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I have mechanically damaged a capacitor on an old motherboard and it made a PFFFT sound like some gas went out of it and then some liquid leaked. What is that? Is it toxic? I hope that it was not mercury!

The capacitor is of a cylindric shape with two wires at bottom, about 7mm in diameter.

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    \$\begingroup\$ It's the electrolyte. As far as I know there is no mercury involved. On wikipedia en.wikipedia.org/wiki/Electrolytic_capacitor you can find what are the most used electrolytes. Open a window, aerate the room and have the board repaired. Eventually, you will die. But it's unlikely the capacitor will be the culprit \$\endgroup\$ – Sredni Vashtar May 6 '15 at 9:49
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Yes it's toxic; No it's not mercury; Yes you'll live :)

If it was a "wet" capacitor type, then most likely that was sulfuric acid or some organic or inorganic solvent. If it was a solid, then perhaps manganese dioxide.

Whatever it was it isn't good for you so don't breath it, take a bath in it, or move to a planet full of it. But... one capacitor one time in your life will not make a difference in your overall health.

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  • \$\begingroup\$ Thanks :-) LOL :-D I was just afraid whether it is mercury or not, buceause the liquid was shiny and I really don't want to have liquid mercury in my home :-D Thanks again for such a fast reply! \$\endgroup\$ – tomm760 May 6 '15 at 10:01
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    \$\begingroup\$ @ptacektom The "shiny" was most likely aluminium foil that had been ripped to shreds by the venting pressure. \$\endgroup\$ – Majenko May 6 '15 at 10:35
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    \$\begingroup\$ Take a q-tip or similar small absorbent (throw away) cleaner, with the MB powered off, and wipe up any residue. If the liquid was corrosive, it can damage anything it touches. Rubbing alcohol on the q-tip may help. The capacitor can be replaced by a skilled tech, but it's rather tricky on today's ROHS (lead-free) motherboards. \$\endgroup\$ – rdtsc May 6 '15 at 14:27
  • \$\begingroup\$ Oh, and check out: badcaps.net \$\endgroup\$ – rdtsc May 6 '15 at 14:29
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    \$\begingroup\$ In case somebody ever has to deal with such a mess in ancient or military surplus equipment: a) There seem to have been a few (very few) types of electrolytic capacitors in the 70s and earlier that had polychlorinated biphenyls added (far more common in non electrolytics!) b) so called wet slug tantalum types (uncommon in non-military/aerospace stuff) used sulfuric acid. None of these will be found in consumer/prosumer equipment from this century ;) \$\endgroup\$ – rackandboneman May 6 '15 at 22:30
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Whether it is toxic or not, you should treat it as though it is toxic! But there is no need to get paranoid about it. For some reason you seem to be more paranoid about mercury than the one you should worry about - lead. If you are going to repair the board, I recommend that you cut & remove the remainder of the capacitor, clean the board with q-tips and alcohol, and wash your hands, and place an equivalent capacitor in its place. If a tech is going to do it, leave the board alone.

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The capacitor people use a variety of electrolytes and some could be mildly toxic. All are corrosive because they contain things like boric acid and salycilic (sp) acid. None use strong acids or mercury. Rinse the board with hot water and replace the capacitor.

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