Polymers and elastomers · Workhorse
PEEK, Kapton (polyimide), Vespel
PIvalues describe: read per grade
Why it wins
The only polymers routinely allowed inside UHV: low outgassing after bake, radiation tolerant, machinable (PEEK, Vespel). Harness and MLI of spaceflight run on Kapton.
Why not the alternative
PTFE cold-flows and permeates; PVC and nylon are banned outright.
Watch out
Still polymers: keep total mass low, bake, never load-bear hot.
Properties
The values below are candidate: compiled from the sources named, not yet individually validated. Provisional provenance: Vacuum polymer datasheets and outgassing compilations; NASA outgassing database.
Wet cleaning
| Recipe | isopropanol wipe or short ultrasonic in IPA, then vacuum bake 150 °C; Vespel is hygroscopic and must be baked and stored dry |
|---|---|
| Forbidden | aqueous soaking of Vespel; solvents that attack tape adhesive |
| Limit | absorbed water, which dominates the first pump-down on all three |
Vacuum and outgassing
| Vapour pressure | low; the adhesive on Kapton tape is the real source |
|---|
Temperature
| Vacuum degas | same as bake |
|---|
Thermal
| Emissivity | 0.9 |
|---|
Mechanical
| Tensile | as ys |
|---|
Electrical and magnetic
| Relative permeability | 1.0 |
|---|---|
| Resistivity | >1e15 Ω·cm |
Engineering
| Corrosion | excellent; radiation tolerant |
|---|---|
| Joining | machined and bolted; Kapton laminated or taped |
| Process notes | three materials on one card: read the grade before quoting a number |
| Availability and cost | stock; Vespel expensive |
By grade
These grades differ by an order of magnitude, so their values are carried per grade and override the card.
| Parameter | PEEK unfilled (natural) | Kapton HN / VDA | Vespel SP-1 |
|---|---|---|---|
| Outgassing, unbaked (10 h) | 5e-8 mbar·L/s/cm² | 1e-7 mbar·L/s/cm² | 5e-8 mbar·L/s/cm² |
| Outgassing, baked | 1e-10 mbar·L/s/cm² | 1e-9 mbar·L/s/cm² | 1e-9 mbar·L/s/cm² |
| Bake, assembled | 250 °C | 350 °C | 300 °C |
| Metallurgical limit | Tg 143 then melt 343 | decomposes 520 | no melt |
| CTE | 47 ppm/K | 20 ppm/K | 54 ppm/K |
| Thermal conductivity | 0.25 W/m·K | 0.12 W/m·K | 0.35 W/m·K |
| Specific heat | 1340 J/kg·K | 1090 J/kg·K | 1130 J/kg·K |
| Melting / softening | 343 °C | 520 dec. °C | no melt |
| Strength | 90–100 MPa | 165–230 MPa | 86 tens MPa |
| Elongation | 20–45 % | 70–80 % | 7–9 % |
| Young's modulus | 3.6 GPa | 2.5 GPa | 3.1 GPa |
| Hardness | 85 | — | 88 Shore D |
| Density | 1.32 g/cm3 | 1.42 g/cm3 | 1.43 g/cm3 |
| Dielectric strength | 23 | 150–300 | 22 kV/mm |
Outgassing
4 sourced measurements for this card, 3 declared absences, 1 prescribed condition or published threshold. A rate means nothing without the pumping time it was read at, so each one states it or declares it missing. The whole base, filters included, is at /tools/outgassing/.
Signature: no unbaked reading unbaked to 1e-13 baked.
This card also carries outgassing values on 3 of its grades, in the Properties block above. Those are not the same claim as the ones below: they carry no source key, no species and no pumping time, and the base does not resolve its entries to a grade. Neither layer is merged into the other and no grade correspondence is invented here.
| Material as published | Species | State | Pumping time | Rate |
|---|---|---|---|---|
| PEEK disks, 2 mm thick | H2O | baked | not applicable, the source states the rate independent of pumping time | about1.00e-8mbar·L/s/cm² |
| PEEK disks, 2 mm thick | N2 | baked | not applicable, the source states the rate independent of pumping time | 2.50e-10mbar·L/s/cm² |
| PEEK disks, 2 mm thick | CO2 | baked | not applicable, the source states the rate independent of pumping time | 1.30e-10mbar·L/s/cm² |
| PEEK, Semitron ESd 480 from Boedeker Plastics, a static dissipative reinforced PEEK | total | baked | NOT STATED by the source | 9.60e-12mbar·L/s/cm² |
- PEEK disks, 2 mm thick. Hydrogen outgassing could not be measured on this sample after the bake.The source states that the very high partial pressure of water made the 2 amu peak mainly due to the fragmentation pattern of the water molecule, so the hydrogen rate could not be extracted. This is a measurement limit reported by the source, not a missing entry.
- PEEK disks, 2 mm thick. The argon rate published for this sample is not written into the base.Section 6.3 publishes an argon outgassing rate alongside the N2 and CO2 values, but the exponent did not survive text extraction of the source and reads as 8e-1, which is physically impossible for this quantity. The activation energy for argon, 0.27 eV per molecule, is legible and stated here. The value itself waits for a reading of the figure or of the typeset article. Nothing approximate is written.
- Kapton HN foils, 0.0125 mm to 0.125 mm thick. Water outgassing rates of Kapton HN foils are published as curves, no tabulated value is available.Section 6.4 gives q(t) for several thicknesses in Fig. 34 only. The behaviour is stated: the rate follows the inverse square root of pumping time at short times, then falls much faster, with tails most likely going as t to the power minus three rather than the exponential predicted by the slab diffusion model, which the source attributes to water dissolved in the micro-voids of the amorphous phase. The time at which the regime changes increases with sample thickness. Underlying study: S.G. Sammartano, Outgassing rates of PEEK, Kapton and Vespel polymers, Master Thesis, Arcada, Helsinki, 2020. Measurements at CERN by Sergio Giacomo Sammartano, Ivo Wevers and Giuseppe Bregliozzi.
Prescribed, not measured
- procedure, PEEK connectors, Kapton cabling and wire harnesses. Bake 200 C, 48 h, vacuum.
Sources: S-CHIGGIATO-CAS-2017, S-LIGO-E960050-V13, S-LIGO-E960022-V24. Full citations and conditions at the base and in /data/outgassing.json.
Grades
| PEEK unfilled (natural) | UHV screws and insulators; avoid glass-filled, fibers shed |
|---|---|
| Kapton HN / VDA | film and aluminized MLI layers |
| Vespel SP-1 | machined insulators |
| Vespel SP-3 | MoS2 filled: dry bearings in vacuum |
| Vespel SP-22 | graphite filled: dimensional stability and wear |