I need to temporarily plug the end of a 3 mm ID copper tube with some sort of malleable solid solute that I can dissolve at later point by flushing with a solvent/acid via syringe. I need to keep the area at around room temperature, so I cannot use dry ice or excessive heat. I'm using it to prevent liquid silicone from seeping up the end of a tiny copper tube while I seal the tube, so it needs to be relatively inert to the copper tube and the silicone.

I've tried using Styrofoam and acetone (which is almost ideal), but this leaves behind a residue of slimy gunk that is difficult to remove, and I need the tube to be clear of foreign residues. Low melting point solid materials may be possible to use, but they can't leave behind any residue for my purposes. I can obtain any special chemicals through my university.

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    $\begingroup$ Crystalbond might be a good choice. $\endgroup$
    – Jon Custer
    Commented Jun 21, 2017 at 23:21
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    $\begingroup$ If the temperature is low enough you could use a gallium alloy? $\endgroup$
    – Equinox
    Commented Jun 21, 2017 at 23:37
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    $\begingroup$ Gallium alloy looks promising, I'm going to run that in my next batch of tests. Thanks! $\endgroup$
    – uberdanzik
    Commented Jun 22, 2017 at 3:09

2 Answers 2


If the cavity in which you insert silicone is not air tight I would use and air pump to blow in the tube.

The easiest chemical I could imagine using is a low melting point salt such as ammonium acétate. If the tube is removable you dip in the liquid and upon solidification you can remove the excess. It's water soluble.

Sugar toffee will have a similar behavior and is malleable at a certain proportion of water.

Plumber use bread.

  • $\begingroup$ These are all excellent suggestions. I'm going to go grab all of these and run a few tests. You might have just started a trend of grad students using sugar toffee on their thesis projects. $\endgroup$
    – uberdanzik
    Commented Jun 22, 2017 at 3:05

Bentonite clay is used to plug the ends of fireworks and is water soluble.

Waxes are available in various types, blends like hot melt glue are a possibility.

Napthalene has a melting point of around 80 degC and a strong smell.

A mechanical plug might be the easiest if possible to remove. Using a thin plastic tube sealed at one end and pressurised from the other end to swell it may be possible to block a tube.

I would love to see what your mechanical arrangement is, there may be other solutions.


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