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Vacuum chambers for physics experiments and scientific equipment are sometimes made of aluminum, though stainless steel and mu-metal chambers are used as well.

Aluminum forms a thin native oxide layer quickly, and this passive surface can have some advantages, but it's a serious impediment to making good, reliable, low-resistance electrical connections for purposes of electrical grounding for safety and for reducing various sources of electronic noise.

Just for example, it's hard to make a good Faraday cage from an aluminum box with vacuum ports and o-ring seals, or from aluminum foil for that matter.

I have come up with one possible solution - Electroless nickel-phosphorus plating of at least selected areas (especially threaded holes) together with the right kind of screw might allow some terminal lugs to provide good, long-term connections, but whenever dissimilar metals are involved, especially in notoriously humid locations, I worry.

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  • $\begingroup$ Laser welding is supposed to work great for mixing all sorts of metals. $\endgroup$
    – Abel
    Commented Jul 7 at 17:18
  • $\begingroup$ @Abel thanks - I think that for thin sheets of dissimilar metal (say aluminum + copper) there are reports of it working, but a 100 kg block of aluminum makes for a huge heat sink with very high thermal conductivity. If you've seen an example of laser welding to big hunks of aluminum, please share it! $\endgroup$
    – uhoh
    Commented Jul 7 at 17:37
  • $\begingroup$ How thick a "thin native oxide layer" do you need? google.com/search?q=laser+weld+aluminum&tbm=vid just use a more powerful laser? Where do I get that? Same place you got that big hunk of aluminum. $\endgroup$
    – Abel
    Commented Jul 7 at 19:12
  • $\begingroup$ Is there something wrong with mechanical connections like nuts and bolts and tapped holes, and two flat surfaces squashed together by fasteners ? May need to lap the mating surfaces before assembly. I have no idea if grease or similar would contaminate the chamber under low pressure, hence the tight flat fit suggested. $\endgroup$
    – Criggie
    Commented Jul 7 at 22:08
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    $\begingroup$ @Criggie Yes there is. Unlike other metals, Aluminum is super-reactive with oxygen. The native oxide that I mention in the question grows in seconds, and Al2O3 in other forms is known as a ceramic (alumina) or crystal (sapphire). It's an excellent insulator. Other metals oxidize much more slowly after machining or cleaning; in hours or days, and very thin layers of those oxides are still partially conducting. But I suppose lapping in dry nitrogen followed by some serious mechanical squishing of a contact and sealing with something that doesn't emit oxygen or water is something to try. $\endgroup$
    – uhoh
    Commented Jul 8 at 0:15

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