Re: Battery damage

On Aug 3, 5:27 pm, "Dan Beck" <biscuitbecks@*nospam*cableone.net>
wrote:
Hi Martin,

I applaud your theory, but I have a question or two...

First, have you ever seen a rechargeable battery on a circuit board that
contains sulfuric acid as an electrolyte? The "acid" damage people report
about their circuit boards is shamelessly erroneous, in my opinion. I have
grown weary of trying to correct people here.

What do you mean by "Potassium hydroxide is neutralized too quickly to
explain the incredible thoroughness of battery damage"? Have you ever used
KOH in chemistry experiments (I have), or used it for drain cleaner (I've
done that, also)? KOH is a VERY potent alkali, and I have cleaned several
KOH-damaged 20+ year old System 80 boards using dilute acetic acid.

Do alkaline cells contain elemental mercury, or a salt of mercury? I think
this distinction would be significant in your theory.

If you propose that the metal "dissolves in the mercury" then that metal
would be surrounded by mercury atoms, and would be unavailable to react with
air. Perhaps the mercury instead acts as a surface catalyst; indeed
elemental platinum (another heavy metal species) acts as a surface catalyst
for certain organic chemistry reactions.

As elegant as your theory is, I think you are underestimating the potency of
potassium hydroxide.

Your observation of mercury forming dendritic "trees" in reaction with other
metals is intriguing, to say the least. My level of inorganic chemistry
studied is woefully inadequate to explain that phenomenon... :-(

Thank you for the interesting post! :-)

Regards,
Dan (chemistry geek in a previous life--now System 80!)

"martin" <martin.reyno...@xxxxxxxxx> wrote in message

news:1186184701.055412.169560@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx



OK, so I am cleaning up a messed-up board. I have come to the
conclusion that the damage from battery leakage is neither acid nor
alkali, but someting else entirely - mercury damage. Potassium
hydroxide is neutralized too quickly to explain the incredible
thoroughness of battery damage.

Alkaline cells still contain a lttle mercury. When I was a kid, I
discovered that mercury causes certain metals to grow trees, dendritic
growths that can get a couple of inches high at a surprising rate.
There's no literature that I have found describing this phenomenon.

My theory is that the metal dissolves in the mercury, which is now
stripped of any protective coating and exposed to the atmosphere. The
air reacts with the metal, forming oxides, which precipitate out of
the mercury, forming the tree. The mercury can now dissolve more
metal, continuing the process without being consumed.

I suspect that the same thing can happen with copper. It is the only
way that I can explain the amount of damage, and the way it travels
down traces underneath the protective film, eating them up as it
passes.

This theory also explains why the board has to be sanded to eliinate
further corrosion.

Anybody else seen these trees? Any other ideas?- Hide quoted text -

- Show quoted text -

Thanks, Dan: you are raising good issues.

KOH is also the primary ingredient in CO2 scrubbers. It reacts with
the CO2 in the air to form potassium carbonate (and, of course, the
green stuff is copper carbonate). The mercury is amalgamated in the
zinc, so it comes free as the zinc is converted in the cell. No
salts.

I had a battery let go in my MM last year, I should have taken
pictures of the inch-long dendrites that grew out of the battery
electrode.

Many metals actually dissolve in mercury, so I believe that we end up
with a solution of copper in mercury. There are enough copper atoms
exposed at the boundary to react with the air. That's the only way I
can explain the migration down the copper traces and UNDERNEATH the
solder (of all things).

In this model, the mercury is acting as a physical catalyst, which one
would expect to see written up. Or maybe there's a mercury-copper
amalgam Cu2Hg that readily lets go in the presence of oxygen or CO2.


(nitrogen triodide, potassium iodate, ammonium disulphide, zinc
sulphide, sodium chlorate - all favorites of mine)




.

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