Light metals · Banned
Anodized aluminum inside UHV
AlOxvalues describe: Type II anodise
Why it's out
The porous oxide is a water reservoir. Semiconductor tools tolerate it because they run warm and never truly bake; UHV systems cannot.
Where it hides
Chamber interiors specified by people mixing the two cultures.
Properties
The values below are candidate: compiled from the sources named, not yet individually validated. Provisional provenance: O'Hanlon, A User's Guide to Vacuum Technology; CERN Accelerator School, vacuum and materials proceedings.
Wet cleaning
| Recipe | not applicable: the sealing step is itself an aqueous process |
|---|---|
| Forbidden | the process itself, in UHV |
| Limit | the pore structure, which is intrinsic to anodising |
Vacuum and outgassing
| Outgassing, unbaked (10 h) | 1e-6 mbar·L/s/cm² |
|---|---|
| Outgassing, baked | 1e-8 at best mbar·L/s/cm² |
Temperature
| Bake, assembled | 200 °C |
|---|---|
| Metallurgical limit | THE CONDEMNING MECHANISM: the anodic layer is a columnar porous oxide with an enormous internal area, sealed by hot water: you have engineered a water sponge onto the surface |
Thermal
| CTE | 23.6 ppm/K |
|---|---|
| Thermal conductivity | reduced by the layer |
| Specific heat | 896 J/kg·K |
| Emissivity | 0.8 |
Mechanical
| Hardness | 400–600 HV |
|---|---|
| Density | 2.7 g/cm3 |
Electrical and magnetic
| Relative permeability | 1.000022 |
|---|---|
| Resistivity | insulating layer |
Engineering
| Corrosion | excellent, which is why people want it |
|---|---|
| Process notes | fine outside vacuum, fine on external surfaces |
| Availability and cost | a standard shop finish, which is the trap |
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-6 unbaked to no baked reading baked.
| Material as published | Species | State | Pumping time | Rate |
|---|---|---|---|---|
| Aluminium (anodised-2 um pores) | total | unbaked | the abscissa of the curve below | 3.68e-7 at 1 h to 4.29e-8 at 10 h |
Sources: S-ELSEY-1975-II. Full citations and conditions at the base and in /data/outgassing.json.
Sources · 1
- O Hanlon, A Users Guide to Vacuum Technology