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In Reply to: RE: Flashlight battery question posted by DavidLD on March 08, 2015 at 14:07:47
Not knowing exactly what is in alkaline batteries, I don't know what the stuff is, but it is corrosion due to the differing electrochemical half-cell potentials (redox potentials) of the various materials involved -- the spring contacts and the battery (cell) materials.
I am sure Google will turn up the materials involved in the electrochemical cell inside an alkaline battery and I know one may find a table of half-cell potentials for many, many common materials.
all the best,
mrh
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from Wikipedia
Once a leak has formed due to corrosion of the outer steel shell, potassium hydroxide absorbs carbon dioxide from the air to form a feathery crystalline structure of potassium carbonate that grows and spreads out from the battery over time, following along metal electrodes to circuit boards where it commences oxidation of copper tracks and other components, leading to permanent circuitry damage.
The leaking crystalline growths can also emerge from seams around battery covers to form a furry coating outside the device, that corrodes any objects in contact with the leaking device.
Potassium carbonate. My experience has been is that if the corrosion can be reached so it can be cleaned, the component usually works ok.
exacerbates the electrochemical oxidation (degradation) of copper.
Who knew? :-P
all the best,
mrh
Can cause potassium hydroxide to lead from the battery. That's the fine white powder. It is corrosive and will react to metals that it touches. Similar reactions or leakage of chemicals cause terminals to corrode in car batteries.
KOH is an irritant, so be careful cleaning it off.
the way I see it is that the white crystal buildup is not potasioum hydroxide but rather potassium carbonate that is made when potassium hydroxide comes in contact with the carbon dioxide in the air.
There may be some corrosion on copper, but the main problem is that the potassium carbonate insulates not conducts electricity. Unless you can get to it to clean it off no current flows, and as I discovered sometimes the buildup is in a spot well away fom the battery terminals not easily reached. I've had issues with remotes with long dead batteries getting corroded in places not easily reached.
Since potassium carbonate is water soluble you could try washing it off of battery contacts using a dampened Q-tip and then drying the same with a dry Q-tip, but my scraping technique using a small screwdriver worked as well. I'm still wondering how the ptotassium hydroxide and carbonate was able to magically migrate to a separate spot so far away from the battery contacts, interestingly, traveling uphill.
from chemical reactions inside battery causes solid salts to form. Solids expand against seals -> leaks.
Similar to what happens to old electrolytic capacitors.
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