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Sodium Silicate dielectric? Vacuum Feedthrough

  1. Apr 16, 2016 #1
    Cant seem to find a kv/mm for waterglass/sodium silicate. I was thinking of using it as an electrical insulator for vacuum feedthroughs, expecting an easy seal as I hear it expands when heat cured, therefore pushing against the chamber wall and the wires to prevent leaks and also seal by its adhesive properties. I think of using spark plugs but 50kv is too much for them.
  2. jcsd
  3. Apr 17, 2016 #2
    After some in depth research I found through search of a sodium silicate based product (stixso rr from pqcorp) that it has about the same dielectric strength and specific resistivity in ohm centimeters as plate glass, a brochure stated.

    the reason this is important for feedthroughs is that stixso rr, which is basically entirely sodium silicate and water, after full dehydrated curing, is incredibly low outgassing, as NASA's outgassing database states. It is suitable for UHV feedthroughs where other adhesives, sealants, and epoxies are not. It expands as it cures so even if it is not truly adhesive to the chamber and the feedthrough, it will be pressing against them by its expansion, when I think of this it reminds me of how knife edge flanges seal just from pressing and biting into the gasket material.

    i wonder if knife edge flanges that are damaged could be used as molds for sodium silicate forms, if easily separated the could maybe make a perfect fit into knicks and dents on the knife edge seal, upon separating them one would place aluminum foil in between and put them back together for a possible seal. I've read a patent where aluminum foil (i think household foil rather than special purpose) was proven as a low cost gasket material.

    i would also think sodium silicate water glass could be used for sight glasses, especially smaller kinds just big enough for laser entry, or larger ones that could have had lead powder added safely to their mix before they were cured, for the purpose of radiation shielding.

    curing temp and time can be found not too difficultly but IIRC they say heat them slowly up to 200 F and hold that temp, i think about 40 minutes in it should be dehydrated/fully cured
  4. Apr 19, 2016 #3
    To make it like a conflat seal you would need to have the end piece molded to something like a knife edge, regular conflats are more like a triangle edge but still sharp at the tip. I think that shape is there for strength. You would have to have some kind of knife edge on the other side of the copper for a UHV seal though. That could be SS though, wouldn't have to be waterglass since the copper or aluminum is already conducting so it would have to have a fair amount of disc space cut out to keep 50KV from arcing there. I would assume you would use something like teflon as an insulator just before the waterglass starts. Is this for some kind of electric field acceleration ring or something like that? In ion implanters we use that rather low voltage for ion extraction from the source and then 4 to 10 times that for the acceleration rings.
  5. Apr 19, 2016 #4
    Oh no just trying to see if I can add a focused ion beam to the SEM im about to finish. I realize its best to get alumina ceramic for these and use the waterglass as the inexpensive UHV adhesive and sealant. That's interesting to hear about your ion implanter
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