Polymers and elastomers · Banned
Silicones
Si-Ovalues describe: silicone grease and RTV
Why it's out
Migrate as monolayers over everything, wreck adhesion, optics, and wire bonding; some crack under electron beams into conductive residue.
Where it hides
Operators hands, RTV brought in for a quick fix, some O-ring lubes.
Properties
The values below are candidate: compiled from the sources named, not yet individually validated. Provisional provenance: ECSS space product assurance standards; NASA outgassing database; O'Hanlon, A User's Guide to Vacuum Technology.
Wet cleaning
| Recipe | not applicable |
|---|---|
| Forbidden | its presence anywhere in the building, honestly |
| Limit | contamination is irreversible: the RGA signature at m/z 73, 147 and 207 never fully leaves |
Vacuum and outgassing
| Outgassing, unbaked (10 h) | 1e-5 and it migrates mbar·L/s/cm² |
|---|---|
| Vapour pressure | THE CONDEMNING MECHANISM: cyclic siloxanes migrate over every surface in the system, and once cracked in a plasma or an electron beam they leave an insulating SiO₂ film nothing removes |
Thermal
| CTE | 300 ppm/K |
|---|---|
| Thermal conductivity | 0.2 W/m·K |
| Specific heat | 1500 J/kg·K |
| Emissivity | 0.9 |
Mechanical
| Strength | 5–10 tens MPa |
|---|---|
| Young's modulus | 0.005 GPa |
| Density | 1.1 g/cm3 |
Electrical and magnetic
| Relative permeability | 1.0 |
|---|
Engineering
| Availability and cost | everywhere, and that is the problem |
|---|
Outgassing
1 sourced measurement for this card. 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: 1e-5 unbaked to no baked reading baked.
| Material as published | Species | State | Pumping time | Rate |
|---|---|---|---|---|
| Silicone | total | unbaked | the abscissa of the curve below | 2.40e-5 at 1 h to 5.87e-6 at 4 h |
Sources: S-ELSEY-1975-II. Full citations and conditions at the base and in /data/outgassing.json.