Joining and consumables · Workhorse
The vacuum lubrication ladder
MoS2values describe: sputtered MoS₂
Space testBig science (accelerators, light sources, public fusion)Vacuum equipment & componentsSemiconductor equipment & lithography
Why it wins
Nothing slides for free in vacuum: cold welding is the default. The ladder runs from sputtered dry films through PFPE greases to cryo thermal contact greases, each rung screened for vapor pressure and radiation.
Why not the alternative
Hydrocarbon greases evaporate, migrate, and polymerize under beams: the classic fogged-optic incident.
Watch out
PFPE breaks down catalytically on fresh aluminum wear surfaces (Lewis acid attack): dry films there.
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.
Wet cleaning
| Recipe | substrate cleaned and grit-blasted before sputtering; the film is never wet-cleaned |
|---|---|
| Forbidden | solvents on a burnished film: it lifts; humidity in storage |
| Limit | MoS₂ performs better in vacuum than in air, and degrades in storage rather than in service |
Vacuum and outgassing
| Outgassing, unbaked (10 h) | MoS₂ film 1e-10 · PFPE grease 1e-7 |
|---|---|
| Vapour pressure | PFPE creeps and its fragments show at m/z 69, 119, 131 |
Temperature
| Bake, assembled | MoS₂ 300 · PFPE 150 |
|---|---|
| Metallurgical limit | MoS₂ oxidises in humid air, which is why it is stored dry |
Mechanical
| Strength | film |
|---|---|
| Elongation | nil |
| Density | 5.06 g/cm3 |
Electrical and magnetic
| Relative permeability | 1.0 |
|---|
Engineering
| Corrosion | MoS₂ oxidises in humid air |
|---|---|
| Joining | sputtered, burnished or bonded |
| Process notes | the ladder: dry film first, solid metal film next, grease last and under protest |
| Availability and cost | space tribology suppliers |
Grades
| Sputtered MoS2, about 1 um | the spaceflight dry film reference |
|---|---|
| Dicronite (WS2) | thin dry film for threads and mechanisms |
| Braycote 601EF / Krytox PFPE | vacuum greases for bearings and O-rings |
| Apiezon L | room temperature UHV grease, taps and joints |
| Apiezon N | cryogenic thermal contact grease |
| Fomblin Z25 | PFPE pump fluid for oxygen and corrosive service |