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Bonding material in a solvent

  1. Feb 9, 2009 #1
    Hello,

    I'm trying to figure out how to seal a circuit as described in this thread:

    https://www.physicsforums.com/showthread.php?p=2068433&posted=1#post2068433

    My question to you chemical engineers, do you guys know of any sort of bonding material (like epoxy) which will not dissolve in porpanol?

    I'm having a tough time water sealing this circuit with my materials because they all seem to fall apart after a period of time in propanol!

    Thanks!
     
  2. jcsd
  3. Feb 9, 2009 #2

    chemisttree

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    Better described as a 'potting material' rather than a bonding agent. Any of the thermoset type of polymers will give you some resistance but you should keep in mind that your circuit will eventually come into contact with water vapor. Water resistance is a meaningless term in circuits like these since water vapor migrates through most materials (especially water resistant epoxies) and accumulates in the interior of the potted component. This component will eventually experience 100% relative humidity. A metal can is probably the best solution with tightly fitted electrically-insulated wires sealed with a bead of epoxy. Better yet a metal tube with the open end well away from the propanol/water solution... starting to sound more and more like an RTD metal probe.

    Propanol is only one facet of your problems! Heat shrink tubing is not the way to go even though it would appear to be a solution. The molecular structure of heat shrink tubing is very open... kind of like expanded metal fabric. Those openings can let a lot of stuff through. Even after applying heat, the structure is more or less an open mesh. Heat shrink was designed to be an electrical insulator, not a solvent/water resistant material!

    Your choice of potting compound will probably be limited to RTV silicones (electronics grade only!) and epoxy. Allow the epoxy to cure normally (as you would treat your sensor).... don't accelerate the cure before testing since an accelerated cure will negatively impact solvent resistance. Plan on this component being a disposable item in your system.
     
  4. Feb 10, 2009 #3
    hey chemisttree, thanks alot for the very informative post!

    I went over to ACE last night to try to find some RTV silicone, but alas it was a shot in the dark. I did, however, find a solution which seems to be holding up.

    I describe it here:

    https://www.physicsforums.com/showthread.php?p=2070305&posted=1#post2070305

    What's your take on that?
     
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