchmark: tml
    - scope: material
      label: Service temperature
      benchmark: max_service_temp
  handling:
    - Mix 10 parts base to 1 part curing agent by weight, and remove trapped air before pouring.
    - Store unopened containers at or below 32 degC; usable life is 24 months from production.
    - Use the quick cure schedules only with care, since large parts need more oven time.
  good_for:
    - Potting electronics, modules and connectors, where low vacuum outgassing and a wide temperature range matter.
    - Encapsulating solar cells and circuit boards.
  watch_out:
    - Cure inhibitors such as tin-catalysed RTVs, polysulfides and amine-cured epoxies.
    - Thin coatings below 0.25 mm do not cure fully unless confined or covered.
    - Low tensile strength (7.0 MPa) and a soft cure (Shore A 40).
  verdict: DOWSIL 93-500 is a sensible potting choice where low outgassing and wide temperature range matter. The file rests on one datasheet, so the manufacturer and NASA checks should be completed before it is treated as verified.