What Causes Corrosion on Car Battery Terminals?

[johnl]

I know only a little about chemistry, but am curious as to what makes up the white/blue crystalized corrosion that sometimes gets into the terminals on car batteries? What reaction is happening, etc. Also, does the polarity of the terminal favor the reaction, one any more than the other + vs - ?

I have truck where the positive battery terminal is corroded on the outside. On removing it the cable itself broke open and you could see the corrosion had actually progressed through the cable under the insulation for quite a distance. The cable looks to be copper. In between the individual strands the corrosion surrounds each wire, kind of cool, but then again I have to replace it, no longer a good enough conductor to carry starter current ;)

In contrast, the negative cable is perfectly clean.

 

[chemisttree]

The corrosion is usually the copper conductor in the battery cable.

 

[RonL]

I know only a little about chemistry, but am curious as to what makes up the white/blue crystalized corrosion that sometimes gets into the terminals on car batteries? What reaction is happening, etc. Also, does the polarity of the terminal favor the reaction, one any more than the other + vs - ?

I have truck where the positive battery terminal is corroded on the outside. On removing it the cable itself broke open and you could see the corrosion had actually progressed through the cable under the insulation for quite a distance. The cable looks to be copper. In between the individual strands the corrosion surrounds each wire, kind of cool, but then again I have to replace it, no longer a good enough conductor to carry starter current ;)

In contrast, the negative cable is perfectly clean.

I used copper wire to suspend lead bars in sulfuric acid, for a test i was conducting, going back about 6 months later the copper had dissolved and the acid was a very pretty blue. The lead had not sulfated one bit.